Advanced Techniques for Bio-remediation and

Advanced Techniques for Bio-remediation and Management of Salt Affected Soils

TRAINING MANUAL ICAR SPONSORED SHORT COURSE ON

Advanced Techniques for Bioremediation and Management of Salt Affected Soils SEPTEMBER 15-24, 2015

Editors

Sanjay Arora Y.P. Singh Atul K. Singh

ICAR-Central Soil Salinity Research Institute Regional Research Station, Lucknow (U.P.)

ii


SHORT COURSE ON

Advanced Techniques for Bioremediation and Management of Salt Affected Soils SEPTEMBER 15-24, 2015

Sponsored by:

Indian Council of Agricultural Research, New Delhi

Course Director: Dr. Sanjay Arora Coordinators:

Dr. Y.P. Singh Dr. Atul K. Singh

Organized by:

ICAR-Central Soil Salinity Research Institute Regional Research Station, Lucknow (U.P.) Edited & Compiled by: Drs. Sanjay Arora, Y.P. Singh and Atul K. Singh Published by: ICAR- CSSRI, RRS, Lucknow 226002 (UP) Citation: Arora, Sanjay, Singh, Y.P. and Singh, Atul K. (2015). Advanced Techniques for Bioremediation and Management of Salt Affected Soils. Training Manual, ICAR-CSSRI, RRS, Lucknow, p.1-261.

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Preface In the past, the increasing needs of expanding population for food, fuel and fiber were met from cultivating progressively larger areas of land and by intensifying the use of existing cultivated land. Under the circumstances when no more additional good quality land is available and the crop yields are stagnated, the food requirement of added population in future has to come from the reclamation and management of degraded lands which include salt affected ones also. India has world’s 2.4 % of land and 4% of fresh water resources of which nearly 6.73 million hectares lands are salt affected and a sizeable area is underlain by poor quality water. With these limited resources we have to support 16% of the global population. Innovative technologies in managing marginal salt affected lands merit immediate attention in view of climate change and its impact on crop productivity and environment. The management of degraded land and water resources on sustainable basis offers an opportunity for horizontal expansion of agricultural area in the country. During the last more than three decades, a number of packages to ameliorate different kinds of marginal lands (including salt affected areas) and poor quality waters have been developed. Adequate knowledge in diagnosis and management technologies for saline and alkali lands/waters and wastewater generated from municipalities and industries is essential to obtain maximum crop production from these resources. Bioremediation is one of the eco-friendly approach for improving productivity of salt affected soils as well as poor quality waters. Central Soil Salinity Research Institute, Karnal since its inception has been in the forefront to develop technologies for diagnosis, reclamation and management of salt affected soils and judicious use of poor quality waters. The regional station at Lucknow has been effectively executing technologies developed by the Institute in its jurisdiction. The capacity building is another aspect of the Institute activities. Keeping in view the technologies developed and expertise available in the field of soil salinity and water quality, ICAR-Central Soil Salinity Research Institute, Regional Research Station, Lucknow was assigned to organize its first 10 days Short Course on ‘Advanced techniques for bio-remediation and management of salt affected soils’ by the Indian Council of Agricultural Research, New Delhi. The course was organized from 15 September – 24 September, 2015 in which 20 Scientists or equivalent officers from ICAR Institutes/SAUs and other institutes participated. The lectures delivered during the training are compiled and brought out in the form of a book titled ‘Advanced Techniques for Bio-remediation and Management of Salt Affected Soils’. The emphasis on characterization, reclamation, bioremediation, phyto-remediation and management technologies of salt affected soils, waterlogged sodic soils and efficient use of saline/sodic water and wastewaters. This publication has come to the reality because of financial support from ICAR, New Delhi and efforts made by the contributors who provided the lecture notes and agreed to share their valuable experiences and thoughts. The editors of this book wish to place on record their heartiest thanks to the DDG (NRM), DDG (Education), ADG (HRD) for providing the opportunity in organizing the short course and publication of this book. The editors have special words of appreciation for all in the last but not the least to one and all that helped directly or indirectly in organization of this training programme and publication of this book. Sanjay Arora Y.P. Singh Atul K. Singh iv


CONTENTS S.No. 1

Topic and Author Sustainable Management of Salt Affected Soils: A brief review of work done in India -

2

3

4

5

6

7

8

9

111

C.L. Verma, Y.P. Singh, T. Damodaran and V.K. Mishra

14 Irrigation Management for Sodic Soils -

105

T. Damodaran and R. Kannan

13 Integrated Farming System model for Flood Prone, Waterlogged and Waterlogged Sodic Areas -

94

Y.P. Singh

12 Bioformulations for Enhancing Productivity of Sodic Soils -

86

O.P. Choudhary

11 Multifunctional Agroforestry Systems: A Potential Option for Restoration of Salt Affected Soils -

73

S.K. Jha

10 Use of Amendments in Ameliorating Soil and Water Sodicity -

60

Atul K. Singh

Assessment and Removal of Toxic ions in Soil and Water -

41

Sanjay Arora

Management of Poor Quality Waters in Agriculture -

37

Ajay K. Bhardwaj

Bio-remediation of Salt Affected Soils through Halophytes and Halophilic Soil Microbes -

31

V.K. Mishra

Nanotechnology for Salt Affected Land and Water Remediation -

28

T. Damodaran

Resource Conservation Approaches for Rice-Wheat Cropping System in Partial Sodic Environment -

19

Y.P. Singh

Technologies for Commercial Cultivation of Horticultural crops in Sodic Soils -

8

Sanjay Arora

Harnessing Productivity Potential of Sodic Soils through Salt tolerant Crops and Cropping sequences -

1

D.K. Sharma and Anshuman Singh

Diagnostic Properties and Constraints of Salt Affected Soils -

Page No.

Atul K. Singh

v

118


S.No.

Topic and Author

15 Protocol for Development of Soil Quality Index: A key to Efficient Management of Soil -

219

V. Tripathi and P.C. Abhilash

24 Participatory Approaches for Sodic Soil Reclamation in Uttar Pradesh -

238

S.K. Jha

26 Laboratory Methods for Estimation of Cations and Anions in Soil and Water -

225

A.K. Mishra

25 Laboratory Methods for Assessment of Soil Sodicity -

203

K. Thimmappa, Y.P. Singh and R. Raju

23 Recent Trends in Bioremediation -

191

B. Singh

22 Impact of Land Reclamation Technology on Livelihood Security of Resource Poor Farmers: Evidence from Indo-Gangetic Plains -

178

Lal Bahadur and S.R. Singh

21 Eco-restoration of Sodic Lands through Afforestation -

167

S.R. Singh, D. Biswas and Lal Bahadur

20 Carbon Sequestration and Management in Salt Affected Soils -

158

Alok Mathur

19 PGPR for Sustaining Crop Productivity under Salt Stress -

153

Naveen K. Arora

18 Remote Sensing and GIS for Delineation and Management of Salt Affected Soils -

140

T.J. Purakayastha

17 Fluorescent Pseudomonads for Enhancing Crop Yields and Remediation of Phytopathogen Infested Saline Soils -

130

T.J. Purakayastha

16 Phytoremediation: An Emerging Green Cure Technology for Remediation of Soil -

Page No.

C.S. Singh and Sanjay Arora

vi

251


Sustainable Management of Salt-Affected Soils: A Brief Review of the Work done in India D. K. Sharma and Anshuman Singh ICAR-Central Soil Salinity Research Institute, Karnal, Haryana-132001, India *Email:[email protected] Introduction Ever increasing global population, rapid depletion of productive soil and water resources, deforestation, climate variability and water shortages have caused a threat to sustainable food production (Sharma et al., 2011; Sharma et al., 2014). Most of the developing countries, due to poor technological capability for adaptation, could be hit hard by these unwarranted challenges. Intensive cropping, burning of forests and unsustainable agricultural practices have caused severe harm to agro-ecosystem health and environmental quality across the world (Foley et al., 2005; Lotze‐Campen et al., 2008). As fertile soils, fresh water, biodiversity and favourable climate are integral to sustainable human living; there is urgency for making adequate provisions to arrest diverse environmental and anthropogenic processes responsible for land degradation and the adverse consequences to human life. Worldwide, diverse forms of land degradation such as soil erosion, water logging and salinity substantially hamper food production (Pimentel, 2006; Lotze‐Campen, et al., 2008). For example, soil erosion alone affects over 40% of the total geographical area in India (Dabral et al., 2008). The unwanted anthropogenic activities such as deforestation and faulty crop management could often worsen the situation as they result in huge greenhouse gas emissions, biodiversity loss and alterations in water and energy balances which together prove disastrous for agricultural productivity (Foley et al., 2005; Lotze‐Campen et al., 2008). The erosion prone, salt-affected soils in arid zones, having low organic matter and poor fertility (Bhatt and Khera, 2006; Singh, 2009) could be worst affected by the compounded impacts of aforementioned constraints as the latter seem to be increasing in propensity with the passage of time. Salinity as a prominent form of land degradation affects over 1100 m ha lands worldwide (Wicke et al., 2011). Although predominant in arid and semi-arid regions, saline and sodic soils occur in almost all climates. Besides high salt concentrations in root zone, saline and sodic soils are also mostly underlain with marginal quality waters (Singh, 2009). Both of these problems are likely to significantly increase in future. In this article, we present a brief summary of characteristics and distribution of salt-affected soils, technological interventions for salinity management and the future requirements to sustain crop production in salt-affected soils. Rampant degradation of many agriculturally important natural resources has created a huge stumbling block in sustainable production of food and other livelihood resources for a burgeoning world population. As productive land and water resources are increasingly becoming scarce and climate change and pervasive land use pose threats to the sustainable farming across the world, the need to harness the productivity of marginal environments through technological interventions has become an urgent priority. Large tracts of saline and sodic soils 1


and the underlying saline aquifers in almost all agro-climatic zones of the world need to be sustainably utilized so as to meet the increasing food demands as well as to minimize the current pressures on overstretched fertile soils and fresh waters. With modest beginnings in 1969, the technologies developed by ICAR-CSSRI for salinity management in agriculture have fetched wide international recognition. In this paper, a brief glimpse of achievements and future agenda consistent with emerging challenges and changing research priorities in productive utilization of salt-affected environments are critically examined. Characteristics and distribution of salt-affected soils Two distinct classes of salt-affected soils- saline and sodic- vary with each other in genesis and physico-chemical properties. Saline soils, due to presence of excess soluble salts, exhibit saturation extract electrical conductivity (EC e) values equal to and/or above 4 dS m-1 at 25°C and higher salt concentrations render them unsuitable for majority of the arable crops. The sodic soils, on the contrary, have high exchangeable sodium percentage (ESP; >15) which adversely affects the crop growth (Singh, 2009). While the physical properties and water permeability in saline soils is comparable to their normal counterparts (Singh, 2009), plant growth in sodic soils is hampered due to poor physical environment which adversely affects water and air flux, water holding capacity, root penetration and seedling emergence (Murtaza et al., 2006). Salt-affected soils globally occupy about 1128 m ha area and the Middle East (189 m ha), Australia (169 m ha) and North Africa (144 m ha) are worst affected by this problem. The South Asian region, including India, has about 52 m ha salt-affected area. A large pool (~85%) the global saline area is only slightly to moderately affected by high salt concentrations while the remainder (15%) suffers from severe to extreme limitations for crop cultivation (Wicke et al., 2011). In India, the present estimated area under salt-affected soils- 6.73 million ha could significantly increase in ensuing decades. The five leading states accounting for almost 75% of saline and sodic soils in the country are Gujarat (2.23 m ha), Uttar Pradesh (1.37 m ha), Maharashtra (0.61 m ha), West Bengal (0.44 m ha) and Rajasthan (0.38 m ha). Many of the salt-affected states, particularly those in aridand semi-arid climates such as Rajasthan, Haryana and Punjab also greatly suffer from the problem of saline and sodic waters (Singh, 2009). Salinity management in agriculture Concerted research experiments in the last 45 years have resulted in the development of different technologies based on agronomic manipulations, chemical amendments, engineering interventions and salt tolerant cultivars for profitable cropping in salt-affected regions (Singh, 2009; Sharma et al., 2011). To sustain agricultural productivity of ameliorated soils in post-reclamation phase, the focus has gradually shifted to standardize resource conservation technologies, identification of promising high value horticultural crops and agro-forestry models, crop diversification through low water requiring crops and integrated farming systems for small farmers (Sharma et al., 2011). Increasing menace of secondary salinity in many canal commands has necessitated prioritized research on land modification models and saline aquaculture to harness the productivity of difficultto-cultivate waterlogged salt-affected soils (Sharma and Chaudhari, 2012). To expedite the reclamation programmes, soil salinity mapping on 1:250000 scale has been done in 15 states of India and efforts are in progress to digitize the maps on 1:50000 scale. Saline and sodic soils represent about 40% and 60%, respectively of the total salt-affected soils in country. Data on state-wise distribution of saline and sodic soils have facilitated the reclamation of vast tracts of salt-affected lands using 2


the best technologies (Singh et al., 2010). The first approximation water quality map of India has also been published (Sharma et al., 2011). Different technologies available for the reclamation and utilization of salt-affected soils, their strengths and weaknesses are briefly discussed under the following heads: Saline and sodic soil reclamation: The subsurface drainage technology, based on a network of concrete or PVC pipes installed at a particular spacing and depth below the soil surface, has proved highly successful in reclamation waterlogged saline soils in Haryana, Rajasthan, Gujarat, Punjab, Andhra Pradesh, Maharashtra, Madhya Pradesh and Karnataka states. The reclaimed soils put under crop production exhibit considerable increase in cropping intensity and yields. Substantial gains in terms of on-farm employment generation and productivity gains notwithstanding, the adoption of this technology at farmers’ field is limited due to higher establishment costs and operational difficulties, lack of community participation and the problems in safe disposal of drainage effluents (Singh, 2009). This situation highlights the need to sensitize the farmers about the importance of appropriate institutional arrangements for smooth run of subsurface drainage projects (Sharma et al., 2011). The immense popularity of gypsum-based sodic soil reclamation package is evident from profitable cropping in once barren, alkali soils covering large area. Besides quantum jump in contributions to the national food basket, wide adoption of this technology has generated huge employment opportunities and has ensured tangible improvements in rural livelihoods and environmental quality (Sharma et al., 2011; Sharma and Chaudhari, 2012). As gypsum availability is gradually diminishing due to quality, cost and supply constraints (Qadir and Oster, 2004), research on other viable approaches such as salt tolerant cultivars and phytoremediation, microbial inoculants and organic amendments, alternative amendments (e.g., fly ash and distillery spent wash) and alternate land uses has gained momentum (Sharma et al., 2011). Technologies for coastal saline soils and black vertisols: Technologies developed and demonstrated for sustainable agriculture in coastal saline tracts include ‘Dorovu technology’ to skim fresh water floating on saline water, rabi cropping in mono-cropped areas, salt tolerant rice varieties (Sumati and Bhootnath), integrated nutrient management, rainwater harvesting in farm ponds and integrated rice-fish culture. Difficult to cultivate salt-affected black vertisols, which occupy about 1.22 million hectare in Gujarat alone and are increasing in Karnataka, Maharashtra and Rajasthan states, could give higher returns through commercial cultivation of halophyte Salvadora and moderately salt tolerant dill, castor and sunflower crops (Sharma and Chaudhari, 2012). Salt tolerant cultivars and agro-forestry models: Realizing the fact that small and marginal farmers often fail to bear the costs involved in gypsum-based reclamation package, the salt tolerant cultivars have been developed in rice, wheat, mustard and chickpea to provide consistent yields while ensuring significant reductions in gypsum use. A number of agro-forestry models have also been developed to rehabilitate the large tracts of salt-affected community and government lands lying barren. The promising tree species for phytoremediation of sodic soils include Prosopis juliflora, Acacia nilotica, Casuarina equisetifolia, Tamarix articulate and Leptochloa fusca (Singh et al., 1994). Agro-forestry plantations in such unproductive lands could not only alleviate fuel wood and forage scarcities in rural areas but may also substantially contribute to carbon sequestration to mitigate the dangers of climate change to a great extent.

3


Bio-drainage of waterlogged lands: To overcome operational difficulties and social constraints in the adoption of sub-surface drainage for waterlogged saline lands, bio-drainage technology based on perennial trees has been developed (Ram et al., 2011). Similar to energy-operated water pumps, bio-drainage involves the use of salt tolerant trees having high transpiration rates (e.g., eucalyptus, popular, and bamboo) to arrest the processes of water logging and salt accumulation in canal commands (Singh, 2009). Available evidence indicates that appropriate land modification models could significantly enhance the potential of this technique. Saline aquaculture: It appears that shrimp and fish farming could be an attractive economic option in waterlogged soils as inland saline aquaculture has become a commercial venture in many salinity affected parts of the world (Allan et al., 2009). Initial efforts to demonstrate the practical feasibility of commercial fish culture in an extreme saline environment have given very encouraging results. Despite the very high salinity of pond water (25 dS m-1), low water availability and high evaporative losses, fish growth was about 400-600 g in 6 months and 600-800 g in 1 year (CSSRI, 2013). Integrated farming model: As landholdings are becoming smaller with each passing day and higher resource use efficiencies are a pressing need for the sustainability of agriculture, an integrated model consisting of field and horticultural crops, fishery, cattle, poultry and beekeeping has been developed for 2 ha area for ensuring food and nutritional security of and regular incomes to a farm family consisting of 4-5 members. This model substantially reduces the production costs by synergistic recycling of resources among different components (Singh, 2009). Similar models are in experimental stage of development for waterlogged sodic soils in Uttar Pradesh, highly saline black soils in Gujarat and coastal saline soils of West Bengal (Sharma and Chaudhari, 2012). Resource conservation technologies: The adverse effects of Green Revolution, mostly due to heavy and indiscriminate use of agro-chemicals and irrigation water in rice and wheat crops, are being seen as stagnant yields, decreasing factor productivity, degrading soil and water quality, environmental pollution and secondary salinization. To overcome these constraints, increased adoption of resource conservation technologies has become imperative. ICAR-CSSRI, Karnal has made significant contributions in this direction by successfully demonstrating the efficacy of different technologies- zero tillage in wheat, direct seeded rice, residue incorporation and mulching, sprinkler irrigation- for optimum resource use by rice and wheat crops for sustaining production and bringing improvements desirable soil properties (Sharma and Chaudhari, 2012). Microbial consortia for salt stress alleviation: To expedite the use of low cost crop growth bio-enhancers in stressful saline environments by sensitizing the farmers about their practical utility, a microbial bio-formulation named ‘CSR‐BIO’ has been developed. It acts as a soil conditioner and nutrient mobilizer and significantly increases the productivity of rice, banana, vegetables and gladiolus in sodic soils (Damodaran et al., 2013) Emerging constraints and future perspectives The foregoing account of technologies and agronomic practices is a credible proof of concerted research and extension activities carried out in the past four decades under the aegis of ICAR-CSSRI. Most of these technological breakthroughs have ensured tangible improvements in farmers’ livelihoods in salt-affected regions. Many emerging challenges, however, appear to pose formidable stumbling blocks to sustainable cropping in salt-affected environments. Secondary salinity in irrigated 4


commands of north-western India has caused huge land degradation (Datta and De Jong, 2002). Intensive rice-wheat rotation, faulty water management and clearing of vegetation seem to be the primary causes behind excessive salinity build-up in these regions. To prevent the problem of secondary salinity from becoming an ecological threat, an integrated approach based on precision land levelling, judicious resource use, crop diversification, adoption of salt tolerant trees and crops, organic nutrient management and conjunctive use of fresh and saline waters are recommended (Sharma et al., 2011, Sharma and Chaudhari, 2012). The recent instances of resodification of amended alkali soils is also a cause for concern as it could dilute the gains achieved in past (Garg, 2002). Most of the factors responsible for reappearance of sodicity are due to poor crop and water management practices and accordingly warrant agronomic practices similar to those required for the prevention of secondary salinity (Sharma and Chaudhari, 2012). In near future, extreme climate variability could prove disastrous to cropping in saline environments as erratic rainfall, high temperature and droughts could increase the propensity of salt stress and could further undermine the productivity of these inherently vulnerable agro-ecosystems (Enfors and Gordon, 2007; Yeo, 1998). Agriculture and allied activities currently account for about 10% of the global greenhouse-gas emissions which is expected to substantially increase by 2030 (Friel et al., 2009). The measures to minimize harmful emissions as well as to turn the crop lands into efficient carbon sinks range from resource conservation agricultural practices to the use of stress tolerant and resource use efficient cultivars. There should also be emphasis on increasing tree cover in degraded and wastelands for carbon sequestration (Sharma et al., 2011; Sharma et al., 2014). The co-existence of many constraints such as drought, heat stress and boron toxicity often accentuates the stress in ways that even salt tolerant crops and cultivars fail to perform. This scenario has necessitated a gradual shift from breeding for salt tolerance to breeding for multiple stress tolerance (Mittler, 2006). To realize this goal, detailed knowledge on biochemical and molecular aspects of stress regulation is a prerequisite. It is expected that emerging technologies such as marker-assisted selection, gene tagging and cloning, functional genomics and proteomics could greatly expedite the conventional approaches for developing multiple stress tolerant crop cultivars (Sharma et al., 2011). In India, having 4.2% global water resources, agriculture sector consumes the major chunk (~85%) of the available fresh water. As adequate availability and good quality of water are essential for sustainable crop yields, anticipated water scarcity and increase in saline/sodic water resources would pose an additional burden in salt-affected regions (Singh, 2009). Future research agenda must focus on issues such as use of poor quality waters in soil reclamation, improvements in existing ground water recharge strategies, storage and subsequent use of rain water through land modifications and refinements in existing technologies for optimizing saline/sodic water use in crop production (Sharma et al., 2011; Sharma and Chaudhari, 2012). Application of novel technologies such as solute transport modelling and air-borne sensors would become necessary for speedy and precise mapping of salt affected soils. The time tested technologies of gypsum-based sodic soil reclamation and sub-surface drainage require substantial refinements for continued relevance under changing scenario. Future research experiments must strive to develop cheap and environment-friendly alternatives such as fly ash-, distillery spent wash- and press mud-based reclamation packages for sodic soils. The focus should now shift from breeding for salt tolerance to the development of multiple stress tolerant genotypes. The efficiency of resource conservation technologies must be demonstrated by multi-location trials. Research, extension 5


and demonstration should be integrated into one fold for rapid dissemination of proven technologies to farmers’ doorsteps. Targeted capacity building of farmers and other stakeholders would be equally important in technology-led sustainable management of salt-affected soil and water resources. References Allan, G. L. et al. 2009. Inland saline aquaculture. New Technologies in Aquaculture: Improving Production Efficiency, Quality and Environmental Management, 1119-1147. Bhatt, R. and Khera, K. L. 2006. Effect of tillage and mode of straw mulch application on soil erosion in the submontaneous tract of Punjab, India. Soil and Tillage Research, 88: 107-115. CSSRI. 2013. Annual Report, 2013-14, Central Soil Salinity Research Institute, Karnal, India. Dabral, P. P. et al., 2008. Soil erosion assessment in a hilly catchment of North Eastern India using USLE, GIS and remote sensing. Water Resources Management, 22: 1783-1798. Damodaran, T. et al., 2013. Impact of social factors in adoption of CSR BIO‐A cost effective, eco‐friendly bio‐growth enhancer for sustainable crop production. South Asian Journal of Experimental Biology, 3: 158-165. Datta, K. K. and De Jong, C. 2002. Adverse effect of waterlogging and soil salinity on crop and land productivity in northwest region of Haryana, India. Agricultural Water Management, 57: 223-238. Enfors, E. I. and Gordon, L. J. 2007. Analysing resilience in dryland agro-ecosystems: a case study of the Makanya catchment in Tanzania over the past 50 years. Land Degradation and Development, 18: 680–696. Foley, J. A. et al. 2005. Global consequences of land use. Science, 309: 570-574. Friel, S. et al. 2009. Public health benefits of strategies to reduce greenhouse-gas emissions: food and agriculture. The Lancet, 374: 2016-2025. Garg, V. K. 2002. Sustainable rehabilitation of sodic soils through biological means-A case study. In: proceedings of the 12th ISCO Conference, Beijing, pp. 149-155. Lotze‐Campen, H., et al. 2008. Global food demand, productivity growth, and the scarcity of land and water resources: a spatially explicit mathematical programming approach. Agricultural Economics, 39: 325-338. Mittler, R. 2006. Abiotic stress, the field environment and stress combination. Trends in Plant Science, 11: 15-19. Murtaza, G. et al., 2006. Irrigation and soil management strategies for using saline-sodic water in a cotton-wheat rotation. Agricultural Water Management, 81: 98-114. Pimentel, D. 2006. Soil erosion: a food and environmental threat. Environment, Development and Sustainability, 8: 119-137. Qadir, M. and Oster, J. D. 2004. Crop and irrigation management strategies for saline-sodic soils and waters aimed at environmentally sustainable agriculture. Science of the Total Environment, 323: 1-19. Ram, J. et al. 2011. Biodrainage to combat waterlogging, increase farm productivity and sequester carbon in canal command areas of northwest India. Current Science, 100(11): 1673-1680. Sharma, D. K. and Chaudhari, S. K. 2012. Agronomic research in salt affected soils of India: An overview. Indian Journal of Agronomy, 57: 175-185. Sharma, D.K. et al. 2011. CSSRI Vision 2030. Central Soil Salinity Research Institute, Karnal. Sharma, D.K., et al. 2014. In salt-affected soils agroforestry is a promising option. Indian Farming, 63: 19-22. Singh, G. 2009. Salinity-related desertification and management strategies: Indian experience. Land Degradation and Development, 20: 367-385. Singh, G., et al. 1994. Agroforestry techniques for the rehabilitation of degraded saltaffected lands in India. Land Degradation and Development, 5: 223–242.

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Singh, G., et al. 2010. Remote sensing and geographic information system for appraisal of salt-affected soils in India. Journal of Environmental Quality, 39: 5-15. Wicke, B., et al. 2011. The global technical and economic potential of bioenergy from saltaffected soils. Energy and Environmental Science, 4: 2669-2681. Yeo, A. 1998. Predicting the interaction between the effects of salinity and climate change on crop plants. Scientia Horticulturae, 78: 159-174.

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Diagnostic Properties and Constraints of Salt Affected Soils Sanjay Arora Senior Scientist ICAR-Central Soil Salinity Research Institute Regional Research Station, Lucknow 226002, U.P. Introduction Since time immemorial the man has been relying on the soil for his sustenance for food, clothes, shelter and energy requirements. The pressure on this vital resource has increased to such an extent that the relationship between the living beings and the soil has become critical. A systematic and scientific appraisal of natural resources, especially soils and their database are important parameters, which may help to augment the food production. Soil resource inventory, therefore is basic for rationalizing land use according to its capability. Since no two soils are alike and have their own potential and/or problems and behave differently to management inputs, their use as per their capability is imperative for sustainable agricultural production. For sustained utilization of soil resource, it is imperative to know the nature, characteristics and extent of different soils, their qualities, productive capacity and suitability for alternative land uses. Soil is defined as a naturally occurring body that has been evolved owing to the combined influenced of climate and organisms, acting on parent materials, as conditioned by relief over a period of time. According to the Glossary of Soil Science Terms (Soil Science Society of America, 1970), “Soil is (i) the unconsolidated mineral materials on the immediate surface of the earth that serves as a natural medium for the growth of land plants, (ii) the unconsolidated mineral matter on the earth surface that has been subjected to and influenced by genetic and environmental factors of parent materials, climate (including moisture and temperature effects), macro and microorganism and topography, all acting over a period of time and producing a product that is soil, that differs from the material from which it is derived in many physical, chemical, biological and morphological properties and characteristics. Estimates of salt affected soils According to the FAO Land and Plant Nutrition Management Service, over 6% of the world's land is affected by either salinity or sodicity. The term saltaffected refers to soils that are saline or sodic, and these cover over 400 million hectares, which is over 6% of the world land area (Table 1). Much of the world’s land is not cultivated, but a significant proportion of cultivated land is salt-affected. Of the current 230 million ha of irrigated land, 45 million ha are salt-affected (19.5 percent) and of the 1,500 million ha under dry land agriculture, 32 million are saltaffected to varying degrees (2.1 percent). In India, about 6.73 M ha of land is affected by salinity and sodicity problems. Soil Resources of India India’s share in land resources of the world is only 2%, on which 18% of the world’s population and over 15% of the world’s livestock survive. However, with its diverse agro-climate, topography and soil types, India is capable of producing a wide range of crops and vegetation. The land surface of the country is spread over an area of 329 M ha and is represented by different types of soils which are given in the Table 2. The Indian soils are broadly classified under 8 soil taxonomic orders (Table 3). 8


Table 1. Regional distribution of salt-affected soils, in million hectares Regions Total Area Saline Soils Sodic soils M ha

M ha

%

Mha

%

Asia, the Pacific and Australia

3,107

195

6.3

249

8.0

Europe

2,011

7

0.3

73

3.6

Latin America

2,039

61

3.0

51

2.5

Near East

1,802

92

5.1

14

0.8

North America

1,924

5

0.2

15

0.8

Total

12,781

397

3.1

434

3.4

Source: FAO Land and Plant Nutrition Management Service National Bureau of Soil Survey and Land Use planning, Nagpur has developed a detailed soil map of the country at soil suborder association level (totaling about 103 soil suborders). The soils were further classified following Soil Taxonomy up to family level. Table 2. Major soil groups in India Soils

Area (Mha)

Red and laterite soils

117.2

Black soils

73.5

Alluvial soils

58.4

Desert soils

30.0

Other soils {Saline alkali soils, Forest and hill soils, Peaty and Marshy Soils}

49.6

Table 3. Distribution of soils of India Soil Order Entisols Inceptisols Vertisols Aridisols Mollisols Ultisols Alfisols Oxisols Non classified Total

Area (M ha) 80.1 95.8 26.3 14.6 8.0 0.8 79.7 0.3 23.1 328.7

9

Percent 24.37 29.13 8.02 4.47 2.43 0.24 4.25 0.08 7.01 100%


Threats to Soil Resources The massive post-independence development of irrigation has brought sufficient water for crops in millions of farms in India. Irrigation development, though a major factor in India’s ability to enhance food production in irrigated areas and attain self-sufficiency in cereal grain production, in many canal commands, a rise in water table has been noticed consequent leading to the degradation of soils through water logging and secondary salinisation. Soil degradation The primary cause of degradation is the demographic pressure on land, resulting in loss of vegetal cover through deforestation. The land degradation occurs mainly due to uncontrolled deforestation followed by agricultural/farm activities (Fig. 1). Hence, planning for productive land use is necessary to meet the growing challenges of food security since the land resource is not expandable physically. It is estimated that in India, about 174.4 M ha of land is potentially exposed to various degradation forces like Water (153.2 Mha) and wind erosion (15.0 Mha). About 40.0 M ha is subjected to floods and 22.0 M ha is not reclaimable for agricultural use. Loss of vegetal cover results in huge run-off, lowered recharge of ground water and subsequently development salinity. Salt affected soils occur at a tune of 6.73 Mha in our country. Salinisation, or soil degradation caused by increase of salt in the soil, is caused by incorrect irrigation management or intrusion of sea water into coastal soils arising from over-abstraction of groundwater. It is severe on irrigated lands of the dry zone. It reduces crop yield and in severe cases causes complete abandonment of agriculture. Salt affected soils In India salt affected soils are mainly confined to the arid and semi-arid and subhumid (dry) regions and also in the coastal areas. The salt deposits are of sodium carbonate, sulphate and chloride with calcium and magnesium. 

These soils vary in nature from saline to non-saline sodic.



In coastal regions saline soils are most predominant. They have high soluble salts (EC >4 dS/m) of chloride and sulphate of sodium, calcium and magnesium, Low ESP and have pH value less than 8.2.

Extent of Salt Affected Soils in India National Remote Sensing Agency (NRSA), Hyderabad in association with other National and State level organizations like Central Soil Salinity Research Institute, Karnal; National Bureau of Soil Survey & Land Use Planning, Nagpur; All India Soil Survey & Land Use, Delhi; and State Government Agencies conducted survey and uses remote sensing data to prepare the maps of salt affected soils of India in 1996. The Landsat satellite images were used in mapping salt affected soils at 1:250,000 scale. Satellite images were interpreted for broad categorization of different types of salt-affected soils, sample areas for field verification were identified and surveyed for soil sampling and characterization. The salt affected soils were classified according to norms for pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP). The state wise extent of salt affected soils in India is given in Table 4. It shows that maximum area of salt affected soils occur 10


in Gujarat followed by Uttar Pradesh and Maharashtra which account for about 62.4 per cent. Due to the limitation of small scale some very small and isolated patches of salt affected soils occurring in the states of Delhi and Himachal Pradesh could not be detected. The salt affected soils accounts for 6.727 m ha equivalent to 2.1 per cent of the geographical area of the country. Out of the total 6.727 million ha of salt affected soils, 2.956 million ha are saline and the rest 3.771 million ha are sodic. Out of the total 2.347 million ha salt affected soils in the Indo-Gangetic Plains, 0.56 million ha are saline and 1.787 million ha are sodic. Table 4. Extent of salt-affected soils India (‘000 ha) State

Saline

Sodic

Total

Andhra Pradesh

77.598

196.609

274.207

Andaman & Nicobar Island

77.000

0

77.000

Bihar

47.301

105.852

153.153

1680.570

541.430

2222.000

49.157

183.399

232.556

1.893

148.136

150.029

20.000

0

20.000

0

139.720

139.720

Maharastra

184.089

422.670

606.759

Orissa

147.138

0

147.138

0

151.717

151.717

195.571

179.371

374.942

Tamil Nadu

13.231

354.784

368.015

Uttar Pradesh

21.989

1346.971

1368.960

441.272

0

441.272

2956.809

3770.659

6727.468

Gujarat Haryana Karnataka Kerala Madhya Pradesh

Punjab Rajasthan

West Bengal Total Source: NRSA & Associates (1996) Characteristics of Salt affected soils

The term “soil” is considered to be a three-dimensional piece of landscape having shape, area and depth. Saline and alkali soils are defined and diagnosed on the basis of EC and SAR determination made on soil samples and the information

11


thus generated contributes substantially to the scientific agriculture based on USDA classification is given in table 4. Natural or primary salinity Salinity, primarily results from the accumulation of salts over long period of time, in the soil or groundwater, which is generally caused by two natural processes. 

  

Weathering of parent materials breaks down rocks and release soluble salts of various types, mainly chlorides of sodium, calcium and magnesium, and to a lesser extent, sulphates and carbonates. With sodium chloride is the predominant soluble salt. The deposition of oceanic salt carried in wind and rain forms the second cause. Rainwater contains from 6 to 50 mg kg-1 of salt, the concentration of salts decreasing with distance from the coast to the inland areas. The amount of salt stored in the soil varies with the soil type, being low for sandy soils and high for soils contain a high percentage of clay minerals. It also varies inversely with average annual rainfall.

Secondary or human-induced salinity Salinity occurs through natural or human-induced processes that result in accumulation of dissolved salts in the soil water to an extent that inhibits plant growth. Secondary salinisation results from human activities (anthropogenic) that change the hydrologic balance of the soil between water applied (irrigation or rainfall) and water used by crops (transpiration). The important causes for secondary salinisation are: (i) land clearing and the replacement of perennial vegetation with annual crops; (ii) use of salt-rich irrigation water; and (iii) lands having insufficient drainage. Sources and Causes of Accumulation of Salts The main causes of salt accumulation include:  Capillary rise from subsoil salt beds or from shallow brackish ground water;  Indiscriminate use of irrigation waters of different qualities  Weathering of rocks and the salts brought down from the upstream to the plains by rivers and subsequent deposition along with alluvial materials  Ingress of sea water along the coast  Salt-laden sand blown by sea winds Lack of natural leaching due to topographical situation, especially in arid and semi-arid conditions. Saline soils: These soils will have electrical conductivity of the saturation extract more than 4 dS m-1, the exchangeable sodium percentage less than 15 and the pH is less than 8.5. With adequate drainage, the excessive salts present in these soils may be removed by leaching thus bringing them to normalcy. Saline soils are often recognized by the presence of white crusts of salts on the surface. The important soluble salts in these soils are cations sodium, calcium and magnesium with low amounts of potassium and anions, chloride, sulphate and some times nitrate. Owing to the presence of excess salts and the absence of significant amounts of 12


exchangeable sodium, saline soils generally are flocculated and as a consequence the permeability is equal to or higher than that of similar nonsaline soils. Saline–alkali soils: These soils will have electrical conductivity of the saturation extract more than 4 dS m-1, the exchangeable sodium percentage greater than 15 and the pH is seldom higher than 8.5. These soils form as a result of combined process of salinisation and alkalisation. As long as excess soluble salts are present, these soils exhibit the properties of saline soils. Leaching of excess soluble salts downward, the properties of these soils will become like that of non-saline alkali soils. On leaching of excess soluble salts, the soil may become strongly alkaline (pH reading above 8.5), the particles disperse and the soil becomes unfavourable for the entry and movement of water and for tillage. Non-saline alkali soils: These soils will have their exchangeable sodium percentage greater than 15, the electrical conductivity less than 4 dS m-1 and the pH range between 8.5 and 10. The exchangeable sodium content influences significantly the physical and chemical properties of these soils. As the ESP tends to increase, the soil tends to become more dispersed. In addition to the parameters proposed by the USDA, Indian scientists considered the nature of soluble salts. Further the pH value of 8.5 is too high, as isoelectric pH for precipitation of CaCO3 at which sodification starts is 8.2 and mostly the pH is associated with the ESP of 15 or more. The classification according to the Indian system is presented in Table 5. Table 4. Properties of Saline, Saline-Alkali and Non-saline-Alkali Soils Properties Electrical conductivity (dS m-1) pH Exchangeable Sodium Per cent

Saline soils > 4.0 < 8.5 < 15

Saline alkali soils > 4.0 > 8.5 > 15

Non-saline alkali soils < 4.0 > 8.5 > 15

Table 5. Indian System of classification Soil Saline soils Characteristics pH < 8.2

Alkali soils

ESP

< 15

> 15

ECe

> 4 dS m-1

Variable, mostly < 4 dS m-1

Nature salts

of

> 8.2

soluble Neutral, mostly Cl-, SO42-, Capable for alkaline HCO3- may be present but hydrolysis, CO32- is absent. preponderance of HCO3and CO32- of Na+

13


Constraints   

Excess sodium on the soil exchange complex and/or soluble salts in the soil reduces the productivity of these soils. Soil physical condition, particularly soil structure sets posing problem of water and nutrient availability. These soils show micronutrient deficiency.

Saline Vertisols Vertisols and associated soils cover nearly 257 million ha of the earth’s surface of which about 72 million ha occur in India. This shows that nearly 22% of total geographical area of the country is occupied by Vertisols. In the central part of India known as the Deccan Plateau, the soils are derived from weathered basalts mixed to some extent with detritus from other rocks. In other areas, particularly in the south, the soils are also derived from basic metamorphic rocks and calcareous clays. Similarly, in the western region, these are derived from marine alluvium that account for nearly 19.6 million ha. Of this about 1.12 million ha are affected by salinity and water logging problems. These soils are generally deep to very deep and heavy textured with clay content varying from 40-70%. Further, these are also low in organic carbon content, high in cation exchange capacity, slight to moderate in soil reaction and are generally calcareous in nature. Vertisols, when kept fallow during Kharif season are exposed to soil erosion hazards. Their inherent physicochemical characteristics such as poor hydraulic conductivity, low infiltration rates, narrow workable moisture range, deep and wide cracks pose serious problems even at low salinity level. However, the Vertisols of Bara tract in Gujarat are generally very deep (150 to 200 cm), fine textured with clay content ranging from 45 to 68% with montmorillonite dominant clay minerals. The soils exhibit high shrink and swell potential and develop wide cracks of 4-6 cm extending upto 100 cm depth. The soils are calcareous in nature having calcium carbonate ranging from 2 to 12% in the form of nodules, kankar and powdery form. Waterlogged soils An area is said to be waterlogged when the water table rises to an extent that soil pores in the root zone of a crop become saturated, resulting in restriction of the normal circulation of the air, decline in the level of oxygen and increase in the level of carbon-dioxide. The water table, which is considered harmful, would depend upon the type of crop, type of the soil and the quality of underground water. It may vary over a wide range from zero for rice, 1.5 m for other arable crops and more than 2 m for horticultural and forest plantations. From practical point of view, a Working Group constituted by the Ministry of Water Resources has suggested the following norms:

Depth to water table (m)

Nomenclature

3

Safe

14


The development of water logging and soil salinization upon introduction of irrigation in arid and semi-arid regions is a global phenomenon. It is estimated that about 10-33% of irrigated lands in various countries have adversely been affected due to water logging and soil salinization. It seems that since 1979-80, the area under water logging and soil salinization is increasing at the rate of 3,000 to 4,000 ha per annum. It is estimated that around 4.5 million ha area in India is affected by the problem of water logging (Table 6). Coastal soils: Characteristics and distribution Areas quoted under different soil groups do not appear to have been precisely made since the coastal plains are not yet well defined. Of the two coastlines in India length of the East coast is higher than that of the West. The continental shelf is more stable than the coast. The continental shelf of 0-50 m depth spreads over 1,91,972 sq km and that of 0-200 depth over 4,52,060 sq km area. The shelf is wide (50-340 m) along the East coast. The Exclusion Economic Zone is estimated at 2.02 million sq km. Table 6. Extent and distribution of waterlogged and salt-affected soils in India (000’ ha) State

Waterlogged area Canal

Unclassi-

Comm-

fied

Salt-affected area Total

ands Andhra

Canal

Outside

Comm-

Canal

Coastal

Total

ands

266.4

72.6

339.0

139.4

390.6

283.3

813.3

Bihar

362.6

NA

362.6

224.0

176.0

Nil

400.0

Gujarat

172.6

311.4

484.0

540.0

372.1

302.3

1214.4

Haryana

229.8

45.4

275.2

455.0

NA

Nil

455.0

Karnataka

36.0

NA

36.0

51.4

266.6

86.0

404.0

Kerala

11.6

NA

11.6

NA

NA

26.0

26.0

Madhya

57.0

NA

57.0

220.0

22.0

Nil

242.0

6.0

105.0

111.0

446.0

NA

88.0

534.0

Orissa

196.3

NA

196.3

NA

NA

400.0

400.0

Punjab

198.6

NA

198.6

392.6

126.9

NA

519.5

Rajasthan

179.5

168.8

348.3

138.2

983.8

NA

1122.0

Tamil Nadu

18.0

109.9

127.9

256.5

NA

83.5

340.0

Uttar Pradesh

455.0

1525.6

1980.6

606.0

689.0

Nil

1295.0

West Bengal

NA

NA

NA

Nil

NA

800.0

800.0

Total

2189.4

2338.7

4528.1

3469.1

3027.0

2069.1

8565.2

Pradesh

Pradesh Maharashtra &Goa

Note: NA means data not available; Source: Singh (1994)

15


Practically, no systematic study was earlier made to demarcate the coastal soils based on well- defined scientific indices valid for the different sub-ecosystems in this country. Among the past works some have suggested 3.1 million hectare area (including mangrove forests), while others suggested 23.8 million hectare under coastal salinity in India. The coastal saline soil has been used by various workers almost synonymously with coastal soil per se which is not correct since all coastal soils are not saline in nature. None of the above estimates appears to have been made on sound scientific basis. However, the latest compilation made by Velayutham et al. (1998) on the soil resources and their potentials for different Agro-ecological Sub Regions (AESR) of India show total 10.78 million hectare area under this ecosystem (including the islands) in India, which was the first scientific approach for delineation of the coastal soils. Salient features of coastal problem soils Coastal soils in a number of situations are constrained by various technological factors limiting the agricultural productivity and therefore, merit attention. Salinity in the soils and ground waters has, however, become a major environmental issue, and excessive salinity in the soil or irrigation water has been considered as the main limiting factor for the distribution of plants in natural habitats. The salient factors in the coastal plains are: (i) Excess accumulation of soluble salts and alkalinity in soil, (ii) Pre-dominance of acid sulphate soils, (iii) Periodic inundation of soil surface by the tidal water, and (iv) Eutrophication and hypoxia. All the above factors affect nutrient balance in soil and, in turn, plant growth. Salinization is a major form of land degradation in agricultural areas, including the coastal soils. Statistics about the extent of total salt affected soils in the world vary. However, general estimates are close to 1 billion hectare, which represent about 7% of the earth’s continental extent. Salinity build-up in coastal soils takes place mainly due to salinity ingress of ground water aquifers, for which the main factors responsible are: (1) excessive and heavy withdrawals of ground water from coastal plain aquifers, (2) seawater ingress, (3) tidal water ingress, (4) relatively less recharge, and (5) poor land and water management. Attempts have been made on modeling of ground water behaviour with respect to seawater intrusion. Salt water intrusion takes several forms. Horizontal intrusion occurs as the saline water from the coast slowly pushes the fresh inland ground water landward and upward. Its cause can be both natural (due to rising sea levels) and man induced, (say, by pumping of fresh water from coastal wells). Pumping from coastal wells can also draw salt water downward from surface sources, such as tidal creeks, canals, embayment. This type of intrusion occurs within the zone of capture of pumping wells, which is local in nature, where significant drawdown of the water table causes induced surface infiltration. A third of intrusion is called ‘upconing’. Upconing also occurs within the zone of capture of a pumping well, with salt water drawn upward toward the well from the salt water layer or well existing in deeper aquifers. Salt accumulation: Salt accumulation in soil affects plant growth in the coastal soil in much the same way as in inland soils except for the effects due to specific toxicity of ions under given situations. Three major types of salt affected soils exist in the coastal plain. Soil Fertility: With regard to soil fertility, the coastal soils are usually rich in available K and micronutrients (except Zn), low to medium in available N and are 16


having variable available P status. Major portion of the applied N fertilizer is lost through volatilization. Coastal Saline Soils Of all the major ecosystems, which factor in agriculture or food production, ‘coastal’ has a significant role, wherein about 50-70 % of the global population lives within 100 km of the coastline covering only about 4 % of earth’s land. Besides, the ecosystem is highly risk prone and vulnerable causing colossal damage to lives and properties, and this is further compounded due to climate change. Agriculture, on the coastal plain is constrained by a number of technological, social or anthropological, and climatic factors limiting the productivity. Coastal saline soils occur along the 6100 km long coastline of India. Salinity problems in coastal areas occurred during the process of their formation under marine influences and subsequent periodical inundation with tidal water, and in case of low lands having proximity to the sea, due to high water table with high concentration of salts in it. The coastal soils exhibit a great deal of diversity in terms of climate, physiography and physical characteristics as well as in terms of rich stock of flora and fauna. These soils comprise deltas, lacustrine fringes, lagoons, coastal marshes and narrow coastal plains or terraces along the creeks. About 3.1 million hectares of coastal soils are widely distributed in the coastal belt of West Bengal, Orissa, Andhra Pradesh, Pondicherry, Tamil Nadu, Kerala, Karnataka, Maharashtra, Gujarat, Goa and Andamans and Nicobar Islands. The coastal soils may be either saline or acid sulphate in nature. The saline soils are dominant with NaCl and Na2SO4 with abundance of soluble cations in the order of Na>Mg>Ca>K and Chloride as the predominant anion. The major problems encountered in these areas are:      

These lands are subjected to the influence of tidal waves and periodical inundation by tidal water; Shallow water table enriched with salt contributes to increase in soil salinity during winter and summer months; Heavy rainfall resulting in excess water during Kharif season; Poor surface and subsurface drainage conditions; Lack of good quality irrigation water and acute salinity during Rabi; Poor socio-economic conditions of the farming community limiting introduction of high investment technologies.

Inundation and flooding of soils A flood is an overflow or accumulation of an expanse of water that submerges land. In the sense of ‘flowing water’, the word may also be applied to the inflow of the tide. ‘Coastal flood’ is caused by severe sea storms, or as a result of another hazard (e.g. tsunami or hurricane). A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category. Coastal flooding is a problem wherever development has occurred adjacent to, or on, beach systems. The problems of maintaining these areas are accentuated by naturally rising sea levels due to global climate change. Floods usually occur when storms coincide with high tides. Very often the problem becomes much more severe with increase in salinity in the flood water caused by breaching or overflowing of the sea dykes, etc. Flooding thus causes significant change in soil properties depending on the soil, hydrological properties of the flood water, and duration of flood. Among others the most significant changes in soil properties of relevance to plant growth are silt deposition, accumulation of salts, erosion of top soil, organic C status in soil, 17


depletion of soil oxygen resulting in lack of plant metabolic activities, and overall reduced soil atmosphere causing significant change in soil nutrient dynamics. References Rao, G. Gururaja, Chinchmalatpure, A.R., Khandelwal, M.K., Arora, Sanjay and Singh, G. (2009) Management of salt affected black soils – impact of technological interventions. Journal of Soil Salinity and Water Quality 1(1&2): 55-62. Yadav, J.S.P. (2008). Sustainable management of coastal ecosystem for livelihood security: a global perspective. Journal of Indian Society of Coastal Agricultural Research 26(1): 5-11.

18


Harnessing Productivity Potential of Sodic Soils through Salt Tolerant Crops and Cropping Sequences Y.P. Singh Principal Scientist ICAR-Central Soil Salinity Research Institute, Regional Research Station, Lucknow Email: [email protected] Introduction Sodicity and salinity are the major abiotic stresses in arid and semi arid regions of the country. In India there is about 6.73 million ha of salt affected soils out of which, 2.8 million are sodic in nature and primarily occurring in the Indogangetic alluvial plains. These soils are different from arable soils with respect to two important properties, viz. the soluble salts and the soil reaction. Soluble salts in soils may influence the crop production through changes in the proportion of exchangeable cations, soil reaction, the physical properties and the osmotic and specific ion toxicity. The replacement of exchangeable Na+ with Ca2+ require the application of amendments which can either supply soluble calcium ions directly or induce its solubility from the soil constituents. Nutritional imbalance or specific ion toxicity also adversely affect the yields. For reclamation of these soils a suitable amendment is required to neutralize the soluble salts. Complete reclamation of these soils is a gradual process and increases with time. Selection of suitable crops and cropping system during and after reclamation is very important. During initial years of reclamation salt tolerant varieties of selected crops like rice, barley, wheat and mustard should be grown and gradually shifted to the non salt tolerant and high value crops to get higher income. Due to poor physical properties, the management practices during initial years of reclamation for cultivation of crops in sodic soils are quite different than the same crop grown in normal soils. The studies conducted at Central Soil salinity Research Institute, Karnal and its Regional Research Station, Lucknow it is proved that selection of suitable crops and cropping systems along with recommended management practices during and after reclamation of sodic soils, their productivity can be enhanced. From the study conducted at CSSRI, Regional Research station, Lucknow, it has been observed that with the application of reduced dose of gypsum (25% GR) salt tolerant varieties of rice should be replaced with high yielding varieties after four years and of wheat after three years. If the gypsum is applied @ 50% GR, salt tolerant variety of rice should be replaced with high yielding varieties after three years and wheat after two years or diversify the rice –wheat cropping system with highly remunerative medicinal and aromatic crops like sweet basil in kharif and Matricaria in rabi to enhance the productivity potential of reclaimed sodic soils and to save the natural resources. In this article, an attempt is made to highlight the reclamation methodology of sodic soils and harnessing their productivity through management of crops and cropping systems during and after reclamation. Area and distribution of Salt affected soils Salt-affected soils are commonly found in Indo-gangetic plains of Uttar Pradesh, Punjab, Haryana, Rajasthan, Bihar, and West Bengal. Different workers have reported variable estimates of salt-affected soils in India. According to the latest estimation in India salt-affected soils occupy about 6.73 million hectare of land, 19


which is 2.1% of the geographical area of the country (Sharma et al., 2004). Out of 584 districts in the country, 194 have salt-affected soils (Table 1). Table 1. State-wise extent of salt-affected soils in India (million ha) State Andhra Pradesh Andman & Nicobar Bihar Gujrat Haryana Kranataka Kerala Madhya Pradesh Maharashtra Orissa Punjab Rajasthan Tamilnadu Uttar Pradesh West Bengal Total Source: Sharma et al. (2004)

Saline 0.78 0.08

Sodic 1.97 0.00

0.47 1.68 0.49 0.02

1.06 0.54 1.83 1.48

0.20 0.00 1.84 1.47 0.00 0.20 0.01 0.22 0.44 2.96

0.00 1.40 4.23 0.00 0.15 0.18 0.35 1.35 0.00 3.77

Total 2.75 0.08 1.53 2.22 2.32 1.50 0.20 1.40 6.07 1.47 0.15 0.38 0.36 1.57 0.44 6.73

Characteristics of sodic soils These soils have higher proportion of sodium in relation to other cations in soil solution and in exchange complex. These soils contain excess of salts capable of alkaline hydrolysis such as sodium carbonate, sodium bicarbonate and sodium silicate; and sufficient exchangeable sodium to impart poor physical conditions to soil and affecting growth of most plants. These soils have saturated paste pH>8.5, exchangeable sodium percentage (ESP)>15 and different levels of salinity (EC). The presence of calcium carbonate concretions at about 1m depths causes’ physical impedance for root proliferation. The growth of most crop plants is adversely affected because of poor physical conditions, disorder in nutrient availability and suppression of biological activities due to high pH and exchangeable sodium percentage. These soils are deficient in organic carbon, available N, Ca, and Zn. Reclamation and management The reclamation of sodic soil may require technique modified from that used for reclamation of saline soils. In sodic soils, exchangeable sodium destroys the physical structure of the soil and makes it almost impervious to water. The sodium must first be replaced by Calcium cation and then leached downward and out of root zone. Calcium is often used to replace sodium in sodic soil, all calcium compounds, calcium sulphate (gypsum, CaSO4.2H2O) is considered best and cheapest for this purpose. Calcium from gypsum replaces sodium, leaving soluble sodium sulphate in water which is then leached out.

20


Major Components of Reclamation Technology The major technological steps involved in reclamation process consisted of the following: a Delineation of affected areas b Provision of assured water supply/Development of irrigation system, preferable through installation of bore wells c On-farm Development (land levelling, bunding, construction of field irrigation and drainage channels) d Drainage System Development e Application of Chemical Amendments, Leaching and f The Agronomy of Sodic Land (including crop selection and cropping pattern, soil fertility management, other improved cultural practices etc.) The amount of gypsum to be added depends upon the severity of the sodicity, soil texture and selection of crop to be grown. The studies conducted at CSSRI, Karnal, revealed that application of gypsum @ 50% GR in 0-15cm soil dept is sufficient to grow shallow rooted crops. However, a hybrid approach (chemical + biological) developed at CSSRI, RRS, Lucknow revealed that application of gypsum @ 25% GR and mixing in 10cm surface layer and growing of salt tolerant varieties of rice proved economical and sustainable for reclamation of sodic soils (Singh et al., 2009 ).The chemical amendment should be added only once at the initial stage of reclamation and grow crops continuously to add biomass through root residues to boost further reclamation. Various organic amendments like green manure, compost, farm yard manure, pressmud, crop residues such as paddy straw have also fond effective in reclamation of sodic soils but their effectiveness as sole application is much lower than the chemical amendments. Decomposition of organic matter improves soil permeability and also increases water-soluble aggregates. Table 2. Combined effect of gypsum and FYM on sodic soil reclamation Amendment dose Gypsum % GR 0

Grain yield (t /ha)

Change in ESP after wheat

FYM (t /ha)

Rice

Wheat

0

5.2

1.2

64

25

0

5.3

2.3

55

50

0

5.3

2.4

50

0

20

5.3

2.2

58

25

20

5.8

2.8

45

50

20

5.9

2.9

45

0.4

0.3

CD(P=0.05)

Source: Singh (1998) Initial pH 10.2, ESP 89

21


Swarup and Singh (1989) observed that the use of FYM in conjunction with gypsum enhanced the yield of rice and wheat significantly over application of gypsum alone. The decomposition of organic matter releases CO 2 and other by products like acids or acid products depending upon the PO 2 in the soil. These decomposed products enhance solubility of native CaCO 3, and thus provide Ca for the removal of exchangeable Na. Organic matter along with inorganic amendment quickens the reclamation of alkali soils. Application of FYM combined with gypsum can help reduce the gypsum dose to half of that needed in the absence of manure. There is thus , a vast scope for exploiting the synergistic effect of locally available organic materials like FYM, municipal solid waste compost, pressmud for minimizing the dose of chemical amendments and reducing the reclamation cost (Table 2). Selection of crops and cropping sequences Selection of proper crop in the initial stages of reclamation is very crucial because crop differs widely in their tolerance to soil sodicity. Some crops are sensitive, whereas others are either semi tolerant or tolerant to a given level of sodicity (Table 3). The selected crops should not only be tolerant but should also exert reclaiming effect on the soil. Therefore in the initial years of reclamation, only tolerant crops should be grown and gradually choice may be shifted to relatively less tolerant and sensitive crops. Among the agricultural crops rice in Kharif season is most ideal as the first crop because it can tolerate standing water and has very high tolerance to sodicity, extensive shallow root system, and ability to accelerate availability of native Ca for replacement of exchangeable Na through root activities and in rabi season only shallow rooted crops like wheat , barley, berseem and mustard could be grown in the initial years (Yadav and Agarwal, 1959). In Uttar Pradesh rice in kharif season followed by berseem, wheat or barley in winter season reported better crops in the initial years of reclamation. when salt tolerant varieties of rice was grown in crop sequences for three years the reclamation of sodic soils was increased and the pH of surface soils reduced and it becomes possible to grow highly value crops like oil seed crops (mustard, linseed) and medicinal and aromatic crops (Tulsi and Matricaria). Study conducted at CSSRI, Regional Research Station, Lucknow determined the time frame for substitution of salt tolerant varieties of rice and wheat with non-salt tolerant high yielding varieties or high value crops to get higher return (Singh et al., 2010). Table 3. Relative crop tolerance to sodicity 30-50 Moderately tolerant Barley Mustard Rapeseed Wheat Sunflower Sorghum Shaftal Berseem

ESP range 20-30 Semi tolerant Linseed Garlic Sugarcane Cotton Guar Groundnut Onion Pearl millet Tulsi Matricaria Bakla

22

0.8 dSm-1) or soil (ECse>1 dSm-1 in saturated soil extracts. Salt stress is one of the most widespread abiotic constraints in food production.It may also result in the negative ecological, social and economic outcomes. However, recent advances in technologies like nanotechnology may be used to investigate the increasing salt tolerance in cultivated plants and that could be one of the most promising and effective strategies for food production in salt-affected environments. In the current ties, a pressing need exists to elucidate the basic properties of nano-particles and different processesthat govern their fate in the salt-affected soils and their bioavailability. This understanding will help us to reap the benefit of nanotechnology without producing adverse ecological consequences. Determination of the bioavailability of nano-particles in soil is required. If nano-materials are not bioavailable, they are not likely to have impacts. The extent and mechanisms of NPs uptake by plants in soil and subsequent translocation remain to be precisely determined. Characterizing intracellular transformation is also necessary to assess bioavailability. Research efforts need to focus on understanding responses to nano-material inputs on agroecology and biogeochemical processes at relevant environmental concentrations and forms. Assessing these processes and effects requires 39


developing methods and perhaps new instrumentation capable of quantifying nano materials in environmental matrices and in organisms. A broader range of species needs to be investigated for nano-particles impacts. There is a need for measurements of the stability of NPs, and their longterm fate. The measurements need to focus on particle concentration and surface characteristics. Development of increasingly more sensitive analytical equipment should provide means by which to analyze quantitatively the nanoparticle stability in aqueous environments. Limited information is available on natural nanoparticle formation and their stability in the soil systems.The conditions and geo/soil variables that promote their formation or control their stability are not known. This is an area that requires concentrated research efforts. The issues related to nanoparticles role in affecting or controlling the extent and rates of soil processes and reactions and overall nutrients and contaminants mobility need to be considered seriously. Studies are required with different types of engineered nanoparticles to provide evidence and measure in a more rigorous manner in relation to the effects of a variety of soil variables, in addition to soil solution pH and ionic strength. Studies are needed to determine the roles and contributions of these processes to the overall mobility of nutrients and salts in terrestrial systems. References Bhardwaj, A.K., Mandal, U.K., Bar-Tal, A., Gilboa, A. and Levy, G.J. (2008). Replacing saline-sodic irrigation water with treated wastewater: effects on saturated hydraulic conductivity, slaking, and swelling. Irrigation Science 26: 139-146. Bhardwaj, A.K., McLaughlin, R.A. and Levy, G.J. (2010). Depositional seals in polyacrylamide-amended soils of varying clay mineralogy and texture. Journal of Soils and Sediments10: 494-504. Bhardwaj, A.K., McLaughlin, R.A., Shainberg, I. and Levy, G.J. (2009). Hydraulic characteristics of depositional seals as affected by exchangeable cations, clay mineralogy, and polyacrylamide.Soil Science Soc. Am. Journal73 (3): 910-918. Bhardwaj, A.K., Shainberg, I., Goldstein, D., Warrington DN and Levy GJ (2007). Water retention and hydraulic conductivity of cross linked polyacrylamides in sandy soils. Soil Science Society of America Journal71: 406-412. Fiorani, D. (2005).Nanostructure science and technology. In: Surface Effects in Magnetic Nanoparticles, XIV. 300 p. Maji, A.K., Obi Reddy, G.P. and Meshram, S. (2008).Acid soil map of India.Annual Report2008.NBSS&LUP, Nagpur, India. Mandal, A.K., Sharma, R.C., Singh, G. and Dagar, J.C. (2010) Computerized Database on Salt Affected Soils in India. Technical Bulletin No. 2/2010. Central Soil Salinity Research Institute, Karnal, India, pp 28. NAAS, 2010.Degraded and waste lands of India-Status and spatial distribution.Indian Council of Agricultural Research.Pp.158. Sharma, R.C., Rao, B. R. M. and Saxena, R.K. (2004).Salt Affected soils in IndiaCurrent Assessment. In: Advances in Sodic Land Reclamation, pp.1-26. International Conference on Sustainable Management of Sodic Lands, held on 914 February at Lucknow, India.

40


Bio-remediation of Salt Affected Soils through Halophytes and Halophilic Microbes Sanjay Arora Senior Scientist ICAR-Central Soil Salinity Research Institute, Regional Research Station, Luckow (U.P.) Introduction Halophytes are remarkable plants that tolerate salt concentrations that kill 99% of other species. However, although halophytes have been recognized for hundreds of years, their definition remains equivocal. Definition on ability ‘to complete the life cycle in a salt concentration of at least 200 mm NaCl under conditions similar to those that might be encountered in the natural environment’ (Flowers et al., 1986). Adopting a definition based on completion of the life cycle should allow separation of what might be called ‘natural halophytes’ from plants that tolerate salt but do not normally live in saline conditions .Other classifications of halophytes have been suggested that are based on the characteristics of naturally saline habitats or the chemical composition of the shoots or the ability to secrete ions. However, although saline habitats do differ in many regards (e.g. soil water content) and differences do exist amongst species in the balance of Na + and K+ in shoot tissues, we have not, at this stage, embraced the suggested subdivisions of halophytes, as the underlying mechanisms remain unclear (salt glands expected). The general physiology of halophytes has been reviewed occasionally (Flowers et al., 1986) and since then other reviews have examined their eco-physiology, photosynthesis, response to oxidative stress and flooding tolerance as well as the physiology of sea grasses. The potential of halophytes as donors of tolerance for cereals (Colmer et al., 2005) and as crops in their own right has also been reviewed (Glenn et al., 1999; Colmer et al., 2005), as have the effects of salinity on plants in general. In the following pages, we discuss the basic physiology of salinity tolerance in halophytes – growth, osmotic adjustment, ion compartmentation and compatible solutes; limitations of space have precluded a review of transpiration in halophytes and of salt glands. What are Halophytes? The prefix ‘halo’ and root ‘phytes’ are translated as salt and plant, respectively. Thus halophytes are often described as salt-tolerant, salt-loving, or saltwater plants whereas practically all of our domesticated crops are considered glycophytes (‘glyco’ or sweet) having been selected and bred from sweet or freshwater ancestors. Halophytes are generally defined as rooted seed-bearing plants (i.e. grasses, succulents, herbs, shrubs and trees) that grow in a wide variety of saline habitats from coastal sand dunes, salt marshes and mudflats to inland deserts, salt flats and steppes. These highly adaptable plants, which can accrue relatively large amounts of salt, are found in every climatic zone where there is vegetation, from the tropics to tundra. Halophytes have been divided into two groups, obligative halophytes, which invariably need salt for their growth and metabolism, and facultative halophytes, which grow and adapt to saline as well as non-saline conditions. Halophytes are also divided based on their occurrence with respect to water i.e., hydro-halophytes, which grow in saline water medium and xerohalophytes which grow mainly dry land saline conditions.

41


Distinguishing features of halophytes Majority of the halophytes are deep-rooting perennials that achieve their optimum growth and yield potential at thresholds between 6-25 dS m-1 (EC), levels at which virtually all of our modern crops would perish. Some of the more prolific ones thrive in the coastal saline soils and arid inland saline areas with concentrations of 45 dS m-1 (seawater) and above eg., Salvadora persica. With their vigorous growth and root development, these plants are often able to take advantage of less saline moisture within the soil profile and adapt to seasonal variability in salinity by altering germination, growth, and reproduction cycles to best suit their survival needs. In general, halophytes produce by and large salt-free seeds which require freshwater for proper germination. However, there are exceptions among the extreme ones which are able to germinate even at half the concentration of seawater eg., Salvadora persica (Rao et al., 2003, 2004). As they grow into seedlings and mature, halophytes begin to develop and exhibit the salt-tolerance mechanisms for which they are known. In certain halophyte species, distinct lifecycle variations in salt-tolerance have been observed which include increased sensitivity when a plant is producing seed or forming buds. Once established, halophytic perennials are better able to retain moisture in the root zone than shallow-rooting annual crops. Although well-adapted to sandy well-drained soils, persistent root penetration also enables them to perform in clayey soils. In recent years, however, the attention is being paid worldwide to accommodate the salt tolerant species of industrial importance for highly saline degraded areas including coastal marshes. Some oil yielding species such as Salicornia bigelovii, Salvadora persica, S. oleoides, Terminalia catappa, Calophyllum inophyllum and species of Pandanus are important and can be grown in highly saline areas irrigating with sea water or water of high salinity. Borassus flabellifer Calophyllum inophyllum, Pongamia pinnata and Nypa fruticans are other important coastal plants of economic importance. Similarly many inland salt-tolerant species find industrial application. The petro-crops like Jatropha curcas and Euphorbia antisyphilitica can successfully be grown irrigating with water of high salinity. Capparis decidua found in saline arid regions is highly medicinal and valued for commercial pickle. Simmondsia chinensis with seed-oil similar to that of spermwhale; aromatic species like Matricaria chamomilla, Vetiveria zizanioides, Cymbopogon martinii and C. flexuosus; and medicinal plants such as Isabgol (Plantago ovata), Adhatoda vasica, Withania somnifera, Cassia angustifolia and many others can be grown successfully on alkali soil (up to pH 9.6) as well as calcareous saline soil irrigating with saline water up to EC 12 dS/ m (Dagar, 2005). There are also many other salt-tolerant fruit, forage, oil-yielding, medicinal and fuelwood species, which have been tried and found suitable for highly saline situations. The scopes of many of these species of high economic value for saline and sodic habitats along with their management and utilization. Halophytes and Saline Lands India scenario A sizeable portion of these salt affected soils are highly deteriorated making rehabilitation of such lands difficult due to lack of resources, such lands being community lands and being owned by resource poor farmers using costly chemical 42


amendments. Re-vegetation of such lands through different land uses viz. plantation of multipurpose tree species including energy plantation are some of the options to meet the fuel, fodder, timber and energy needs is promising in view of fuelwood, energy, fodder shortages and environmental benefits. This approach is known to have the potential to reclaim wastelands and provide livelihood security through regular employment generation. Due to large population, India can not afford any diversion of agriculture land to meet its fast rising energy demands which have to be met from such marginal areas only. Scenario in Coastal Gujarat The total salt affected soil in India was reported approx. about 6.74 M ha out of which 3.2 M ha is coastal soil and 2.8 mha is sodic land rest is inland saline soil. Gujarat with 2.2 Mha contributes to 20 percent of the total salt affected soil in country. Gujarat comes second after West Bengal in the total extent of coastal salt affected soil with estimated area of about 7.2 lakh hectare. This 7.2 lakh hectare is distributed in district of Kutch, Saurastra region and districts of South Gujarat. The wide variety of halophytes and of their characters permits to envision a profitable use of vast barren extensions of saline lands by selecting the appropriate species best fitting local conditions. Possible actions in dependence of peculiar soil and water conditions are synthetically shown in the table 1. Table 1. Possible actions for coastal and inland saline lands Case 1

Soil Coastal lands

Main water source Seawater

Principal possible actions Fixing dunes, landscaping, growing mangroves, fodder production

2 3

Inland saline areas Inland saline areas (dry)

Brackish/saline water Various scopes Rain Erosion control, fodder production

4

Salinized agricultural lands

Fresh/brackish water

5

Endangered agricultural

Fresh/brackish water

Lands

Soil rehabilitation, agricultural production Soil protection, agricultural production

All the possible actions listed in the table can be easily undertaken after an appropriate plant selection but a preliminary analysis assessing their environmental, economic and social feasibility is in all cases required. Salt Tolerance of Halophytes Although there are many aspects of the physiology of salt tolerance that are yet to be understood, it is clear that the trait is complex in that, at a minimum, it 43


requires the combination of several different traits: the accumulation and compartmentation of ions for osmotic adjustment; the synthesis of compatible solutes; the ability to accumulate essential nutrients (particularly K) in the presence of high concentrations of the ions generating salinity (Na); the ability to limit the entry of these saline ions into the transpiration stream; and the ability to continue to regulate transpiration in the presence of high concentrations of Na+ and Cl– (Flowers and Colmer, 2008). K/Na selectivity The selectivity of halophytes for K over Na varies between families of flowering plants (Flowers et al., 1986). Net selectivity (net SK : Na) calculated as the ratio of K concentration in the plant to that in the medium divided by the ratio of Na concentration in the plant to that in the medium, ranges between average values of 9 and 60 (Flowers and Colmer, 2008) with an overall mean of 19; it is only in the Poales that net SK : Na values of the order of 60 are found. Within the monocots there are three orders with halophytes, but no data are available for the net S K : Na values of species within the Arecales. In the Alismatales, the average net SK : Na (across just three species) is 16 (range 10 to 22), suggesting that high selectivity has evolved only in the Poales (for halophytes within this order, average selectivities of are 58 in the Juncaginaceae (two species) and 60 in the Poaceae (nine species). There is too little data to analyse the net SK : Na values within the dicots, but the average value is 11 compared with 60 in the Poales (Flowers and Colmer, 2008). Salt glands Glandular structures are not uncommon on plants; they can secrete a range of organic compounds (Wagner et al., 2004). However, the ability to secrete salt appears to have evolved less frequently than salt tolerance. Salt glands, epidermal appendages of one to a few cells that secrete salt to the exterior of a plant (Thomson et al., 1988) have been described in just a few orders of flowering plants– the Poales (e.g. in Aeluropus littoralis and Chloris gayana), Myrtales (e.g. the mangrove Laguncularia racemosa), Caryophyllales (e.g. Mesembryanthemum crystallinum and the saltbush Atriplex halimus), Lamiales (e.g. the mangroves Avicennia marina and Avicennia germinans) and the Solanales (e.g. Cressa cretica). Their distribution across the orders of flowering plants suggests at least three origins, although there may have been more independent origins within orders. Whether salt glands evolved from glands that originally performed some other function is unclear, but it is difficult, at least in the Poaceae, to get glandular hairs on non-halophytes (such as Zea mays L.) to secrete salt. Importance of Halophytes Agriculture and Land Management Salt-affected land is increasing worldwide through vegetation clearance and irrigation, both of which raise the watertable bringing dissolved salts to the surface. It is estimated that up to half of irrigation schemes worldwide are affected by salinity (Flowers and Yeo, 1995). Although irrigated land is a relatively small proportion of the total global area of food production, it produces a third of the food (Munns and Tester, 2008). Salt stress has been identified as one of the most serious environmental factors limiting the productivity of crop plants (Flowers and Yeo, 1995), with a huge impact on agricultural productivity. The global annual cost of salt-affected land is likely to be well over US$12 billion (Qadir et al., 2008). Future agricultural production will rely increasingly on our ability to grow food and 44


fibre plants in salt-affected land (Rozema and Flowers, 2008; Qadir et al., 2008). Halophytes as Crops Naturally salt-tolerant species are now being promoted in agriculture, particularly to provide forage, medicinal plants, aromatic plants (Qadir et al., 2008) and for forestry. Examples of useful halophytes include the potential oil-seed crops Kosteletzkya virginica, Salvadora persica, Salicornia bigelovii and Batis maritima; fodder crops such as Atriplex spp. Distichlis palmeri and biofuels. Growing salttolerant biofuel crops on marginal agricultural land would help to counter concerns that the biofuel industry reduces the amount of land available for food production (Qadir et al., 2008). At the extreme, plants that can grow productively at very high salt levels could be irrigated with brackish water or seawater (Rozema and Flowers, 2008). Although plants that put resources (Yeo, 1983) into developing salttolerance mechanisms (e.g. the production of compatible solutes to maintain osmotic balance is an energetic cost) may do so at the expense of other functions, many halophytes show optimal growth in saline conditions (Flowers and Colmer, 2008) and salt marshes have high productivity. The fact that dicolytedonous halophytes can grow at similar rates to glycophytes suggests that salt tolerance per se will not limit productivity. Here the contrast with drought tolerance is stark: without water plants do not grow, but may survive; with salt water, some plants can grow well. Apart from direct use as crops, we may increasingly need to rely on halophytes for re-vegetation and remediation of salt-affected land. Over the last 200 years, industrialization in Europe and elsewhere has lead to an enormous increase of production, use and release of traces of heavy metals into the environment. A large portion of these toxic materials, including Cd, Cu, Pb and Zn, accumulate in sediments, including the soils of tidal marshes. Recent studies showed that some sea grasses and salt marsh plants are capable of extracting heavy metals from sediments and accumulating them in belowground or aboveground tissues (Weis and Weis, 2004). The processes and potential application of these aquatic halophytes merits much greater research and development. Growing salt-tolerant plants, including species of Kochia, Bassia, Cynodon, Medicago, Portulaca, Sesbania, and Brachiaria, may also improve other soil properties, such as increasing water conductance or increasing soil fertility (Qadir et al., 2008). Halophytes may also lower the watertable, thereby allowing growth of salt sensitive species in salt-affected land. Food Yielding Halophyte and Salt-Tolerant Plants Among conventional crops, beetroot (Beta vulgaris) and date palm (Phoenix dactylifera) are well known for their food value and these can be grown successfully irrigating with saline water. Fruit bearing gooseberry (Emblica officinalis), karonda (Carissa carandas), ber (Ziziphus mauritiana), and bael (Aegle marmelos) withstand drought as well as salinity. These can be cultivated with success irrigating with water up to 12 dS/ m. These along with guava (Psidium guajava) and Syzygium cuminii could be grown on highly alkali soil (pH up to 9.8) with application of amendments (gypsum) in augerholes. Pomegranate (Punica granatum) is salttolerant but does not withstand waterlogging. This when grown on raised bunds in alkali soil (pH 10) performed well along with kallar grass (Leptochloa fusca) producing 15-20 Mg/ ha fresh forage and rice (var. CSR-10) producing up to 4 Mg /ha grains when grown in sunken beds without applying any amendments. Raw fruits of kair (Capparis decidua) are used for pickles and possess medicinal value. It grows naturally on both saline and sodic soils and can be cultivated raising from rootstocks, seeds and also stem cuttings in nursery and then transplanting. It may 45


be irrigated with saline water. The coastal badam (Terminalia catappa) and species of Pandanus are known for their oils of industrial application. Fruits of Pandanus are staple food for coastal population of bay, islands and both of these plants are found natural growing in tidal zone. These can be cultivated successfully in coastal areas. Palmirah palm (Borassus flabellifer) is widely used for toddy, jiggery, vinegar, beverage, juice for sugar and edible radicles and fruits, is found widely distributed all along Andhra coast. It needs to be genetically improved for wider cultivation. The use of is paper industry in Rajasthan and Gujarat is well known. The young leaves and shoots of Chenopodium album, species of Amaranthus, Portuleca oleracea, Sesuvium portulacastrum and many others are used as vegetable and salad in many parts of the country. Many of these are even cultivated (Dagar, 2005). Forages In many coastal areas where mangroves occur sporadically and there is scarcity of fodder, the foliage of many mangrove and associated plants such as species of Avicennia, Ceriops, Rhizophora, Terminalia, Pongamia and others, are used as forage for cattle, goats and camel. Among other trees, species of Acacia, Prosopis, Salvadora, Cordia, Ailanthus and Ziziphus are traditional fodder plants of arid regions. Species of Salicornia, Chenopodium, Kochia, Atriplex, Salsola, Suaeda, Trianthema, Portulaca, Tribulus and Alhagi along with several grasses such as Leptochloa fusca, Aeluropus lagopoides, Cynodon dactylon, Dactyloctenium sindicum, Paspalum vaginatum, Sporobolus airoides, S. marginatus, Chloris gayana, Echinochloa turnerana, E. colonum, Eragrostis tanella, Dichanthium annulatum, D. caricosum, Brachiaria mutica, Bothriochloa pertusa and many others are commonly used as forages from alkali and saline areas. Many of these forages can be cultivated successfully on degraded salt-affected soils or in drought prone areas irrigating with saline water, where other arable crops cannot be grown. Industrial oil production Salinity and alkalinity are the two most important factors limiting agricultural productivity in arid and semiarid regions. Reclaiming these lands for commercial crops is too costly for most countries to afford. Faced with a declining base of arable farmland and increasing demand for food, fiber and energy, this warrants the need for utilization of naturally salt tolerant species (halophytes) in irrigated and non-irrigated agriculture. Salvadora persica, a facultative halophyte appears to be a potentially valuable oilseed crop for saline and alkali soils, since the seed contains 40–45% of oil rich in industrially important lauric (C 12) and myrestic (C14) acids. Attempts were made to assess the performance of the species on saline and alkali soils. From the results it was evident that the species can be grown on both soil types, however height, spread and seed yield were significantly higher for plants grown on saline soils as compared to plants cultivated on alkali soils. No significant difference was observed in oil content between seed obtained from plants grown on saline and alkali soils. The study indicated that S. persica can be cultivated as a source of industrial oil on both saline and alkali soils for economic and ecological benefits, otherwise not suitable for conventional arable farming (Reddy et al., 2008). Recently Salicornia bigelovii has been evaluated as a source of vegetable oil and the cake as animal feed, is being grown in some areas of Gujarat and Rajasthan. It withstands high salinity both of soil and water. Recently Salicornia bigelovii has been evaluated as a source of vegetable oil and the cake as animal feed, is being grown in some areas of Gujarat and Rajasthan. It withstands high salinity both of soil and water (Dagar, 2005). Several studies have 46


shown that the oil seed halophyte Salcornia irrigated with seawater displayed high seed and biomass production (Pandya et al., 2006). Cakile maritime also a halophyte reported for the same results. Phytoremediation Phytoremediation is the cultivation of plant for the purpose of reducing soil and water contamination (by organic and inorganic pollutants ) that are result from improper disposal of aquaculture, agriculture, and industrial effluent .On salt affected soil, phytoremediation is often effective and economical method of removing or reducing contaminates. Salicornia cultivation may also confer economic benefits as the plants can be harvested for selenium rich animal feed. A number of halophytic grasses have been proven to be effective in re-vegetating brine contaminated soil that typically result from gas and oil mining. Environmental Conservation Halophytes are especially well-suited for using brackish/saline water often requiring little or no freshwater in order to rehabilitate degraded vegetative habitats. For many, the application of both fresh and saline waters in mixed or alternating irrigation programs can provide appreciable cost reductions and resource savings. Integrated resource management schemes and the multiple use of drainage water for increasing salt-tolerant crops can significantly reduce on-farm consumption and replenish freshwater reservoirs. With proper management and waste disposal, these schemes can also prevent the further salinization of aquifers and groundwater of surrounding lands and habitats. Under waterlogged conditions, halophytes have demonstrated the ability to reduce saline water tables and, to a certain extent, reclaim affected lands. These deep-rooting trees and shrubs, with their continuous demand for water, help manage salinity and moisture in the upper soil layers, and tend to drive salts below the root zone of most other plants. Carbon Sequestration All plants extract carbon dioxide from the atmosphere for photosynthesis and biomass production. In general, halophyte biomass yields are comparable to those of glycophytes yet the associated costs of cultivation are often far less particularly in areas where there is an over abundance of saline resources. Halophytic agroforestry plantations may represent a cost-effective option for sequestering carbon and reducing their elevated levels in the biosphere. While trying to determine if indeed halophytes can be effectively utilized as carbon sinks, their potential for meeting our more immediate needs for crop alternatives and environmental conservation could be adequately assessed.

Microbial approach for bio-remediation Both physical and chemical methods for saline/sodic soil reclamation are not costeffective. The biotic approach ‘plant-microbe interaction’ to overcome salt stress has recently received a considerable attention from many workers throughout the world. Plant-microbe interaction is beneficial association between plants and microorganisms and also a more efficient method used for the reclamation of salt affected soils. Bacteria are the most commonly used microbes in this technique. Rhizosphere bacteria improve the uptake of nutrients by plants and /or produce plant growth promoting compounds and regenerate the quality of soil. These plant growth promoting bacteria can directly or indirectly affect plant growth. Indirect 47


plant growth promotion includes the prevention of the deleterious effects of phytopathogenic organisms by inducing cell wall structural modifications, biochemical and physiological changes leading to the synthesis of proteins and chemicals involved in plant defense mechanisms. Halophilic Microbes The existence of high osmotic pressure, ion toxicity, unfavourable soil physical conditions and/or soil flooding, are serious constraints to many organisms and therefore salt-affected ecosystems are specialised ecotones. The organisms found over there have developed mechanisms to survive in such adverse media, and many endemisms. The halophilic microorganisms or "salt-loving" microorganisms live in environments with high salt concentration that would kill most other microbes. Halotolerant and halophilic microorganisms can grow in hypersaline environments, but only halophiles specifically require at least 0.2 M of salt for their growth. Halotolerant microorganisms can only tolerate media containing 4.0

(iii) Highly Alkali

The above categories of irrigation waters may have varying hazardous effect on crop if not managed properly. Different types of hazardous effect are broadly categorized below and described to reflect the impact of irrigation water on crop production and soil quality:     

Salinity hazard - total soluble salt content, Sodium hazard - relative proportion of sodium to calcium and magnesium ions, pH - acid or basic, Alkalinity - carbonate and bicarbonate, Specific ions: chloride, sulfate, boron, and nitrate.

Salinity Hazard The most influential water quality guideline on crop productivity is the salinity hazard as measured by electrical conductivity (ECw). The general guidelines for salinity hazard of irrigation water based upon conductivity are depicted through Table-2. Table 2 - General guidelines for salinity hazard of irrigation water based upon conductivity Sl. No. Limitations for use Electrical Conductivity (dSm-1)* 1.

None

≤ 0.75

2.

Some

0.76 – 1.5

3.

Moderate1

1.51 – 3.0

4.

Severe2

≥ 3.0

1

2

*dSm-1at 25° C = mmhos/cm, Leaching required at higher range, Good drainage needed and sensitive plants may have difficulty at germination. The primary effect of high ECw water on crop productivity is the inability of the plant to compete with ions in the soil solution for water (physiological drought). The higher the EC, the less water is available to plants, even though the soil may 61


appear wet. Because plants can only transpire “pure” water, usable plant water in the soil solution decreases dramatically as EC increases. The amount of water transpired through a crop is directly related to yield, the impact of irrigation water with high EC on yield of various crops are depicted through Table 3. Table 3. Potential yield reduction from saline water for selected irrigated crops1 Crop

0%

Barley Wheat Sugarbeet3 Alfalfa Potato Corn (grain) Corn (Silage) Onion Dry Beans

5.3 4.0 4.7 1.3 1.1 1.1 1.2 0.8 0.7

% Yield Reduction 10% 25% -------------2ECw---------6.7 8.7 4.9 6.4 5.8 7.5 2.2 3.6 1.7 2.5 1.7 2.5 2.1 3.5 1.2 1.82 1.0 1.5

50% 12 8.7 10 5.9 3.9 3.9 5.7 2.9 2.4

1Adapted

from “Quality of Water for Irrigation.” R.S. Ayers. Jour. of the Irrig.and Drain. Div., ASCE. Vol 103, No. IR2, June 1977, p. 140.2ECw = electrical conductivity of the irrigation water in dS/m at 25oC. 3Sensitive during germination. EC w should not exceed 3 dS/m for garden beets and sugarbeets.

It is reported that yield reductions in yield by irrigating high EC water varies substantially. The major factors influencing yield reductions include soil type, drainage, salt type, irrigation system and management. Beyond effects on the immediate crop is the long term impact of salt loading through the irrigation water. Other terms used to reports salinity hazards are: salts, salinity, electrical conductivity (ECw), or total dissolved solids (TDS). These terms are all comparable and quantify the amount of dissolved “salts” (or ions, charged particles) in a water sample. However, TDS is a direct measurement of dissolved ions and EC is an indirect measurement of ions by an electrode. Sodium Hazard One of the major problems emerging due to sodium hazards in soils are infiltration/permeability problems. Although, plant growth is primarily limited by the salinity (ECw) level of the irrigation water, the application of water, with a sodium imbalance, can further reduce yield under certain soil texture conditions. Reductions in water infiltration can occur when irrigation water contains high sodium relative to the calcium and magnesium contents. This condition, termed “sodicity,” results from excessive soil accumulation of sodium. Sodic water is not the same as saline water. Sodicity causes swelling and dispersion of soil clays, surface crusting and pore plugging. This degraded soil structure condition in turn obstructs infiltration and may increase runoff. This result to decrease in the downward movement of water into and through the soil, and actively growing plants roots may not get adequate water, despite pooling of water on the soil surface after irrigation. The most common measure to assess sodicity in water and soil is called the Sodium Adsorption Ratio (SAR). The SAR defines sodicity in terms of the relative concentration of sodium (Na) compared to the sum of calcium (Ca) 62


and magnesium (Mg) ions in a sample. The SAR assesses the potential for infiltration problems due to a sodium imbalance in irrigation water. The SAR is mathematically written below, where

Na, Ca and Mg are the concentrations of these ions in milliequivalents per liter (meq/L). Concentrations of these ions in water samples are typically provided in milligrams per liter (mg/L). To convert Na, Ca, and Mg from mg/L to meq/L, one should divide the concentration by 22.9, 20, and 12.15 respectively. For most irrigation waters the standard SAR formula provided above is suitable to express the potential sodium hazard. However, for irrigation water with high bicarbonate (HCO3) content, an “adjusted” SAR (SARADJ) can be calculated. In this case, the amount of calcium is adjusted for the water’s alkalinity, is recommended in place of the standard SAR. The potential soil infiltration and permeability problems created from applications of irrigation water with high “sodicity” cannot be adequately assessed on the basis of the SAR alone. This is because the swelling potential of low salinity (ECw) water is greater than high ECw waters at the same sodium content (Table 4). Therefore, a more accurate evaluation of the infiltration/ permeability hazard requires using the electrical conductivity (ECw) together with the SAR. Many factors including soil texture, organic matter, cropping system, irrigation system and management affect how sodium in irrigation water affects soils. Soils most likely to show reduced infiltration and crusting from water with elevated SAR (greater than 6) are those containing more than 30% expansive (smectite) clay. Soils containing more than 30% clay include most soils in the clay loam, silty clay loam textural classes and finer and some sandy clay loams. Table 4. Guidelines for assessment of sodium hazard of irrigation water based on SAR and EC w Irrigation Water SAR

Potential for water Infiltration Problem Unlikely Likely 2 ---------------------- ECw---------------0–3 > 0.7 < 0.2 3–6 > 1.2 < 0.4 6 – 12 > 1.9 < 0.5 12 – 20 > 2.9 < 1.0 20 – 40 > 5.0 < 3.0 Modified from R.S. Ayers and D.W. Westcot. 1994. Water Quality for Agriculture, Irrigation and Drainage Paper 29, rev. 1, Food and Agriculture Organization of the United Nations, Rome. pH and Alkalinity The acidity or basicity of irrigation water is expressed as pH (< 7.0 acidic; > 7.0 basic). The normal pH range for irrigation water is from 6.5 to 8.4. Abnormally low pH’s may cause accelerated irrigation system corrosion where they occur. High pH’s above 8.5 are often caused by high bicarbonate (HCO 3-) and carbonate (CO32-) concentrations, known as alkalinity. High carbonates cause calcium and magnesium ions to form insoluble minerals leaving sodium as the dominant ion in 63


solution. As described in the sodium hazard section, this alkaline water could intensify the impact of high SAR water on sodic soil conditions. Excessive bicarbonate concentrates can also be problematic for drip or micro-spray irrigation systems when calcite or scale builds up causes reduced flow rates through orifices or emitters. In these situations, correction by injecting sulfuric or other acidic materials into the system may be required. Chloride Chloride is a common ion in many irrigation waters. Although chloride is essential to plants in very low amounts, it can cause toxicity to sensitive crops at high concentrations (Table 5 and 6). Table 5. Susceptibility ranges for crops to foliar injury from saline sprinkler water, Na or Cl concentration (mg/L) causing foliar injury Na or Cl concentration (mg/L) causing foliar injury Na Concentration < 46

46 – 230

231 – 460

> 460

Cl concentration

< 175

175 – 350

351 – 700

> 700

Crops

Apricot

Pepper

Alfalfa

Sugarbeet

Plum

Potato

Barley

Sunflower

Tomato

Corn

Sorghum

Foliar injury is influenced by cultural and environmental conditions. These data are presented only as general guidelines for daytime irrigation. Source: Mass (1990) Crop salt tolerance. In: Agricultural Assessment and Management Manual. K.K. Tanji (ed.). ASCE, New York. pp. 262-304. Like sodium, high chloride concentrations cause more problems when applied with sprinkler irrigation. Leaf burn under sprinkler from both sodium and chloride can be reduced by night time irrigation or application on cool, cloudy days. Drop nozzles and drag hoses are also recommended when applying any saline irrigation water through a sprinkler system to avoid direct contact with leaf surfaces. Table 6. Chloride classification of irrigation water. Chloride (ppm) Effect on Crops Below 70 Generally safe for all plants. 70-140 Sensitive plants show injury 141-350 Moderately tolerant plants show injury Above 350 Can cause severe problems Chloride tolerance of selected crops. Listing in order of increasing tolerance: (low tolerance) dry bean, onion, carrot, lettuce, pepper, corn, potato, alfalfa, sudangrass, zucchini squash, wheat, sorghum, sugar beet, barley (high tolerance). Source: Mass (1990) Crop Salt Tolerance. Agricultural Salinity Assessment and Management Manual. K.K. Tanji (ed.). ASCE, New York. pp 262-304.

Boron Boron is another element that is essential in low amounts, but toxic at higher concentrations. In fact, toxicity can occur on sensitive crops at concentrations less than 1.0 ppm. Since boron toxicity can occur at such low concentrations, an 64


irrigation water analysis is advised for groundwater before applying additional Boron to irrigated crops. Sulfate The sulfate ion is a major contributor to salinity in many irrigation waters. As with boron, sulfate in irrigation water has fertility benefits. Exceptions are sandy fields with 4) are possible with occasional application of gypsum and FYM. Gypsum to supply 2.5 and 5.0 me L-1 to alkali irrigation water for wheat and rice, respectively, was sufficient for maintenance of higher yields. Sodic soils or soils those are previously deteriorated either due to irrigation with alkali water would require gypsum application for neutralizing both soil and irrigation water sodicity. Subsequent application of gypsum is needed on the basis of irrigation water only. In a long-term experiment (10 years) on sugarcane, Choudhary et al. (2004) observed that the beneficial effect of gypsum was pronounced in increasing cane and sugar yield under sodic (30%) than under saline-sodic water irrigation (13%). Application of gypsum with each irrigation proves better or at least equal in alleviating deleterious effects of RSC waters in rice-wheat system (Bajwa and Josan, 1989). The dissolution of gypsum directly in water through the use of gypsum beds or its application to the irrigation channels, appears economically attractive, as costs involved in powdering, bagging and proper storage before its actual use are eliminated. Dissolution of gypsum with water passing through these beds is affected by factors such as size distribution of gypsum fragments, flow velocity, salt content and chemical composition of water. It should be realised that gypsum bed water quality improvement technique may not dissolve more than 8 me L-1 of Ca2+ otherwise such an application of gypsum has better potential to improve soil’s infiltration rate. Organic amendments 91


Cumulative yield loss (t/ha)

It is generally accepted that additions of organic materials improve sodic soil conditions through mobilization of Ca2+ from CaCO3 and hasten the reclamation process. In saline environment, beneficial effects of organic materials are mainly attributed to improving soil properties, reduction of osmotic stress and their role in reducing N volatilization losses and enhancing N-use efficiency. Choudhary et al. (2011) observed that continual irrigation with sodic water resulted in the gradual increase in soil pH and exchangeable sodium percentage (ESP) in a calcareous soil. The cumulative yield loss in SW plots remained 10.0). After 7 years of planting, only 13 out of 30 species survived. Out of these 13 surviving species only Prosopis juliflora, Tamarix articulate and Acacia nilotica were found suitable for such soils. Eucalyptus tereticornis showed good survival and height but no meaningful biomass was observed. However, Dalbergia sissoo, Pithecellobium dulce, Terminalia arjuna, Kigelia pinnata, Parkinson aculeate and Cordial Rothay showed more than 70% survival but could not attain economically suitable biomass (Dagar and Tomar, 2002). Performance of 10 tree species in sodic soils having ESP 89 was evaluated at CSSRI, Regional Research Station, Lucknow. After 10 years of field study, only 3 species, Prosopis juliflora, Acacia nilotica, and Casuarina equisetifolia recorded survival rates of >90% and attain economical biomass. Eucalyptus tereticornis showed good performance during the initial 4 years, but its growth rate declined thereafter. Azadirechta indica, Melia azadirach, and Dalbergia sissoo were poor performer. On the basis of available information, a short list of consistently better performing species that could be recommended for saline and alkali soils of Indogangetic plains are given in Table 2. Table 2. Recommended tree species for the restoration of salt-affected soils Soil Parameter Firewood/ Timber/ Fruit Species (Common name ) Alkali Soils (pH2) > 10.0 Acacia nilotica (Kikar), Butea monosperma (dhak), Casuarina equisetifolia (Casurina, saru), Prosopis juliflora (mesquite, pahari kikar), Prosopis cinerraria (khejri, jand) 9.0 – 10.0 Albizzia lebbeck (siris), Cassia siamea (cassia), Eucalyptus tereticornis (mysore gum, safeda), Tamarix articulata (faransh), Terminalia arjuna (arjun) 8.6 – 9.0 Azardirachta indica (neem), Dalbergia sissoo (shisham, tahli), Grevillia robusta (silver oak), Hardwickea binnata (anjan), Kajellea pinnata (balam khira), Morus alba (mulberry), Moringa olifera (sonjna), Mangifera indica (mango), Pyris communis (pear, nashpati), Populus delteoides (poplar), Tectona grandis (teak), Syzium cumuni (jamun) Saline and waterlogged soils ECe (dSm-1) 20-30 Acacia farnesiana (pissi babul), Prosopis juliflora (mesquite, pahari kikar), Parkinsonia aculeate (parkinsonia), Tamarix aphylla (faransh) 14-20 Acacia nilotica (desi kikar), A. pennatula (kikar), A. tortilis (Israeli Kikar), Callistemon lanceolatus (bottle brush), Casuarina glauca (casuarinas, saru), C. obese, C. equisetifolia, Eucalyptus camaldulensis (river-red gum, safeda), Ferronia limonia (kainth, kabit), Leucaena leucoephala (subabul), Ziziphus jujube (ber) 10-14 Casuarina canninghamiana (casuarinas, saru), Eucalyptus teriticornis (mysore sum, safeda), Terminalia arjuna (arjun) 5–10 Albizzia caribaea, Darbergia sissoo (shisham), Gauzuma ulmifolia, Pongamia pinnata (papri), Samanea saman 15 and varying electrical conductivity (EC). The sodic lands contain high concentration of sodium in their soil. These soils have high Sodium Absorption Ratio (>13; large number of sodium ions on the clay surface) and often they have a hard calcareous layer at 0.5 to 1 m. depth but real difficulties are encountered in the top 10 centimetres. In contrast the saline soil contains high amounts of soluble salts such as sulphates (SO4), carbonates (CO3) and chlorides (Cl). Sodicity causes the clay particles to disperse instead of remaining in their original compact arrangement. The disruption of the soil structure, together with clay dispersion, greatly reduces the soil permeability since the larger pores are blocked. Generations of farmers in these areas have tried coaxing a living from these lands but they remained adamantly barren. The problems of increasing sodicity, salinity and water logging of soils are clear indications that the modern ways of cropping system and managing soils are not sustainable. There's very poor hydraulic conductivity and high impedance to root growth and poor biological activities in these soils. Chemical amendments such as mineral gypsum have been used extensively so far in the amelioration of these soils @ 1015 tonnes ha-1. Due to the limited availability of gypsum, its cost factor and also the chemical nature of the amendment there is an increased demand for any biological products that can supplement the mineral gypsum or reduce their dosage in amendments. Also it is known fact that though gypsum application reduces soil pH from 10.0 to 9.0 and 9.2 which is still higher for cultivation of most of the economically important horticultural crops like banana, tomato, mango etc. Also, these lands are poor in biological properties of the soil which aggravates the challenge of obtaining higher productivity that play a crucial role in alleviating the 105


rural poverty and providing economic security in the rural households. Even the productivity of salt tolerant varieties of wheat was 1.5 t ha-1 in sodic soils of IndoGangetic plains due to the heavy textured soils and sub-soil sodicity below 30 cm. The productivity of crops particularly high value commercial crops in sodic soils even after the reclamation remains a challenge globally. Restoration of the biological productivity of reclaimed sodic soils is of prime importance in sustainable and commercial crop production. Given the negative environmental impacts of chemical fertilizers and their increasing costs, the use of PGPR (Plant Growth Promoting Rhizobacteria) is thus being considered as an alternative or a supplemental way to increase the productivity of sodic soils and thereby reducing the use of chemicals in agriculture. Currently, there are no efficient strains available to perform under sodic conditions where the soil pH is more than 8.5. Though considerable amount of microbial isolates are available in the country as bio-fertilizers and bio-control agents, for soils of pH 7.0 to 8.5, they are highly location specific and are based on single potential isolate. Furthermore, the cost of commercial product ranges from Rs. 100-150 kg-1 in the open market and public sector institutions. Due to high cost, location specific performance, the small and marginal farmers have reservation over its use and are inclined towards indiscriminate use of chemical fertilizers and fungicides which apart from reducing the sustainability in production also spreads concerns over eco-system contamination with residual toxicity effect. Utilization of rhizosphere diversity The soil rhizosphere harbours great variety of beneficial microbes that play a prominent role in imparting tolerance to biotic and abiotic stress and thus enhancing the plant growth in the system. However, the soil such a heterogenous and complex medium that identification of potential microbial populations becomes a complex process. Therefore, in line with the concept that single root is the multitude of various bacteria, fungus and other beneficial microbes identification of more than one microbes with inter-compatability and grouping them into an effective consortia (EC) stands as a sustainable solution to perform in the soils under different eco-system. Growth enhancing microbes (PGP – Plant growth promoters) Certain bacteria and fungi possess the property of promoting growth in the target system through various process like fixation of the atmospheric nitrogen, solubilization of phosphorous in the soils and production of growth regulators (auxins) in interaction with dynamic media and substrate. The rhizosphere is the zone of soil surrounding the roots of the plants and are influenced by root activity. The zone of plant environment interaction is vital for the acquisition of water and nutrients and for beneficial interactions with soilborne microorganisms. Large amounts of nitrate, phosphate, and other minerals which are often not available in free form or in limited quantities in the soil are mobilized by the root-associated beneficial microbes which serve as important partners. Fungi and bacteria are the common microbes that aid in nutrient mobilization process. Unfortnately, this region is more exposed to biotic and abiotic stresses. Salt stress at this region aggravates the mortaility percentage of plants. The physical and chemical properties of the rhizosphere is the integration of many competing processes that depend on the soil type, water content, the composition and biological activities of root associated microbial communities and the physiology of the plant itself (Pinton et al., 2007). Microorganisms form a vital component of the rhizosphere where the total biomass and composition of rhizosphere microbial populations distinctly aid in interactions between plants and the soil environment. 106


Micro-organisms engineered in to the rhizosphere exude exogenous compounds that improve plant nutrition, suppress pathogenic microbes and minimize the consequences of biotic or abiotic stresses like sodicity. Under salt stress, PGPR (Plant growth promoting rhizobacteria) have shown positive effects in plants on parameters like germination rate, tolerance to drought, weight of shoots and roots, yield and plant growth. PGP functions by synthesizing specific compounds which enhance the nutrient mobilization under saline environment and increases plant growth (Damodaran et al., 2014). Salinity decreases nitrogen and Phosphorous ‘P’ availability in plants which is the result of ionic strength effect that reduces the effect of phosphate. Phosphate soulubilizing bacteria (PSB) solubilizes tri-calcium phosphate by binding free ‘P’ in the medium and also by release of organic acids like citric and gluconic acids. There is large demand increases day by day due to replacement of the synthetic fertilizer. Although N2 is abundant (around 80%) the atmospheric N2 is not readily available for plant uptake and some bacteria are capable of N 2 fixation from the atmospheric N2 pool. Many free living N2 fixing bacteria occur in soil. The amount of N2 fixed by these organisms is considerable because of the close proximity they have with their host plant. Efficient plant use of field N2 minimizes volatilization, leaching and denitrification (Nepolean et al., 2012). Azotobacter is major free living in soils so that it can be cultured and produced in artificial medium. It stimulates the density and length of root hairs, increases the growth through hormonal production, increases biomass, increases survival rate and fixes nitrogen. Salinity enhances ethylene production in plants which is a stress harmone resulting in early senescence and also inhibits root and shoots growth at higher concentrations. Certain PGPR are known to produce ACC (1-aminocyclopropane, 1-carboxylate) de-aminase which lowers the synthesize of ethylene by cleaving the ACC to form ammonia and α-ketobutyrate instead of ethylene (Glick et al., 1998). Some PGPR produce IAA (Indole acetic acid) which enters the plant cell and promotes plant growth under sodic conditions. PGPR produce and secrete IAA which gets adsorbed in the root surfaces where tryptophan and other small molecules are present. PGP as a bio-protectant and stress tolerant Plants produce low molecular weight organic solutes such as proline or enzymes like SOD (super oxy dimuatse), PO (peroxidase) to tolerate the effects of salt stress. However, most plant species do not produce sufficient anti-oxidants to fulfil their growth requirements under salt stress. Therefore, bio-inoculation induces salt tolerance by increasing the activity of antioxidant enzymes (SOD, PO and catalase) and organic solutes like proline etc. (Ashraf and Foolad, 2007). The microbial inoculated gladiolus plants produced more defence enzymes and proline than the untreated controls. The higher activities of PO, PPO (plyphenol oxidase), LPAL (L-phenyl alanine lyase), SOD and proline content increased the ability of the plants to tolerate salt stress by acting as ROS (Reserve oxygen scavengers) from phenols and formulate Na+ exclusion mechanism. Since iron is present in ferric or Fe 3+ form which is sparingly soluble it is directly unavailable for direct assimilation of micro-organism. Some soil microorganisms secrete low molecular weight (400-1000 daltons) iron binding molecules known as siderophore which bind Fe3+ with a very strong affinity promoting its growth. The PGPR’s producing siderophores immediately absorbs the iron and thereby create competition among the phyto-pathogens which fails to enter the plant system (Sullivan and Gara, 1992). Also, some plants binds the bacterial 107


siderophore iron complex and transports it into the system where later it is reductively released and used by plants. Bioformulations The term bio-formulation is based on formulations made using the beneficial microbes and/or biological product that either fix atmospheric nitrogen or enhance the solubility of soil nutrients having potential to increase the yield of crops. Being biodegradable, non-toxic and cost effective, bio-fertilizers are emerging as the efficient alternative to agrochemicals used as bio-fertilizers. Formulations generally composed of the active material which must be preserved or maintained in viable condition to produce its biological effect, the carrier material may or may not include the incorporation of enrichment materials or additives. Generally, amendments can be grouped as either carriers (fillers, extenders) or amendments that improve the chemical, physical, or nutritional properties of the formulated biomass (Schisler et al., 2004). The active material is mixed with carrier materials such as water, clay, talc, oil or others to make the formulation safer to handle, easier to apply and better suited for storage. In some formulations, enrichment materials comprising of nutrient-rich medium such as, molasses, trehalose, maltose and sucrose are incorporated to further enhance the viability of core (active) materials. Microbial viability in field condition For agronomic utility, inoculation of plants with target microorganisms at a higher concentration than those normally found in soil is necessary to take advantages of their beneficial properties for plant yield enhancement (Subba Rao, 1993). The erratic performances of bioinoculants under field conditions have raised concerns about the practical potential offered by microbial releases into soil (Arora et al., 2010). Since formulation protects cells against harsh chemical and environmental conditions and since most bioformulations are meant for field application, it is essential that suitable carrier materials are used to maintain cell viability under adverse environmental conditions. A good quality formulation promotes survival of bacteria, maintaining viable population sufficient to exude growth promoting effects on plants. One such approach to ensure the viability of cells is to enrich the carrier material with suitable enrichment materials. Evidence suggests that the addition of nutrients to seed pellets may be a useful strategy for improving inoculant survival. Consortia of bio-formulation The composition developed herein employs the use of microbial consortium and farmyard manure/ organic manure/ agricultural waste and sugar/molasses. Manures will increase the organic matter content of the sodic soil while at the same time sugar will provide the nutrient to microbes for their multiplication and enrichment in the same soil. The microbial composition developed would promote exchange of sodium ions from clay particle followed by leaching, which result in an improvement in soil aggregation property. Moreover, the production of acid by the developed composition lowers down the pH of soil from alkalinity towards normality. These components are being used in agriculture either independently or in combination of other amendments, for increased crop productivity but a combination of all these in a particular manner and organized way are defined in the present invention for the reclamation purpose. Utilization of PGPR’s through media and substrate dynamism

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The microbes possessing the PGP’s properties are marketed as bioinoculants, biostimulants by culturing them in an appropriate media. Several PGPR inoculants that seem to promote growth through at least one mechanism like suppression of plant disease (bioprotectants), improved nutrients acquisition (biofertilizers), or phytohormone are currently being commercialized. From the ecology point of view it is advantageous to have an organic based media as a substrate for microbial growth (Kleiber et al., 2012). Biofertlilizers, meeting the requirements of growing plant, act as a consortium along with other microorganisms in the rhizosphere. Understanding the interaction of the prepared consortia in a particular ecology aids in harnessing the benefits of microbial inoculants for improving plant growth. The bio-fertilizers are commercialized according to the regulations governed of fertilizers control act 1985, where a rigorous screening for two seasons followed by a multilocational field trial confirming the nutrient uptake are conducted. The strains used as biofertilizers are to be studied for the toxicology parameters before being recommended for use in agriculture and also to be registered with National Bureau of Agricultural Important Micro-organism, Mau or at Institute of Microbial Technology, Chandigarh. CSR-BIO is one such bio-stimulant developed for crops grown in sodic soils using consortia of bacteria (Bacillus pumilus and Bacillus subtilis) isolated from sodic rhizosphere. These microbes tend to have higher PGP properties like phosphate solubilization, IAA and siderophore production along with sodium accumulation (Damodaran et al., 2013). Methods of application of bio-formulations It is also important to focus on the critical stages of commercialization of biocontrol agents. Screening for new agents should consider the biology and ecology of the pathosystem, as well as agricultural practices associated with the crop (Fravel, 2007). 

In-vivo Bio-priming of the seed / planting materials for a time period ranging from 1-2 hours before sowing had profound influence in enhancing the germination percentage and root-shoot growth of the plants.  Soil application of bio-formulations with appropriate substrates like FYM or vermicompost found to increase the organic carbon and mobilize nutrient to plants. It also protects plants from soil borne diseases like Fusarium, Phtophthora etc. PGPRs based bio-inoculants are thus can be used as potential tools for sustainable agriculture in salt affected and sodic lands. Combinations of beneficial bacterial strains that interact synergistically are currently being devised and numerous recent studies show a promising trend in the field of inoculation technology for attributing tolerance to sodicity and promoting growth of crops. References Arora NK, Maheshwari DK and Khare E, 2010. PGPR: Constraints in bioformulation, commercialization and future strategies. Bacteria and plant Health, D.K. Maheshwari, eds., Springer Publication, Netherland, 97-116. Damodaran T, Rai RB, Kannan R, Pandey BK, Sharma DK, Misra VK, Vijayalaxmi Sah and Jha SK (2014). Rhizosphere and endophytic bacteria for induction of salt tolerance in gladioulus grown in sodic soils. Journal of Plant Interaction 9(1): 577-584. Damodaran T, Rai RB, Sharma DK, Mishra VK and Jha SK (2013). Rhizosphere engineering-An approach for sustainable vegetable production in sodic soils. National Symposium on Abiotic and Biotic Stress Management in Vegetable

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Crops,North America, 150% NPK > 100% NPK> 100% NP > 100% N = 50% NPK > control (Purakayastha et al., 2008). There was deterioration of soil quality in terms of loss of native soil carbon and nitrogen in the 0-15 cm surface under N and NP plots of LTFEs at Barrackpore and Ranchi whereas impact of these treatments was positive at Akola (Manna et al., 2006). Organic recycling Application of organic amendments such as FYM, straw or green manure crops, tends to build up soil organic matter and soil quality in all rice-based cropping systems (Regmi et al., 2002). Green manures incorporated in the soil before rice transplanting had residual effect on the succeeding wheat crop as evident from the grain yield. Such residual effects are often associated with the presence of more hydrolysable organic N in the soil (Chakraborty et al., 1988). Results indicated that partial substitution of fertilizer NPK with Sesbania green leaf manuring in rice was as good as 100% recommended NPK through chemical fertilizers (Yadav et al., 2000). As green manure is an organic material, incorporation of green plant material (Sesbania rostrata, Sesbania aculeata, Vigna radiata residues) obviously, increased the accumulation of soil organic matter and total nitrogen concentrations and overall soil quality during the growth period of rice and wheat. Residue management The incorporation of residues has favourable effect on soil quality parameters (physical, chemical and biological properties) such as pH, organic carbon, and water holding capacity and bulk density of the soil (Singh et al., 2005). In an 11 years field experiment on a loamy sand soil in Punjab, India the 135


incorporation of residues of both the crops in the rice-wheat cropping system increased the total P, available P, and K contents in the soil over the removal of residue removal. In another study over a 5-year period on a silt loam soil at Palampur in Himachal Pradesh, India having a relatively cooler climate than Punjab, the incorporation of rice straw in wheat caused a slight increase in availability of P, Mn and Zn and a marked increase in the availability of K (Verma and Bhagat, 1992). The incorporation of crop residues on a long-term basis increased the DTPA-extractable Zn, Cu, Fe. The decrease in bulk density with straw addition definitely has a bearing on wheat yield in rice-wheat rotation, where soil aeration becomes a limiting factor. The incorporation of residue also prevents the leaching of nitrates. It adds a plenty of organic carbon and thus increases bacteria and fungi in the soil. In a rice-wheat rotation, Mohanty et al. (2007) reported as the puddling intensity for rice increased, sustainability without returning crop residues decreased from 6 to 1 year. When residue was returned, the time for sustainable productivity increased from 6 to 15 years for direct seeded rice, 5 to 11 years with low-intensity puddling and 1 to 8 years for high intensity puddling. For sustainability and productivity, the best practice for this or similar Vertisols in India would be direct seeding of rice with conventional tillage and residue returned. Use of Biochar There is currently great interest in the application of biochar to agricultural lands as a means of improving soil quality while sequestering carbon (C) in soils (Lehmann et al., 2006; Laird, 2008). Biochar is a fine-grained, carbon rich, porous product remaining after plant biomass has been subjected to thermo-chemical conversion process (pyrolysis) at low temperatures (~350-600oC) in an environment with little or no oxygen (Amonette and Joseph, 2009). Corn stover biochar (CSBC) prepared at 600 _C showed greater stability in both the Mollisol and Ultisol. The WSBC and CSBC prepared at 600 _C which showed negative priming of native soil organic matter (SOM) had greater potential for long term carbon sequestration in soil (Purakaystha et al., 2016). In another study Purakayastha et al. (2015) reported that because of higher stability of maize stover biochar due to the presence of stronger structural surface functional groups including aromatic C=C stretching, it might be having greater potential for long-term C sequestration in soil. The biochar amendments significantly increased total N (up to 7%), organic C (up to 69%), and Mehlich III extractable P, K, Mg and Ca but had no effect on Mehlich III extractable S, Cu, and Zn (Laird et al., 2010). Land use Alternate land use systems, viz., agro-forestry, agro-horticulture and agrosilviculture are more remunerative for SOC restoration as compared to sole cropping system. Das and Intal (1994) reported that organic C content was about double in agro-horticultural and agro-forestry systems as compared to sole cropping. Purakayastha et al. (2007) reported that vegetable growing plots exhibited similar SOC contents as rice-wheat growing plots. Soil organic C and microbial biomass C in agro-forestry was significantly higher than in either of the two systems reported above. Dhaliwal (2003) showed higher soil organic C and microbial biomass C in natural forest system followed by cultivated and pasture ecosystem. Soil quality and environmental quality Improvement in soil quality has a direct influence on improving the environmental quality. The environmental quality can be measured in the changes in soil 136


environment as well as atmosphere. It is a well-known fact that improvement in soil quality is well associated with improvement in soil biodiversity and better cycling of nutrients. The change in soil quality is reported to increase the release of greenhouse gases. As for example, positive changes is soil organic carbon which is considered as one of the powerful soil quality indicators might increase the emission of greenhouse gases. It was reported that increasing the mulch rate increased the soil organic C as well as global warming potential (Mg CO 2e-C ha-1yr1) and it was more in presence of fertilizer than without fertilizer (Lenka and Lal, 2013). There was no difference in CO2 emission between conventional tillage and reduced tillage while N2O emission was significantly higher in latter tillage management than the former tillage management (Abdalla et al., 2014). Conclusion The concept and framework owing to their strong scientific base could be successfully used for development of soil quality indices. The major challenge before development of soil quality indices is development of appropriate scoring functions for scoring the data. The weightage for individual soil quality indicator in a particular soil function or all the soil functions integrated into unified soil quality indices is determined by existing published literature and expert opinion. The management goal, the supporting soil functions describing the goal and the indicators describing the soil functions are the new paradigm to develop soil quality indices. Thus the protocol which is used to develop soil quality indices is a powerful tool to assess the management induced changes in soil quality. There is distinct promising land, soil and crop management practices which could be implemented for enhancing soil quality and sustainable crop productivity. The adoption appropriate management strategies e.g., conservation tillage, balanced fertilization, organic manuring, integrated nutrient management, appropriate crop rotation, residue retention and incorporation, biochar application and alternate land use etc. are promising for maintaining or enhancing soil quality, sustainable crop productivity. Overall the improvement in soil quality could result in soil environment as well as above ground environment. References Abdalla, M., Hastings, A., Helmyc, M., Prescher, A., Osborne, B., Lanigane, G., Forristal, D.,Killi, D.,Maratha, P., Williams, M., Rueangritsarakul, K., Smith, P., Nolang, P., Jones, M.B. (214) Assessing the combined use of reduced tillage and cover crops formitigating greenhouse gas emissions from arable ecosystem. Geoderma 223-225: 9-20. Acton, D.F. and Gregorich, L.J. (1995) Understanding soil health. In: The Health of Our Soils--Towards Sustainable Agriculture in Canada. Acton, D.F. and Gregorich, L.J. (eds.). Center for Land and Biological Resources Research, Research Branch, Agriculture and Agri-Food Canada, Ottawa, ON 11: 5-10. Andrews, S.S., Mitchell, J.P., Mancinelli, R., Karlen, D.L., Hartz, T.K. and Horwath, W.R. (2001) On-farm assessment of soil quality in California’s central valley.Agron. J.94: 12–23. Andrews, S.S. (1998) Sustainable agriculture alternatives: Ecololgical and managerial implications of poultry litter management alternatives applied to agronomic soils. Ph.D.dissertation. University of Georgia, Athens. Arshad, M.A. and Coen, G.M. (1992) Characterization of soil quality. Am. J. Alt. Agric. 7: 25– 31. Bezdick, D.F., Papendick, R.I. and. Lal, R. (1996) Introduction: Importance of soil quality to health and sustainable land management. In: Methods for assessing soil quality. Doran, J.W. and Jones, A. (eds) SSSA Special Publication. 49: 1-8.

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Bhaduri, D., Purakayastha T. J. (2014). Long-term tillage, water and nutrient management in rice–wheat cropping system: Assessment and response of soil quality. Soil and Tillage Research 144 (2014) 83–95. Bhattacharya, R., Prakash V., Kundu, S., Srivastava, A. K., and Gupta, H.S. (2004) Effect of long-term manuring on soil organic carbon, bulk density and water retention characteristics under soybean-wheat cropping sequence in north-western Himalayas. J. Indian Soc. Soil Sci. 52: 238-242. Chakraborty, P.K., Mandal, L.N., Majumdar, A. (1988) Organic and chemicalsources of nitrogen: its effect on nitrogen transformation and riceproductivity under submerged conditions. J. Agric. Sci. 111: 91-94. Das, S. K. and Itnal, C. J. (1994) Capability based land use systems: role in diversifying dry land agriculture. In: Soil management for sustainable agriculture in dryland areas. Bull. Indian Soc. Soil Sci. 16: 92-100. Dhaliwal, S. S. (2003) Effect of different land use systems on soil quality in Kandi region of Punjab. Ph.D. Thesis. PAU, Ludhiana. Doran, J.W. and Parkin, T.B. (1994) Defining and assessing soil quality. In: Defining Soil Quality for a Sustainable Environment. Doran, J.W., Coleman, D.C., Bezdicek, D.F. and Stewart, B.A. (eds.), SSSA Special Publication No. 35, ASA and SSSA, Madison, WI. 3–21 pp. Dunteman, G.H. (1989) Principal Components Analysis. Sage Publications, London, UK. Kaiser, H.F. (1960). The application of electronic computers to factor active soil organic matter pools. Soil Sci. Soc. Am. J. 58: 1130–1139. Karlen, D.L., Mausbach, J.W., Doran, J.W., Cline, R.G., Harris, R.F. and Schuman, G.E. (1997). Soil quality: a concept, definition and framework for evaluation. Soil Sci. Soc. Am. J.61: 4–10. Karlen, D.L., Eash, N.S. and Unger, P.W. (1992) Soil and crop management effects on soil quality indicators. Am. J. Altern. Agric.7: 48-55. Kumari, Mamta, Chakraborty, D., Gathala, M. K., Pathak, H., Dwivedi, B. S., Tomar, R. K., Garg, R. N., Singh, R., Ladha, J. K. (2011) Soil aggregation and associated organic carbon fractions as affected by tillage in a rice–wheat rotation in north India. Soil Sci. Soc. Am. J. 75: 1-8. Laird, D., 2008. The charcoal vision: a win-win-win scenario for simultaneously producing bioenergy, permanently sequestering carbon, while improving soil and water quality. Agron. J. 100, 178−181. Laird, D.A., Fleming, P. Davis, D. D., Horton, R., Wang, B.. Karlen, D.A.(2010) Impact of biochar amendments on the quality of a typical Midwesternagricultural soil. Geoderma 158: 443–449. Lehmann, J., Gaunt, J., Rondon, M., 2006. Biochar sequestration in terrestrial ecosystems a review.Miti.Adap.Strat.Glob.Change 11, 403−427. Larson, W.E. and Pierce, F.J. (1991) Conservation and enhancement of soil quality. Evaluation of sustainable land management in developing world. International board for soil research and management, Bangkok, Thailand. Lenka, N.K. and Lal, R. (2013) Soil aggregation and greenhouse gas flux after 15 years of wheat straw andfertilizer management in a no-till system. Soil Till. Res. 126: 78-89. Manna, M. C., Swarup, A., Wanjari, R. H., Ravankar, H. N., Misra, B., Saha, M. N., Singh, Y. V., Sahi, D. K., and Sarap, P. A. (2006) Long-term effect of fertilizer and manure application on soil organic carbon storage, soil quality and yield sustainability under sub-humid and semi-arid tropical India. Field Crops Res. 93: 264-280. Masto, R. E., Chhonkar, P. K., Singh, Dhyan and Patra, A. K. (2007) Changes in soil biological and biochemical characteristics in a long-term field trial on a sub-tropical inceptisol.Soil Biol. Biochem. 38 (7), 1577- 1582. Masto, R.E., Chhonkar, P. K., Purakayastha,T.J. , Patra, A. K and Singh, D.(2008) Soil quality indices for evaluation of long term land use and soil management practices in semi-arid sub-tropical India. Land Degrad. Develop. 19: 1–14. Mohanty, M., Painuli, D. K., Misra, A. K., Ghosh, P. K. (2007). Soil quality effects of tillage and residue under rice–wheat cropping on a Vertisol in India. Soil and Tillage Research, 92, 243–250. Pierce, F.J. and Larson, W.E. (1993) Developing criteria to evaluate sustainable land management. In:Kimble, J.M. (ed.) Proceedings of The Eighth Intern. Soil

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Management Workshop: Utilization Of Soil Survey Information For Sustainable Land Use. USDA, Soil Conservation Service, National Soil Survey Center, Washington, D.C. 7-14 pp. Purakayastha, T.J., Kumari, Savita, Pathak, H. (2015) Characterisation, stability and microbial effects of four biochars produced from crop residues. Geoderma 239-240: 293-303. Purakayastha, T. J., Das, K. C. Gaskin, Julia, Harris, Keith, Smith, J. L., Kumari, Savita (2015) Effect of pyrolysis temperatures on stability and priming effects of C3 and C4 biochars applied to two different soils. Soil and Tillage Research155: 107-115. Rudrappa, L., Purakayastha, T. J., Singh, Dhyan, Bhadraray, S. (2006) Long-term manuring and fertilization effects on soil organic carbon pools in a TypicHaplustept of semi-arid sub-tropical India. Soil and Tillage Research 88: 180-192. Regmi AP, Ladha JK, Pathak H, Pasuquin E, Dawe D, Hobbs PR, Joshy D, Maskey SL, Pandey SP. 2002. Analysis of yield and soil fertility trends ina 20 years old rice wheat experiment in Nepal. Soil Science Society of America Journal 66: 857–867. Subehia, S. K., Verma, S., and Sharma, S. P. (2005) Effect of long-term use of chemical fertilizers with and without organics on forms of soil acidity, phosphorus adsorption and crop yields in an acid soil.J. Indian Soc. Soil Sci. 53: 308-314. Verma, T. S., Bhagat, R.M. (1992) Impact of rice straw management practice on yield, nitrogen uptake and soil properties in rice-wheat rotation in northern India. Fert. Res. 33: 97-106. Wander, M.W. and Bollero, G.A. (1999). Soil Quality Assessment of Tillage Impacts in Illinois. Soil Sci. Soc. Am. J. 63:961–971. Yadav, R.L., Dwivedi, B.S., Pandey, P.S., 2000. Rice–wheat cropping system assessment of sustainability under green manuring and chemical fertilizer inputs. Field Crops Res. 65, 15–30.

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Phytoremediation: An Emerging Green Cure Technology for Remediation of metal and Salt Affected Soil T. J. Purakayastha Principal Scientist Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi 110012 E-mail: [email protected] Introduction The unscientific disposal of untreated or undertreated effluentshas resulted in an accumulation of heavy metals in land and water bodies.Cultivated areas under peri-urban agriculture are worst affected by this problem. Excessive metal accumulation in contaminated soilscan result in decreased soil microbial activity, soil fertility, and overall soil quality,and reductions in yield (McGrath et al., 1995) and the entry of toxic materials intothe food chain (Hann and Lubbers 1983).Salinity and sodicity are among the main causes of land degradation that retards plant growth and productivity worldwide (Qadir and Schubert, 2002), and affects roughly 7% of the words total land area, particularly in arid and semi-arid regions.The effects of high salt concentrations in soils are markedin plants, which exhibit physiological changes including stomataclosure, hyper osmotic shock, inhibition of cell division,and photosynthesis; however, the most common effects arenutrient imbalance, low osmotic potential and toxicity of specificions such as Na+ and Cl−, resulting in plant growthinhibition or death (Aslam et al., 2011).Although it is necessary to clean up contaminatedsites, the application of environmental remediation strategies is oftenvery expensive and intrusive (McGrath et al., 1995). Thus, it is important to developlow-cost and environmentally friendly strategies. In recent years, phytoremediation with the aid of metallophytes is vigorously pursued for remediation of heavy metal contaminated soils. Phytoremediation or vegetative bioremediation of saltaffectedsoils can simply be defined as the cultivation of saltaccumulating or salt-tolerant plants for the reduction of soilsalinity and/or sodicity (Qadir and Oster, 2002). The phytoremediation with special reference to “phytoextraction” has lot of implications on remediation of heavy metal and salt affected soils. As such the phytoremediation process is slow in nature and therefore it could be repeated several times to reduce the level of contaminants to the safe limit. However, the efficiency of phytoremediation can be improved by proper manuring and fertilization, soil amendments, chelating agents. As phytoextraction process is slow therefore microbially enhanced phytoextraction is an emerging area of research which uses hyperaccumulator plants in combination with rhizosphere microorganisms for efficient extraction of pollutants especially metals from soil. Food chain contamination Besides adversely influencing plant growth, the toxic effects of heavy metalsare amplified along the food chain at each stage of the food web (Fig. 1).

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Fig.1. Heavy Metal Contamination in the Food Chain (Purakayastha and Chhonkar, 2010) In an Indian context, Rattan et al. (2005) observed increasing accumulations of Zn, Ni, Cu, and Fe in different fields containing vegetable and fruit crops such as maize, mustard, rice, jowar, spinach, cauliflower, brinjal, radish, guavas, citrus, etc., which were grown under sewage irrigation from the Keshopur Effluent Irrigation System in Western Delhi. The agricultural sustainability of such production system depends to a large extent upon maintaining or enhancing the soil quality, which is rapidly deteriorating due to the disposal of untreated effluents onto it. About 9.5% of rice paddy soils have been rendered unsuitable for growing rice for human consumption because of excessive metal contamination.Different doses of heavy metals can cause undetectable, therapeutic, toxic, oreven lethal effects. Selenium, copper, and zinc often become toxic as the dose of the metal and exposure to it increases. These metals enter livestock as well as our own bodies through the food chain. Zinc toxics are manifested as gastrointestinal distress, decreased food consumption, anorexia, hemoglobinuria, anemia, poor bone mineralization, and arthritis. Lead poisoning is the most frequently diagnosed toxicological condition in veterinary medicine. Its occurrence has been reported in all domestic species. Remediation approaches The remediation processes are classified in physic-chemical and biological approaches. The details of remediation processes are described in Fig. 2. The physic-chemical approach is costly, intrusive and sometimes disturb the soil biota. The biological approaches are gentle and non-intrusive and economically favourable without disturbing the ecosystem. The microbial assisted processes are very slow and temporarily relieve the problem by immobilising the metals. The phytoremediation approach involving hyperaccumulating plants to clean up the legacy contamination including metal and salts are promising as the contaminants are completely removed from the soil system. The microbial approach alone may not be effective but when it is linked to phytoremediation approaches then the efficiency of this approach increased.

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Fig. 2 Methods for remediation of heavy metals from soil (Khan et al., 2009) Definition Phytoremediation can be practiced in order to scavenge both organic and inorganicpollutants present in solid substrates (e.g., soil), liquid substrates (e.g., water), andthe air. There are various phytoremediation approaches that can be employed: • Phytoextraction. This involves growing plants that are selected for their capacity to concentrate one or more heavy metals on contaminated soil. The plants arethen harvested, incinerated, and the ash related to a confined area or the heavymetals are extracted from it. • Phytodegradation. This approach involves the use of plants and associatedmicroorganisms to degrade organic pollutants into less toxic forms or to renderthem immobilized in order to prevent their entry into the food chain orenvironment. • Rhizofiltration. This is the use of plant roots to absorb and adsorb pollutants,mainly metals, from water bodies and aqueous waste streams. Artificially createdmarshes are planted with plant species capable of absorbing or adsorbing metals. Contaminated water passes through these rhizofilters, and the plants take up heavy metals. The plants are regularly harvested and incinerated. These systems can also be applied to treat sewage. • Phytostabilization . This method uses plants to reduce the bioavailability of pollutants in the environment by reducing leaching, runoff, and soil erosion. 142


• Phytovolatilization. This is the use of plants to volatilize pollutants (Salt et al., 1998). Bioremediation is any process that uses organisms (microorganism, algae and plant) or their enzymes to manage the polluted environment and return to its original condition either by degrading or transforming toxic, hazardous chemicals to nontoxic form. OR Phytoremediation has been defined as the use of green plants and their associated microorganisms, soil amendments and agronomic techniques to remove, contain or render harmless environmental pollutants (Khan et al., 2009). Table 1: Different phytoremediation processes Process

Mechanism

Contaminants

Typical Plants

Phytoextraction

Hyper accumulation

Metals (Pb, Cd, Zn, Ni, Cu) with EDTA addition for Pb, Se

Sunflowers, Indian mustard, Rape seed plant

Rhizofiltration

Rhizosphere accumulation

Metals (Pb, Cd, Zn, Ni, Cu)Radionuclides (137Cs, 90Sr, 238U)Hydrophobic organics

Aquatic Plants: (pondweed, duckweed); Hydrilla

Phytostabilization

Complexation

Metals (Pb, Cd, Zn, As, Cu, Cr, Se, U)Hydrophobic Organics (PAHs, PCBs, dioxins,furans, pentachlorophenol, DDT

Phreatophyte trees to transpire large amounts of water for hydraulic control

Phytovolatization

Volatization by leaves

Mercury, Selenium, Tritium

Poplar, Indian mustard, Canola

Phytodegradation

Degradation in plant

Herbicides (atrazine, alachlor) Aromatics (BTEX) Chlorianatedaliphatics

Phreatophyte trees poplar, willow, sorghum, clover, alfalfa,cowpeas

Source: Mukhopadhyay and Maiti(2009) Types of phytoextraction I. II.

Natural: where plants naturally take up contaminants from the soilunassisted. Assisted: use of chelating agents, microbes and plant hormones to mobilize and accelerate contaminant uptake ➔ Uptake of contaminants also accelerated by use of hyperaccumulators e.g. Thlaspicaerulescens

Hyperaccumulators plants Phytoremediation is an environmentally friendly technology that heavily depends on the efficiency of the metal hyper-accumulating plants used. A plant is classified as a hyperaccumulator when it takes up heavy metals against their concentration gradient between the soil solution and cell cytoplasm, and thus acquires the 143


capacity to accumulate a very high metal concentration in tissues without impacting on basic growth and metabolic functions. The phenomenon is viewed as an evolutionary selection process that protects against herbivores and pathogens. The criteria for designating a plant as a hyperaccumulator for different metals are given below:  Shoot metal concentration (oven dry basis) should be more than 1% for Mn and Zn; 0.1% for Cu, Ni and Pb; and 0.01% for Cd and As.  Should be fast growing with a high rate of biomass production.  Should be able to accumulate metals, even from low external metal concentrations.  S hould be able to transfer accumulated metals from root to shoot (aboveground) quite efficiently (often with more than 90% efficiency). There are many reports on the hyper-accumulating potentials of different species of plants, as mentioned in (Table 2) Table 2. Important Hyperaccumulator plants used for phytoextraction of heavy metals (Source: Sinhaet al. 2009) Contaminant

Medium

Plant

Arsenic

Soil

Pterisvittata L

Cadmium

Soil

Oryzasativa L.

Chromium

Soil

Brassica juncea L.

Copper

Soil

Elsholtziasplendens

Lead

Soil

Chenopodium album L

Mercury

Soil

Marrubiumvulgare

Nickel

Soil

Alyssum lesbiacum

Selenium

Soil

Brassica rapa L.

Fig. 3. Phytoextraction of metals from soil and their utilization (Purakayastha & Chhonkar, 2010)

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Phytoremediation Metal contaminated soil Different species of Brassica are widely reported hyperaccumulator of various metals. In this respect, Purakayastha et al. (2008) screened five species of Brassica, (1) B. juncea (Indian mustard) cv. Pusa Bold, (2) B.campestris (Yellow mustard) cv. Pusa Gold, (3) B.carinata (Ethiopian mustard) cv. DLSC-1, (4) B.napus cv. Early napus, (5) B. nigra cv. IC-247 for identifying a suitable species for hyperaccumulation of heavy metals, viz. Zn, Cu, Pb, Ni and Cd. It was concluded that Brassica carinata cv. DLSC1 could reduce the metal load by 15% for Zn, 12% Pb and 11% for Ni from a naturally contaminated soil from peri-urban Delhi, while Brassica juncea cv. Pusa Bold emerged promising that reduced soil Cu content by 21% in a single cropping. Castor (Ricinus communis L.) was reported to accumulate large amount of Ni and therefore, it could be used as a potential plant for phytoremediation of Ni-contaminated soils (Adhikari and Ajay, 2012). Dheri et al. (2007) studied the potential of fenugreek (Trigonella foenumgraecum L.), spinach (Spinacia oleracea L.), and rye (Brassica campestris L.) for clean-up of Cr contaminated silty loam and sandy soils. The findings indicated that family Cruciferae (raya) was the most tolerant to Cr toxicity, followed by Chenopodiacea (spinach) and Leguminosae (fenugreek). Ramasamy (1997) observed that Jasminumauriculatum was relatively tolerant up to 1000 μg g-1 Cr in soil than Crossandrain fundibuliformis and Jasminum sambac, which were found very sensitive at this concentration. Anandhkumar (1998) examined the level of Cr accumulation in flower plants, Viz., Jasminum sambac, (Gundumalli), Jasmium grandiflorum (Jathimalli), Polyanthus tuberose (Tuberose) and Nerium oleander (Nerium) and found that a considerable amount of Cr was accumulated in flower crops due to irrigation with tannery effluent. Shankar et al. (2005) conducted a pot culture experiment to study the potential of Cr phytoaccumulatory capabilities of four promising agroforestry tree species viz., Albizia amara, Casuarina equisetifolia, Tectona grandis and Leucaena luecocephala. The results suggested that Albizia amara is a potential Cr accumulator with citric acid as soil amendment. Mandal et al. (2012a) reported that two successive harvests with DAP as the phosphate fertilizer emerged as the promising management strategy for amelioration of arsenic contaminated soil of West Bengal through phyotoextraction by Pterisvittata. The phytoextraction of arsenic contaminated soil by P. vittatawas beneficial for growing rice resulted in decreased As content in rice grain of 4 dS m−1 and SAR>13) to values that may be considered non-saline or sodic (Fig. 6.). The highest reduction in SAR was obtained with Suaedamaritime. The reduction in SAR was dramatically decreased at 60th day onwards.

Fig. 6. Effect of six halophytes on reduction of sodium adsorption ratio (SAR) in natural saline soil. Values shown are mean±SD for five replicate experiments. *significant at 5% level. Source: Ravindran et al. (2007) The application of non-leaching conditions provides furtherinformation on salt uptake capacity of plants in soils. Rabhi et al. (2009) reported that in the field, Suaedafruticosa contributed to desalination of the surrounding rhizosphere mostly by improved leaching due to enhancement of soilstructure, while the contribution of Arthrocnemum indicum was by salt uptake. When both plants were tested in nonleaching conditions, the maximum salt uptake of S. fructicosa was in fact higher. It is possible, therefore, that S. fructicosa improves the structure of the soil in a more efficientway than A. indicum, possibly due to different root systems, and in such a way that leaching occurs too quicklyto enable significant amounts of salt uptake. Advantages of microbially enhanced phytoextraction   

Biological, ‘green’ approach to soil clean-up Contaminant permanently removed from soil Amount of waste material that must be disposed of is decreased up to 95% 149


 

Soil retains its structure and microbiological activity It can clean up the soil without causing any kind of harm to soil quality

Disadvantages of microbially enhanced phytoextraction    

Only effective within the rhizosphere zone Slow compared with physico-chemical techniques Specialized harvesting techniques required Disposal problems for metal-enriched biomass

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Rattan, R.K., Datta, S.P., Chhonkar, P.K., Suribabu, K. and Singh, A.K. (2005) Long-term impact of irrigation with sewage effluents on heavy metal contents in soils, crops and ground water – A case study.AgricEcosysEnv109:210–322. Ravindran KC, Venkatesan K, Balakrishnan V, Chellappan KP, Balasubramanian T (2007) Restoration of saline land by halophytes for Indian soils. Soil BiolBiochem 39:2661– 2664. Salt, D.E., Smith, R.D. andRaskin, I. (1998): Phytoremediation. Ann. Rev. Plant Mol. Biol. 49: 643-668. Schimper, A. F. W. (1903) Plant Geography upon a Physiological Basis, Clarendon Press, Oxford, UK. Setkit, K., Kumsopa, A., Wongthanate, J. and Prapagdee, B. (2014) Enhanced Cadmium(Cd) Phytoextraction from Contaminated Soil using Cd-Resistant Bacterium. Environment Asia 7:89-94. Shelef, O., Gross, A., Rachmilevitch, S. (2012) The use of Brassica indica for salt phytoremediation in constructed wetlands. Water Res 46:3967–3976. Shanker, A.K., Ravichandran, V., Pathmanabhan, G., 2005.Phytoaccumulation of chromium by some multipurpose tree seedlings.Agroforestry Systems 64, 83-7. Sinha, R. K., Valani, D., Sinha, S., Singh, S. and Herat, S. (2009) Bioremediation of Contaminated Sites: A Low-Cost Nature’s Biotechnology for Environment clean up by versatile microbes, plants and earthworms. Solid Waste Management and Environmental Remediation.ISBN: 978-1-60741-761-3 Stocker, O. (1928) “Das Halophytenproblem,” in Ergebnisse der Biologie, K. V. Frisch, R. Goldschmidt, W. Ruhland, and H. Winterstein, Eds., pp. 266–353, Springer, Berlin, Germany, (German). Walker DJ, Lutts S, Sánchez-García M, Correal E (2013) Atriplexhalimus L.: its biology and uses. J Arid Environ. doi:10.1016/j. jaridenv.2013.09.004. Yoon J, Cao X, Zhou Q, Ma L. (2006) Accumulation of Pb, Cu, and Zn in native plants growing on a contaminated Florida site. Science Total Environ. 368: 456- 464.

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Fluorescent Pseudomonads for Enhancing Crop Yields and Remediation of Phytopathogen Infested Saline Soils Naveen Kumar Arora Department of Environmental Microbiology BBA University, Lucknow - 226025 Email: [email protected] Introduction For centuries, agriculture in arid and semiarid environments has faced challenge due to salinity. Salinity is considered as one of the major abiotic stress factor limiting plant growth and productivity (Khan and Panda, 2008). The total saltaffected land worldwide is estimated to be 900 million ha, 6% of the total global land mass (Flowers, 2004). According to the Food and Agricultural Organization (FAO), if corrective measures are not taken, salinization of arable land will result in 30% land loss in the next 25 years and up to 50% by the year 2050 (Munns, 2002). However, estimates show that about 955×106ha of the world is under different categories of salt affected soils and this is still increasing day by day due to various anthropogenic activities. A number of major irrigation schemes throughout the world have suffered to some extent from the effects of salinity and or sodicity. Many once productive areas have become salt affected wastelands. Salt related problems occur within the boundaries of at least 75 countries (Szabolcs, 1994) and countries with serious salinity problems include Australia, China, Egypt, India, Iraq, Mexico, Pakistan, the Soviet Union, Syria, Turkey and the United States (Rhoades, 1998). An understanding of saline soil management and amelioration practices is important for long term sustainable agriculture. Microorganisms could play an important role in adaptation strategies and increase of tolerance to abiotic stresses including salinity in agricultural plants (Arora et al., 2012). When plants are exposed to stress conditions, these rhizospheric microorganisms affect plant cells by different mechanisms but induction of osmoprotectors and heat shock proteins are mainly responsible.Whenchanges in external osmolarity occur, microbes counterbalancethis osmotic difference. Furthermore bacteriatake up suitable compounds from their surroundings and can help the plant/ crop in acquiring nutrients from even saline soils like through nitrogen fixation, phosphate, zinc and iron solubilisation, etc. Antagonistic plant growth promoting rhizobacteria such as fluorescent pseudomonads can also combat soil borne phytopathogens in saline conditions. Overall such PGPRs can be of great help in remediation of barren saline soils and enhancing the productivity in sustainable manner. Salinity in soil: A real challenge to agroecosystem Saline soils as those containing sufficient salt content in the root zone to impair the growth of crop plants (Ponnamperuma, 1984). However, since salt injury depends on species, variety, growth stage, environmental factors, and nature of the salts, it is difficult to define saline soils precisely. The USDA Salinity Laboratory defines a saline soil as having an electrical conductivity of the saturation extract (ECe) of 4 dS m-1 or more and soils with ECe exceeding 15 dS m-1 are considered strongly saline. Traditionally, 4 levels of soil salinity based on saline irrigation water have been distinguished, low salinity defined by electrical conductivity of less than 0.25 dS m-1; medium salinity (0.25 to 0.75 dS m-1); high salinity (0.75 to 2.25 dS m-1), and very high salinity with an electrical conductivity exceeding 2.25 dS m-1 (US 153


Salinity Laboratory Staff, 1954). According to Grattan and Grieve (1999) the direct effect of salts on plant growth may be divided into three broad categories: (i) reduction in the osmotic potential of the soil solution that reduces plant available water, (ii) deterioration in the physical structure of the soil such that water permeability and soil aeration are diminished, and (iii) increase inthe concentration of certain ions that have an inhibitory effect onplant metabolism (specific in toxicity and mineral nutrientdeficiencies). Highly saline soil (ECe> 16 dS/m) can severely interfere with germination and growth of plants. As water and nutrients move from areas of low salt concentration to areas of high salt concentration, soil salinity prevents plant roots from taking up water and other nutrients into the plant, resulting in osmotic and nutrient imbalances that impair proper plant growth. Munns (2002) has summarized the sequential physiological responses of plants under salinity stress. The root tip acts as a finely tuned sensor for various kinds of stresses (Colmer et al., 1994). Han and Lee (2005) observed that increasing salinity in the soil decreased plant growth, photosynthesis, stomatal conductance, chlorophyll content and mineral uptake compared to soil without salinity.

Fluorescent pseudomonads (FLPs): Versatile microbes Pseudomonas are gram negative rod shaped bacteria. The interface between soil and plant roots (i.e., the rhizosphere) is a microbial hot spot in which root colonizing pseudomonads play a prominent role (Bossis et al., 2000). The most effective strains of Pseudomonas have been the fluorescent Pseudomonadssp. (FLPs) .FLPs make up a dominant population in soil along with other soil beneficial bacteria such as Agrobacterium, Arthrobacter, Azotobacter, Azospirillum, Bacillus, Burkholderia, Caulobacter, Chromobacterium, Erwinia, Flavobacterium, Micrococcous, and Serratia. Considerable research is under way globally to exploit the potential of FLPs. (Haas and Défago, 2005). FLPs help in the maintenance of soil health and are metabolically and functionally most diverse (Tewari and Arora, 2014a). Isolatesof salt-tolerant FLPs from halophilic environment, where the soils are severely affected by high pH characterized by high Na+ and other toxic ions in the soil revealed that exposure of stress (drought, excess moisture, high and low temperatures, metal toxicity) is overridden by FLPs and they do this by production of exopolysaccharides (EPS), induction of resistance genes, increased circulation of water in the plant, and the synthesis of ACC-deaminase, indole-acetic acid and proline. In this way the possible measures to improve crop health in saline condition is to use salt-tolerant bacterial inoculants which can control diseases and/or which promote plant growth. Tewari and Arora (2014b) reported role of EPS produced by FLPs in stimulation of plant growth and suppression of Macrophomina phaseolina in saline soils. Tewari and Arora (2015) reported the ability of FLPs producing diverse metabolites in enhancing yields of sunflower in saline soils. Development of such a stress-tolerant microbial strain associated with roots of agronomic crops can lead to improved fertility of salt-affected soils. Abbaspoor et al. (2009) mentioned that PGPR Pseudomonas fluorescens, effectively multiply in saline soil. Whereas few plant growth promoting Pseudomonas had ability tosurvive under saline conditions and enhanced the plantgrowth in maize (Kausar and Shahzad, 2006), cottonseedling (Yao et al., 2010) and Cicer arietinum L. (Mishra et al., 2010). Pseudomonas strains have capability tosurvive and multiply in saline conditions. Matsuguchi and Sakai (1995) reported populations of total bacteria andgram negative bacteria did not change significantlythrough salinity, while the populations of total fluorescentpseudomonads apparently increased. In a similar study Nadeem et al. (2007) among various plant growth-promoting rhizobacterial strains tested for salt tolerance in maize P. fluorescens were the most effective 154


strains for promoting the growth and yield of maize, even at high salt stress. The relatively better salt tolerance of inoculated plants was associated with a high K+/Na+ ratio as well as high relative water and chlorophyll and low proline contents.

Exploiting the bio control potential of fluorescent pseudomonads against soil borne phytopathogens Saline soil has distinct effects on pathogen growth, reproduction, the virulence of the pathogen, and on the susceptibility of the plant (Rasmussen and Stanghellini, 1988), whereas higher salinity conditions were found to increase fungal disease (Triky-Dotan et al., 2005). Ragazzi et al. (1994) reported that mycelial growth of different Fusarium species were increased under salt-stress conditions. The Pseudomonas species, especially FLPs, are particularly suitable to be used as agricultural biocontrol agents because they can produce large amounts of secondary metabolites to protect plants from phytopathogens and stimulate plant growth in stressed saline soils (Tewari and Arora, 2014b). The root colonization potential of the salt tolerant Pseudomonas strains is beingutilized in arid region (Paul and Nair, 2008) and they are known to confer their biocontrol potential in treating soil infested with phytopathogens. FLPs produces several antifungal activities/secondary metabolites in which pyrrolnitrin, pyoluteorin, 2, 4diacetylphloroglucinol, hydrogen cyanide, the siderophores pyochelin (or related compounds) and pyoverdine, and a lipopeptide are of great importance in controlling soil borne fungi. The importance of these bioactive metabolites in biocontrol were evaluated in many reports and review articles (Weller and Thomashow, 1990; Keel et al., 1992; Aldesuquy et al., 1998; Boruah et al., 1999). Various approaches for formulation design for exclusive use in arid region have been tested. Understanding the mechanism of osmo-adaptation in FLPs contributed better option of growth enhancement and disease suppression in saline soils. Among the best tested formulation exopolysacchride based formulation has gained much attention. Besides this applying direct to osmo-protectant is also a good approach. Generally decrease in root growth under salt stress is related to a decline of endogenous levels of phytohormones such as auxins, gibberellins, jasmonic acid and salicylic acid caused by NaCl toxicity (Alqarawi et al., 2014) but application of salt tolerant FLPs induces auxin like substances and subside the potential loss due to salt toxicity Whereas biosynthesis of various secondary metabolites and resistance to stressful conditions prevents from disease development. For further details on applications of FLPs and other PGPR readers can go through Arora (2015). Hurdles in application As the salinity is the global problem most of the saline fields are being treated by various physico chemical approaches such as scraping, flushing, leaching using chemicals and even application of composts, and all are known to restore up to a certain level of fertility and reduce the impact of salinity. Application of microbes may have vast applications and can be cheaper alternatives. Although numerous FLPs have been identified as potent salt tolerant candidates but their use is limited due to various reasons but some of the hurdles include their application anddelivery methods which need to be improved particularly when designing formulations for saline soils. Recently, Tewari and Arora (2014b) reported a talc based bioformulation utilizing EPS from FLPs for treating seeds to be sown in 155


saline soils. It was reported that the formulation based on FLPs and their metabolites proved to be most effective. Conclusion Biological control of plant diseases by salt tolerant FLPs is a promising tool in saline soil remediation. Production of inhibitory metabolites, which directly inhibit the pathogens, such as antibiotics, hydrogen cyanide, iron-chelating siderophores, and cell wall-degrading enzymes, induction of systemic resistance, and all such attributes can be used in formulating of product that would work in high saline conditions. Research focused on elucidating themolecular mechanisms of salttolerance of rhizobacteriaand screening salt-tolerant strains is of great importancefor development and improvement of agriculturalproduction as the saline areas under agriculture areincreasing every year, across the globe and current methods of remediation are not only costly but also are not environmental friendly. References Abbaspour KC, Faramarzi M, Ghasemi SS, Yang H (2009) Assessing the impact of climate change on water resources in Iran. Water Resources Research 45. Artn W10434 DOI: 10.1029/2008wr007615 Alqarawi AA, Hashem A, Abd-Allah EF, Alshahrani TS, Huqail AA (2014) Effect of salinity on moisture content, pigment system, and lipid composition in Ephedra alataDecne. ActaBiol Hung. 65:61–71. Arora NK (Ed) 2015. Plant Microbes Symbiosis: Applied Facets. Springer publication. Arora NK, Tewari S, Singh S, Lal N, Maheshwari DK (2012)PGPR for Protection of Plant Health Under Saline Conditions. Bacteria in Agrobiology: Stress Management, Springer Berlin Heidelberg, pp 239-258. Bossis, E, Lemanceau, P, Latour, X and Gardan, L (2000) The taxonomy of Pseudomonas fluorescens and Pseudomonas putida: current status and need for revision. Agronomie 20, 51–63. Colmer TD, Epstein E, Dvorak J (1995) Differential solute regulation in leaf blades of various ages in salt-sensitive wheat and a salt-tolerant wheat × Lophopyrumelongatum (Host) A. Love amphiploid. Plant Physiol 108:1715–1724. Flowers, T T (2004) Improving crop salt tolerance. Journal of Experimental Botany, 396:307-319. Grattan SR, Grieve CM (1999): Mineral nutrient acquisition and response by plants grown in saline environments. In: Pessarakli M. (ed.): Handbook of Plant and Crop Stress. Marcel Dekker, New York: 203–229. Haas, D and De´fago, G (2005) Biological control of soil borne pathogens by fluorescent pseudomonads. Nat Rev Microbiol 3:307–319. Han HS, Lee KD (2005) Plant growth-promoting rhizobacteria: effect on antioxidant status, photosynthesis, mineral uptake and growth of lettuce under soil salinity. Research Journal of Agricultural and Biological Science, 1, 210–215. Khan, MH and Panda SK, (2008). Alterations in root lipid peroxidation and ant oxidative responses in two rice cultivars under NaCl-salinity stress. ActaPhysyol Plant, 30, 91-89. Matsuguchi, T and Sakai, M (1995) Influence of soil salinity on the populations and composition of fluorescent pseudomonads in plant rhizosphere. Soil Sci. Plant Nutr. 41: 497-504. Munns R (2002) Comparative physiology of salt and water stress. Plant, Cell and Environment, 25:239-250. Nadeem, SM, Zahir ZA, Naveed M, Arshad M (2007) Preliminary investigations on inducing salt tolerance in maize through inoculation with rhizobacteria containing ACCdeaminase activity. Canadian Journal of Microbiology 53:1141-1149. Ponnamperuma, F.N. (1984) Role of cultivar tolerance increasing rice production in saline lands In: RC. Staples and G.H. Toemnnniessen (Eds.), Salinity Tolerance in Plants. Willey-Interscience, New York. pp 255-271.

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Ragazzi, A, Vecchio, V, Dellavalle, I, Cucchi, A, Mancini, F (1994). Variations in the pathogenisity Fusarium oxysporumf.sp. vasinfectum in relation to salinity of the nutrient medium. Zeitschrift fur Pflanzenkrankheiten und Pflanzenschutz, 101:263266. Rhoades, Gary (1998). Managed Professionals: Unionized Faculty and the Restructuring of Academic Labor. Albany: State University of New York Press Szabolcs I (1994). Prospects of soil salinity for the 21st century. 15th World Congress of Soil Science. Acapulco; 123-141. Tewari S, Arora NK (2014a) Multifunctional exopolysaccharides from Pseudomonas aeruginosa PF23 involved in plant growth stimulation, biocontrol and stress amelioration in sunflower under saline conditions. Curr. Microbiol. 4:484-94. Tewari S, Arora NK (2014b) Talc based exopolysacchride formulation enhancing growth and production of Hellianthusannuus under saline condition. mCell Mol. Biol, 60:73-81. Tewari S, Arora NK (2015) Plant growth promoting fluorescent Pseudomonas enhancing growth of sunflower crop. International Journal of Science Technology and Society, 1:51-54. Triky-Dotano, S, Yermiyahu, U, Katan, J, Gamliel (2005). Development of crown and root rot disease of tomato under irrigation with saline water. Phytopathology 95:14381444.

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Remote Sensing and GIS for Delineation and Management of Salt Affected Soils Alok Mathur Head Soil Resources Division UP Remote Sensing Application Centre, Lucknow Introduction Remote Sensing is the science of making inferences about material objects from measurements, made at a distance, without coming into physical contact with the objects under study. When viewed in this context, any force field - gravity, magnetic, electromagnetic could be used for remote sensing, covering various disciplines from astronomy to laboratory testing of materials. However, currently the term remote sensing is used more commonly to denote identification of earth features by detecting the characteristic electromagnetic radiation that is reflected and or emitted by the earth surface. Every object reflects/scatters a portion of the electromagnetic energy incident on it depending upon its physical properties. In addition objects emit radiation depending on their temperature and emissivity. If we study the reflectance/emittance of any object at different wavelengths, we get a reflectance/emittance pattern which is characteristic of that object - this is called ‘Spectral signature’. It is like finger prints. Just as we are able to use the finger prints to identify a person, the spectral signatures enable, in principle, to identify the objects. Visual perception of objects is the best example of remote sensing. We see an object by the light reflected from the object falling on the human eye. Here, eye is the sensor and the nervous system carries information to the brain, which interprets the information in terms of the identification and location of the objects seen. Modern remote sensing is an extension of this natural phenomenon. However, apart from visible light, the electromagnetic radiation extending from the ultraviolet to the far infrared (IR) and the microwave regions are also used for remote sensing of the earth resources. A remote sensing system consists of a sensor to collect the radiation and a platform - an aircraft, balloon, rocket, satellite or even a ground-based sensor-supporting stand - on which a sensor can be mounted. The information received by the sensor is suitably manipulated and transported back to the earth - may be telemetered as in the case of unmanned spacecraft, or brought back through films, magnetic tapes, etc as in aircraft or manned spacecraft systems. The data are reformatted and processed on the ground to produce either photographs, or computer compatible digital devices. The photographs/digital data are interpreted visually/digitally to produce thematic maps and other resources information. Concept of Signatures Any set of observable characteristics which directly or indirectly lead to the identification of an object and/or its condition is termed signature. Spectral, spatial, temporal and polarisation variations are four major characteristics of the targets which facilitate discrimination. Spectral variations are the changes in the reflectance or emittance of objects as a function of wavelength. Spatial arrangements of terrain features providing attributes such as shape, size and 158


texture of objects which lead to the identification of objects are termed as spatial variations. Temporal variations are the changes of reflectivity or emissivity with time. They can be diurnal and/or seasonal. The variation in reflectivity during the growing cycle of a crop helps distinguish crops which may have similar spectral reflectances but whose growing cycles may not be same. Polarisation variations relate to the changes in the polarisation of the radiation reflected or emitted by an object. The degree of polarisation is a characteristic of the object and hence can help in distinguishing the object. Such studies have been particularly useful in microwave region. Spectral response of some natural earth surface features Vegetation The spectral reflectance of vegetation is quite distinct. Plant pigments, leaf structure and total water content are the three important factors which influence the spectrum in the visible, near IR and middle IR wavelength regions respectively. Low reflectance in the blue and red regions corresponds to two chlorophyll absorption bands centered at 0.45 and 0.65 mm respectively. A relative lack of absorption in the green region allows normal vegetation to look green to ones eyes. In the near infrared, there is high (~45 percent) reflectance, transmittance of similar magnitude and absorptance of only about five percent. This is essentially controlled by the internal cellular structure of the leaves. As the leaves grow, inter cellular air spaces increases and the reflectance increases. As vegetation becomes stressed or senescent, chlorophyll absorption decreases, red reflectance increases and also there is a decrease in inter cellular air spaces, decreasing the reflectance in the near infrared. This is the reason why the ratio of the reflectance in the near infrared to red or any of the derived indices from this data are sensitive indicators of vegetation growth/vigour. In the middle infrared region of the spectrum, the spectral response of green vegetation is dominated by strong absorption bands due to water molecules at 1.4, 1.9 and 2.7 mm.In the middle IR reflectance peaks occur at 1.6 and 2.2 mm. It has been shown that total incident solar radiation absorbed in this region is directly proportional to the total amount of leaf water content. Water Water absorbs most of the radiation in the near infrared and middle infrared regions. This property enables easy delineation of even small water bodies. In the visible region the reflectance depends upon the reflectance that occurs from the water surface, bottom material and other suspended materials present in the water column. Turbidity in water generally leads to increase in its reflectance and the reflectance peak shifts towards longer wavelength. Increase in the chlorophyll concentration leads to greater absorption in the blue and red regions. Dissolved gases and many inorganic salts do not manifest any changes in the spectral response of water. Soil In the initial years B & W aerial photographs were used but with the advent of satellite based multispectral remote sensing, the mapping of soils has become more rapid & delineation of soil units more dependable, which is primarily based on spectral behaviour of soils. Remote sensing utilises electromagnetic energy which ranges from short wavelength ultra violet through visible, near infrared, and thermal infrared, to the longer wavelength active radar and passive microwave 159


systems. Data from several wavelength regions are used together for various applications. A knowledge base has been developed for the relationship between physical & chemical characteristics of the soils and the reflected and emitted radiation. A number of studies have shown that spectral properties of soils is useful in their identification and characterisation. The advantage of using satellite images is not only periodic availability of data but also the range of electromagnetic radiation which can be sensed by detectors that respond in spectral regions beyond those discernible by the human eye – specifically in the infrared and microware regions. Like any other objects, soils also emit, reflect & absorb incident electromagnetic radiation in varying proportion depending upon the soil properties. The soil properties which affect the spectral behaviors of soils are soil color, mineral content, organic matter content, moisture content, soil texture, soil structure, roughness and soil emissivity. Reflectance from soil surface in the field is affected by presence of vegetation and atmospheric interference. Electromagnetic energy interacts with atmospheric gas molecules and aerosol particles that may cause misinterpretation of soil reflectance. Instruments like spectrometers and radiometers are used to measure the intensity of radiation reflected by soils across the wavelength range of natural solar illumination. A soil spectrum is a set of data or a graph that provides the relative intensity of reflected radiation as a function of wavelength. Soil reflectance values are often determined by taking a ratio of the energy reflected by a soil surface to the energy reflected by a bright, diffuse reference material. Visual Analysis Visual interpretation methods have been the traditional methods for extracting information, based on the characteristics such as tone, texture, shadow, shape, size, association, etc. seen in a photograph. Though this approach is simple and straight forward it has some shortcomings. The range of gray values recorded on a film or print is limited; the number of colour tones recognized by the human brain is quite large still limited. The interpreter is likely to be subjective in discerning subtle differences in tones. Generation of photographic products from digital data, degrades the contrast. It is difficult to achieve precise registration of multiband and multitemporal images. It is difficult to be quantitative. Above all when large volume of data has to be analysed, it cannot meet the throughput requirements. Digital Techniques Digital techniques facilitate quantitative analysis, use of full spectral information and avoid individual bias. Simultaneous analysis of multitemporal and multisensor data is greatly facilitated in digital methods. In digital classification the computer analyses the spectral signature, so as to associate each pixel with a particular feature of imagery. The reflectance value measured by a sensor for the same feature say wheat field will not be identical for all wheat pixels i.e. response variation within a class is to be expected for any earth surface cover due to various reasons. Therefore the radiance value for a class will have a mean and a variance. One finds a natural clustering of classes in groups indicating the signature differences of resource. When the clusters corresponding to different ground covers are distinct it is possible to associate localised regions of the feature space with specific ground covers. Such distinct clusters do not happen in real life situation. The digital classification technique essentially partitions this feature space in some fashion so 160


that each pixel in the feature space can be uniquely associated with one of the classes. This is achieved by suitable statistical methods and a number of such algorithms are available in the literature. Table 1. Major Specifications Of LANDSAT, SPOT HRV 1 & 2 and IRS LISS-I, LISSII, LISS-III, LISS-IV, WiFS & PAN Satellite sensor (year of launch)

Spectral bands (in mm)

Ground QuantisaResolution tion level (m)

LANDSAT 1,2,3,4,5 (1972,75,78,82,84) MSS 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-1.1

TM

SPOT 1,2,3 (1986,90,93) PAN HRV IRS-1A & 1B (1988,91) LISS-I & II

0.45-0.52,0.520.60, 0.630.69,0.76-0.90, 1.55-1.75,2.082.35, 10.4-12.5

79

128

30

256

Swath (km)

18 (LANDSAT 1,2,3) 16 (LANDSAT 4,5) 16

185

185

120

0.51-0.73,0.610.68 0.50-0.59,0.790.89

10

256

26

60

20

256

26

60

128

22

148.48 145.48 (LISS-IIA&B)

37x32

128

24

131

~23.5 VNIR ~69 MIR

128

24

140

188

128

5

804

5.8 above 5.8

64 10 bit

5(revisit) 24

70 140

0.45-0.52,0.5272.5 (LISS-I) 0.59, 0.62- 36.25(LISS-II) 0.68,0.77-0.86

IRS-P2 (1994) LISS-II

0.45-0.52,0.520.59, 0.62-0.68,0.770.86 IRS-1C/1D (1995,97) LISS-III 0.52-0.59,0.620.68 0.77-0.86,1.551.70 WiFS 0.62-0.68,0.770.86 PAN 0.50-0.75 Resourcesat 2 (2011) as L3

Repetition Cycle (days)

LISS-IV

161


The classification techniques used can be broadly categorised as either supervised or unsupervised approaches. In the former, the analyst as a first step, called the training stage, ‘trains’ the computer by compiling an ‘interpretation key’. Spectral attributes for each cover type of interest are numerically developed. This is generally done by examining representative sample areas of known cover type, called training areas. In the second step, called the classification stage, each pixel in the image data set is compared to each category in the numerical interpretation key. This comparison is made numerically, using any one of a number of different strategies to decide which category an unknown pixel belongs to. Each pixel is then labelled with the name of the category it resembles, or labelled “unclassified” if it is not similar to any category. An output image data set is then generated using the category label assigned to each pixel. Thus, the multidimensional input image is used to develop a corresponding classified image of interpreted category types. In contrast to supervised procedure, unsupervised classification is based on the exploitation of the inherent tendency of different classes to form separate spectral clusters in the feature space. Unsupervised classification uses algorithms which examine a large number of unknown pixels and groups them into clusters. Each cluster is then associated with a physical category. Geographic Information System Techniques GIS is a computer assisted system for the capture, storage, retrieval, analysis and display of spatial data. The applications of GIS range from simple database query systems to complex analysis and decision support systems. Areas of applications range from natural resources management to crime control and near real time application like flood warning. Analysis models comprise simple user defined views to complex stochastic models. Some of these are reclassification, aggregation, overlays, suitability analysis, flow models, network and route, optimisation allocation / sitting etc. Geographic Information System techniques are playing an increasing role in facilitating integration of multilayer spatial information with statistical attribute data to arrive at alternate developmental scenarios. Remote Sensing and salinity Salts in soils and irrigation water are important factors limiting productivity in many croplands. Remedial solutions require mapping of affected areas in space and time. This can be accomplished using remote sensing measurements which identify contaminated soils by their unusually high surface reflectance factors or by detecting reduced biomass or changes in spectral properties of plants growing in affected areas. Studies have also shown an increase in canopy temperature of plants exposed to excessive salts in irrigation water, suggesting the possibility of pre visual detection of stress which could be remedied by increasing the leaching fraction or switching to a higher quality of water. Extent of wastelands and sodic wastelands Remote sensing data has been used extensively for more than three decades for mapping of wastelands including salt affected wastelands in India utilizing the satellite data of then available satellites. The table below (Table 2) shows the changes in the extent of salt affected wastelands between 1982 and 2008-09. In 1982 Landsat MSS data was used and report was published in 1985. In 2008-09 IRS LISS-III data was used and its report was published in 2012. In U.P. the salt affected wastelands have reduce substantially (Table 2). 162


Table 2. Changes in Area under salt affected wastelands in U.P. AREA (in sq. km.) UTTAR PRADESH

1985

2000

2005

2010

2012

12,823

5811.94 4842.49 2911.74 2553.18

The wasteland mapping carried out using the IRS LISS-III data of 2005-06 and 2008-09 also show reduction in various wasteland categories including the salt affected wastelands in Uttar Pradesh. At times the moisture content of soil and tall grasses over sodic areas have hampered in the identification of extent of sodic wastelands. The table-3 below shows the changes in wasteland area between 2005-06 and 2008-09 in Uttar Pradesh. Table 3. Changes in wasteland area in Uttar Pradesh (Based on three season

LISS-III data) S.NO.

Wasteland Class

Area ( km2) 2005-06

2008-09

Change

1

Gullied and /or ravinous land (medium)

1216.48

923.99

-292.49

2

Gullied and /or ravinous land (Deep)

264.63

274.59

9.96

3

Land with Dense Scrub

1160.19

939.01

-221.18

4

Land with Open Scrub

1835.12

1975.49

140.37

5

Waterlogged and Marshy land (Permanent)

376.54

226.76

-149.78

6

Waterlogged and Marshy land (Seasonal)

721.12

638.97

-82.15

7

Land affected by salinity/alkalinity (Moderate) 2193.28

2051.89

-141.39

8

Land affected by salinity/alkalinity (Strong)

501.29

-217.17

9

1843.65

-13.66

10

Under - utilised/degraded forest (Scrub 1857.31 domin) Under - utilised/degraded forest (Agriculture) 64.61

64.07

-0.54

11

Degraded pastures/grazing land

21.47

9.66

-11.81

12

Degraded land under plantation crop

3.48

12.15

8.67

13

Sands - Riverine

109.92

48.01

-61.91

14

Mining Wastelands

16.16

26.75

10.59

15

Industrial Wastelands

18.07

10.24

-7.83

16

Barren Rocky/Stony waste

411.75

334.72

-77.03

Total

10988.59 9881.24

718.46

T.G.A.

240928

% to T.G.A.

4.56 163

4.10

-1107.35

-0.46


Fig.1

Fig.2

164


Role of Remote Sensing and GIS in U.P. Sodicland reclamation Project District Sodic land maps were generated on the basis of wasteland (2008-09 L-3 satellite data) and degraded land maps for all the 28 districts in 2009-2010. Following the process and criteria as defined in the PAD/PIP, the sodic land villages in the UPSLRP districts are selected and supplied to RSAC,U.P. for detailed mapping using satellite data. District maps with drainage and micro-watershed boundaries were generated for selection of villages. Detailed Sodicland mapping at cadastral level through interpretation of high-resolution satellite data is being carried out. Cadastral maps of the villages are supplied by UPBSN. IRS LISS –IV digital data is obtained from NRSC, Dept of Space, Govt. of India. These data are then processed and images for different villages are generated on screen in GIS environment. On these images scanned cadastral maps are registered which is followed by on screen visual interpretation based on spectral signatures ( fig. 3) in preparing sodic land map on 1:4,000 scale with limited ground field verification indicating B+, B and C sodic land classes. Area of these classes and khasra numbers involved are listed and supplied to implementing agency with prints of classified maps. If required from selected plots, surface soil samples are collected and pH, EC are determined to ascertain sodicity.

Fig.3 So far in the III project over a period of five years 1,75608 ha. sodic lands at cadastral level have been mapped which include 12673.6 ha. B+ land, 22440.7 ha. B class land and 1,40581 ha. C class sodic lands in 2088 villages of 29 project districts (Table 4).

165


Table 4. Area mapped at cadastral level in two phases of the project Phase

No. of Districts

No. of villages mapped

B+ B C Total sodicland sodicland sodicland ha. ha. ha.

Phase-I

10

785

6469.7

12558.3

50001.5

Phase-II

21

3369

28868.1

63685.6

245874.6 338428.3

4154

35337.8

76243.9

295876.1 4,07,457.8

Total

69029.5

Remote sensing and GIS techniques have been utilized in monitoring the changes in sodic areas after reclamation activities in many areas. Information on ground water levels and quality have helped the implementing agencies and scientists in understanding the issues related to sustainability. The figure 4 below shows the changes in sodic areas and the depth to ground water in a reclamation area. Sodicland Reclamation Status in Different Ground Water Zones District :Etawah Reclamation Site - II

N

St at us of Reclamat ion in Diff erent GW zones 35 30 25 20

Reclaim ed

15

Unreclaim ed

% Area

10 5 0 Shallow

Moderat e

Deep

Sodicland Reclaimed Sodicland Not Reclaimed Shallow Water Table (0-3 mtrs) Moderate Water Table (3-5 mtrs) Deep W ater Table (>5 mtrs)

RSAC - UP

Fig.4 References 1. Wasteland atlas of India, NRSC, Hyderabad. 2012 2. RSAC,U.P. UPSLRP-III Reports. 2015

166


PGPR for Sustaining Crop Productivity under Salt Stress S. R. Singh, Debarshi Biswas and Lal Bahadur* Division of Crop Production, ICAR-IISR, Raibareli Road, Lucknow-226002 * Scientist, NBRI, Lucknow Introduction Soil bacteria inhabiting around/on the rootsurface and are directly or indirectly involved in promoting plant growth and development via productionand secretion of various regulatory chemicals in the vicinity of rhizosphere are considered as plant growth promoting rhizobacteria. These rhizobacteria facilitate the plant growth directly by either assisting inresource acquisition (nitrogen, phosphorus and essential minerals) or modulating plant hormonelevels, or indirectly by decreasing the inhibitory effects of various pathogens on plant growth and development in the forms of bio-control agents. Various studies have documented the increasedhealth and productivity of different plant species by the application of plant growth promoting rhizobacteria under both normal and stressed conditions. Salt stress may reduces by the inoculation of PGPR which mediated oxidative stress under saline conditions, plants detoxify reactive oxygen species (ROS), which trigger phytotoxic reactions such as lipid peroxidation, protein and degradationby upregulating antioxidant enzyme, like superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and catalase. Salt tolerance is often correlated with the efficient oxidative system. The SOD plays a key role in the antioxidative defence system and it is most effective antioxidant enzyme in preventing cellular damage. Several findings indicated that increased SOD activity in plant exposed to different environmental stresses, including salinity. Plant growth promoting rhizobacteria which possess the enzyme, 1-aminocyclopropane1-carboxylate (ACC) deaminase, facilitate plant growth and development by decreasing ethylene levels, inducing salt tolerance and reducing drought stress in plants.The plant-beneficial rhizobacteria may decrease the global dependence on hazardous agricultural chemicals which destabilize the agro-ecosystems. Areas of salt affected soils are occupied about 6.80 lakh ha in India. Uttar Pradesh is the largest state of the country having 2.55 lakh ha (37.5%) area under salinity and sodicity. These soils arisen from natural causes like accumulation of salts over a period of time in arid and semiarid zones,weathering of parental rocks, which releases soluble salts (chlorides of sodium, calcium, and magnesium, and to a lesser extent, sulphates and carbonates). Sodium chloride is the most soluble and abundant salt released and accountable for the development of salinity. The intrusion of sea water is anotherimportant cause for the development of salinityin coastal areas. Rainwater containing 10 mg kg-1 of sodium chloride would deposit 10 kg ha-1 of salt for each 100 mm of rainfall per year. Soil suffers with varying levels of degradation in structural, chemical, nutritional, hydrological and biological properties are compact due to the high amount of clay and concrete pan in the sub-surface horizon. Poor water permeability (hydraulic conductivity and infiltration rate) due to interlocked pore spaces results in water-logging during rainy season. In the salt stress condition, root respiration and development inhibited due to high concentration of salts, which increases the osmotic potential in the root zone. In these soils, losses of soil organic matter occur due to solubilisation under extreme salinity which affected nutrientsupply and microbial 167


activity adversely. In clay soils, poor management of salinity may lead to soil sodicity, where sodium (Na) binds to negatively charged clay causing clay swelling and dispersal, which decreases crop growth. Plant productivity in saline soils is considerably reduced due to poor plant nutrition and osmotic stress. Salt stress affects all the major plant processes, such as growth, photosynthesis, protein synthesis, energy and lipid metabolism. Proline may act in osmotic adjustment, protect macromolecules during dehydration and participate in the pentose phosphate pathway as an important component of antioxidative defence. An understanding of ecological conditions affecting bacterial inoculants is important when introducing microbes for increasing plant growth and productivity. Plant growth promoting rhizobacteria (PGPR) are a group of heterogeneous bacteria that can be present in the rhizosphere as free living soil bacteria at root surface are actually divided into three functional group: Plant growth promoting bacteria, biocontrol agent proposed by Bashan and Holguim (1998) and plant stress homeoregulating bacteria proposed by Cassan et al. (2009), that can either directly or indirectly facilitate the plant growth in optimal, biotic or abiotic stress conditions. Indirect plant growth promotion induced by bio-control includes a variety of mechanism by which the bacteria prevent the phytopathogen deleterious effect on plant growth or development. Several PGPR produce metabolites like chelate which bind available forms of environmental iron thus making it unavailable to pathogen. Several disease suppressive antibiotics compounds have also been characterized which includes acilysin, itruiln-like lipopeptides, diacetyl phloroglucinol, pyrrolnitrin, HCN, pheazine-1-carboxylate phinazine, pyrrole type antibiotics, pyo-compounds, and indole derivative. Direct promotion induced by the PGPR may include plant provision with nitrogen fixation, phytohormones such as indole-3-acetic acid (IAA), gibberellic acid (GA3) and cytokinin such as zeatin (Z), iron sequestered by bacterial siderophores (Glick, 1999) and phosphate solubilization and acquisition of other essential macro and micronutrient. Direct stimulation induced by PGPR may include providing plants with stress-related phytohormones, like abscisic acid (Cohen et al., 2008); plant growth regulators like cadaverine (Cassan et al., 2009); and catabolism of some molecule related with stress signaling such as bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase. This enzyme reduces plant ethylene level which is increased various unfavorable conditions and thus confers resistance to stress (Glick et al., 1993). Beneficial soil microorganisms such as PGPRs (plant growth promoting rhizobacteria) have received in agriculture attention of scientists throughout the world (Berg, 2009). PGPRs have been reported for the plant growth under normal and stress condition like saline (Upadhyay et al., 2012), so that the osmotolerance mechanisms of these PGPRs are quite important to hyper osmotic injury. Osmoregulation in bacteria has captured major interest, not only to understand cell response and adaptation to varying environmental condition, but also because of the applied aspect of this field (such as interaction between microbe and plant). Most of the bacteria adopted universal mechanisms of osmo adaptation, which consist of accumulation of potassium and/or small molecular weight organic solutes, designated compatible solutes (Upadhyay et al., 2012). Compatible solutes are known to protect cells and biological macromolecules against denatured effect of not only hyper osmotic stress, but also other stresses such as heating, freezing and desiccation (Paul and Nair, 2008). Accumulation of these solutes, in response to the osmotic constraint, is carried out by synthesis and/or by active transport from the surrounding environment and they consequently stimulate the endogenous capacities of osmo-protection in this bacterium (Welsh, 2000). The crop productivity can be sustained for long timeby improving plant microbe interactions even in stress conditions by understanding the interaction mechanism 168


among plant, microbes and stressesof soil. Tripathi et al. (2002) reported that in Azospirillum sp. there is an accumulation of compatible solutes such as glutamate, proline, glycine betaine and trehalose in response to salinity/osmolarity, proline plays a major role in osmo adaptation through increase in osmotic stress that shifts the dominant osmolyte from glutamate to proline in A. brasilense. Bacteria from the genera have evolved highly sophisticated regulatory networks for protection against sudden unfavorable environmental changes, including nutrient starvation, changes in temperature and humidity, oxidative stress, sudden elevation in medium salinity. Plant Growth Promoting Rhizobacteria The plant growth promoting rhizobacteria (PGPR), arecharacterized by the following inherent distinctiveness’s: (i) they must be proficient to colonize the root surface (ii) theymust survive, multiply and compete with other microbiota, at least for the time needed to express their plant growth promotion/protection activities, and (iii) they must promote plant growth (Kloepper, 1994). About 2–5% of rhizobacteria, when reintroduced by plant inoculation in a soil containing competitive microflora, exert a beneficial effect on plant growth and are termed as plant growth promoting rhizobacteria (Kloepper and Schroth, 1978). Several researchers (Vessey, 2003, Upadhyay et al., 2012) reported that soil bacterial species burgeoning in plant rhizosphere which grow in, on, or around plant tissues stimulate plant growth by a plethora of mechanisms are collectively known as plant growth promoting rhizobacteria (PGPR). Alternatively, Somers et al. (2004) classified PGPR based on their functional activities as (i) bio-fertilizers (increasing the availability of nutrients to plant), (ii) phytostimulators (plant growth promotion, generally through phytohormones), (iii) rhizoremediators (degrading organic pollutants) and (iv) biopesticides (controlling diseases, mainly by the production of antibiotics and antifungal metabolites). Furthermore, in most studied cases, a single PGPR will often reveal multiple modes of action including biological control. Furthermore, Gray and Smith (2005) have recently shown that the PGPR associations range in the degree of bacterial proximity to the root and intimacy of association. In general, these can be separated into extracellular plant growth promoting rhizobacteria (ePGPR), existing in the rhizosphere, on the rhizoplane, or in the spaces between cells of the root cortex, and intracellular (iPGPR) viz., Agrobacterium, Arthrobacter, Azotobacter, Azospirillum, Bacillus, Burkholderia, Caulobacter, Chromobacterium, Erwinia, Flavobacterium, Micrococcous, Pseudomonas and Serratiaetc. (Bhattacharyya and Jha, 2012). Similarly, some examples of the iPGPR are Allorhizobium, Azorhizobium, Bradyrhizobium, Mesorhizobium and Rhizobium of the family Rhizobiaceae. Some examples of ePGPR are like, Most of rhizobacteria belonging to this group are Gram-negative rods with a lower proportion being Gram-positive rods, cocci or pleomorphic. Moreover, numerous actinomycetes are also one of the major components of rhizospheremicrobial communities displaying marvellous plant growth beneficial traits (Merzaeva and Shirokikh, 2006). Among them, Micromonospora sp., Streptomyces sp.., Streptosporangium sp., and Thermobifida sp., which have shown an enormous potential as biocontrol agents against different root fungal pathogens, are worthy of mention (Franco-Correa et al., 2010). Mechanisms of plant growth promotion According to Kloepper and Schroth (1981), PGPR mediated plant growth promotion occurs by the alteration of the whole microbial community in rhizosphere niche through the production of various substances. Generally, PGPR 169


promote plant growth directly by either facilitating resource acquisition (N, P and essential minerals) or modulating plant hormone levels, production of siderophores, ACC deaminase or indirectly by decreasing the inhibitory effects (through production of HCN, catalase) of various pathogens on plant growth and development in the forms of biocontrol agents (Glick, 2012). Direct mechanisms Nitrogen fixation Nitrogen (N) is the most vital nutrient for plant growth andproductivity. Although, there is about 78% N2 in the atmosphere but it is unavailable to the growing plants. The atmospheric N2 is converted into plant-utilizable forms bybiological N2 fixation (BNF) which changes nitrogen to ammonia by nitrogen fixing microorganisms using a complex enzyme system known as nitrogenase (Kim and Rees, 1994). Nitrogen fixing organisms are generally categorized as (a) symbiotic N2 fixing bacteria including members of the family rhizobiaceae which forms symbiosis with leguminous plants (e.g. rhizobia) and non-leguminous trees (e.g.Frankia) and (b) non-symbiotic (free living, associative and endophytes) nitrogen fixing forms such as cyanobacteria (Anabaena, Nostoc), Azospirillum, Azotobacter, Glucono acetbacter diazotrophicus and Azocarus etc (Bhattacharyya and Jha, 2012). However, non-symbiotic nitrogen fixing bacteria provide only a small amount of the fixed nitrogen that the bacterially-associated host plant requires (Glick, 2012). Symbiotic nitrogen fixing rhizobia within the rhizobiaceae family infect and establish symbiotic relationship with the roots of leguminous plants.The establishment of the symbiosis involves a complex interplay between host and symbiont (Giordano and Hirsch, 2004) resulting in the formation of the nodules wherein the rhizobia colonize as intracellular symbionts. Plant growthpromoting rhizobacteria that fix N2 in non-leguminous plants are also called as diazotrophs capable of forming a non-obligate interaction with the host plants (Glick et al., 1999). The process of N2 fixation is carried out by a complex enzyme, known as nitrogenase complex (Kim and Rees, 1994). Dinitrogenase reductase provides electrons with high reducing power while dinitrogenase uses these electrons to reduce N2 to NH3. Based on the metal cofactor three different N fixing systems have been identified (a) Mo-nitrogenase, (b) V-nitrogenase and (c) Fenitrogenase. Structurally, N2-fixing system varies among different bacterial genera. Most BNF is carried out by the activity of the molybdenum nitrogenase, which is found in all diazotrophs (Bishop and Jorerger, 1990).The genes for nitrogen fixation, called nif genes are found in both symbiotic and free living systems (Kim and Rees, 1994). The symbiotic activation of nif-genes in the Rhizobium is dependent on low oxygen concentration, which in turn is regulated by another set of genes called fix-genes which are common for both symbiotic and free living nitrogen fixation systems (Kim and Rees, 1994). Since nitrogen fixation is a very energy demanding process, requiring at least 16 mol of ATP for each mole of reduced nitrogen. Phosphate solubilization Phosphorus (P), the second important plant growth-limiting nutrient after nitrogen, is abundantly available in soils in both organic and inorganic forms. Despite of large reservoir of P, the amount of available forms to plants is generally low. The low availability of phosphorous to plants is due to the majority of soil P existed in insoluble forms, while the plants absorb it only in two soluble forms, the monobasic (H2PO4) and the diabasic (HPO4) ions. To overcome the P deficiency in soils, there are frequent applications of phosphatic fertilizers in agricultural fields. 170


Plants absorb fewer amounts of applied phosphatic fertilizers and the rest is rapidly converted into insoluble complexes in the soil (Mckenzie and Roberts, 1990). The regular application of P fertilizersis the cost expansive process causes undesirable effect on environment. This has led to search for an ecologically safe and economically reasonable option for improving crop production in low P soils. In this context, organisms coupled with phosphate solubilising activity, often termed as phosphate solubilizing microorganisms (PSM), may provide the available forms of P to the plants and hence a viable substitute to chemical phosphatic fertilizers (Khan et al., 2006). Plant growth-promoting rhizobacteria can directly increase nutrient supply in the rhizosphere and/or stimulate ion transport systems in root. With regards to increased nutrient supply, two main types of bacterial activities can be considered. Firstly, phosphate solubilisation is one key effect of PGPR on plant nutrition. Soils generally contain a large amount of phosphorus, which accumulates in the wake of regular fertilizer applications, but only a small proportion of the latter is available for plants. Plants are able to absorb on their own mono and dibasic phosphate; organic or insoluble forms of phosphate need to be mineralized or solubilised by microorganisms, respectively (Richardson et al., 2009; Ramaekers et al., 2010). Many PGPR–such as Pseudomonas, Bacillus, Burkholderia, Enterobacter, Erwinia, Flavobacterium, Microbacterium, Serratiaare and Rhizobium are able to dissolve insoluble forms of phosphate (Richardson et al., 2009). Two main processes exist : acidification of the external medium through the release of low molecular weight organic acids (such as gluconic acid) that chelate the cations bound to phosphate (Miller et al., 2009), and production of phosphatases/phytases that hydrolyse organic forms of phosphate compounds. Siderophore production Iron is a vital nutrient for almost all forms of life. Most of the microorganisms are well known to essentially require iron their growth and development (Neilands, 1995). Iron occurs principally as Fe 3+and is likely toform insoluble hydroxides and oxy-hydroxides under aerobic environment, which may in accessible to both plants and microorganisms (Rajkumar et al., 2010). Commonly, bacteria acquire iron by the secretion of low-molecular mass iron chelators referred to as siderophores which have high association constants for complexing iron. Most of the siderophores are water-soluble and can be divided into extracellular siderophores and intracellular siderophores. Generally, rhizobacteria differs regarding the siderophore cross-utilizing ability; some are proficient inusing siderophores of the same genus (homologous siderophores) while others could utilize those produced by other rhizobacteria of different genera (Khan et al., 2009). In both Gram-negative and Gram-positive rhizobacteria, iron (Fe 3+) in Fe3+siderophore complex on bacterial membrane is reduced to Fe2+which is further released into the cell from the siderophore via a gating mechanism linking the inner and outer membranes (Rajkumar et al., 2010). Thus, siderophores act as solubilizing agents for iron from minerals or organic compounds under conditions of iron limitation (Indira Gandhi et al., 2008). Binding of the siderophore to a metal increases the soluble metal concentration (Rajkumar et al., 2010). Hence, bacterial siderophores help to alleviate the stresses imposed on plants by high soil levels of heavy metals. Plants assimilate iron from bacterial siderophores by means of different mechanisms, for instance, chelate and release of iron, the direct uptake of siderophore-Fe complexes, or by a ligand exchange reaction (Schmidt, 1999). Numerous studies of the plant growth promotion vis-à-vis siderophore-mediated Fe- uptake as a result of siderophore producing rhizobacterial inoculations have been reported (Rajkumar et al., 2010). Crowley and Kraemer (2007) revealed a siderophore remediated iron transport system in oat plants and inferred that 171


siderophores produced by rhizosphere microorganisms deliverer on to oat, which has mechanisms for using Fe-siderophore complexes under iron-limited conditions. Similarly, the Fe-pyoverdine complex synthesized by Pseudomonas fluorescens C7 was taken up by Arabidopsis thaliana plants, leading to an increase of iron inside plant tissues and to improved plant growth (Vansuyt et al., 2007). Phytohormone production Synthesis of the phyto hormone auxin by microbial agents (indole-3-acetic acid/indole acetic acid) has been known for a long time. It is reported that 80% of microorganisms isolated from the rhizosphere of various crops possess the ability to synthesize and release auxins as secondary metabolites (Patten and Glick, 1996). Generally, IAA secreted by rhizobacteria has a significant role in the developmental processes of plant due to endogenous pool of plant. IAA has been implicated in virtually every aspect of plant growth and development, as well as defence responses. This diversity of function is reflected by the extraordinary complexity of IAA biosynthetic, transport and signaling pathways (Santner et al., 2009). Generally, IAA affects plant cell division, extension, and differentiation; stimulates seed and tuber germination; increases the rate of xylem and root development; controls processes of vegetative growth; initiates lateral and adventitious root formation; mediates responses to light, gravity and florescence; affects photosynthesis, pigment formation, biosynthesis of various metabolites, and resistance to stressful conditions. IAA produced by rhizobacteria likely, interfere the above physiological processes of plants by changing the plant auxin pool. Moreover, bacterial IAA increases root surface area and length, and there by provides the plant greater access to soil nutrients. Also, rhizobacterial IAA loosens plant cell walls and as a result facilitates an increasing amount of root exudation that provides additional nutrients to support the growth of rhizosphere bacteria (Glick, 2012). An important molecule that alters the level of IAA synthesis is the amino acid tryptophan, identified as the main precursor for IAA and thus plays a role in modulating the level of IAA biosynthesis (Zaidi et al., 2009). Strangely, tryptophan stimulates IAA production while, anthranilate, a precursor for tryptophan, reduces IAA synthesis. By this mechanism IAA biosynthesis is finetuned because tryptophan inhibits anthranilate formation by a negative feed back regulation on the anthranilate synthase, resulting in an indirect induction of IAA production (Spaepen et al., 2007). Starting with tryptophan, at least five different pathways have been described for the synthesis of IAA. (1) IAA formation via indole3-pyruvic acidand indole-3-acetic aldehyde is found in a majority of bacteria like, Erwiniaherbicola; saprophytic species of the genera Agrobacterium and Pseudomonas; certain representatives of Bradyrhizobium, Rhizobium, Azospirillum, Klebsiella, and Enterobacter, (2) The conversion of tryptophan into indole-3-acetic aldehyde may involve an alternative pathway in which tryptamine is formed as in Pseudomonads and Azospirilla and (3) IAA biosynthesis via indole-3-acetamide formation is reported for phytopathogenic bacteria Agrobacteriumtume faciens, Pseudomonas syringae, and E. herbicola; saprophytic Pseudomonads like (e.g. Pseudomonasputida and P. fluorescens). (4) IAA biosynthesis that involves tryptophan conversion into indole-3-acetonitrile is found in the cyanobacterium (Synechocystissp.) and (5) the tryptophan-independent pathway, more common in plants, is also found in Azospirilla and cyanobacteria. Most Rhizobium species have been shown to produce IAA (Ahemad and Khan, 2012b). Since, IAA is involved in nodule formation. Hence, it seems likely that auxin levels in the host legume plants are necessary for nodule formation (Glick, 2012). It is also reported that the inoculation with Rhizobium leguminosarum bv.viciae wherein the IAA biosynthetic pathway had been introduced, produced potential nitrogen fixing root nodules 172


containing up to 60-fold more IAA than nodules formed by the wild-type counter part invicia hirsute (Camerini et al., 2008). 1-Aminocyclopropane-1-carboxylate (ACC) deaminase Generally, ethylene is an essential metabolite for the normal growth and development of plants. It is produced endogenously by most of the plants under different biotic andabiotic stresses in soils. Apart from being a plant growth regulator, ethylene has also been established as a stress hormone. Under stress conditions viz., salinity, drought, water logging, heavy metals and pathogenicity, the endogenous ethylene level is significantly increased which negatively affects the overall plant growth. For instance, the high concentration of ethylene induces defoliation and other cellular processes that may lead to reduced crop performance (Saleem et al., 2007). Plant growth promoting rhizobacteria which possess the enzyme, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, facilitate plant growth and development by decreasing ethylene levels, inducing salt tolerance and reducing drought stress in plants (Nadeem et al., 2007). Currently, bacterial strains exhibiting ACC deaminase activity have been identified in a wide range of genera such as Acinetobacter, Achromobacter, Agrobacterium, Alcaligenes, Azospirillum, Bacillus, Burkholderia, Enterobacter, Pseudomonas, Bacillus, Ralstonia, Serratia and Rhizobium Variovorax, Rhodococcus, Ochrobactrumsp etc. (Kang et al., 2010). These rhizobacteria take up the ethylene precursor ACC and convert it into 2oxobutanoate and NH3. Several forms of stress are relieved by ACC deaminase producers, such as effects of phyto pathogenic microorganisms (viruses, bacteria, and fungi etc.), and resistance to stress from polyaromatic hydrocarbons, heavy metals, radiation, wounding, insect predation, high salt concentration, draft, extremes of temperature, high light intensity, and flooding (Glick, 2012; Lugtenberg and Kamilova, 2009). As a result, the major noticeable effects of seed/root inoculation with ACC deaminase-producing rhizobacteria are the plant root elongation, promotion of shoot growth, and enhancement in rhizobial nodulation and N, P and K uptake as well as mycorrhizal colonization in various crops (Nadeem et al., 2007; Shaharoona et al., 2008; Nadeem et al., 2009; Glick, 2012). Glick et al. (1998) revealed that all the plant growth parameters were significantly higher in Alcaligenes sp. treated plants relative to without treated plants. The longest roots and shoots, highest root fresh weight and dry weight were observed in plants treated with Alcaligenessp. Also, positive correlation between ACC deaminase production and plant root elongation was found (r=0.559), suggesting a direct impact of ACC deaminase activity on root elongation. Inoculation with rhizobacteria having ACC deaminase activity resulted in the development of a better root system, which subsequently affected shoot growth positively. Inoculation with ACC-deaminase containing bacteria promotes root growth of developing seedlings of various crops (Zahir et al., 2008). The variation in plant growth promotion activities was recorded which attributed to their individual rhizospheric competencies and hydrolyzing the ACC synthesized in roots. PGPRs having ACC deaminase activity help plants to withstand stresses (biotic or abiotic) by reducing the level of stress ethylene (Mayak et al., 2004). Similarly, improvement of seed germination has been reported with other cereals such as sorghum and pearl millet (Gholami et al., 2009). Seeds treated with the isolates showed a considerable increase in seedling vigour index under salt stress conditions and Alcaligenes significantly increased vigour index compared to the negative control. This might be due to increased synthesis of phytohormones like IAA, which would have triggered the activity of enzymes like α-amylase that promoted early germination by bringing an increase in availability of soluble sugars from starch decomposition (Kim et al., 2006). Besides, significant increase in seedling vigour 173


would have occurred by better synthesis of plant growth hormones. The microorganisms which have the ability to produce both ACC deaminase and IAA they promoted root, shoot and other growth indices of rice to a greater extent. It is likely that IAA and ACC deaminase stimulate root growth in a coordinated fashion (Glick et al., 2007b). Root growth is relatively more affected compared to shoots in the presence of an inhibitory level of salt (Lin and Kao, 2001). This might be due to the stress induced ethylene disrupting the metabolic activity and physiological processes more in roots than shoots. In addition, this might be due to the roots being in more intimate contact with the salt solution with the shoots experiencing a lower salt concentration (Mayak et al., 2004). Mayak et al. (2004) and Madhaiyan et al. (2007) reported that ACC deaminase-producing bacteria increased root growth of rice plants as compared to the negative control plants. Simple correlation analysis between ACC deaminase production microbial isolates and the root elongation under the salt stress condition indicated a highly significant positive relationship (r=0.991). Inoculation with the PGPR isolates also increased the fresh and dry weight of both root and shoot. It was assumed that higher dry weight would mean longer and stronger roots and shoots as well as plants that would be able to better withstand salt stress (Mayak et al., 2004). Indirect Mechanisms The application of microorganisms to control diseases, which is a form of biological control, is an environment-friendly approach. The major indirect mechanism of plant growth promotion in rhizobacteria is through acting as biocontrol agents (Glick, 2012). In general, competition for nutrients, niche exclusion, induced systemic resistance and antifungal metabolites production are the chief modes of bio-control activity in PGPR. Many rhizobacteria have been reported to produce antifungal metabolites like, HCN, phenazines, pyrrolnitrin, 2,4diacetyl phloroglucinol, pyoluteorin, viscosinamide and tensin (Bhattacharyya and Jha, 2012). Interaction of some rhizobacteria with the plant roots can result in plant resistance against some pathogenic bacteria, fungi, and viruses. This phenomenon is called induced systemic resistance (ISR). Moreover, ISR involves jasmonate and ethylene signaling within the plant and these hormones stimulate the host plant’s defence responses against a variety of plant pathogens (Glick, 2012). ISR induces by many individual bacterial components such as lipopolysaccharides (LPS), flagella, siderophores, cyclic lipopeptides, 2,4-diacetyl phloroglucinol, homoserine lactones, and volatiles like, acetoin and 2,3-butanediol (Lugtenberg and Kamilova, 2009). Salt stress Management through PGPR The colony forming units of rhizospheric soil indicated that both Azospirillum and Pseudomonas successfully survive and proliferate in the presence of 20 dSm -1 NaCl. Though the value was less than that of control but Azospirillum further augmented their survival efficiency significantly reported that Azospirillum can tolerate 300 mM/L NaCl in the absence of osmo-protectants and upto 600 mM/L NaCl in the presence of osmoprotectant. Pseudomonas was reported to alleviate NaCl stress and significantly promote the seedling growth of annual rye grass under NaCl stress in gnoto biotic growth pouch assay. Pseudomonas induced growth under saline conditions is possibly mediated by solubilization of soil P in available form to plant. Soil under saline conditions retained high moisture content but the relative water content of the leaves of salt treated plants were less than that of control, this is because of the osmotic imbalance under salt stress conditions roots may fail to absorb water from the soil and even loss of water from the roots may occur (Blum and Johnson, 1992). The less available moisture in soil treated 174


with Azospirillum possibly indicate the treatment induced increase in hydraulic conductivity of the root, resulting in better water uptake by the root. Azospirillum and Pseudomonas did not ameliorate the salt induced inhibition in shoot length but partially inhibit the adverse effects of salt stress. Combination inoculation of Azospirillum and Pseudomonas ameliorated the salt induced inhibition in growth. Azospirillum have been catching researcher’s interest on account of remarkable ability to improve plant growth and productivity under various environmental stresses. A decrease in water availability under soil salinity causes osmotic stress, which leads to decreased turgor. Osmotic potential was increased by inoculation with Pseudomonas and Azospirillum. The inoculation of Pseudomonas under unstressed conditions maintains the osmotic potential of leaves in maize have suggested that plant survival depends on maintaining a positive turgor, which is indispensable for expansion growth of cells and stomatal opening. Azospirillum applications also results in increase of osmotically active components of the cell sap of maize plants under salinity, Salt stress disturbs the ion homeostasis resulting in osmotic stress and ion toxicity both of which cause generation of reactive oxygen species (ROS), which trigger phytotoxic reactions such as lipid peroxidation, protein degradation. To overcome salt mediated oxidative stress, plants detoxify ROS by upregulating antioxidant enzyme, like superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and catalase and demonstrated that salt tolerance is often correlated with the efficient oxidative system. The SOD plays a key role in the anti oxidative defence system and it is most effective antioxidant enzyme in preventing cellular damage. Several findings reported increased SOD activity in plant exposed to different environmental stresses, including salinity The H2O2 generated as a result of scavenging action of SOD is detoxified by POD. Developing salt-tolerant crops has been a much desired scientific goal but with little success to date, as few major-determinant genetic traits of salt tolerance have been identified. An alternative strategy to improve crop salt tolerance may be to introduce salt-tolerant microbes that enhance crop growth. The ability of soil microbes to improve crop water relations, perhaps by enhancing the accumulation of specific metabolites, Water homeostasis and osmolyte accumulation, although maintaining leaf turgor of salinized plants did not prevent the long-term growth inhibition of salinized plants (Munns et al., 2000). As plant meristems are actively growing tissues where cell division and further expansion governs sink strength and affects plant carbohydrate status. These changes occur rapidly after imposing salt stress, as the slowing of leaf growth causes the accumulation of carbohydrates that otherwise would be used in growth. Although changes in ion uptake occur within minutes of a step change in salinity ion (e.g. Na +, Cl) accumulation to toxic levels in photosynthetically active mature leaves occurs much later. Evidence that soil microbes alter ion homeostas and improve plant nutrition in salinized crops. Furthermore, as plant growth under saline stress may be regulated via changes in phytohormone concentrations, which can rapidly respond to a step change in salinity. PGPR can have multiple impacts on phytohormone status, the possibility that these change scan attenuate the effects of salinity are considered. These mechanisms do not work in isolation but rather in an integrated manner to finally affect the major physiological processes limiting growth under salinity. Although salt stress commonly results in foliar oxidative damage this occurs much later than the initial effects on water, carbohydrate, nutrient, and phytohormone relations. Conclusion Plant growth promoting rhizobacteria, having multiple activities had direct or indirect role in plant growth promotion as well as exhibiting bio-remediating 175


potentials by detoxifying salinity/pollutants like, heavy metals and pesticides and controlling a range of phytopathogensas biopesticides, have shown spectacular results indifferent crop studies. The productive efficiency of a specific PGPR may be further enhanced with the optimization and acclimatization according to the prevailing soil conditions. In future, they are expected to subsidize the chemical fertilizers, pesticides and artificial growth regulators to some extent which have numerousside-effects to sustainable agriculture. Further research and understanding of mechanisms of PGPR mediated-phyto stimulation would pave the way to find out more competent rhizobacterial strains which may work under diverse agro-ecological conditions. References Ahemad, M., Khan, M.S., 2009b. Toxicity assessment of herbicides quizalafop-p-ethyl and clodinafop towards Rhizobium pea symbiosis. Bull. Environ. Contam. Toxicol. 82, 761– 766. Bashan, Y., Holguin, G., 1997. Azospirillum-plant relationships: Environmental and physiological advances (1990–1996). Can. J. Microbiol. 43, 103–121. Belimov, A.A., Hontzeas, N., Safronova, V.I., Demchinskaya, S.V.,Piluzza, G., Bullitta, S., Glick, B.R., 2005. Cadmium-tolerant plantgrowth promoting rhizobacteria associated with the roots of Indianmustard (Brassica juncea L. Czern.). Soil Biol. Biochem. 37, 241–250. Bhattacharyya, P.N., Jha, D.K., 2012. Plant growth-promoting rhizobacteria (PGPR): emergence in agriculture. World J. Microbiol. Biotechnol. 28, 1327–1350. Bishop, P.E., Jorerger, R.D., 1990. Genetics and molecular biology of an alternative nitrogen fixation system. Plant Mol. Biol. 41, 109–125. Camerini, S., Senatore, B., Lonardo, E., Imperlini, E., Bianco, C., Moschetti, G., Rotino, G.L., Campion, B., Defez, R., 2008. Introduction of a novel pathway for IAA biosynthesis to rhizobiaalters vetch root nodule development. Arch. Microbiol. 190, 67–77. Crowley, D.E., Kraemer, S.M., 2007. Function of siderophores in the plant rhizosphere. In: Pinton, R. et al. (Eds.), The Rhizosphere, Biochemistry and Organic Substances at the Soil-Plant Interface. CRC Press, pp. 73–109. Franco-Correa, M., Quintana, A., Duque, C., Suarez, C., Rodrı´guez, M.X., Barea, J.M., 2010. Evaluation of actinomycete strains for key traits related with plant growth promotion and mycorrhizahelping activities. Appl. Soil Ecol. 45, 209–217. Glick, B.R., 2012. Plant Growth-Promoting Bacteria: Mechanismsand Applications. Hindawi Publishing Corporation, Scientifica. Glick, B.R., Patten, C.L., Holguin, G., Penrose, G.M., 1999.Biochemical and Genetic Mechanisms Used by Plant GrowthPromoting Bacteria. Imperial College Press, London.Gray, E.J., Smith, D.L., 2005. Intracellular and extracellular PGPR: commonalities and distinctions in the plant–bacterium signaling processes. Soil Biol. Biochem. 37, 395–412. Indiragandhi, P., Anandham, R., Madhaiyan, M., Sa, T.M., 2008.Characterization of plant growth-promoting traits of bacteriaisolated from larval guts of diamond back moth Plutellaxylostella (Lepidoptera: Plutellidae). Curr. Microbiol. 56, 327–333. Khan, M.S., Zaidi, A., Wani, P.A., 2006. Role of phosphatesolubilizingmicroorganisms in sustainable agriculture – a review. Agron. Sustain. Dev. 27, 29–43. Khan, M.S., Zaidi, A., Wani, P.A., Oves, M., 2009. Role of plantgrowth promoting rhizobacteria in the remediation of metalcontaminated soils. Environ. Chem. Lett. 7, 1–19. Kim, J., Rees, D.C., 1994. Nitrogenase and biological nitrogenfixation. Biochemistry 33, 389–397. Kloepper, J.W., 1994. Plant growth-promoting rhizobacteria (othersystems). In: Okon, Y. (Ed.), Azospirillum/Plant Associations. CRCPress, Boca Raton, FL, USA, pp. 111–118. Kloepper, J.W., Schroth, M.N., 1978. Plant growth-promoting rhizobacteria on radishes. In: Proceedings of the 4th InternationalConference on Plant Pathogenic Bacteria, vol. 2. Station dePathologieVe´ge´ tale et de Phytobacte´ riologie, INRA, Angers,France, pp. 879–882.

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Kloepper, J.W., Schroth, M.N., 1981. Relationship of in-vitroantibiosis of plant growth promoting rhizobacteria to plant growthand the displacement of root microflora. Phytopathology 71, 1020–1024. Kloepper, J.W., Zablotowick, R.M., Tipping, E.M., Lifshitz, R., 1991. Plant growth promotion mediated by bacterial rhizospherecolonizers. In: Keister, D.L., Cregan, P.B. (Eds.), The Rhizosphereand Plant Growth. Kluwer Academic Publishers, Dordrecht,Netherlands, pp. 315–326. Lugtenberg, B., Kamilova, F., 2009. Plant-growth-promoting rhizobacteria. Annu. Rev. Microbiol. 63, 541–556. Madhaiyan, M., Poonguzhali, S., Sa, T., 2007. Metal toleratingmethylotrophic bacteria reduces nickel and cadmium toxicity and promotes plant growth of tomato (Lycopersicon esculentum L.).Chemosphere 69, 220–228. Mayak, S., Tirosh, T., Glick, B.R., 2004. Plant growth-promotingbacteria confer resistance in tomato plants to salt stress. PlantPhysiol. Biochem. 42, 565–572. McKenzie, R.H., Roberts, T.L., 1990. Soil and fertilizers phosphorusupdate. In: Proceedings of Alberta Soil Science WorkshopProceedings, Feb. 20–22, Edmonton, Alberta, pp. 84–104. Nadeem, S.M., Zahir, Z.A., Naveed, M., Arshad, M., 2007. Preliminary investigations on inducing salt tolerance in maizethrough inoculation with rhizobacteria containing ACC deaminase activity. Can. J. Microbiol. 53, 1141–1149. Nadeem, S.M., Zahir, Z.A., Naveed, M., Arshad, M., 2009. Rhizobacteria containing ACCdeaminase confer salt tolerance inmaize grown on salt-affected fields. Can. J. Microbiol. 55, 1302–1309. Neilands, J.B., 1995. Siderophores: structure and function of microbialiron transport compounds. J. Biol. Chem. 270, 26723–26726. Patten, C.L., Glick, B.R., 1996. Bacterial biosynthesis of indole-3-acetic acid. Can. J. Microbiol. 42, 207–220. Rajkumar, M., Ae, N., Prasad, M.N.V., Freitas, H., 2010. Potentialof siderophore-producing bacteria for improving heavy metal phytoextraction. Trends Biotechnol. 28, 142–149. Saleem, M., Arshad, M., Hussain, S., Bhatti, A.S., 2007. Perspectiveof plant growth promoting rhizobacteria (PGPR) containing ACCdeaminase in stress agriculture. J. Indian Microbiol. Biotechnol. 34,635–648. Santner, A., Calderon-Villalobos, L.I.A., Estelle, M., 2009. Plant hormones are versatile chemical regulators of plant growth. NatureChem. Biol. 5, 301–307. Schmidt, W., 1999. Mechanisms and regulation of reduction-basediron uptake in plants. New Phytol. 141, 1–26. Shaharoona, B., Naveed, M., Arshad, M., Zahir, Z.A., 2008. Fertilizer-dependent efficiency of Pseudomonads for improvinggrowth, yield, and nutrient use efficiency of wheat (Triticumaestivum L.). Appl. Microbiol. Biotechnol. 79, 147–155. Somers, E., Vanderleyden, J., Srinivasan, M., 2004. Rhizospherebacterial signalling: a love parade beneath our feet. Crit. Rev. Microbiol. 30, 205–240. Spaepen, S., Vanderleyden, J., Remans, R., 2007. Indole- 3-aceticacid in microbial and microorganism-plant signaling. FEMS Microbiol. Rev. 31, 425–448. Tripathi, M., Munot, H.P., Shouch, Y., Meyer, J.M., Goel, R., 2005. Isolation and functional characterization of siderophore- producing lead- and cadmium-resistant Pseudomonas putida KNP9. Curr. Microbiol. 5, 233–237. Vansuyt, G., Robin, A., Briat, J.F., Curie, C., Lemanceau, P., 2007. Iron acquisition from Fe-pyoverdine by Arabidopsis thaliana. Mol.Plant Microbe Interact. 20, 441–447. Vessey, J.K., 2003. Plant growth promoting rhizobacteria as biofertilizers. Plant Soil 255, 571–586. Zahir, Z.A., Munir, A., Asghar, H.N., Shaharoona, B., Arshad, M., 2008. Effectiveness of rhizobacteria containing ACC-deaminase for growth promotion of pea (Pisum sativum) under drought conditions. J. Microbiol. Biotechnol. 18, 958–963.

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Carbon Sequestration and Management in Salt Affected Soils Lal Bahadur1 and S. R. Singh2 National Botanical Research Institute, Rana Pratap Marg, Lucknow, 226 001 2ICAR-Indian Institute of Sugarcane Research, Raebareli Road, Lucknow, 226 002 1CSIR-

Introduction Despite having only about 2.4% of the total land area, India accounts for nearly 8.0 % of the biodiversity of the world. Though having great biodiversity, a very large part (14.75%) of total geographical area of the country is occupied by the degraded land. Out of the degraded lands, salt affected soils are estimated to 6.80 lakh ha in India and Uttar Pradesh is the largest state of the country having 2.55 lakh ha area (Table 1) under salinity and sodicity (NRSC, 2011). Most of the salt affected land has arisen from natural causes from the accumulation of salts over long periods of time in arid and semiarid zones (Rengasamy, 2002). Weathering of parental rocks releases soluble salts of various types, mainly chlorides of sodium, calcium, and magnesium, and to a lesser extent, sulphates and carbonates (Szabolcs, 1989). As per the soil characteristics, salt affected soils are classified in three groups- i. Saline, when the chloride and sulphate are present with Sodium, Calcium or Magnesium, ii. Sodic, when carbonate and bicarbonate are present with Sodium, Calcium or Magnesium, iii. Saline- Sodic, when chloride, sulphate, carbonate and bicarbonate are present with Sodium, Calcium or Magnesium. Table 1. Salt affected soils of India (2008-09) Sl. No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

States Uttar Pradesh Andhra Pradesh Gujarat Rajasthan Karnataka Tamilnadu Haryana Jammu and Kashmir Maharashtra Punjab Orissa Bihar Chhattisgarh Union Territory Delhi Total

Moderately Saline/ Alkali 205088 116563 112973 32384 34658 23959 6621 1547

Highly Saline/ Alkali 50130 49012 22657 20 2919 1977 5266

4106 2863 536 28 20 06 5,41,352

2636 2352 2076 165 1,39,210

Total Area (ha)

Percentage

255218 165575 112973 55041 34678 26878 8598 6813

37.51 24.33 16.60 8.09 5.09 3.95 1.26 1.00

6742 5215 2612 165 28 20 06 6,80,562

0.99 0.77 0.38 0.02 0.01 0.00 0.00 100.00

In saline soils, white powder like substances appears on the surface of the soil; so, the saline soil is also called as white alkali. Low status of organic carbon in sodic soil due to solubilization of organic carbon in alkaline medium and black spots may also appear on the surface of this type land, so, the alkaline soil is called 178


as black alkali soil. The nature and properties of salt affected soils vary considerably, which required specific approaches for their reclamation and management to maintain their sustainable productivity. Management is one of the important aspects of salt affected soil due to its poor fertility status and toxicity of salts reduces the availability of nutrients and affects soil physico-chemical and biological properties of the soil. The objective of this study is to find out the different management practices to improving soil carbon for their long term sustainability and productivity. Sodic soils suffer with varying levels of degradation in structural, chemical, nutritional, hydrological and biological properties. These soils are compact due to the high amount of clay and kankar pan in the sub-surface horizon. A cemented bed of calcium carbonate gravels is found in subsurface horizon called calcic horizon. Ca++ precipitated as CaCO3 in the presence of high amount of sodium (Na+) salt. The Presence of the hard CaCO3 layer at about one meter depth in the profile, acts as a physical barrier to vertical penetration of roots. The location of this layer in the profile and its thickness varies in different soils. Often compact subsurface horizons also restrict root penetration in alkali soils. Poor water permeability (hydraulic conductivity and infiltration rate) due to interlocked pore spaces results in water-logging during rainy season. Soil profiling of farm site have been dug out at the Aurawan Research Centre of CSIR-NBRI for identification, characterization and economic utilization. After profiling of the farm site, wide variations were recorded in farm site land. At some places, calcic horizon was found under endopedon with fine particles to very hard kankar pan in different depth of soil from 0.25 m to 1.30 m. Soil pH varied from 7.2 to 10.2. The major cause of sodicity is poor infiltration of water (Fig. 1).

a b Fig.1 Calcic horizon under endopedon between 70-100cm (a) between 80-130cm (b) in sodic soil In the salt stress condition, root respiration and development get inhibited because of high concentration of salts, which increases the osmotic potential in the root zone. In these degraded areas, soil organic carbon (SOC) levels are likely to be affected by declining vegetation, hence, decreasing biomass inputs and concomitant lower levels of organic matter accumulation. Moreover, potential SOC losses can also be affected from dispersed aggregates due to sodicity and solubilisation of soil organic matter (SOM) due to salinity (Wang, 2007). For cultivation in salt affected soils, it is required to reclaim and manage this type of sodic land by gypsum application and/or cultivation of salt tolerant varieties of

179


rice, wheat/barley, Sesbania green manuring, Mustard, Chickpea, sugarcane, forage crops, grasses, medicinal plants, fruit trees, fuel wood tree shop. etc. An increase in salinity and sodicity directly impacts upon plant vigour through changes in osmotic potential, ion toxicities and deficiencies. Indirect effects on vegetation can result from altered soil conditions such as increased dispersion and decreased permeability. Moreover, potential SOC losses can be higher from dispersed aggregates due to sodicity and solubilisation of SOM as a result of salinity. Therefore, changes in salinity and sodicity affect soil physico-chemical properties, which subsequently alter nutrient cycles and decomposition processes. The risk of erosion is increased, while soil physico-chemical properties are altered, impacting upon aggregation and nutrient cycling as well as biotic activity. Therefore, there is a linkage between land management practices through their effect on salinity and sodicity and their potential to alter soil C stocks and fluxes in the soil, particularly in degraded land and subsequent rehabilitation efforts (Wong et al., 2005). Salt affected soils have lost their significant amount of SOC pools and have the capacity to sequester C by converting to a restorative land use and adopting recommended management practices. Salt affected soils are very low in organic matter and biological activity. Tree growth provides a green cover and improves the soil environment for enhanced biological activity, better water relations and increased organic matter and fertility status. Tree roots increased the CO 2 levels in the soil which help in mobilizing soil CaCO3 and the releasing Ca exchange with Na on the soil exchange complex. Further litter produced also hasten the process of reclamation (Ghosh et al., 2014). In saline soils, loss of SOC is also enhanced as organic material can become more readily available or easily decomposable due to the presence of alkali salts, which have the potential to dissolve, disperse, or cause chemical hydrolysis of the organic material (Laura, 1976). The accumulation of SOC is a balance between inputs by plants and losses by decomposition, erosion, burning, and leaching, with accumulation occurring where inputs are greater than the losses. The importance of maintaining SOC levels, particularly in agricultural soils, is well established. In salt-affected soils, plant growth is directly affected by osmotic and specific ion effects, loss of plantavailable nutrients, and indirect effects related to adverse soil physical properties. Because SOC is dependent on biomass C inputs, processes such as salinization and sodification will influence the level of SOC. Carbon accounting in saline and sodic areas is complicated by topographic factors, high spatial and temporal heterogeneity, and opposing processes due to salinity and sodicity (Dalal et al., 2005). In general, SOC concentration increases with increase in clay content and rainfall, and decreases with increase in mean annual temperature. Some of these soils have been cultivated for centuries and often with low off-farm input, based on systems that involve removal of crop residue and dung for fuel and other purposes. The SOC concentration of most soils is low; most soils are less than 10 g kg -1, and are generally less than 5 g kg-1 (Lal, 2004). Because of the low clay contents, the SOC concentration is especially low in the alluvial soils of the Indo-Gangetic Plains, coarse-textured soils of southern India, and arid zone soils of northwestern India (Dhir et al., 1991). The total soil C pool also comprises the soil inorganic carbon (SIC), which is generally higher in calcareous soils of arid and semi-arid regions. Calcareous soils are widely distributed covering 54% of the geographical area of India, but especially occur in Rajsthan, Gujrat, Punjab, Haryana, Uttar Pradesh, Maharashtra, Karnataka, Tamil Nadu, Andhra Pradesh and parts of Madhya Pradesh and Bihar. Total SIC pool in soils of India is estimated at 196 Pg to 1-m depth (Pal et al., 2000). The SIC pool in world soils is estimated at 722 Pg to 1-m depth (Batjes, 180


1996). Therefore, the SIC pool in soils of India comprises about 27% of the world total. Pedogenic or secondary carbonates play a significant role in C sequestration through the formation of CaCO3 or MgCO3 and leaching of Ca(HCO3)2 especially in irrigated systems (Pal et al., 2000). The principal cause of the decline in the SOC pool in degraded soils is a reduction in biomass productivity and the low amount of crop residue and roots returned to the soil. A typical example of the low SOC pool is in salt-affected soils of Haryana, Andhra Pradesh and West Bengal. Even on the surface 0 to 10 cm layer, the SOC pool may be lower than 5 g kg-1 (Singh and Bandyopadhyay, 1996). Accelerated soil erosion depletes the SOC pool severely and rapidly. The SOC fraction is preferentially removed by surface runoff and wind because it is concentrated in the vicinity of the soil surface and has a low density (1.2 to 1.5 Mg/m3 compared with 2.5 to 2.7 Mg/m3 for the mineral fraction). Consequently, eroded sediments are enriched with SOC pool compared with the field soil with an enrichment ratio of 1.5 to 5.0 (Lal, 1999). The SOC loss by erosion and runoff can be high even on gentle slopes of 0.5 to 3.0% (Banerjee et al., 1991). Soil erosion is a four-step process. It involves detachment, breakdown, transport and deposition of soil particles. Soil detachment and breakdown are caused by soil slaking or disruption of aggregates by raindrop impact, shearing force of flowing water or blowing wind, and collision between particles. Breakdown of aggregates exposes SOC hitherto encapsulated and physically protected to microbial processes. Although the fate of SOC displaced along with eroded sediments is governed by a series of complex and interacting processes, a considerable part of it is mineralized leading to release of CO2 under aerobic conditions and CH4 under anaerobic environments. Lal (1995) assumed that 20% of the SOC displaced by erosion is mineralized. Technological options The overall strategy is to increase Soil carbon sequestration (SOC) density, distribution of SOC in the sub-soil, aggregation and formation of secondary carbonates. It can be managed through Increasing C input into the soil and decreasing losses by erosion, mineralization and leaching  The depth distribution of SOC can be achieved by planting deep rooted species with high bellow-ground biomass production.  Using bio-solids and improving earthworm activity can enhance aggregation. These strategies can be achieved through a wide range of land use and soil/vegetation management options. Restoration of salt-affected soils can increase in SOC pool. Garg (1998) observed a drastic increase in the SOC pool of a sodic soil planted with perennials. The SOC pool increased from about 10 Mg ha-1 to 30-45 Mg ha-1 over an 8-year period of establishing tree species. Bhojvaid and Timmer (1998) also reported a substantial increase in the SOC pool by restoration of salt-affected soils. A similar potential exists in restoring vast tracts of wastelands throughout India (Gupta and Rao, 1994). Potential of restoration of degraded soils of India, upon conversion to a restorative land use at modest rates of 40 to 150 kg ha-1 y-1, the potential of SOC sequestration is 2.6 to 3.9 Tg C y-1 for restoring soils prone to water erosion, 0.4 to 0.7 Tg C y-1 for wind erosion, 3.5 to 4.4 Tg C y-1 for the soil fertility decline, 0.1 to 0.2 Tg C y-1 for waterlogged soils, and 0.5 to 0.6 Tg C y-1 for salinized soils. The total potential of restoring degraded soils in India is 7 to 10 Tg C y -1. Similarly, a large potential of SOC sequestration exists for desertification control (Lal, 2001, 2002). 181


Carbon Sequestration Carbon sequestration means capturing carbon dioxide (CO 2) from the atmosphere or capturing anthropogenic (human) CO2 from large-scale stationary sources like power plants before it is released to the atmosphere. Once captured, the CO2 gas (or the carbon portion of the CO2) is put into long-term storage (Pacala and Socolow, 2004). The Earth's surface through management practices that increase the amount of the carbon portion of the CO2 that can be stored in the roots and vegetable matter above ground and in the soil. The soil layer that covers the landscape can be thought of as a thin carbon "sink." The amount of carbon that can be stored in the soil through terrestrial sequestration depends on vegetation type and other factors. Promising land and water management practices that lead to terrestrial sequestration of carbon include adopting conservation tillage, reducing soil erosion, and minimizing soil disturbance; using buffer strips along waterways; enrolling land in conservation programs; restoring and better managing wetlands; eliminating summer fallow; using perennial grasses and winter cover crops; and fostering an increase in forests (Paustian and Cole, 1998; Peterson et al., 1999) Soil can only take in and store a limited amount of carbon. After a 50- to 100-year time frame, the soils will have reached equilibrium and will not accept any more carbon (de Silva et al., 2005). Once this "steady state" has been reached, the carbon will remain sequestered in the soil as long as the land remains undisturbed or conservation land management practices are continued. The greatest potential would be in converting marginal agricultural lands and degraded lands to grasslands, wetlands, and forests under appropriate conditions (Paustian and Cole, 1998). A number of factors affect the rate at which organic carbon can accumulate in soils. These factors include land cover and land use, land management practices, the biological activity within the soil, soil properties, the application of waste to the land, and climate. Through an assessment and understanding of the primary variables governing soil carbon, the optimum factors that promote carbon accumulation can be determined (Anonymous, 2002). Enhancing soil quality is important to increasing use efficiency of inputs (e.g., fertilizers, irrigation), increasing biomass/agronomic yields, and improving the environment. Improving quality and quantity of SOC concentration are important to enhancing soil quality. In fact, there is a strong linkage between low SOC concentration in soils of India and the widespread problem of soil degradation. Therefore, reversing soil degradation trends necessitates increasing SOC concentration through adoption of no-till farming, use of crop residue mulch and compost on soil, and legume-based rotations. A major constraint in adopting conservation tillage and mulch farming in India is the non-availability of crop residue for returning to the soil. Most of the crop residue is removed from the fields for use as fodder and fuel. Dung is also used as fuel for cooking. Thus, adoption of mulch farming techniques is possible only if economic sources of fuel and alternative sources of fodder are identified. Emissions from fossil fuel combustion in India are increasing. The soil C sequestration potential of 39.3 to 49.3 Tg C y -1 (mean of 43.3 Tg C y-1) can be significant towards reducing the net emission from fossil fuel combustion. Further, there is an additional potential of C sequestration in biomass, especially by forest and other biota. This potential is considerable in terms of the negotiation under the provision of Clean Development Mechanisms under IPCC, and for trading C in the national and international markets. Biosequestration of C, both by soil and biota, is a truly win-win situation. While improving agronomic/biomass productivity, these options also improve water quality and mitigate climate change by decreasing the rate of enrichment of 182


atmospheric CO2. Realization of this vast potential, which is in interest of India, requires the adoption of recommended management practices, including the use of mulch farming and conservation tillage, integrated nutrient management and manuring, agroforestry systems, restoration of eroded and salinized soils, and conversion of agriculturally marginal lands into restorative land uses (Lal, 2004) in table-2 and ecologic and economic benefits of soil organic carbon are given in table3 (Lal, 2007). Table-2: Comparison between traditional and recommended management practices in relation to SOC sequestration S. No.

Recommended (RMPs)

Traditional methods and

Biomass removal

2

Conventional cultivation

3

Bare/idle fallow

Growing cover crops during the off-season

4

Continuous monoculture

Crop rotations with high diversity

5

Low input subsistence farming and Judicious use of off-farm input soil fertility mining

6

Intensive use of chemical fertilizers

Integrated nutrient management with compost, biosolids and nutrient cycling, precision farming

7

Intensive cropping

Integrating trees and livestock with crop production

8

Surface flood irrigation

Drip furrow or sub-irrigation

9

Indigenous use of pesticides

Integrated pest management

Cultivating marginal soils

Conservation reserve program, restoration of degraded soils through land use change

tillage

and

residue

Practices

1

10

burning

Management

Residue returned as surface mulch

clean Conservation tillage, no till and mulch farming

Source: Lal (2004a) There are numerous agricultural sources of GHG emissions (Duxbury, 1994) with hidden C costs of tillage, fertilizer, pesticide use and irrigation. In general, net C sequestration must take into account these costs. It is assumed, however, that these inputs are needed for enhancing agricultural production to meet food demands of increasing population. Therefore, soil C sequestration is a by-product of adopting RMPs on agricultural land and restoring degraded soils. Carbon (C) sequestration in agricultural soils is an important option. Soil C pool comprises two components: soil organic carbon (SOC) and soil inorganic carbon (SIC). The SIC pool includes elemental C and carbonate minerals (e.g., gypsum, 183


calcite, dolomite, arrogant, and siderite). There are two predominant components of SIC pool: primary or lithogenic carbonates, and secondary or pedogenic carbonates. Primary carbonates are derived through weathering of parent material. In contrast, secondary carbonates are formed through the dissolution of CO 2 in soil air to form carbonic acid and its reprecipitation with Ca+2 or Mg+2 added into the soil as amendments or from other sources. Table 3: Ecological and economic benefits of soil organic carbon On site benefits 1. Improvement in soil quality.

Off site benefits 1. Reduction in erosion

• Increase in available water capacity

• Decrease in sedimentation

• Increase in aggregation

• Reduction in non-point source pollution

• Increase in nutrient use efficiency

• Improvement in water quality

2. Improvements in soil tilth

• Benefits to agriculture

3. Decrease in the cost of seedbed preparation 4. Increase in crop yields

• Decrease in economic losses caused by flooding 2. Soil carbon sequestration

5. Sustainable use of soil and water

• Decline in net CO2 emission • Improvement in air quality

Source: Lal (2007) Soil organic carbon (SOC) sequestration The SOC pool includes highly active humus. Humus is a dark brown or black amorphous material characterized by a large surface area, high charge density, high affinity for water, and ability to form organo-mineral complexes through reaction with the clay fraction. Charcoal is a product of incomplete combustion of plants, and is recalcitrant with relatively long residence time. The generic term soil organic matter (SOM) refers to the sum of all organic substances in the soil comprising(i) A mixture of plant and animal residues at various stages of decomposition, (ii) Substances synthesized through microbial and chemical reactions, (iii) Biomass of living soil micro-organisms and other fauna along with their metabolic products. Soil C sequestration is the transfer of atmospheric CO2 into the soil(i) Humification of crop residue and other bio-solids added to the soil, and (ii) Formation of secondary carbonates or leaching of bicarbonates into the ground water The residence period of carbon sequestered ranges from weeks to millions of years depending on the nature of substances and their stability; secondary carbonates formed and depth of leaching. Leaching of bicarbonates and using biofuel to offset fossil fuel are not strictly soil C sequestration, but they have an important impact on the global C cycle (Lal, 2007). 184


Soils in their natural state contain a substantial amount of SOC pool. The magnitude and properties of the SOC pool depend on soil properties (e.g., clay content and type, soil water retention, nutrient reserves), profile characteristics (more in young soils with deep, effective rooting depth), landscape position (more in foot slopes than summit or shoulder slopes), terrain characteristics (more in north facing and concave slopes than in south facing and convex slopes), temperature (more in cold than warm climates), and rainfall (more in humid than dry regions). The SOC pool ranges from 40 to 400 Mg C ha-1 under undisturbed natural vegetation cover (Post et al., 1982). Dispersed and dissolved organic matter present in the soil solution of highly sodic soils may be deposited on the soil surface by evaporation causing a dark surface which is why these soils have also been termed as black sodic soils. There are several factors which enhance the SOC pool upon conversion to a restorative land use and adoption of recommended management practices (RMPs). In general, structurally-active soils have a higher SOC capacity than structurally inert soils (e.g., Kaolinite clay, low surface area, low aggregation, etc.). In general, a perennial land use, which causes less soil disturbance and adds a higher biomass amount enhances SOC pool more than seasonal crops (Lal 2007). Soil inorganic carbon (SIC) Sequestration The SIC pool is important in soils of arid and semi-arid climates (Schlesinger 1982, 1997), and mostly comprises of carbonates, including calcite, dolomite, aragonite and siderite. The formation of secondary or pedogenic carbonates is an important mechanism of soil C sequestration. Monger (2002) describes four mechanisms of formation of secondary carbonates: (i) Dissolution of existing carbonates in the upper layers, translocation onto the sub-soil, and reprecipitation with cations added from outside the ecosystem (Marion et al., 1985), (ii) Rise of Ca+2 from shallow water table by capillarity and subsequent precipitation in the surface layer through reaction with carbonic acid formed through dissolution of CO2 in soil air (Sobecki and Wilding, 1983), (iii) Carbonate dissolution and reprecipitation in situ with addition of cations from elsewhere (Rabenhorst and Wilding 1986), and (iv) Carbonate formation through activity of soil organisms (e.g., termites and micro-organisms) (Boquet et al. 1973; Monger et al. 1991; Zavarzin 2002). The depth of the formation of secondary carbonates increases with an increase in mean annual precipitation, being shallow in arid and deep in semi-arid and subhumid climates. The depth of leaching may depend on soil pH, amount of infiltrating water and the concentration of carbonates in the soil horizons. The deposition of secondary carbonates may occur near subtle textural break in the lower solum (Schaetzl et al., 1996). The boundary zone may have unique pedologic characteristics (Allen and Hole 1968). In some soils, the depth of the formation may be 1-m or even deeper, especially if the active organic matter is deposited in the sub-soil layers by plants characterized by a deep root system. The dissolution of CO2 into carbonic acid increases with increase in easily decomposable biomass in the sub-soil either from decaying roots (e.g., grasses) or addition of biosolids (e.g., crop residues, compost, etc.). In all four processes outlined above, the cations (Ca+2, Mg+2) must come from outside the system either through weathering of bedrock, fertilizer use, irrigation, water run on, dust deposition or applications of biosolids, etc. Increase in activity of soil micro-organisms and termites are also important. Indeed, visible accumulations of secondary carbonates are common, where carbonate films, threads, concretions and pendants occur below peds and 185


especially around the roots (Gillam, 1937; Sherman and Ikawa, 1958; Wilding et al., 1990; Schaetzl et al., 1996). Lundi et al. (2003) measured the rate of formation of secondary carbonates in the Boreal grassland and Boreal forest regions of Saskatchewan, Canada. The rate of carbonate-C accumulation was 10 to 15 Kg ha-1 yr-1. They also observed that prairie soils sequestered 1.4 times more C in the form of pedogenic carbonates than as organic matter. In northern China, Qi et al. (2001) also reported that the SIC pool was 1.8 time the SOC pool in soils prone to desertification. Leaching of carbonates into the ground water is another mechanism of SIC sequestration. The rate of leaching may be as high as 0.25 to 1.0 Mg C ha -1yr-1 (Wilding, 1999). This mechanism is especially important when waters unsaturated with Ca (HCO3)2 are used for irrigation. This mechanism is extremely relevant to 275 M ha of irrigated cropland in arid and semi-arid regions of the world. Adoption of RMPs which enhance crop yields and reclaim salinized soils (e.g., use of gypsum, application of compost and other biosolids) accentuate leaching of biocarbonates, especially if irrigation water is not saturated with carbonates. Management of Soil Carbon There are three principal options to achieve soil carbon that’s are(i) Converting degraded lands to perennial vegetation, (ii) Increasing net primary productivity (NPP) of agricultural ecosystems, and (iii) Converting plough tillage to no-till farming The strategy of soil C management is to increase the amount of crop residues and biosolids to the soil surface through: (i) Minimizing soil disturbance, (ii) Providing continuous ground cover, (iii) Strengthening nutrient recycling mechanisms, (iv) Creating a positive nutrient balance, (v) Enhancing biodiversity, and (vi) Reducing losses of water and nutrients out of the ecosystem. Residence Time or Permanence of Sequestered Carbon The SOC sequestration is a natural process and is subject to leakage if the recommended land use and soil management practices are discontinued. Longterm maintenance of restorative practices is essential to the permanence of SOC sequestered. The residence time of SOC can be enhanced through(i) Returning of the crop residues and other biosolids at a rate in excess of the rate of decomposition, (ii) Minimizing soil disturbance by ploughing or other activities, (iii) Incorporating SOC in sub-soil occurs through deep root system development and bioturbation, (iv) Meeting nutrient requirements (for N, P, S), and (v) Creating soil conditions (e.g., clay content, landscape position) conducive to maintaining the inherent C sink capacity. Sollins et al. (1996) presented a conceptual model of the processes by which plant leaf, litter, root etc. is transformed to soil organic C and CO 2. Stability of the organic carbon in soil is the result of three general sets of characteristics. Recalcitrance comprises molecular-level characteristics of organic substances, including elemental composition, presence of functional groups, and molecular conformation, that influence their degradation by microbes and enzymes. Interactions refers to the inter-molecular interactions between organics and either inorganic substances or other organic substances, that alter the rate of degradation 186


of those organics or synthesis of new organics. Accessibility refers to the location of organic substances as it influences their access by microbes and enzymes. Stability is the integrated effect of recalcitrance, interactions, and accessibility. By definition, it increases with recalcitrance and decreases with accessibility. Whether it increases with interactions is an important issue that we explore further here. Humification efficiency of biomass C (e.g., crop residues, leaf litter and other detritus material) depends on climate, soil properties, tillage methods and nutrient availability. The humification efficiency is more in cool and humid climates than warm and dry regions. Furthermore, clayey soils with high surface area have higher humification efficiency than coarse-textured soils. No-till farming positively impacts the humification efficiency. The humification efficiency is also strongly influenced by nutrient availability because C is only one of the building blocks of humus, the others being N, P, S, Zn, Cu, etc. Thus, humification of residue C can occur only if essential nutrients (e.g., N, P, S) are available. With the low mulch application, SOC stocks were similar (25.6 Mg C ha-1) with and without fertilizer application. However, when the mulch rate was high, additional SOC accretion occurred only in plots receiving additional fertilizer. Campbell et al. (2001) indicated that without adequate fertilization, the adoption of no-till does not necessarily increase SOC pool. Nitrogen fertilization rate and placement have a significant impact on SOC sequestration rate (Gregorich et al., 1995, 1996; Wanniarachchi et al., 1999). Illuviation and translocation of C into sub-soil horizons is another important mechanism. Deep translocation, away from the zone of anthropogenic and climatic disturbances, can occur due to bioturbation by earthworms (Lavelle and Pashanasi, 1989) and termites, and deep root system development (Lorenz and Lal, 2005). Role of inorganic (colloidal) substrate in organic carbon sequestration in soils With respect to soil carbon sequestration it is important to fix atmospheric carbon in those pools which have long turnover times. To model the cycling of C in the soil, soil organic matter could be divided into four pools based on carbon dynamics (Bhattacharyya, 2011)(i) Active or labile pool: This pool is readily oxidized compounds, the formation of which largely depends upon plant residue inputs and climate. This pool has a proportion of organic matter to the tune of 2-5% and not apparently influenced by soil (mineralogy) substrate. (ii) Moderately oxidized pool: Moderately oxidized pool is associated with soil micro-aggregates, the dynamics and pool size of which are affected by soil properties such as mineralogy. This pool has a portion of 18-40% of total organic matter. Since soil mineralogy has a major role in storing OM in this pool, a minimum value of 18% of total OM in soil could therefore be attributed to soil mineralogy. (iii) Slowly oxidized pool: Slowly oxidized pool associated with micro aggregates, where the main controlling factor is water stability of the aggregates and agronomic practices have only little effect. Since water stability of aggregates is determined the type of exchangeable cations (mostly Ca, Mg and Na) which are again controlled by soil mineralogy. The slowly oxidized pool is indirectly influenced by mineral make-up of soils. This pool has a proportion of OM to the tune of 20-35%. (iv) Passive or recalcitrant pool: Passive or recalcitrant pool consists of two different types of OM namely (i) physically sequestered OM and (ii) chemically sequestered OM. This pool is mainly controlled by soil mineralogy and there are probably no effects due to 187


agronomic practices. The relative proportion of total OM physically and chemically sequestered is 20-40% in both the cases. If the minimum values are considered we find that 20% physically and another 20% chemically sequestered OM will be controlled by soil mineralogy. The total proportion of OM which will be controlled by soil mineralogy is thus estimated at 78%. This shows that at least at least 78% of the total OM in soil is controlled by inorganic substrate (precisely phyllosilicate minerals and amorphous materials with higher surface area in the finer fractions). Future Research Strategies: • The effective carbon trade market should develop • Quantify different land uses for C sequestration potential • Identify site specific effective soil carbon sequestration plants and tree species and effective technology • Identify the locally crop management practices which may lead to carbon sequestration References Allen, R.J. and Hole, F.D. (1968) Clay accumulation in some Hapludalfs as related to calcareous till and incorporated loess on drumlins in Wisconsin, Soil Science Society of America 32, 403–408. Anonymous (2002) Centre for Ecology and Hydrology (Natural Environment Research Council), CEH Project C01920, Environment Agency/National Assembly for Wales Contract 11406, Critical Appraisal of State and Pressures and Controls on the Sustainable Use of Soils in Wales; Final Report to Welsh Assembly Government, September 2002, on Behalf of the Project Consortium: CEH Bangor, National Soil Resources Institute, Institute of Grassland and Environment Research, Geoenvironmental Research Centre (Cardiff University), Cynefin Consultants http://www.bangor.ceh.ac.uk/English/reports/SSS Finalreport.htm. Banerjee, S.K., Chinnamani, S. and Jha, M.N. (1991) Forest Soils of North and Northeast Himalayas and Constraints Limiting their Productivity, in Biswas, T. D. et al. (eds), Soil-Related Constraints in Crop Production, Indian Society of Soil Science, Bulletin No. 15, New Delhi, India, pp. 164–176. Batjes, N.H. (1996) Total Carbon and Nitrogen in Soils of the World, European Journal of Soil Science 47, 151–163. Bhattacharyya, T. (2011) Carbon capture and storage: Role of soil as substrate, Indian Society of Soil Science News Letter, 31 (1-2). Bhojvaid, P.P. and Timmer, V.R. (1998) Soil dynamics in an age sequence of Prosopis juliflora planted for sodic soil restoration in India, Forest Ecology and Management 106, 181–193. Boquet, E., Bononat, A. and Ramos-Cormenzana, A. (1973) A production of calcite crystals (Calcium carbonate) by soil bacteria is a general phenomena, Nature 246: 527–528. Campbell, C.A., Sellers, F., Lafond, G.F. and Zentner, R.P. (2001) Adopting zero tillage management: Impact on soil C and N under long-term crop rotations in a thin black Chernogen, Canadian Journal of Soil Science 81, 129–148. Dalal, R.C., Harms., B.P., Krull, E. and Wang, W.J. (2005) Total soil organic matter and its labile pools following Mulga (Acacia aneura) clearing for pasture development and cropping 1. Total and labile carbon. Australian Journal of Soil Research 43, 13–20. doi: 10.1071/SR04044. de Silva, L.L., Cihacek, L.J., Leistritz, F.L., Faller, T.C., Bangsund, D.A., Sorensen, J.A., Steadman, E.N., and Harju, J.A. (2005) The contribution of soils to carbon sequestration: Plains CO2 Reduction (PCOR) Partnership topical report for the U.S. Department of Energy and multiclients, Grand Forks, North Dakota, Energy & Environmental Research Center, June. Dhir, R.P., Chaudhary, M.R., Nath, J., and Somani, L L. (1991) Constraints of Sandy Soils of Arid and Adjoining Areas of Western and Northern India and their Management, in Biswas, T. D. et al. (eds.), Soil-Related Constraints in Crop Production, Indian Society of Soil Science, Bulletin No.-15, New Delhi, India, pp. 52–69.

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Eco-restoration of Sodic lands through Afforestation Bajrang Singh Ex. Sr. Principal Scientist National Botanical Research Institute, Lucknow Consultant, ENV DAS (I) Pvt. Ltd. Lucknow

Introduction The widespread degradation of alluvial soil in the Indo-Gangetic plains affected by varying degree of sodicity has received priority attention for cropping and afforestation during past few decades. Development of modest sodic land for crop production and highly sodic land in plantations/forest has been advocated in current agricultural and forest policies of India for sustainable resource management, food security, biodiversity conservation and maintaining ecosystem services to the ever-increasing human population of the country. Degraded sodic lands of UP are being developed under crop production through World Bank assistance using an age-old technology with gypsum treatment. Chemical treatment of soil with gypsum dose not optimize climate based yields particularly during initial 2-3 years and often resodification occurs where cultivation is dropped for few years. Afforestation is therefore a stable solution for adequate resource management as also to retrieve the soil fertility. Presently we have little understanding in the function of soil microflora, their population and diversity which play a vital role for optimum plant production as well as restoration process. Forest area is shrinking day by day and new forests are not being developed proportionally. It is estimated that about 53% of the total geographical area of the country is subjected to erosion and land degradation problems. Intensive afforestation efforts are required to rehabilitate such sites under productive forest ecosystems. It has been observed that population and diversity of microorganism decreased with increasing pH and EC levels. If sodic soils of high pH are managed for crop production or tree plantations, biotechnological approaches for enhancing the functional groups of microorganisms are essential tools to optimize yield in a relatively short time. Therefore, detail understanding is required to enhance the restoration process with special emphasis on microorganism population, diversity, microbial biomass and enzymatic activity which are largely responsible for catalyzing the nutrient use efficiency of the growing plants as well as ecosystem resilience. Sodic Soil Constraints Sodic soils are characterized with a high level of exchangeable sodium percent (ESP), high pH, high sodium adsorption ratio (SAR), and presence of a calcic horizon in subsoil, clay dominant texture, poor water permeability and low fertility which adversely affect crop / vegetation growth and yield (Abrol et al., 1988; Shukla et al., 2011). These soils are unfit for agricultural production due to deterioration in physical, chemical and biological properties (Heneghan et al., 2008). Sodic soils represent unique physical structures (clayey), processes (slaking, swelling and dispersion of clays or quasi-crystals or tactoids) and conditions (surface crusting or flocculation and hard-setting) as described by Sumner (1993). These physical constraints in sodic soils are mainly due to chemical imbalance, caused by excess level of sodium ions (Na+) in soil solution and on the cation exchange complex as well (Qadir et al., 2007). Sodium toxicity and high pH affect adversely nutrients availability, microbial communities and therefore natural 191


vegetation remains very poor consisting of sporadic patches of few tolerant grasses. These constraints of sodic soils provide an opportunity as well as challenges for soil use and sustainable management through the efficient restoration process. Protocol of plantation establishment Since sodic soils constitute a hard calcic pan of calcium carbonate gravels and iron granules in sub-soils (60-100 m depth) in varying thickness, soil working is rather difficult. A trial laid in 1965 at Makdoompur in Unnao (UP) by Forest Department has clearly shown that breaking of hard calcic pan positively helps the growth and establishment of plants. About 1 m3 size pit (1x1x1 m) has been found to be appropriate in sodic land plantations. After soil has weathered it should be filled back after mixing farmyard manure or leaf-mold. Chaturvedi (1985) observed that the mixing of sand into this soil increased growth of plants. Adding soil amendments like gypsum is also helpful in early stage. Removing the sodic soil and replacing it with good fertile soil in pits has been found to be a costly affair and later studies indicate, that this treatment is no longer much effective on account of the movement of salts from the surroundings into the refilled pits. Irrigation Management of irrigation is an essential input in afforestation because concentration of sodium salts generally increases during summer when warm wind blows which readily evaporates the water from the soil surface. Light and frequent irrigation is therefore applied to bring down the harmful level of salt concentrations below the root zone of planted saplings. Although the sprinkler system of irrigation is the best method for post planting maintenance, it is hardly in practice due to various reasons. Irrigation once in a week in summer and once in a month during winter season has been found optimum. Usually irrigation is not required in rainy season except during periods of a long drought. Afforestation Barren sodic land can be afforested well under the significant forest cover following the appropriate silvicultural technology, soil and water management practices. It has been observed that monsoon season which is the most favorable time for plantation work does not suit much for the plantation on sodic soils due to poor drainage and the best time of planting is immediately after the rainy season (September and October) when waterlogged conditions just disappear (Chaturvedi, 1985). A study conducted in Kurukshetra Forest Division, Haryana on sodic soil revealed that post monsoon season was the most favorable for tree planting (Sharma et al., 1995). However, if suitable drainage is developed and maintained, plantation may be done successfully in rainy season (Khanna, 1993). Previously many trials failed to rehabilitate sodic bare lands under tree cover due to lack of proven technology, proper financial support and dedication (Yadav, 1975, 1980). The trials that succeeded led to the identification and selection of tolerant species on the basis of their growth performance (Khan and Yadav, 1962; Pandey, 1966; Srivastava, 1970; Yadav and Singh, 1970; Yadav, 1980; Sandhu and Abrol, 1981; Khoshoo, 1987). These studies concluded that many tree species can be established on sodic soils with concentrated efforts but their growth is not encouraging due to various soil constraints. Such soils are generally poor in organic matter and nitrogen contents (Abrol and Bhumbla, 1971; Agrawal and Gupta, 1968) and therefore their enhancement is vital for better growth and productivity. A man-made forest was developed by planting suitable species on sodic land at Banthra Research Station of the National Botanical Research Institute, 192


Lucknow, India. This is the oldest successful endeavor of afforestation with multiple species, which was studied for its potential impact on restoration of the degraded ecosystems in a functional forest ecosystem. The forest ecosystem was developed during the last 50 yr which consists of all sorts of organisms including

Fig. 1: Execution of layout plan of barren sodic land and initial stage of plantation mammals, reptiles, birds, insects, rodents etc. The tolerant tree and shrub species made the soil hospitable for less tolerant species. Thus a portion of land that was once totally barren and desolate is now recognized as a functional forest ecosystem with a top story of trees, middle story of small trees and shrubs; and a ground layer of herbs and seedlings of the perennials indicating their natural regenerations.

Prosopis juliflora

Derris indica

Leucaena leucocephala

Terminalia arjuna

Fig. 2: Young plantations on sodic wasteland (4-yr-old) Srivastava (1987) described the occurrence of species in this forest in which some were introduced, while others invaded naturally and colonized by the induced succession. Verma et al. (1982) reported that a mixed canopy cover was more 193


effective in the reduction of pH than that of individual species. This is a good indication to diversify the monocultures with various indigenous species which also aid to counter the effects of epidemic and allelopathy. A generalized impact of soil reclamation in this forest was assessed by Singh (1996, 1998), Tripathi and Singh (2005). Other species viz. Acacia auriculiformis, Acacia leucopholea, Aegle marmelos, Albizia lebbeck, Albizia procera, Butea monosperma, Cassia fistula, Cassia siamea, Cordia mixa, Derris indica, Ficus bengalensis, Haplophragma adinophyllum, Mitrigyana parviflora, Parkinsonia aculeata, Pithecellobium dulce, Syzygium cumini, Tamarindus indica were found to be resistant in general and adaptable for plantation on sodic lands (Chaturvedi, 1987). Generally the species are ranked on the basis of survival, growth and yield performance. However, nutrient use efficiency and uptake of sodium are equally important for the eco-restoration and sustainable production on such degraded sites (Singh, 1998b; Singh et al., 2000). Growth performance of the species depends on the pH and salt concentration in the soil (Yadav and Pathak, 1967). Growth response of a few species on the highly sodic soils, revealed that Eucalyptus tereticornis and Acacia nilotica performed better than others but the seedlings of both species were started dying where soil amendment was not applied (Sandhu and Abrol, 1981). Prosopis juliflora and Tamarix articulata had a relatively high survival and establishment percent in other field trials also (Jain et al., 1985). Under field condition, salt tolerance limit of tree, shrub and grass was observed at Aligarh, Mainpuri and Agra in UP state. The species like Prosopis juliflora, Acacia leucopholea, Tamarix species, Sporobolus marginatus, Desmostachya bipinnata and Diplachne fusca were observed suitable for sodic soils (Singh, 1994). These species were found to grow well on indurated Kankar pan at high pH (

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