Current Nutrient Management Approaches Issues and

Indian J. Fert., Vol. 10 (5), pp.14-27 (14 pages)

Current Nutrient Management Approaches Issues and Strategies Kaushik Majumdar

International Plant Nutrition Institute - South Asia Program, Gurgaon

P. Dey

Indian Institute of Soil Science, Bhopal and

R.K. Tewatia

The Fertiliser Association of India, New Delhi

Fertiliser use has radically changed the crop output since the green revolution era in India. The momentum, however, slowed in the past decade. Imbalanced fertiliser application in crops is identified as one of the major reasons for decreasing crop response to fertiliser application and the consequent lower crop production growth rate in the country. Despite the proven economic, social and environmental benefits of balanced fertilisation, its adoption at farm level is low. The lack of appropriate tools and implementation mechanisms has been a major hindrance that restricted widescale adoption of balanced fertilisation by farmers. Generally imbalanced fertiliser use by farmers has raised concerns about the environmental sustainability of such practice. Several new approaches to facilitate largescale adoption of balanced fertilisation have been discussed that may help achieve the future food production targets, improve farmer profitability and reduce the environmental footprint of fertiliser application.

Introduction

I

ncreasing world population in the coming decades would require increased production of food, feed, fuel and raw materials from limited land area. The current world population of 7.2 billion is projected to increase by 1 billion over the next 12 years and reach 9.6 billion by 2050 (73). Recent estimates indicate that global crop demand will increase by 100 to 110% from 2005 to 2050 (69). Other estimates suggest that 60% more cereals need to be produced to meet world requirement in 2050 (17). Glenn et al (2008) earlier predicted that food demand would double within 30 years, which is equivalent to maintaining a proportional rate of increase of more than 2.4% per year. Sustainably meeting such demand is a huge challenge, especially when compared to historical cereal yield trends which have been linear for nearly half a century with slopes equal to only 1.2 to 1.3% of 2007 yields (17). Indian population is expected to be around 1.33 billion by 2020 (24), reaching 1.66 billion by 2050 (74). IFPRI (2012) summarized several studies that showed foodgrain demand in India reaching 293 million tonnes (Mt) by 2020 and increasing to 335 Mt by 2026. The

scope of horizontal expansion of cultivated area is limited, as the competition for scarce land resources between agriculture and urban interests are leading to a decline in per capita land availability. Unfortunately, it is often the best agricultural land that is used for urban expansion (42). All these factors contribute to the need for an increasing intensity of agricultural production. Inevitably most of the higher production must come from higher yields per unit area, which will require a correspondingly larger quantity of plant nutrients, from one source or another. Food Production and Fertiliser Use Global food production has increased significantly during the past 50 years through the use of better agronomic practices and improved crop cultivars. Although food production employs a number of inputs, fertilisers is the key input to support ecologically sustainable production. It is estimated that around half of the current global crop yield is attributable to commercial fertiliser use (63). The role of chemical fertilisers for increased agricultural production, particularly in the developing countries, is now well established. Some argue that fertiliser was as important as seed in the Green Indian Journal of Fertilisers, May 2014 14

Revolution (71), contributing as much as 50% of the yield growth in Asia (18, 28). Others have found that one-third of the cereal production worldwide is due to the use of fertiliser and related factors of production (6). Subba Rao and Srivastava (1998) suggested that the contribution of fertilisers to total grain production in India has increased from 1% in 1950 to 58% in 1995. Since 1960, world fertiliser use has risen by around 3.2% per year (27), whereas world grain production has risen by 2.4% per year during the same period. The International Fertiliser Industry Association (IFA) projections suggest that this rate of growth will continue at around 2.5% annually until 2015 (27). In 1960, the developed countries, including the USSR and the countries of Central Europe, accounted for 87% of the world fertiliser consumption. From 1980 to 1990 consumption tended to stabilize in these regions, apart from the USSR, where it increased until 1988. Between 1989 and 1994 fertiliser consumption in developed countries as a whole fell from some 84 Mt nutrient in 1988 to 52 Mt nutrient in 1994. The fall was greatest, by 80% in total, in the formerly communist countries of

Table 1 – Effect of potassium additions in rice, wheat and rice-wheat system (SREY) yields Parameter

Fatehgarh Sahib

Meerut

Rice grain yield (t/ha) No K 5.9 4.9 +K 6.5 5.7 Difference 0.6** 0.9*** Wheat grain yield (t/ha) No K 4.6 4.3 +K 4.8 5.0 Difference 0.2*** 0.7*** Rice equivalent yield for system (SREY) (t/ha) No K 11.7 10.0 +K 12.5 11.8 Difference 0.8*** 1.8*** Source: 62 Central Europe and the former Soviet Union (FSU) (32). In developing countries, until the 1960s fertilisers were applied mostly to plantation crops such as tea, coffee, oil-palm, tobacco and rubber, while application to field crops was either small or nonexistent. The introduction of high yielding, fertiliser-responsive dwarf varieties in the mid to late sixties gave a considerable boost to fertiliser consumption in annual field crops. Since 1960, fertiliser consumption in the developing countries has increased more or less continuously, and today accounts for about 60% of the world total, compared with 12% in 1960, a trend that is continuing. With their rapidly increasing populations, many developing countries are compelled to give agricultural production and the development of fertiliser use a high priority. Between 1993-94 and 1997-98 world total fertiliser nutrient consumption increased from 120 to 136 Mt, an average rate of increase of about 3% per annum. Consumption in China, South Asia and Latin America increased by 10, 5 and 2 Mt, respectively (32). Current data shows that China and India together accounts for 47%, 48% and 28% of the world consumption of N, P 2O5 and K 2O (16). Fertiliser Consumption in India India accounted for 16% of N,

Banda

Bhagalpur

2.7 3.7 1.0***

5.0 5.6 0.6***

3.5 4.6 1.2***

2.5 2.9 0.4***

3.7 4.1 0.4***

2.5 3.2 0.7***

5.7 7.2 1.5***

9.5 10.6 1.1***

6.4 8.4 2.0***

19.4% of P 2 O 5 and 9.3% of K 2 O consumption in the world in 2011 (16). The total nutrient consumption (N+P 2 O 5 +K 2 O) was about 70 thousand tonnes in the early ‘50s that increased to 5.5 Mt in 1980-81, reaching an all time high of 28.1 Mt in 2010-11 (16). The expansion of irrigation infrastructure, introduction of high yielding varieties, favourable government policies, improved last-mile delivery of fertiliser at affordable prices, and expansion of dealer/retailer network were the major drivers for such rapid increase in fertiliser consumption in India (58). However, the rate of increase in fertiliser consumption between 1950-51 to present has been quite variable. Fertiliser consumption increased by more than 19% in the pre-green revolution period (1950-51 to 1966-67), that went down considerably to 1.35% during the 9th five-year plan (1997-98 to 200102). Overall, growth rate of fertiliser consumption during 1991-92 to 2009-10 was 3.98% compared with over 8.75% during 1966-67 to 1991-92. Recent data shows that percent increase in N+P 2O 5 +K 2O consumption in the terminal year of XIth Five-year Plan (2007-08 to 2011-12) was 2.4%, mainly driven by a 12% increase in N consumption over the previous year while P 2O5 and K2O consumption declined by 3.7% and 18.3%, respectively (16). Between 1990-91 and 2012-13, per hectare Indian Journal of Fertilisers, May 2014 15

Barabanki

consumption of N+P 2 O 5 +K 2 O increased from about 68 kg/ha to 128 kg/ha, with highest consumption of 141 kg/ha recorded in 2010-11. Ratio of N:P 2O5:K 2O use in Indian soils also went through ups and down over the years with the narrowest ratio of 4.3:2.0:1.0 recorded in 200910. With recent upsurge of fertiliser prices, the ratio widened to 8.2:3.2:1.0, with the North zone of the country recording a very wide 30.8:10.1:1.0 ratio of N: P 2O5: K2O use (16). Classically, nitrogenous fertilisers accounted for nearly two-third of total nutrient consumption in the country. In 2012-13, N contributed to 66% of the total N+P 2 O 5 +K 2 O consumption in India, while P 2O 5 and K 2 O share was 26 and 8%, respectively. This is particularly alarming in cereal-based cropping systems where removal of K is equal to or more than N. Researchers have estimated that such inadequate use of K to crops has led to an annual deficit of nearly 10 Mt of N+P 2 O 5 +K 2 O in Indian soils, majority (69%) of which is potassium (49). There is an increasing concern that soil K reserves are being depleted to levels insufficient to sustain high yields (2, 78) in Indian soils. Several recent on-farm (Table 1) and on-station studies in rice, wheat and maize, occupying about 83 million hectares of cultivated land in India,

showed significant yield and economic improvement with adequate and balanced application of potassium (62, 70). Recent onfarm nutrient response studies across the Indo-Gangetic Plains showed that no application of potassium reduced average grain yield of rice, wheat and maize by 621, 723 and 699 kg/ha, respectively (43). Average yield loss due to P omission was 711 kg/ha in rice, 969 kg/ha in wheat and 854 kg/ ha in maize in the same study (34). Average yield loss was far higher due to N omission in rice (1738 kg/ ha), wheat (2566 kg/ha) or maize (2155 kg/ha) that highlights the reason for farmers’ inclination towards over-application of nitrogenous fertilisers in these cereals (53). Secondary and micronutrient deficiencies in Indian soils are emerging as significant limitations to productivity of several crops and cropping sequences (36, 59, 62). It is expected that crop response to secondary and micronutrient application will be more evident as attainable yield of crops increase due to better genetics and/or management. Timsina et al (2013) showed that maize yield in Comilla district of Bangladesh increased from 3.4 t/ha in K omission treatment (- K) to 9.0 t/ha in full NPK treatment. Such large increase in productivity, due to adequate and balanced application of major nutrients, is expected to stretch the native secondary and micronutrient supplying capacity of the soil. A soil sufficient in secondary/micronutrients to support 3 t/ha yield of a crop may turn out to be severely deficient for 9 t/ha of maize yields. Tandon (2013) compiled a large number of studies that showed significant yield responses to micronutrients in Indian soils. This is in line with the analyzed data of nearly 300,000 soil samples (60) that indicated 49, 12, 4 and 3 per cent deficiency of Zn, Fe, Mn and Cu in Indian soils, respectively. This definitely has serious consequences towards food and nutritional security of the country. Shukla and Behera (2012) estimated that application

of recommended rate of zinc contributes to 18.4 Mt of foodgrain in the country while boron application in 25% of the cultivated area could increase the national foodgrain production by nearly 10 Mt. The exact consumption of micronutrients in Indian agriculture is at the best sketchy. However, Table 2 provides some estimates about the disparity between removal and application of some micronutrients in Indian soils. Nutrient Approaches

Management

This above discussion suggests that there must be some inherent flaws in fertiliser application practices adopted by farmers that probably promotes imbalance in nutrient applications. The nutrient management approaches prevalent in the country and adopted by farmers can be categorized into the following four groups:

* Soil-test based recommendation

fertiliser

* Ad-hoc fertiliser recommendation * Farmers’ nutrient management decisions influenced by progressive farmer * Farmer applying fertiliser according to their own perception The approaches are discussed briefly in the following paragraphs: These soil-test based recommendation is developed through several steps that entail careful sampling of soil from the target location, extraction and analysis of available nutrients, using the data through appropriate correlation and calibration and finally using one of the common fertiliser recommendation philosophy (sufficiency, build and maintenance etc). In this approach, soils are grouped into different fertility classes such as low, medium and high with respect to status of the Indian Journal of Fertilisers, May 2014 16

nutrient in question, and the recommendation is developed for the medium fertility class. For soils testing low or high, the fertiliser recommendation for the medium fertility class is increased or decreased by 25% (40). A large number of studies conducted in different parts of the country, across a wide range of agroecological regions, proved that soil test based fertiliser application resulted in higher response ratios and benefit: cost ratios over the existing fertiliser application approaches (10, 11). The soil testbased approach relies mainly on the soil test data and usually do not include other growing environment information, such as yield and residue management in previous crop etc., to develop the fertiliser recommendation of the target crop. Several authors recently questioned the chemical methods adopted for analyzing available nutrients in the soil (45), the lack of correlation between soil-test based data for available nutrients and crop yield (13) or the approaches for developing integrated nutrient recommendations from soil test data (67). The ad-hoc recommendations, developed by different state governments, are based on crop responses over large areas and provide recommendations for medium fertility soils. These recommendations are periodically revised, although the periodicity may be as long as 10-15 years in certain cases. The recommendations are prescribed for large areas and do not take into account the spatial and temporal variability in soil nutrient supplying capacity. This often results in over- or underfertilisation leading to yield and economic losses and may also reduce nutrient use efficiency. Besides, the recommendations are generally for medium yield targets and often fall short for higher yield targets achievable through use of better seeds and good management. The ad-hoc recommendation does not have the flexibility to factor in farmer resource

Table 2 – Micronutrient removal and application in Indian soils Micronutrient

Iron

Total Nutrient Product-wise removal consumption (tonnes/year) (tonnes in 2012-13) 123152

Manganese

23405

Zinc

15184

Boron

13519

Copper Molybdenum

3753 676

Source: (15,59)

endowment and do not provide critical guidance to small holder farmers who do not have the resources to adopt the single recommendation provided for a large area. Alternately, farmers apply much higher rates of fertilisers than the ad-hoc recommendation, particularly in cash crops or when they have resources to target higher yields than what could be achieved using the ad-hoc recommendations. Although a lot of effort has gone in developing and popularizing the ad-hoc recommendations, the acceptability and adoption are far lower than expected. Progressive farmers, with access to information on modern agrotechnologies, are identified as one of the major avenues of information dissemination to the grass-root level. They receive information on improved crop management, particularly nutrient management, from diverse sources like agricultural universities, research institutes as well as the private sector, and pass it on to the neighbouring farmers. These progressive farmers effectively communicate the information on improved practices like balanced fertilisation or deficiency of a particular nutrient to other farmers in a region, and the acceptability and adoption is high as the trust level of peers are high. The fertiliser management

Actual nutrient consumption (tonnes in 2012-13) 4328

22781 (Ferrous sulphate) 5248 (Manganese sulphate) 160324 (Zinc sulphate) 17626 (Borax/Boric acid) 1686 (Copper sulphate) 107 (Ammonium molybdate)

1600 33668 1851 404 56

adopted by the farmers is far more influenced by the outcome of onfarm demonstrations in progressive farmers’ fields or through verbal communication between them, than other extension mechanisms. This usually results in substantial improvement in farmers’ fertilisation practices, in terms of balance and adequacy of fertiliser use, and results in increased productivity and farm profitability. Farmers applying fertiliser in their fields based on their own perception is probably the most common among the approaches mentioned above. Resource availability largely drives farmer fertiliser practices. Fertiliser price, crop prices, access to input and output market and risk perception (abiotic and biotic) determine fertiliser application, more than the science of crop requirement or balanced fertilisation. This often leads to imbalanced fertilisation, with over-enthusiastic application of the cheapest nutrient (N) and neglect of costlier inputs such as P, K and secondary/micronutrients. The first and foremost concern farmers have regarding fertiliser use is the profitability as determined by yield response and input and output prices. Fertiliser demand increases with farmers’ perception of increased net returns buoyed by high yield response and Indian Journal of Fertilisers, May 2014 17

favorable price relationships between input and output. Kelly (2006) suggested that farmers’ perception of response and profitability is generally much lower than what is perceived by a scientist in a particular situation. This is understandable as smallholder farmers do not perceive cultivation as a business venture with clear check on inflow and out-flow of resources. So sudden increase in fertiliser price or lower farm-gate price of commodities can quickly change fertiliser application practices, which may not have any connection with rational plant nutrient management. Unfortunately, this is probably the case for more than 70% farmers in the country. At present, probably 70-80% of farmers, involved mainly in field crop production, apply fertiliser based on their own perception or as advised by their progressive peers. This has promoted over- or under-use of fertiliser, large-scale imbalance in nutrient application, and improper timing of fertiliser application. Scientists and policy makers have pointed out the declining nutrient use efficiency/ fertiliser response, farm profitability as well as sharp increase in areas with multiple nutrient deficiencies as clear indicators of inappropriate fertilisation approaches adopted by farmers. This may adversely affect future food and nutritional security of the country, while creating a large environmental footprint of imbalanced fertiliser use. Environmental Concerns Associated with Fertiliser Use It would be unscientific to assume that the application of fertilisers could be considered without detrimental effect under all bioclimatic and edaphic conditions, and irrespective of the knowledge and experience of the user. Application of fertilisers,

* through an inappropriate source without matching the soil physico-

chemical properties;

* in wrong amounts without taking into account plant requirements; * applied at the wrong time without matching crop physiological demands; * or through a wrong method; may produce detrimental effects. This may give rise to environmental concerns in countries like India, where farmer awareness in general is limited. However, most of the detrimental effects of the fertiliser use could be traced back to flawed management decisions rather than over-use of fertilisers. Effect on Soil Mineral fertilisers were suggested to have an adverse effect on soil structure. However, evidence from long-term experiments indicates that aggregating action from enhanced root proliferation and greater amount of decaying residues from well fertilised crops makes soils more friable, easier to cultivate and more receptive to water. Buol and Stokes (1997) suggested that organic carbon contents that become lower under inadequate fertilisation appear to recover when adequate fertiliser is applied. Adequate fertilisation also contributed to greater biomass production tending to protect soil from erosion and providing greater quantities of residue critical to soil aggregation and they concluded that long-term, high-input agriculture has a strong positive effect in improving agronomic properties of soils. Field plots at the Rothamsted Experimental Station in the United Kingdom, which have received chemical fertilisers since 1843, are more productive today than at any time in the recorded past. At the Askov experimental station in Denmark, after 90 years, the plots receiving NPK fertilisers had an 11% higher organic C content than the control plots. The increase in organic matter content induced by NPK applications resulted in a decrease in soil bulk

density and a concomitant increase in total porosity (26). The authors conclude that the long-term positive effect of continual application of fertiliser materials on soil organic matter content and soil physical conditions is an important, although often neglected, factor that needs to be considered when contemplating sustainability. A recent metaanalysis based on 107 datasets from 64 long-term trials from around the world revealed that mineral fertiliser application led to 15.1% increase in the microbial biomass above levels in unfertilized control treatments (21). Mineral fertilisation also increased soil organic carbon content, which was found to be a major factor influencing the microbial biomass in the soil. Continuous use of nitrogen fertiliser acidifies soils, although some soils are naturally able to cope. The use of organic residues at normal levels of application may not avoid acidification but may slow the process. The acidifying effects of nitrogen fertiliser can be corrected if lime is economically available and is applied. Apart from neutralizing soil acidity, liming improves the availability of other nutrients such as phosphate, and lowers the toxicity of aluminium and manganese. However, increases in crop yields can sometimes be achieved with minimal applications of lime due to alleviation of aluminium toxicity and/or calcium deficiency and care must be taken to avoid over-liming (26). Inappropriate application of certain fertiliser nutrients may induce nutrient imbalance. For example, the interaction between P and Zn are often viewed as an antagonistic one. However, many field experiments have indicated that the P-Zn interaction is synergistic within the normal rates of their application (68). The synergistic effect may shift towards antagonism when the optimum balance between the two tilts in favour of one of them. Similarly, leaching of potassium in Indian Journal of Fertilisers, May 2014 18

acid, sandy soils may be reduced by liming the soil to pH 6.2-6.5; however, application of high rates of lime to a soil low in potassium may induce potassium deficiency in crops growing in these soils (64). Examples of such antagonistic nutrient interactions are frequent in literature, which often results from imbalanced nutrient application. India has vast potential of organic waste resources, recycling of which is vital for supplementing plant nutrients and maintenance of soil fertility (50). However, use of untreated organic wastes has certain drawbacks. Jeevan Rao and Shantaram (1995) evaluated the status of heavy metals and micronutrients in crop plants grown on farmers’ fields where fresh untreated wastes is being used regularly for the past ten years or more. They suggested careful monitoring when root crops are cultivated on such soils and concluded that Fe, Mn, Cr, Cd and Co did not pose any pollution problem in the food chain whereas elevated levels of Zn, Cu, Pb and Ni were observed in some plant species studied. The addition of sewage sludge to soil provides a useful source for supply of plant nutrients, especially N and P and also organic matter, which improves soil physical properties. However, sewage sludge is enriched by heavy metal contents, such as Zn, Mn, Cd, Pb and Cr, which can be toxic to animals and humans when applied above certain limits (47). Effects on Water Whilst the use of nitrogen containing fertilisers and manure is necessary, any imbalanced use of fertilisers and manure constitutes an environmental risk. In general, in developed countries, mineral nitrogen fertiliser is a major source of water pollution in areas of vegetable production or irrigated sandy soil, or where the optimum rates are exceeded. There is generally little danger of the nitrate pollution of ground water due to the application of fertiliser

on rain-fed crops in India, both because the application rates tend to be well below the optimum and leaching losses are minimum (3). However, rice grown in wet season receives around 150 cm of irrigation water besides 33 cm of average rainfall, may require careful management of nitrogen to restrict losses of nitrate via leaching. Rice grown in the coarse textured highly permeable soils experiences alternating aerobicanaerobic cycles that facilitates production of nitrates, increasing the potential for leaching losses of N. Problem of groundwater pollution by nitrates in fine textured lowland rice soils are limited because nitrate is not normally formed under flooded conditions. Bijay-Singh and Sekhon (1976) were able to show that balanced application of N, P, and K could significantly reduce the amount of unutilized nitrateN in the root zone. Bijay-Singh et al (1995) suggested that enhancing fertiliser N use efficiency in ricebased cropping systems by ensuring balanced application of nutrients, coordinating N and irrigation management, and matching N management with crop requirement can substantially control the leaching of nitrate-N beyond root zone of crops. Recently, Singh et al (2013) suggested that the problem is not solely caused by N fertiliser management or by any other single factor, but is a combination of soil management practices and inherent physical, chemical, and biological characteristics of the soil as well as the physiological and environmental factors. The authors suggested that a combination of several different management practices would be required to address the issue of nitrate accumulation in crop plants and leaching to groundwater. The transfer of soil P (derived from fertilisers and organic manures) is a major cause of P-induced eutrophication in surface waters. The environmental significance of soil P lies in its dominant role in the eutrophication of aquatic

ecosystems, where it is commonly regarded as the limiting nutrient governing primary production (19). While the low availability of P in many parts of the world is one of the leading causes for poor crop yields, excess application of manure and fertilisers in high runoff and erosion prone ecosystems has become a significant source of water pollution (48). Phosphorus can exist in either inorganic or organic forms in the soil and can be mobilized both in soluble and insoluble forms (25). Soil P status is particularly important in governing the amount of soluble P that is available for transfer to water. Particulate and colloid P transport is most commonly associated with soil erosion that arises from raindrop impact and overland flow. All forms of P within the soil system are subjected to a variety of pathways of transport at the soil profile, hillslope, or catchment scale. Additionally, when fertiliser or manure application is coincident with fast or energetic water flows, this will contribute to particularly high losses (20). Loss of soil P to water bodies causes undesirable changes in the ecology of aquatic ecosystems, resulting in a decline in the provision of eco-services, often with serious economic consequences and constitutes a major impetus for improving P use efficiency in crop production systems. Apart from crop removal, the two primary pathways of loss of phosphorus from the soil, erosion (wind and water) and runoff, could be effectively managed if balanced fertilisation is practiced and higher phosphorus use efficiency is maintained. Effect on Air Nitrogen can be lost from agricultural systems as ammonia, nitrous oxide (N 2 O) or nitrogen oxides (NOx). N 2O is emitted into the atmosphere from both natural (like water bodies and soils) as well as from anthropogenic activities like agriculture, transport, industries and waste-management practices. Sharma et al. (2008) Indian Journal of Fertilisers, May 2014 19

summarized the results of N 2 O emission from agricultural soils based on actual field measurements. These experiments reveal average N 2O-N emission of 0.0025 and 0.0055 kg kg–1 N applied from rice and wheat fields, respectively. Results indicate that N 2O emission is more in aerated crops such as wheat than in rice, which is grown in flooded anaerobic soil condition. Nitrogen oxides (NOx) emission from soils is primarily a result of NO production by the microbial oxidation of ammonium, the process known as nitrification (57). NO production in the soils also occurs through microbial reduction of nitrate (denitrification). Estimates (76) suggest that about 0.5% of fertiliser-N applied to agricultural fields was emitted to the atmosphere as NO. Application of fertilisers in the agriculture fields and the livestock population are mainly responsible for NH 3 emission. Although most emissions of ammonia are from manure or natural sources, experiments demonstrate that nitrogen losses to the atmosphere in the form of ammonia following the application of urea can amount to 20% or more, under temperate conditions. Losses occur when the urea is not incorporated into the soil immediately after spreading and they are particularly high on calcareous soils. Losses are even higher, up to 40% or more, under tropical conditions, on flooded rice and on perennial crops to which the urea is applied on the surface, such as bananas, sugar cane, oil palm and rubber. Some studies have shown leaching loss of N from soils in the Indo-Gangetic-Plains (IGP) as 10–15 kg N ha –1 , while ammonia volatilization loss is 20– 30 kg N ha–1 with application of 120 kg N ha–1 in rice and wheat ( 1, 38). In general, fertiliser management strategies that increase the efficiency of N uptake by crops are likely to reduce emission of greenhouse gases to the atmosphere. A recent on-farm

study (51) on wheat, comparing different nutrient management strategies in Haryana, showed that farmers’ practice of nutrient management emitted signicantly higher CO2 per unit of wheat yield than site specific fertiliser management. In the same study, estimated N 2O emission and the total estimated GHG emission per hectare as well as per tonne of wheat was the highest under farmers’ fertilisation practice while it was lowest under site specific management of fertiliser nutrients. Improved Fertiliser Management If any plant nutrient, whether a major, secondary or a micronutrient, is deficient in the soil then crop growth is likely to be affected. So nutrients should be applied in the right rate and proportion keeping in mind the yield target of the crop grown and the nutrient supplying capacity of the soil. Traditionally balanced fertilisation in India means use of N, P2O5 and K2O in a certain ratio, ideally 4:2:1, on a gross basis both in respect of areas and crops. Whatever may be the origin of 4:2:1 ratio, farmers in India do not follow it under most circumstances. The application of nitrogen fertilisers tends to be preferred by farmers, because of their relatively low cost per unit of nutrient, their widespread availability, and the quick and evident response of the plant. P and K use are low as compared to N, and secondary and micronutrients are generally omitted from fertilisation schedule. This is one of the main reasons for traditionally low nutrient use efficiency of crops in India. In a 1995 FAO document “Rice and the environment: production impact, economic costs and policy implications” it is stated that incorrect fertiliser use in much of Asia, unbalanced in favour of nitrogen, results in lodging, greater weed competition and pest attacks, with a financial loss varying from 4 to 30% of the rice price (32). Balanced fertilisation on the other hand provides the required nutrients to the plants in a balanced manner, keeping into

account the native nutrient availability in soils and the nutrient requirement of the crop. The concept of balanced fertilisation, when applied in a location specific manner incorporating site specific details of the location, led to the development of the site-specific nutrient management (SSNM) approach for Asian rice-producing countries that emphasizes supplying rice with nutrients as needed. It strives to enable farmers to adjust fertiliser use in their fields to meet the deficit between a highyield crop and the nutrient supply from naturally occurring indigenous sources in the soil. It recognizes the inherent spatial variability associated with fields under crop production and ensures that all the required nutrients are applied at proper rates and in proper ratios commensurate with the crop’s nutrient needs. The universality of the principles of the SSNM approach has led to its application to different crops and agro-ecologies. The 4R Nutrient Stewardship Principles (31) of applying the right source of plant nutrients at the right rate, at the right time, and in the right place is at the core of the SSNM approach. The source, rate, time and place essentially defines fertiliser application in any context, be it at the broad acreage farms where sophisticated machinery is used for precision application of nutrients or in smallholder systems where fertiliser is manually mixed and applied by farmers in their small fields. The 4R Nutrient Stewardship essentially provides the scientific principles that are at the core of all fertiliser management approaches but also connects the outcome of nutrient managements to social, economic and environmental sustainability of production systems. Thus, their definition of perfor-mance will include the productivity and profitability of the system (the economic dimension), its impacts on soil, water, air, and biodiversity (the environmental dimension), and its impacts on quality of life Indian Journal of Fertilisers, May 2014 20

and employment opportunities (the social dimension). Implementation Mechanism Balanced fertilisation is a robust scientific concept and when applied in a site-specific manner improves crop yields and farm profits in all soil-crop systems. This has been proven in thousands of scientific studies without any reasonable doubts, and numerous scientific and technical articles have been written on this issue. However, the acceptance and adoption of balanced fertilisation at famers level is far from the expectation. Farmers generally adopt an agricultural technology within a reasonable period of time if it shows significant yield advantage and farm profitability. In case of Bt cotton, the replacement of other varieties with Bt varieties was very fast to say the least as farmers perceived economic advantage of the technology quite quickly. On the other hand, balanced fertilisation concept is in discussion in the policy-making, scientific and private industry circle since long back, still the adoption level is poor. Part of the reason probably lies in our inability to present the balanced fertilisation concept as a flexible technology that can factor in other volatile determinants of farmer fertiliser application decisions, such as fertiliser and crop prices, farmer resource endowment etc. That a farmer can still apply the concept, tailoring it to his/her resource availability or at times of fluctuating fertiliser and crop prices, and can make profit at difficult times has rarely been espoused. An other major issue that restricted the adoption of balanced fertilisation is the lack of easily available and usable tools that can allow farmers and their advisors (extension system) to implement balanced fertilisation quickly in their fields. The following section describes some of the available approaches that might help large-scale implementation of balanced fertilisation in farmers’ fields.

Soil Test-based Approach of Fertiliser Management GIS-based Fertility Maps Soil test-based fertility management is an effective tool for increasing productivity of agricultural soils that have high degree of spatial variability resulting from the combined effects of physical, chemical or biological processes (23). However, major constraints impede wide scale adoption of soil testing in most developing countries. In India, these include the prevalence of small holding systems of farming as well as lack of infrastructural facilities for extensive soil testing (55). Under this context, Geographic Information System (GIS)-based soil fertility mapping has appeared as a promising alternative. Use of such maps as a decision support tool for nutrient management not only be helps in adopting a rational approach compared to farmer ’s practices or blanket use of ad-hoc recommendation but also reduces the necessity for elaborate plot-byplot soil testing activities. Recent works in this area showed promising results where GISbased fertility maps were used as fertiliser decision support tools (30, 54, 55). These studies showed that the GIS-based fertility maps, based on soil sampling at 100 m 2 grid (1 sample per hectare), helped estimate fertiliser requirement in farmers’ fields that resulted in comparable crop yield and profitability with soil-test based fertiliser recommendation for individual field. The GIS-based approach, applied at a village scale, sampled 76 locations within a village of 543 land holdings but provided adequate fertiliser recommendation support to random field plots within the village to improve yield and profitability. Several national agencies and ICAR Institutes, most notably the National Bureau of Soil Survey & Land Use Planning (NBSS&LUP), Indian Institute of Soil Science (IISS), and Project Directorate of Farming Systems Research (PDFSR), have undertaken GIS-based fertility mapping

initiatives at the State or Regional scales that are expected to help implement the soil-test based fertiliser recommendation to larger domains without stressing the soil-testing services. As a matter of fact, this is probably the only approach that can produce visible impact of soil-test based fertiliser recommendation at the current soil-testing infrastructure available in the country. The Soil Test Crop Response Equations-based fertiliser Recommendation Nutrient supplying capacity of soils, crop responses to added nutrients, and requirement of amendment can be assessed by soil testing. Soil test calibration that is intended to establish a relationship between the levels of soil nutrients determined in the laboratory and crop response to fertilisers in the field helps in balanced fertilisation through right kind and rate of fertilisers. Ramamoorthy et. al. (1967) established the theoretical basis and experimental proof that Liebig’s law of the minimum operates equally well for N, P and K. This forms the basis for fertiliser application for targeted yields, first advocated by Truog (1960). Ramamoorthy et al (1967) refined the procedure of fertiliser prescription as given by Truog (1960) and later extended it to different crops and soils. The Indian Council of Agricultural Research (ICAR) supported All India Coordinated Research Project

(AICRP) on Soil Test Crop Response (STCR) was initiated in 1967-68 with eight centers, which has now increased to seventeen centers at different agro-eco regions across the country. The STCR project has used the multiple regression approach to develop relationship between crop yield on one hand, and soil test estimates and fertiliser inputs, on the other. Based on a large number of complex field experiments on diverse soils at different centers of STCR employing major crops, a technology for fertiliser recommendations based on soil tests for targeted yields of crops has been evolved. During last fifteen years, the different centers of AICRP on STCR developed prediction equation by using the targeted yield equation for different cropping systems like rice-rice, rice-maize, rice-wheat, maize-tomato, maize-wheat, potato-yellow sarson, paddy-ragi, maize-Bt. Cotton, wheatgroundnut, okra-wheat, paddychick pea, soybean-wheat, ricepumpkin, bajra-wheat, cottonmaize and soybean-onion. The predicted values can be utilized for recommending the fertiliser doses for succeeding crop thus eliminating the need of soil test after each crop. This provides the way for giving the fertiliser recommendations for whole cropping system based on initial soil test values. Financial returns vary from across soils, crops and locations. However, frontline demonstrations confirmed an increase in benefit: cost ratios

Table 3 – Benefits of STCR technology as demonstrated in Frontline Demonstrations Crop

Yield (kg ha -1) Farmers STCR- IPNS practice recommended practice

Benefit : cost ratio Farmers STCR- IPNS practice recommended practice

Rice

5800

6850

6.8

17.8

Maize Sunflower

4015 1020

4600 1490

8.2 4.2

12.5 10.5

Cotton Wheat

2753 3600

2837 5000

22.7 4.5

37.1 4.7

Bajra

2280

3000

2.7

3.1

Indian Journal of Fertilisers, May 2014 21

Figure 1 – Internet enabled soil test based fertiliser application software

through STCR technology over control / farmer ’s practices / application of general recommended dose (Table 3). Among the various methods of fertiliser recommendation, the one based on yield targeting is unique in the sense that this method not only indicates soil test based fertiliser dose but also the level of yield the farmer can hope to achieve if good agronomic practices are followed in raising the crop. The essential basic data required for formulating fertiliser recommendation for targeted yield are (i) nutrient requirement in kg q -1 of grain or other economic produce (ii) the per cent contribution from the soil available nutrients (iii) the per cent contribution from the applied fertiliser nutrients. The fertiliser recommendations based on yield targets concept have been tested in the follow up trials in about 1800 frontline demonstrations in 15 states in the farmers’ fields to verify the technology. Ready reckoners making use of targeted yield equations were developed for a large number of crops on different soils in 16 states. These recommendations are now available with the

respective State Departments of Agriculture for implementation in the farmers’ fields. Linking Soil Fertility Maps with STCR Parameters for Spatial Recommendation Despite many efforts over the years to disseminate and transfer agriculture knowledge to the stakeholders, large extent of expertise and knowledge are still out of reach to most of them. Agriculture knowledge may be contained in the corporate database, or it may reside undocumented inside the brain of the researchers or even stored in locations unknown to the majority of the people in an organization. Large sections of the farming community do not have access to the huge knowledge base acquired by agricultural universities, agricultural extension centers and the Ag Industry. In this respect the main challenge is to apply knowledge in the decision making process involved in agriculture development. (9). All India Coordinated Research Project on Soil Test Crop Response (AICRP-STCR) based at Indian Institute of Soil Science has developed an Expert System (8) in collaboration with the National

Information Center, Pune, that calculates the amount of nutrients required for specific yield targets of crops based on farmers’ soil fertility (Figure 1). It is accessible on Internet (http:// www.stcr.gov.in). This software programme reads data, performs calculations and generates graphical and tabular outputs as well as test reports. This system has the ability to input actual soil test values of the farmers’ fields to obtain optimum dose of potassium apart from other nutrients. The application is a user-friendly tool. It will aid the farmer in arriving at an appropriate dose of fertiliser nutrient for specific crop yield for given soil test values. Plant-based Approach of SiteSpecific Nutrient Management The plant-based approach of Sitespecific nutrient management (SSNM) for irrigated rice systems for Asia was developed in the 1990s by the International Rice Research Institute (IRRI) in collaboration with national partners across Asia to address serious limitations arising from blanket fertiliser recommendation for large areas in Asia. The development of SSNM represented recognition that future gains in productivity and input-use efficiency required soil and crop management technologies that are more knowledge intensive and tailored to the specific characteristics of individual farms and fields. A generalized SSNM approach was developed in 1996 (14) and subsequently tested in more than 200 irrigated rice farms across

Figure 2 – Nutrient Expert® fertiliser decision support tool for wheat and maize Indian Journal of Fertilisers, May 2014 22

Asia. It focused on managing fieldspecific spatial variation in indigenous NPK supply, temporal variability in plant N status occuring within a growing season and medium-term changes in soil P and K supply resulting from actual nutrient balance. The approach required a data management option to predict soil nutrient supply and plant uptake in absolute terms in the highyielding irrigated rice systems in Asia. A modified QUEFTS model (33, 77) was used for this purpose. It described the relationship between grain yield and nutrient accumulation as a function of climatic yield potential and the supply of the three macronutrients. In a situation of balanced nutrition, the QUEFTS model assumed a linear relationship between grain yield and plant nutrient uptake or constant internal efficiencies until yield targets reach about 70-80% of yield potential. As yields approach the potential yield, the internal nutrient efficiencies decline as the relationship between grain yield and nutrient uptake enters a non-linear phase. To model this in a generic sense required the empirical determination of two boundary lines describing the minimum and maximum internal efficiencies of N, P and K in the plant across a wide range of yields and nutrient status. A database containing more than 2000 entries on the relationship between rice grain yield and nutrient uptake was used to derive the generic boundary lines of internal efficiencies (12). The balanced N, P and K uptake requirements for 1000 kg of rice grain yield were estimated from the respective envelope functions as 14.7 kg N, 2.6 kg P and 14.5 kg K, which is valid for the linear phase of the relationship between yield and nutrient uptake. The corresponding borderlines for describing the minimum and maximum internal efficiencies were estimated at 42 and 96 kg grain kg-1 N, 206 and 622 kg grain kg-1 P and 36 and 115 kg grain kg-1 K, respectively (77). The parameters were found to be valid

for any site in Asia at which modern rice varieties with a harvest index of about 0.45-0.55 were grown. Similar work was later done for maize (56) and wheat (IPNI, Unpublished data). Implementation of Plant-based SSNM in Farmers’ Fields-Nutrient Expert® The plant-based SSNM approach is a knowledge-intensive technology in which optimum fertiliser management for a crop field is tailored to specific local conditions for crop yield, growth duration of the variety, crop residue management, past fertiliser use, and input of nutrients from external sources. Such knowledge requirements have slowed the wide-scale promotion and adoption by the farmers. The need for more rapid uptake of the technology by farmers led to the consolidation of research conducted over the last 15 years across Asia into simple delivery systems enabling farmers to rapidly implement SSNM. The delivery system, Nutrient Expert®, (Figure 2) is an easy-to-use, interactive computer-based decision tool that focuses on rapidly providing fertiliser recommendation to farmers while minimizing production risks and increasing the likelihood of profit. The tool acquires the necessary information required for decision making on nutrient management through a series of easy-toanswer questions, which essentially mask the rigors of the SSNM principles from the end users while maintaining the robustness of the process. The Nutrient Expert®, developed by International Plant Nutrition Institute and its partners, is a tool that is based on the plant-based approach of SSNM (44). It utilizes information provided by a farmer or a local expert to suggest a meaningful yield goal for his location and formulates a fertiliser management strategy required to attain the yield goal. The required information about the production system is gathered through a set Indian Journal of Fertilisers, May 2014 23

of simple, easily answerable questions that analyses the current nutrient management practices and develops guidelines on fertiliser management that are tailored for a particular location, cropping system and considers the organic inputs as a part of the system nutrient balance. Farmers’ field validation of the Nutrient Expert® for Wheat and Maize across 15 states in India showed that nutrient recommendation from the software achieved higher yields and profit over existing practices across the region (41, 52). A recent study on the environmental sustainability of the recommendations from Nutrient Expert® showed that recommendations from the tool significantly reduced greenhouse gas emission, as compared to farmers’ fertilisation practice and ad-hoc recommendation, from wheat fields of Haryana (51). Nutrient Expert® tools for Maize and Wheat has been released for free public use. IPNI and its partners are working on the development of Nutrient Expert® for Rice, Cotton and Soybean. Areas Requiring Research

Focused

Cropping System-based Fertiliser Management Crops are generally grown in a cropping system mode where two or more crops are grown in a sequence within a year or in multiple years. This is true for most parts of India except where climatic or other factors restrict growing multiple crops. Crops grown in rotation influence each other in more than one way. Delay in planting of one crop can reduce yield of the subsequent crop, or fertiliser applied in the previous crop may reduce the need of fertiliser application in the next crop. Micronutrients like Zn is applied in one crop within a rotation, while the other crops in sequence receive residual benefit. There are numerous other

examples, which suggests that it makes more sense to manage crops as a system, rather than as individual crops. However, fertiliser recommendation in India is done on individual crop basis, ignoring the impact of other crops grown in rotation. As a consequence, the management of the previous crop is not taken into account, precluding the benefits that could be accrued. For example, if the residue of the previous crop is retained in field, the benefits from mineralization of nutrients from the residue are not taken into account while recommending fertiliser for the next crop. Recent studies show that almost 100% of the potassium retained in rice residues became available to the next wheat crop. A soil testing done between harvests and planting, however, would not show the potassium from residue because of the delay in mineralization and provides no option to integrate such information in the recommendation process. A fertiliser recommendation on a cropping system basis, on the other hand, would have the flexibility to include the nutrient balance of a cropping system as a factor affecting fertiliser recommendation, taking into account the management activities in previous crops that may alter the nutrient dynamics of the soil. This will probably allow better management of nutrients, integrating the variance in nutrient dynamics in variable crop growing environments (aerobic/anaerobic, residue/no-residue, tilled/no-till), providing opportunities to improve nutrient use efficiencies (NUE). Developing nutrient recommendations for cropping systems, however, is far complicated than individual crops. If not exact, a reasonably good estimation of nutrient cycling within the cropping system needs to be done for making cropping system-based nutrient management strategies. However, such an exercise is expected to significantly benefit all the stakeholders by improving onfarm yield and profitability, by maintaining soil fertility and

reducing nutrient losses thereby increasing NUE. This area needs attention from researchers for providing the necessary guidance to the extension system as well as the farmers. Nutrient Management Conservation Agriculture

in

The interest for conservation agriculture (CA) in India is increasing, mainly driven by increasing water scarcity and labour costs. Success of conservation agriculture, however, depends on how well the component technologies, such as water, weed and nutrient management strategies, are developed to support the newly introduced form of agriculture without tillage. The three pillars of conservation agriculture, no tillage and minimum soil disturbance, permanent organic soil cover and diversified crop rotations, including legumes, do influence the soil nutrient dynamics. For example, when tillage is reduced, greater crop residues accumulate on the soil surface minimizing wind and water erosion and improving the quality of the soil. Crop residues on the soil surface increase water infiltration and reduce evaporation losses, reduce nutrient losses through erosion, and also lower the surface temperature. Cooler soil temperatures will slow nutrient release from soil organic matter, reduce diffusion of nutrients to the plant roots, and can affect root growth. In the absence of frequent tillage, mineralization is slowed and the release of plant nutrients declines, making fertilisation more important in producing higher yields. Initially, when no-till is first adopted the increased carbon (C) from the crop residues causes immobilization of soil N as decomposing microorganisms use soil N to maintain their C:N ratios during the decomposition process. With time the turn-over, or breakdown, of soil organic matter reaches a new equilibrium and the pool of potentially mineralizable N increases resulting in more plantIndian Journal of Fertilisers, May 2014 24

available nitrate (NO 3 - )-N and ammonium (NH4+)-N. Soil P and K tend to be immobile in the soil and without tillage and soil mixing, immobile nutrients may accumulate at the soil’s surface (05 cm). An understanding of how nutrients move and react in the soil is necessary for proper fertiliser management in reduced tillage systems. However, studies on understanding nutrient dynamics in CA systems are limited, and fertiliser recommendations developed for conventionally tilled systems are generally used for crops grown under conservation agriculture practices. Kassam and Friedrich (2009) even suggested that conventional soil analysis data might not necessarily be a valid basis of fertiliser recommendations for CA, since the available soil volume and the mobility of nutrients through soil biological activities tend to be higher than in tillage-based systems against which the existing recommendations have been calibrated. The authors also suggested that the nutrients and their cycles must be managed more at the system or crop mix level in a fully established CA system so that fertilisation is not strictly crop specific, rather nutrients are provided at the most convenient time during the crop rotation to maximize benefit. The importance of nutrient management in CA systems were well articulated in a recent article (75) where the authors argued that a fourth principle of CA– the appropriate use of fertiliser – is required to enhance both crop productivity and produce sufcient crop residues to ensure soil cover under smallholder conditions in SubSaharan Africa. The authors proposed fertiliser application as a separate principle for CA in contrast to other agronomic practices, including planting time, spacing, and weeding regime, because fertiliser is essential for CA to work, whilst the sub-optimal implementation of other crop management practices do not lead to the failure of CA as such. They suggested that without acknowledging this fourth

principle the chance of success for CA, especially with smallholder farmers, is limited. The topic of nutrient management in CA systems is a complex issue and needs attention from researchers for successful adoption of conservation agriculture practices at the farm level. CONCLUSION Nutrient application in agricultural systems is expected to increase in the coming years to produce more food, feed and fiber from lesser land area. Efficient utilization of applied nutrients will be the key to sustainability in such high input-high output systems. Efficient fertilisation is important from both an economic and an environmental point of view. It is synonymous with minimizing nutrient losses to the environment, while optimizing crop yields. It is appropriate here to mention that efficient nutrient use is essentially an offspring of balanced fertiliser use and sound management practices and decisions. Balanced fertiliser use is not only the first requirement; it is rather a pre-requisite since no amount of agronomic manipulation can produce high system efficiency out of an imbalanced fertiliser dose. Farmer adoption of the simple and proven concept of balanced fertilisation is limited in India. Lack of site-specific recommendation and one crop-one recommendation approaches disregarding farmer resource availability are major reasons for low adoption. Several existing approaches, such as GIS-based fertility maps, STCR equations and the Nutrient Expert® fertiliser decision support tool can provide the necessary support for largescale on-farm implementation of balanced fertilisation. Developing cropping system-based fertiliser recommendation and fertiliser recommendation for crops grown under conservation agricultural practices are areas that needs further research.

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77.Witt, C., Dobermann, A., Abdulrachman, S., Gines, H.C., Wang, G.H., Nagarajan, R., Satawathananont, S., Son, T. T., Tan, P.S., Tiem, L.V., Simbahan, G.C. and Olk, D.C.Field Crops Res., 63:113-138 (1999) 78.Yadvinder-Singh, Bijay-Singh, and Timsina, J. Adv. Agron., 85:269– 407 (2005)

Indian J. Fert., Vol. 10 (5), pp.30-38 (9 pages)

Nitrogen Management Issues and Strategies Bijay Singh

Department of Soil Science, Punjab Agricultural University, Ludhiana 141 004, Punjab

There is an evolutionary trend in research on how to best manage fertiliser nitrogen (N) in cereals. Since the beginning of Green Revolution era in India, fertiliser N has been managed in rice, wheat and maize generally following blanket recommendations consisting of two or three pre-set split applications of the total amount of N. Several N management strategies such as optimum fertiliser N rates, improved methods and timings of application and placement and new forms of fertiliser continued to be formulated to meet the criteria of productivity, profitability, environmental impact, and sustainability. However, to further improve the N use efficiency, recently emphasis has been shifted towards achieving high agronomic efficiency along with high yields by following strategies revolving around feeding the crop N needs. Over the last decade, technological developments have made it possible to quickly and non-destructively quantify spectral characteristics of leaves, which can then be used to diagnose plant N deficiency and, indirectly, to correct N fertilisation in real time and Site-Specific manner leading to improved N use efficiency in cereal crops.

Introduction

N

itrogen (N) is the nutrient that most limits growth of cereals and fertiliser N is one of the key inputs in food grain production. It is typically required in larger quantities than any other nutrient if farmers are to reap high yields and profits. However, in appropriate N management has detrimental effects on crop yield and the environment, and can aggravate disease and pest incidence. Rice, wheat, and maize account for more than half of the total fertiliser N consumption in India. In cereal cropping systems, only 30 to 50% of the applied fertiliser N is recovered by the first crop; remaining N is either lost from the soil-plant system causing serious disruptions in ecosystem functions, or remains in the soil, the recovery of which in the following crops is very limited ( LCC shade 4 or 7.5 P is again sorbed by silicate and calcium minerals. Phosphorus in soil reacts with Al, Fe and Ca gets transformed into sparingly soluble compounds which become unavailable for crop uptake. The transformation of inorganic P fractions in 22 cycles of maizewheat rotation declined with cropping cycles in the order of saloid P 100%) indicating a manure provided a major portion of applied P in plant- available form (Table 2). In another study on soybean- wheat system illustrated that conjoint use of 16 t ha-1 of FYM with 44 kg P ha-1 gave the highest yield in both the crops and the APR ranged from 24.9 to 15.1%, the lower APR values with higher fertiliser P application. With FYM applied at 4, 8 and 16 t ha -1, crops recovered 96, 66 and 45% of manure P, respectively.

Table 2 – Phosphorus balance and changes in Olsen P in soil after five cycles of soybean-wheat rotation Treatments

APR by soybean (%)

APR by wheat (%)

Total P added (kg P ha -1)

Manure Fertiliser (Mg ha-1) (kg P ha-1)

Total P removed (kg P ha-1)

P removed of total P added (%)

Apparent P balance (kg P ha -1)

Change in Olsen P (mg P kg-1)

0(0)

0 11 22 44

0 36.6 30 19

0 35.1 27.8 17.7

0 88 176 353

44 84 106 127

0 95.45 60.23 35.98

-44 4 70 225

-0.54 0.72 3.16 5.55

4 (5.6)

0 11 22 44

0 44.1 31.8 19.1

0 33.4 32.8 19.2

28 116 204 380

84 113 151 157

300.00 97.41 74.02 41.32

-56 3 53 223

0.53 3.42 8.60 13.32

8 (11.2)

0 11 22 44 0 11 22 44

0 46.5 35.2 22.7 0 47 35.8 23.3

0 35.9 33.9 23.1 0 40.3 38.5 26.9

56 144 232 408 112 200 278 464

99 140 171 189 119 157 196 227

176.79 97.22 73.71 46.32 106.25 78.50 70.50 48.92

-43 4 61 219 -7 43 82 237

2.70 9.74 16.19 18.72 9.15 16.65 20.28 22.24

16 (22.4)

(Source : 59)

Irrespective of manure addition, continuous application of fertiliser P resulted in larger positive P balance (74). The high P build up in soils of long term fertility experiment of Rothamsted indicated that yield of arable crops increased up to 25 mg P kg -1, and further increase in application led to P concentration increase in drainage water once Olsen P

reached 60 mg kg-1 (Figure 5). Such critical values should be defined for Indian soils based on different soil types to determine the threshold values for crop yield and environmental quality. The threshold values for crop yield and environmental quality for some major soil orders of India (Table 3) in terms of degree of P saturation in those soils. These values are

dependent on the extractants (55).

nature

The recovery of applied P is only approximately one quarter and the rest remains in the soil and get fixed which acts as sink of residual P and helps in sustaining productivity of succeeding crops in a system (54) and transformation of residual P result in its accumulation which

Figure 5 – A schematic representation of crop yield and Olsen P and drainage P leaving agricultural soil (Johnston, 1997) Indian Journal of Fertilisers, May 2014 46

of

Table 3 – Crop and environmental threshold for DPS in four soil orders using different reagents Soil type

Productivity threshold (%)

Vertisol DPS M3 DPS A.O. DPS OL Inceptisol DPS M3 DPS A.O. DPS OL Alfisol DPS M3 DPS A.O. DPS By Ultisol DPS M3 DPS A.O. DPS By

Environmental threshold (%)

16.0 11.7 20.5

37.5 19.3 52.7

2.5 3.1 3.2

15.6 8.1 29.1

4.94 4.0 6.8

27.6 11.2 33

10.3 6.7 16.2

30.8 14.5 45.9

Influence of Organic Matter and Other Nutrients on P Absorption and Utilization

M3= Mehlich-3; A.O. = ammonium oxalate; By = Bray’s I; OL = Olsen reagent (Source : 55)

govern the P availability to following crops. Residual effects on yield of subsequent crops of phosphorus applied either to soybean or wheat and on recoveries of the added P and changes in available P were studied in soybean-wheat cropping system in Typic Haplustert (73). Phosphorus was applied at rates of 0- 52 kg P ha-1 to soybean and 039 kg P ha -1 to wheat during the first year and in subsequent years the residual effects were studied in relation to fresh application of 39 kg P ha-1 to each crop. Phosphorus applied to soybean showed residual effects in two succeeding crops, whereas P applied to wheat showed residual effect in only one succeeding crop. The total P uptake of both soybean and wheat was higher where P was applied to soybean only as compared to the total uptake in the subsequent year (Table 4) resulting a overall positive P balance. This indicated that recoveries of added P were higher in succeeding two crops or one crop. This study indicated that P recommendation based upon the preceding crop and residue left over for the following crop improved the benefit: cost ratio of the entire system (54). In rice-

(31). Under irrigated condition soybean showed significant response to P application (80 kg P 2 O 5 ha -1 ) where the preceding wheat did not receive any fertiliser P. On the other hand, where wheat received 60 kg P 2 O 5 ha -1 , the response of succeeding soybean was restricted up to 60 kg P2O5 ha-1. It obtained the remaining P from residual fertiliser (5). P solubilises more rapidly under submerged conditions in rice-wheat cropping system. Reduction of Fe and Mn and oxidation of organic matter increases P availability to crops (70). This occurs by forming phosphor-humate complexes, replacing phosphate ions by humate ions and coating sesquoxides particles by humus to form protective cover which reduces P fixing capacity (7).

wheat cropping system rice is known to utilize residual P more efficiently under submerged condition and therefore wheat crop responded significantly in such soil, while the response reduced with successive rice crops (27). However, some studies on long term fertility experiment had shown that skipping P doses or blanket reduction of P can adversely affect crop yield in IGP

Organic matter increases P availability by forming complexes with Al and Fe as phosphates by humus coating and reduces P sorption by displacing sorbed phsophate through organic anions, by complexing with organic phosphate and by mineralization reactions (28). The major mechanisms involved in enhancing P availability are orthophosphate

Table 4 – Effect of fresh and residual P on P uptake and P balance for 1 year period Treatment (kg P ha-1)

Soybean

Wheat

P uptake Soybean & wheat (1992 & 1992/93)

P uptake Wheat & soybean (1992/93 & 1993)

P uptake

P balance

0 13

0 0

9.55 20.64

-

11.09

1.91

26 39

0 0

29.22 36.58

-

19.67 27.03

6.33 11.97

52 0

0 13

41.12 -

15.76

31.57 6.21

20.43 6.79

0 0

26 39

-

21.9 26.39

12.35 16.84

13.65 22.16

(Source : 73) Indian Journal of Fertilisers, May 2014 47

incorporations, lower soil pH, increased enzymatic activity, complexing of exchangeable ions like Al, Fe, Ca and Mn rather than P. Addition of soybean or wheat residues (SR and WR) to the soil increased labile P fractions and the increase was larger with the SR and SR+FP than the WR and WR+FP (58). The integrated approach of manure and fertiliser was greater than their sole application in improving P fertility status, and efficient utilization of added P by crops (59). Repeated application of P as inorganic viz, fertiliser either alone or in conjunction with organics like cattle manure may affect P balance and its forms and distribution in soil. A long term experiment for six years carried out at IISS, Bhopal under soybean –wheat rotation revealed that conjunctive use of cattle manure with fertiliser P increased P pools (NaHCO 3 -Pi followed by NaHCO 3 -Po and NaOH-P) and favoured accumulation of P in organic fractions and encouraged movement of top layer P to subsoil (57). Phosphorus uptake and available soil P increased significantly with increasing rates of both FYM (16 t) and fertiliser P (44 kg ha -1 ) in soybean – wheat cropping system in a study carried out on Typic Haplustert, Bhopal (74). In soils P interacts with other nutrients like N, K, S, Ca, Zn, Mo, Cu, Mn, B. Many studies have shown positive effect on crop yield when N and P are applied together. In studies on interaction between P and K in laterite soils of Kerala, application of 900 and 450 g palm-1 year-1 of P 2O5 and K2O to coconut palm together yielded 233 additional nuts ha -1 (86). A lot of literature has shown the beneficial effect of liming on P availability and reduction of Al toxicity. In P deficient acid sulphate soils of lowland paddy, application of P and lime improved available soil P status (82). The P and S interaction was synergistic in soybean, mustard, pigeonpea, potato, ricepeanut crops at lower rates of application, but could become

antagonistic at higher rates (56). Phosphorus has both synergistic and antagonistic relations with micro nutrients, among which Zn X P interaction is antagonistic, where P induced Zn deficiency or vice versa is reported in many crops. However P interacts synergistically with B and Mn in legume crops. Management and Efficient Utilization of Applied P The efficient utilization of P in soil depends upon the P recovery by different crops which ranges from 20 to 30%. Based upon world P literature, recovery due to fertiliser application and residue together can be upto 50-90% when measured by a suitable method over appropriate time scale based upon many cropping systems, across soil types and climatic conditions (77). This clearly indicates that application of P into soil can lead to accumulation and enrichment of soil with P if not balanced crop wise or based on cropping systems. The approach “P bank in soil’ is more applicable for developed countries with enriched soil P whereas for developing countries like India with low to medium soil P status measure should be taken for judicious use of P fertilisers in conjunction with other resources like organic residues, industrial and municipal solid waste, RP with improved technologies so as to maintain soil fertility levels for sustaining crop productivity. Inorganic Sources : Phosphorus fertilisers are the best inorganic sources of P applied to soil. Phosphorus fertilisers are divided into three classes based upon their solubility: water soluble (mono (MAP) and di ammonium phosphates, superphosphate), citrate soluble (Dicalcium phosphate, Thomas slag, basic slag, deflourinated phosphate and fused magnesium phosphate) and acid soluble (phosphate rock and bone meal). The rock phosphate and bone meal are applied in large quantities on acid soils which are sparingly soluble and converted to Indian Journal of Fertilisers, May 2014 48

usable form for plant uptake over a period of time. The water soluble P fertiliser is readily available for crop uptake, but the major problem is that these fertilisers quickly get fixed and become unavailable for crops. The water soluble fertilisers (SSP, DAP, MAP) were found superior over partially water soluble NP and acid soluble RP in term of grain yield and P uptake in wheat (60). The use of magnesium ammonium phosphate (MgAP), a highly citrate soluble material prepared out of low grade indigenous phosphate rock was tested for suitability for rice (47). Application of high analysis P fertilisers like polyphosphates reduce P fixation and increases P availability in high P fixing soils. The rice crop yield increased by 13% when 80 kg P 2O5 ha -1 was applied through ammonium polyphosphate compared to SSP (84). Organic Sources: The organic manure during decomposition forms organic acids, humic acids and chelating substances which help in liberation of insoluble P into soil solution. Organic acids are released by root exudates and micro organisms which are byproducts of degradation of complex organic molecules (87). The organic sources can even replace 20 to 40% or recommended dose of P fertiliser and can sustain higher productivity. This is supported by the study with the highest productivity in potato – radish system of Himachal Pradesh where 25 to 50% of recommended P and K fertiliser could be replaced with FYM (32). Continuous recycling of green manures with organic amendments not only improve organic carbon but also contribute to P pools in the soils (8). In a long term study carried out in ricewheat cropping system in calcareous soils of Bihar addition of green manure (dhaincha) and organic manure (5t ha-1) along with 100% NPK increased available soil P and was on par with 100% NPK and green manure. The decomposition of organic matter released CO 2 which enhanced P

availability in 6 year study (36). Many studies have reported that use of organic with RP is also known to improve P solubility and residual effect on cropping system. Application of lower doses of 30 kg P 2O 5 ha -1 with FYM for five years on P deficient soils of Typic Hapludalf of Meghalaya RP improved P use efficiency in soybean crop (40). Application of P rich residues also improves the mineralisable P fractions in soil. Long-term use of fertilisers and FYM decreased P adsorption even more than a super-optimal application of P fertilisers (65). Table 5 shows the potential organic P resources which can be used and can provide a better complementary source with P fertiliser for Indian soils. Best Management Practices for Soluble P Best management practices for P should aim in ensuring P availability in soil solution at appropriate time at a reasonable cost, thus increasing P use efficiency (PUE) in sustaining crop productivity. This can be achieved by using suitable P source which minimise reaction with soil components and makes P pools available to crop, modifying soil component or application method (of P fertiliser) to reduce P fixation. For P ‘4R nutrient management’ i.e., the right fertiliser, the right amount (soil test based), the right time of application (crop growth stage) and the right application method (band placement) and precision application based on management zones is the need of the hour. The best management practices (BMPs) are based upon nutrient requirement of individual crops, the extent of response to crops to P application and the capacity of crops to utilise the residual effect for succeeding crops as shown in the Table 6 for some cropping systems of India. Some specific P particular to cropping systems are given in Table 7. Some agronomic techniques like placement, time and application of P fertilisers are known to improve

Table 5 – Availability of P2O5 from Organic Resources Resource Nutrients (theoretical potential)

2010

2025

Human excreta (million t P2O5)

0.64

0.76

Livestock dung (million t P 2O5)

1.31

1.45

Crop residues (million t P2O5)

0.21

0.36

Human excreta (million t P2O5)

0.51

0.62

Livestock dung (million t P 2O5)

0.66

0.73

Crop residues (million t P2O5)

0.07

0.12

Total P2O5 (million t)

1.24

1.47

Nutrients (considered tappable)

(Source : 80)

Table 6 – Some best P management practices (BMPs) Management Practices

Situation/ Condition

Phosphorus broadcast P application rates Phosphorus placement season stress Fertigation

Under high speed operations and heavy In low soil test P where early Good under intensive agricultura; increase P fertiliser efficiency; irrigated agriculture Incubation with organic matter; during composting Root symbiosis with arbascular

protects environment; sustains Use treated rock phosphate addition of P solubiliser, A.awamori, Increasing the effective rooting area mycorrhizal fungi (AMF) Increase P availability through rhizosphere modification Use of earthworms

Root exudates: phosphatase, oxalates (genotypic difference) Enhance nutrient availability mainly in tropical soils through casting A rise in pH in acid soils accompanied by P solubilisation; Production and release of organic anions; increased enzymatic activity; compleaxation of exchangeable ions such as Al3+, Fe3+

Organic residue amendments

Table 7 – Nutrient BMPs in some cropping system in India Cropping sequence

Strategy

Rice-wheat, pearl millet- wheat, soybean-wheat

Apply phosphorus to winter (Rabi) wheat and skip P application to Kharif crops

Maize- wheat, sorghum- wheat Gram- rice harness the residual effect on rice Sorghum-castor

Prefer to apply P to wheat Apply super phosphate to gram and

Potato based system potato based cropping system Groundnut-wheat (Source : 1)

Apply P at recommended dose to sorghum and castor crop may be given a reduced dose P should be applied to potatoes in a Apply recommended dose of P to wheat and skip application to groundnut

Indian Journal of Fertilisers, May 2014 49

PUE and therefore are important aspects in BMP. Phosphatic fertiliser should be placed near root zone for efficient utilization by crops and for improving seedling vigor. Phosphatic fertilisers applied as basal dose after broadcasting should be incorporated in soil during preparation of the field before crop sowing. Among the different methods band placement of P is the best method for many crops which can be practised in high P fixing soils having low soil P status and during dry season. Liming improve P use efficiency by improving soil pH to neutrality and resulting in more uptake of P by crops. Phosphatic fertiliser is totally imported in India and therefore fertiliser application based on soil testing should be followed for sustaining optimum crop productivity. At the same time this would also improve plant nutrient use efficiency and minimise P accumulation and loss of P from soil subjected to erosion. Selection of crops with high P utilization like cowpea, black gram and green gram should be encouraged which absorb more P from applied P fertilisers. Among the different crops P use efficiency is found highest in pea followed by lentil and chickpea as reported in a study (35). Cereal crops are known to extract more P efficient from soils because of the fine roots which are highly efficient in drawing P from soil solution. A certain annual increment in crop yield to some extent can cope up with increasing P fertiliser scenario with better crop management practices. Opportunities for Use of Rock Phosphate The total resources of rock phosphate as per UNFC are placed at 305.3 mt. The production of RP in 2007-08 was 1.86 mt. Of the total resources, 36% are in Jharkhand, 30% in Rajasthan, 17% in Madhya Pradesh, 9% in Uttar Pradesh and 8% in Uttarakhand. Meager resources are located in Gujarat and Meghalaya (30). Rajasthan continued to be the principal producing state, contributing 94%

of the total production followed by Madhya Pradesh with 6%. Grade wise about 43% of the total production of RP was 30-35%, 4% of 25-30% and 53% of 15-20 % P2O5 (25). Most of the rock phosphates are reasonably suitable for direct use in acid soils, but have not given satisfactory results in neutral to alkaline soils (49). Most of Indian RP is of low grade having 25-30% P 2 O 5 . The efficiency of the RP applied to the soil depends upon the chemical and mineralogical composition, physical nature of the material, soil properties and crop management practices. The RP sometimes is not favourable for direct application due to their insolubility which can be improved by treating them with organic acids or acidifying agents or biological means to enhance their effectiveness in neutral to alkaline soils. Many Indian studies are focused on the use of organic residue with RP to enhance P solubilisation. The mobilization of P in low grade rock phosphate can be enhanced by addition of crop residue and activity of PSM. The microorganism like A. awamori, which supplied sufficient P due to organic acids produced by microorganism during decomposition of crop residues like mung bean and rice straw (38). The use of cow dung solubilised P in RP in 15-20 days (11) which was also reflected well in P extracted by 2% formic acid, 2% citric acid and Olsen‘s reagent. Addition of pyrite (10%) to cow dung did not increase P solubility initially but maintained larger amount of 2.46 g and 3.51 g kg-1 with 2% formic acid and 2% citric acid respectively at 45 days of incubation in the medium. Low grade RP mixed with spent wash added to P deficient soils solubilised P in RP, increased available P significantly and fodder yield throughout season (37). The Indian RP subjected to technologies of partial acidulation, benefication are also known to improve P solubility. The use of RP like Mussorie, Purulia and Udaipur RP in a study where all the three RP sources were treated with Na2CO3 and heated at 600° C to produce Rhenania type Indian Journal of Fertilisers, May 2014 50

phosphate was evaluated for rice crop (14). They reported that heated products obtained from low grade RP performed better on dry matter, P uptake significantly compared to original RP but was on par with SSP. The direct effect of partially acidulated RP (PARP) application in a cropping system was significant in term of yield and P uptake, and had residual effect on succeeding crops in cowpea- wheat cropping sequence as shown in Table 8 (10). New P Products and Initiatives With the introduction of nutrient based subsidy and opening up of phosphate fertiliser sector new generation fertilisers which are having high recovery efficiency like polymer coated water soluble fertilisers, rhizosphere- controlled fertiliser (RCF fertiliser), organic complexed superphosphate, slow release P fertilisers with superabsorbent property and nanophosphate fertilisers are gaining importance (57). In a study polymer coated MAP improved plant recovery of fertiliser P and provided barley grain yield advantage relative to uncoated MAP (41). In rhizosphere controlled fertilisers water soluble fraction acts as starter dose and insoluble P fraction becomes soluble by crop and micro organisms rhizospheric activity (18) and are proved to be more efficient than superphosphate in both alkaline and acid soils. Organic complexed superphosphate is another option for enhancing agronomic efficiency of superphosphate by reducing P fixation by introducing organic chelating agent during superphosphate production (17). In a pot experiment conducted on wheat results indicated that complexed super phosphate performed better than SSP (Table 9) in both alkaline and acid soils (19). Nanotechnology is being visualized as a rapidly evolving field that has potential to revolutionise agriculture. Presently, the application of

Table 8 – Direct and residual effect of different PAPR fertilisers on yield and uptake by cowpea and wheat grown in sequence Treatments

Direct effect on cowpea Yield (g/pot) P uptake (mg/pot)

Sources of P Control TSP

Residual effect on wheat Grain yield Total P (g/pot) uptake (mg/pot)

7.4

16.3

10.9

21.4

14.9 (100)

44.9 (100)

14.7 (100)

41.7

Mussoorie rock phosphate

11.8 (59)

32.6 (57)

15.9 (130)

36.1

Udaipur rock phosphate

14.3 (92)

35.6 (96)

14.1 (83)

32.0

Purulia rock phosphate 15.3 (105) North Carolina 10.5 (41) CD (P=0.05) 0.71 Acidulation level (%) 25% 12.6 50% 13.0 75% 13.4 CD (P=0.05) 0.62 Acid used for acidulation H 2SO 4 12.2 H3PO 4 13.8 CD (P=0.05) 0.50 (Source : 10)

44.0 (97) 31.7 (54) 2.2

13.3 (63) 14.4 (91) 0.95

36.0 35.9 2.5

33.2 37.6 37.0 1.9

13.6 14.7 14.9 0.82

31.1 36.3 37.5 2.1

32.9 39.0 1.5

14.2 14.6 NS

33.7 36.3 1.7

nanotechnology in soil science research is concentrated on formulation of nano fertilisers, smart delivery systems for nanoscale fertilisers, nanoforms zeolites for slow release and efficient dosage of water and

fertilisers for plants, nanosensors for soil quality and plant health monitoring, nano induced polysaccharide powder for moisture retention or soil aggregation carbon build up and nanomagnets for removal of

Table 9 – Effect of complexed superphosphate and SSP on shoot P concentration of wheat crop (at harvest) cultivated in different soils Treatment

P concentration in wheat shoots (µg P g -1 dry shoot) Alkaline soil Acid soil with low Acid soil with high organic matter organic matter

Control

1155b*

852 b

1203 b

SSP

1279 b

1004 b

1249 b

Complexed super phosphate 1

1423 a

1433 a

1474 a

Complexed super phosphate 2

1341 ab

1389 a

1389 a

Complexed super phosphate 3

1422 a

1383 a

1480 a

Complexed super phosphate 4

1240 b

1480 a

1337 ab

*Different letters indicate significant difference for p illitic (intermediate) > kaolinitic (low) (Figure 6).

Sub Soil K

K fertility of Indian soils Potassium status mainly exchangeable and nonexchangeable K of various soil types in different agroecological regions of India are given in Table 7. Vertisols and its associated soils in AER 5 and 6; and Vertisols and Vertic Ustochrept in AER 10 and 11 are high in both exchangeable and reserve K (58). These soils have high available K and respond better to K application. Most of Alluvial soils in different regions (AER 1, 2, 4, 12, 13, 15 and 18) were observed with a wide variability in status of available and non-exchangeable K ranging from low to high. Soils of different altitudes i.e., soils of hilly regions such as brown forest and acidic hill soils

Surface horizons of soil are regarded as major suppliers of plant nutrients, but contribution from sub-soil to plant nutrition is often considered. Contribution of K from subsoil horizons to plants depends mainly on K status of subsoil, plant rooting characteristics mainly distribution of roots in subsurface layers. Leaching of K from surface layers, continuous K fertilisation and soil mineralogy may enrich the K status in sub-soil horizons. Deep rooted crops better exploit K from these sub-soil layers. Extractable K in sub-soils in comparison to surface soil K (which is taken as 100%) (Table 8) indicates the potential of subsoil K supply. Kaolinitic soils showed more or less similar levels of K both in surface and subsoil evidencing the fact of limited K fixation than smectitic clay minerals. The overall percentage of subsoil K to the surface soil K varied from 71 to 96, 62 to 90, and 60 to 82 in

Figure 5 – Potassium uptake (kg/ha) pattern of sugarcane ratoon crop at different growth stages Indian Journal of Fertilisers, May 2014 64

Table 6 – Mineralogy and K status of important benchmark soils of India Soil Series

Location

Texture

Smectitic Vertisol and Vertic sub-groups Sarol Indore (M.P.) Kamlia-Kheri Indore (M.P.) Pithvajal Amreli (Gujarat) Noyyal Coimbatore (T.N.) Kalathur Thanjavur (T.N.) Hanrgram Bardhaman (W.B.) Illitic Inceptisols, Entisols and Aridisols Nabha Ludhiana (Punjab) Lukhi Gurgaon (Haryana) Masitawali Ganganagar (Raj.) Khatki Meerut (U.P.) Akbarpur Etah (U.P.) Rarha Kanpur (U.P.) Jagadishpur Bagha Muzaffarpur (Bihar) Raghopur Muzaffarpur (Bihar) Mazodar Banaskantha (Gujarat) Kaolinitic Alfisols and Inceptisols Kodad Nalgonda (A.P.) Vijayapura Bangalore (Karnataka) Tyamagondalu Bangalore (Karnataka) Doddabhavi Coimbatore (T.N.) Kumbhave-5 Ratnagiri (Mah.) 214 Kharbona Birbhum (W.B.) Balisahi Puri (Orissa) Source: 52

kaolinitic, illitic, and smectitic soils, respectively. Matching K Release Rates Potassium release patterns were studied by periodical extraction of soils using different extractants. Constant rate K, step K, cumulative K and ratio of step-K to constant K are termed as K supplying parameters used to elucidate the release of K from soil over a period of time. Constant-rate K was taken at a stage when similar amounts of K were extracted in consecutive extractions, whereas step K was computed by subtracting the constant-rate K values from the K extracted in each extraction and by summation of those values. Cumulative K is the sum of the values of K extracted in all the extractions. Strength of acid, soil mineralogy, mineral bonding, period of extraction, efficiency of acid to extract strongly held K are

Mineralogy Clay fraction Silt fraction

c-sic c-sic l-c l-c cl-c sicl-sic

S ML I Ch V S NL Ch V S Am I C K Q SIKQF S K I V Ch S I V K Q F Ch

Q F K Ch I QF Q F N Ch S FQNS QFI QNVF

s-l s-sl ls-l sl-cl sl-l ls-sil l-sil sil-sic s-sl

I V Ch Q F K IK S V Ch Q F I K S Ch Q F I Ch V Q F K I S V Ch K Q I V Ch Q F K I Ch Sm Q F I Ch S Q F I S V K AM Q F

sl-scl l-scl ls-sl s-sl gl-sic ls-sil ls-l

WS

K status (mg kg -1) NH4OAc 1N HNO3

100 9 13 33 12 20

820 151 191 515 173 133

780 800 580 1900 1040 360

QNVF Q F N Ca Ch Q F N Ca Ch QMV QNVF MQVF Q N F Ch V Q N F Ch V Q F N Ch K V

15 21 21 23 31 12 13 9 9

39 69 156 65 133 48 32 48 51

860 350 1460 1300 1340 1470 1636 1936 400

K I MI V S K Am I V Q F K Am I V Q F KIV K I V MI

QFIV QFNK QFNK QFIV -

19 12 13 9

61 19 39 38 4

304 120 320 1040 79

KIS KISQFV

QNVFKQF QKNQF

6 18

97 27

156 142

some of factors which influence K release from a soil. Nutrient management i.e., application of both inorganic fertiliser and

Figure 6 –

Exchange sites of K on different clay minerals

Indian Journal of Fertilisers, May 2014 65

organic manures also have greater impact in cumulative K release. Fourteen years (1980-1994) of intensive rice cropping shown

Table 7 – Potassium status of soils in India categorized according to different agroecological regions Agroecological Soil type region

Exch. K

Non-exch. K

AER 1

Alluvial soils

M

H

AER 2

Arid and Alluvial soils

H

L-H

AER 3

Alfisols

M

L-M

AER 4

Alluvial soils

L-H

M-H

AER 5

Vertisols and associated soils

H

M-H

AER 6

Vertisols and associated Alfisols

M-H

L-H

AER 7

Swell-shrink and red and lateritic soils

H

M

AER 8

Red soils

M

L

AER 9

Iceptisols, Entisols and Mollisols

M

H

AER 10

Vertisols and Vertic Ustochrept

H

M-H

AER 11

Vertisols and Vertic Ustochrept

M-H

M-H

AER 12

Red and Acidic alluvial soils

L-M

L

AER 13

Alluvial soils

M-H

L-H

AER 14

Brown forest and acidic hill soils

L-H

L-H

AER 15

Acidic alluvial soils

H

L-M

AER 16

Acidic hill soils

M-H

M-H

AER 17

Acidic soils

L-M

M-H

AER 18

Coastal and deltaic alluvial soils

H

M-H

AER 19

Red and lateritic soils

M-H

L-H

AER 20

Light textured acid soils

L-M

L

Higher amount of K release in the FYM 10 Mg/ha+100% NPK treatment by all extracting solution was due to higher additions of K than other treatments. Fertiliser K Consumption Scenarios

Note : Exchangeable K: low 120 mg kg-1. Non-exchangeable K: low 600 mg kg-1. Source: 58

reduction in cumulative K release over a period of time from initial soil status (Table 9) (57). Cumulative K released with these two extractants (0.01M CaCl 2 and 0.01M citric acid) differed may be

capacity indicated that cumulative K release of soil profile (0-1.0 m) was higher in 1N HNO3 extraction, followed by that in 0.01M HCl and 0.01 CaCl 2 (Table 10) (56).

due to their extraction efficiency and nature of reaction with soil. Twenty seven years (1978-2004) long-term impact of nutrient management under fingermillet monocropping on K supplying

Earlier most of Indian soils were accepted to be rich in available K and a profitable response to applied K was not so prominent (18). But, later there was an immense raise in fertiliser K consumption from 29000 t in 1960-61 to 3.4 mt in 2010-11 (Table 11). However, compared to fertiliser N and P, usage of K was lower during these years leading to mining of soil K to meet crop demand for K. Use of N and P in Indian agriculture increased gradually from year to year but there is skewed trend in fertiliser K use. Overall consumption of major nutrients (N+P 2 O 5 +K 2 O) increased from 1.93 in 1960-61 to 145.0 kg/ha in 2010-11, but contribution of K to this is very minimum. This scenario also lead to K status in Indian soils from high to medium and medium to low status resulting in widespread K deficiency in soils and crops across the country in recent past. State wise consumption of major

Table 8 – Range for K extracted by different extractants for 22 soils at two different soil depths Extractants

Kaolinitic 0-15 cm 15-30cm

Illitic 0-15 cm 15-30cm

Smectitic 0-15 cm 15-30cm

0.01 M CaCl2 0.01 M Citric acid

12-27 10-40

5-21 8-31

15-69 16-79

10-38 13-68

22-259 37-356

10-136 11-194

1.38 N H2SO4 6N H2SO4

17-98 22-98

21-75 22-152

21-166 120-349

11-159 76-334

125-776 136-1100

57-368 93-512

19-97 320-835

18-88 255-780

32-156 605-2415

28-150 660-2030

133-820 630-2190

98-690 390-1285

1N NH4OAc NaTPB Source: 53

Indian Journal of Fertilisers, May 2014 66

fertiliser nutrients (N, P and K) under both rainfed and irrigated conditions (in year 2006-07) are presented in Table 12. Comparatively use of N and P fertiliser nutrients is greater than K in all parts of country. Variability in fertiliser consumption across the regions may be due to different crops cultivated and cropping systems followed. Nitrogen consumption observed to be two times of P and four times of K. K Balance in India National gross and net balance sheet of major nutrients illustrates the fact that there is a negative balance of K in Indian agriculture with annual depletion to the tune of 10.20 and 5.97 mt, respectively (62) (Table 13). Of the net negative NPK balance or annual depletion of 9.7 mt, K contributes around 69% followed by 19% N and 12 % P. Such an alarming contribution of K towards net negativity of NPK balance in agriculture crop production in India is of major concern. Low addition and high extraction of K from soils of different regions of India lead to negative balance of K (Figure 7).

Table 9 – Cumulative K release (mg/kg) from the non-exchangeable fraction of soils under intensive cropping, fertilisation, and manuring in different media of extraction Treatment

0.01 M CaCl2 1980 1994 70 57

Control

0.01M Citric acid 1980 1994 108 80

100% N 100% NP

64 55

44 34

95 84

72 57

100% NPK 100% NPK + FYM

81 99

60 66

123 140

95 108

Source: 57 Table 10 – Cumulative-K release of soils as evaluated by different extractants following 27 years of cropping and fertility management in Alfisols at Bengaluru (Karnataka) Treatment Cumulative-K release 1N HNO3 0.01M HCl 0.01M CaCl2 Control

660.1

162.7

62.7

FYM 10 Mg/ha

710.3

177.4

74.6

FYM 10 Mg/ ha + 50% NPK

758.3

185.2

95.7

FYM 10 Mg/ha + 100% NPK

806.4

197.8

98.4

100% NPK

759.6

180.5

82.6

Source : 56 Table 11 – All India consumption trend of fertiliser nutrients Year Nitrogen Phosphorus Potassium N+P 2O5+ (N) (P 2O5) (K2O) K 2O (kg/ha) ’000 tonnes

N:P:K

1960-61

212

53

29

1.9

7.3:1.8:1.0

1970-71 1980-81

1479 3678

514 1214

2366 624

13.9 31.8

6.3:2.2:1.0 5.9:1.9:1.0

Overall input of K to soil is 4915.5, but output is nearly double (8219.8) of input which lead to negative status of K (-3295.3).

1990-91 2000-01

7997 11310

3221 4372

1328 1667

67.6 90.2

6.0:2.4:1.0 6.8:2.6:1.0

2007-08 2008-09

14419 15090

5514 6506

2636 3312

115.7 127.7

5.5:2.1:1.0 4.6:2.0:1.0

Potassium addition varied among different states with same soil type (Table 14). Input of K (’000 tonnes) in states with alluvial soils is ranged from 4.6 in Haryana to 113.6 in Uttar Pradesh, whereas removal ranged from 490.1 to 1777.2 in same soils this has lead to negative balance. Similar is the case with black soils of Maharashtra and Madhya Pradesh; red soils of Karnataka, lateritic soils of Kerala and desert soils of Rajasthan. Rajasthan soils are received very low K but observed with higher K removal this has resulted in high mining

2009-10 2010-11

15580 16890

7274 8001

3632 3391

135.8 145.0

4.3:2.0:1.0 5.0:2.4:1.0

Source: 30

index value (152.7) compared to other soils in different states. Red and lateritic soils of Karnataka and Kerala, respectively were with low mining index (2.79 and 2.01) expressing close to equilibrium between additions to removal of K, but still needs better K management. In general, soils with low K addition and high K extraction were resulted in high K Indian Journal of Fertilisers, May 2014 67

mining index values. Priority Districts for Higher K Use Efficiency Indian districts were categorised into low, medium and high exchangeable and nonexchangeable K soils using GIS (Geographic information systems) technology based on information on K status of Indian soils during last 3 decades (NBSS and LUP,

Table 12 – Consumption (kg/ha) of plant nutrients (N+P 2O5+K2O) in major states State Andhra Pradesh Irrigated Unirrigated Assam Irrigated Unirrigated Chattisgarh Irrigated Unirrigated Goa Irrigated Unirrigated Gujarat Irrigated Unirrigated Haryana Irrigated Unirrigated Himachal Pradesh Irrigated Unirrigated Jammu and Kashmir Irrigated Unirrigated Karnataka Irrigated Unirrigated Kerala Irrigated Unirrigated Madhya Pradesh Irrigated Unirrigated Orissa Irrigated Unirrigated Punjab Irrigated Unirrigated Rajasthan Irrigated Unirrigated Tamil Nadu Irrigated Unirrigated Uttarakhand Irrigated Unirrigated Uttar Pradesh Irrigated Unirrigated West Bengal Irrigated Unirrigated

Fertiliser nutrients consumption (kg/ha) 2006-07 N P 2O 5 K2O Total 126.2 64.1

72.3 53.3

39.1 10.1

237.6 127.5

95.8 95.6

59.8 51.3

76.3 48.6

231.9 195.6

56.1 78.6

15.7 35.9

7.1 14.8

79.0 129.3

91.3 87.6

33.2 32.9

54.0 10.2

178.5 130.7

169.5 79.6

75.4 28.0

32.2 6.3

277.1 113.8

151.6 72.1

42.0 12.1

3.6 0.08

197.1 84.3

58.4 41.5

23.0 12.8

11.7 8.7

93.1 62.9

59.5 50.2

28.9 19.3

4.2 8.2

92.6 77.7

142.3 54.6

65.8 38.9

69.7 14.4

277.8 108.0

40.7 37.3

32.4 34.0

55.8 36.5

128.8 107.8

83.5 47.8

41.6 30.5

9.4 3.2

134.5 81.5

74.1 55.6

30.9 23.0

19.3 13.4

124.3 92.1

139.1 101.0

46.6 26.9

2.5 0.61

188.2 128.5

62.9 38.6

28.0 17.2

1.5 0.7

92.4 56.5

155.7 90.7

75.9 45.6

83.5 35.0

315.1 171.4

218.4 405.2

48.8 7.4

17.6 0.3

284.8 412.9

125.9 102.0

40.6 33.2

7.5 9.1

174.0 144.2

102.9 51.9

68.5 27.1

51.8 20.7

223.1 99.7

Indian Journal of Fertilisers, May 2014 68

Nagpur) (39) and further district wise maps of exchangeable and non-exchangeable K were generated using Arcview 3.1 with reference to AERs and AESR (55) (Figures 8 and 9). Fifteen districts were identified with low exchangeable and nonexchangeable K status (Category I) (55). These districts represent mostly red, lateritic soils, light textured and shallow soils. Since both the K fractions were low, K supply to crops grown on these soils is a must and therefore regular K fertilisation should be done considering crop K removal. Another 18 districts are categorized under Category II where exchangeable K was low while non-exchangeable K was medium. These soils also represent light textured and acidic alluvial soils where regular K application is necessary. Two districts with low exchangeable and high nonexchangeable K under Category-III were recommended with K application at critical stages for bettering the crop yields. Light textured alluvial, red and lateritic, acid sulphate and sandy soils with medium exchangeable and low non-exchangeable K were identified in 58 districts coming under Category-IV. These soils need a great attention from K management point of view, as continuous cropping resulted in depletion of soil reserve K. Therefore, K addition at critical stages is required. Frequent additions of K is must to meet the demand of K exhaustive cropping systems like rice-wheat, ricewheat-fodder, sunflower based, potato and other tuber crops, banana, intensive fodder and vegetables based systems. Medium status of both exchangeable and non-exchangeable K pools observed in soils of 115 districts of India where mentioned under Category-V. These regions represent various types of soils from acid to alkaline, red, medium to deep black and alluvial. Hence, K additions are required for improving value and quality of tobacco and to meet the needs of K exhaustive crops such as

textured alluvial soils may satisfy needs of plant K needs for long period as these have greater K supplying power and do not require K application.

Table 13 – An illustrative nutrient balance sheet of Indian Agriculture Nutrient N P 2O 5

K2O Total

Gross balance sheet * (’000 t) Addition Removal Balance

Net balance sheet (’000 t) Addition Removal Balance

10,923 4,188

9,613 3,702

1,310 486

5,461 1,466

7,690 2,961

-2,229 -1,493

1,454 16,565

11,657 24,971

-10,202 -8,406

1,018 7,945

6,994 17,645

-5,976 -9,701

Crop Responses Crop responses to applied K depends on crop type, variety, soil fertility status, soil texture, cation exchange capacity, soil depth, soil moisture and other nutrients application. Crop yield levels and K demand of crop determines the response of applied K.

*Gross balance is calculated on the basis of actual application while net balance is calculated by factoring in the efficiency of 50% for N, 35% for P2O5 and 70% K2O. Source: 62

Combined application of NPK proven to be advantageous in improving and increassing crop yield over NP (Figure 10) and control (32). Absence of K in fertiliser schedule over a period of time declined crop productivity as observed in long term experiments conducted in Alfisols and Vertisols. Irrespective of soils and cropping systems apparent negative balance of K was noted.

Figure 7 – Potassium balance in Indian soils

sugarcane, potato etc. Another 172 districts of Category VI where with medium exchangeable K and high reserve K, representing variety of soils from heavy textured red soils, medium to deep black soils, heavy textured alluvial soils to high organic carbon Mollisols. These soils need application of K only in specific K loving crops like banana and potato. One district in Jaipur fall under Category VII, where exchangeable K was high but nonexchangeable K was low having medium deep alluvial soils with less K bearing minerals. Long term intensive cropping would need some maintenance level of K. Potassium application is not required instantly in medium to deep black soils, fine textured alluvial and red soils with sufficient K rich mica of Category

VIII covering 24 districts having high exchangeable K and medium non-exchangeable K. Around 129 districts of Category IX where both exchangeable and nonexchangeable K was high. These soils represent deep black and fine

Results form different long term experiments practiced at different centres across India revealed that irrespective of climate, crop grown and other factors, application of NPK was better. Other sources of K such as irrigation water, canal water, FYM, green manure etc were also suggetsed to upgrade the crop yields. Increasing yields reported to uptake more K from the soil as

Table 14 – Potassium balance sheet in different states with different soil types Soil Type (R) Alluvial soils

State Balance

Addition (A) Removal Mining index (R/A)

Punjab

18.7

763.5

-744.8

40.7

113.6 4.6

1777.2 490.1

-1663.6 -485.5

15.6 105.7

Black soils

Maharashtra 196.9 Madhya Pradesh 24.1

2095.9 848.8

-1889.1 -824.7

10.6 35.21

Red soils Lateritic soils

Karnataka Kerala

216.1 87.3

603.6 175.6

-387.5 -88.3

2.79 2.01

Desertic soils Rajasthan

7

1068

-1061.1

152.7

Uttar Pradesh Haryana

Indian Journal of Fertilisers, May 2014 69

Figure 8 – District-wise and agro-ecological region wise status of exchangeable K in Indian soils

evidenced by many past studies. Long-term studies conducted at Faizabad and RS Pura (19) upto a decade period with rice-wheat cropping system responded well to K application whereas, response of

crops to N application decreased (Table 15). The mean increase in clusterbean seed yield was 11.7, 18.8 and 20.0% at 20, 40 and 60 kg K 2 O/ha, respectively over control (Figure

11) (68). Pearl millet also showed similar grain yield increments of 5.8, 11.2 and 14.1% at 20, 40 and 60 kg K 2 O/ha, respectively over control. Residual effect of K on mustard

Figure 9 – District wise and agro-ecological region wise status of non-exchangeable K in Indian soils Indian Journal of Fertilisers, May 2014 70

Figure 10 – Effect of balanced nutrition (N+P+K) on crop yields grown under long term experiments at different parts of the country

yield was significant as observed in clusterbean-mustard at 40 kg K2O/ha and pearlmillet-mustard at 60 kg K2O/ha. Field experiments conducted at different locations in Punjab (India) showed that rice and wheat response to applied K was not so pronounced in Ludhiana where sandy loam soils exist (Table 16). Significant response to K additions (upto 60 kg/ha) and increase in yield was observed in Gurdaspur location with loam soils. Soils in both these regions were low in available K status. As per suggestions of Dobermann (1995) yields of irrigated rice and wheat in Asia must be raised to 8.0

t/ha and 6.0 t/ha, respectively. Hence, large quantities of fertiliser K will be needed in the future to achieve predicted yields of rice and wheat. A pot culture study conducted to know the response of high yielding variety of maize in K depleted soils (Table 17) (50). Among 8 soil series (except Palam and Mehrauli) response to applied K upto 100ppm on tuber yield was observed. Conversely Palam soil series with low initial exchangeable K content, response of maize was observed upto 150ppm of added K. Potato is the major tuber crop grown in India. It’s a K exhaustive crop that extracts most of the

applied K and application of K also increased production potential and profitability in parts of the country (41; 48). Fertilisation with K at equal rates to both early as well as late crop of potatoes was necessary because K application has great influence on tuber yield as evidenced by its role in early vegetative growth and increasing the bulkiness of tuber (Table 18) (45). Potassium also has a great influence on cane yield attributes and yield. A study conducted at Indian Institute of Sugarcane Research, Lucknow showed application of 30 kg K 2 O/ha was found to increase the cane girth, cane height, no. of millable canes

Table 15 – Response of crops to N, P and K application over time in rice-wheat cropping system in long-term experiments in India Crop

Year

Control yield (kg/ha)

Response to applied nutrient (kg/ha) N120 P23 K33

Rice

1977-78 1989-90

1008 820

2905 2642

500 925

50 231

Wheat

1977-78 1989-90

833 602

2625 2141

617 1169

35 398

RS Pura Rice

1981-82

1490

2499

654

-250

Wheat

1989-90 1981-82

1550 980

880 873

989 458

666 66

1989-90

730

423

1191

2250

Faizabad

Indian Journal of Fertilisers, May 2014 71

and cane yield under normal and water deficit conditions (Table 19). However, under drought occurrences the value of yield attributes in general were found to be lower than normal conditions. Fibre properties mainly fineness, strength, maturity and uniformity ratio of cotton are greatly influenced by K fertilisation (Table 20). Increasing the dose of K addition increased fineness gravimetric, maturity coefficient and bundle strength tenacity. Interaction between K and Zn levels improved the green forage yield of sorghum (Table 21). The data indicated that the effect of K

Figure 11 – Effect of varied K levels on yield (t/ha) of clusterbeanmustard (2002-2005) and pearlmillet-mustard cropping system (20052008) at Haryana

Table 16 – Response of crops to potassium application in rice-wheat cropping system on two locations in Punjab, India Rate of K2O (kg/ha)

Grain yield of rice (t/ha)

Grain yield of wheat (t/ha)

Ludhiana (sandy loam soil) 0 5.4

4.4

5.7

6.3

4.2

4.9

4.5

6.1

30 60

5.3 5.4

4.6 4.6

5.7 5.6

6.4 6.4

4.3 4.1

5.1 5.0

5.1 5.0

6.5 6.5

LSD (0.05)

NS

NS

NS

NS

NS

NS

0.16

0.17

Gurdaspur (loam soil) 0

5.5

5.7

6.2

5.2

2.9

3.3

4.5

4.4

30 60

5.9 6.2

5.9 6.2

6.6 6.6

5.5 5.4

3.2 3.3

3.5 3.7

4.8 5.0

4.7 4.8

0.44

0.34

0.30

0.27

0.32

0.22

0.18

0.29

LSD (0.05) Source: 44

Table 17 – Effect of increasing levels of K (ppm) addition on dry matter yield (g/kg soil) of maize in different K depleted soils Soil series

Levels of K applied K0

K50

K100

K150

Mean

Hamidpur

54.0

58.4

76.3

77.0

66.4

Hisar Kakra

46.2 22.5

61.8 40.6

92.7 71.3

93.0 65.9

73.4 50.1

Thaska Manesar

41.1 20.2

80.3 26.1

92.7 59.6

73.4 46.6

71.9 38.1

Khoh Palam

43.8 12.9

46.1 39.8

89.4 46.7

86.6 70.8

68.9 42.5

Mehrauli Mean

36.9 34.7

69.8 54.1

56.8 73.1

56.6 71.2

55.0

Source: 50 Indian Journal of Fertilisers, May 2014 72

Table 18 – Effect of K on tuber yield (q/ha) of early and late harvested crop of potato (Kufri Badshah) Harvesting time (Days of planting)

Levels of K (kg/ha)

70 85

0 235 335

50 262 354

100 269 358

150 273 367

100 Mean

366 312

394 337

408 345

405 348

Mean 260 353 393

Source: 45 Table 19 – Effect of potassium on yield attributes of sugarcane under water deficit conditions K2O levels Water Cane girth deficit levels (cm) (-MPa soil Ø) 0 30 90 0 30 90 Source: 16

0.03 0.03 0.03 0.65 0.65 0.65

2.52 2.94 2.62 2.54 2.74 2.40

Cane height No. of Cane yield (cm) millable (t/ha) cane (000/ha) 193.4 219.0 220.3 186.7 210.4 207.2

65.3 68.8 62.8 60.1 65.2 60.4

69.4 82.3 69.1 61.6 69.5 69.1

Critical Limits

Table 20 – Quality characteristics of cotton as affected by potassium application Kg K2O/ha

K 2 O/ha) of K which further enhanced by 35 and 49% with the application of 60 and 90 kg K2O/ha, respectively. Oil yield depends on the increase in both oil content and grain yield. Balanced fertilisation resulted in better oil yield rather than lone nutrient supply. Increase in levels of K viz., K30, K60 and K90 kg K 2O/ha increased the oil content from 35.7 to 38.5% (average), contributed towards increase in the oil yield. Application of K to the oilseed crop of sunflower was highly beneficial. The B:C ratio with application of 30, 60 and 90 kg K 2O/ha was 10.3, 8.1 and 9.2, respectively. Application of K at 90 kg K 2O/ha produced significantly higher curd and bulb yield of cauliflower and onion, respectively in comparison to control. However, the highest curd (42.35 t/ha) yield was recorded with 120 kg K 2O/ha which was 40.6 and 40.4% higher in comparison to control, respectively. The corresponding bulb yield was 41.64 t/ha which was 42.7 % higher than control.

Fineness gravimetric (millitex)

Maturity coefficient

Bundle strength tenacity (g/tex)

0 30

148.2 151.7

0.71 0.72

22.5 22.9

60 90

154.7 158.0

0.74 0.74

23.0 23.1

Source: 25

application rates progressively improved up to 60 kg K2O/ha at Zn levels of 0 and 10 kg ZnSO4/ha. The same improved up to 40 kg K2O/ha along with 20 kg ZnSO 4 /ha obtaining maximum green forage yield (18.5 t/ha) which was higher by about 21.5 % in comparison to control (K 0Zn0). Protein content of the dry forage also increased progressively with the increasing K levels irrespective of Zn levels. Effect of varied K levels on protein content was enhanced by Zn application as evidenced by K60Zn20

proving the best interaction which produced higher protein yield to the extent of 39.4 % in comparison to control. B:C ratio of 2.51 was recorded with K @ 40 kg K 2O/ha along with 20 kg ZnSO 4/ha and was higher by about 32.8 and 12.6 % in comparison to respective control (K 0 Zn 0 ). Optimum sunflower yields in Punjab were obtained with application of N and P only, whereas K application along with NP yielded higher grain yield. The rise in yield to the extent of 26% was attained with the application of lowest dose (30 kg Indian Journal of Fertilisers, May 2014 73

Critical levels of K in crop plants may vary based on soil types they are grown. Critical limit of available K in rice in different soils ranged from 58 mg/kg in calcareous soils of Bihar to 190 mg/ kg in alluvial soils of Andhra Pradesh (Table 22). Sorghum shown higher level values for K than other crops. Disparities of Crop Response to K Application Response of crop to applied K depends on crop K demand, soil K supply and external K supply (fertiliser). Even soils with different K levels respond differently. Tables 23 and 24 describes the two different soil K conditions and response of crop to applied K in these soils. Other Sources of K Crop residue, tanksilt, irrigation water etc., the are other sources of K can be effectively utilized to incorporate K into soil apart from

Table 21 - Effect of K nutrition on quality attributes of different crops Crop and Treatment

Yield (t/ha)

Forage sorghum K0Zn0 15.3

Quality attribute

B:C ratio

Protein content (%) 7.74

2.23

K0Zn10 K0Zn20

15.9 16.6

7.87 7.98

2.25 2.29

15.7 16.6

8.03 8.27

2.26 2.32

K20Zn 20 K40Zn0

17.3 16.0

8.41 8.26

2.37 2.28

K40Zn 10 K40Zn 20

17.8 18.6

8.57 8.7

2.47 2.51

K60Zn0 K60Zn 10

17.4 18.2

8.5 8.66

2.44 2.49

K60Zn 20 Sunflower

18.4

8.86 Oil yield (t/ha)

2.47

N60P30 K0 N60P30 K30

1.57 1.76

0.57 0.66

10.30

N60P30 K60 N60P30 K90

1.87 2.08

0.70 0.79

8.10 9.20

K0 K30

30.1 32.6

6.3 6.6

1.58 1.72

K60 K90

38.1 41.3

6.8 6.9

2.04 2.20

K120 Onion

42.3

7.1 Protein content (%)

2.24

K0 K30

29.2 31.8

6 6.2

1.01 1.13

35.8 40.2

6.3 6.4

1.31 1.49

K120

41.6

6.5

1.55

K20Zn0 K20Zn 10

Cauliflower

K60 K90

Reference

60

K Recommendations

9

Protein content (%)

fertiliser and soil K (both exchangeable and reserve) supply. Crop biomass such as straw, stalks after harvest of economic yield can be an advantageous source because they improve soil quality and fertility. In India, residue generation contribution from different crops accounts 70, 13, 6, 5, 2 % for cereals, fibres, oilseeds, pulses and sugarcane respectively, but most of residue generated burnt after harvest of crop which lead to CO 2 emissions and loss of nutrients through burning. Residues of K exhaustive crops such

20

as rice, maize, wheat, sorghum, sugarcane, pulses etc. are better used to incorporate into soil enabling no loss of K. Tanksilt, sedimented soil in tanks is nutrient rich clay used as an amendment in dryland soils to improve water retention capacity also supplies certain amounts of nutrients (35). Irrigation water contains beneficial nutrients in dissolved form which improves soil fertility and also plants uptake these Indian Journal of Fertilisers, May 2014 74

nutrients easily. Potassium concentration in irrigation water mitigates the effects of Na through replacement of Na by K from soil exchange sites. Supply of K through irrigation water depends on K content of added water and amount of water added during crop period. Contribution of irrigation water in crop K nutrition in different parts of India is presented in Table 25.

Potassium recommendations for crop and cropping systems vary in different regions of the country. Recommendations were made based on soil K status, losses from soil, crop K demand, season (Kharif or Rabi), rainfed or irrigated condition and many others (Table 26). Major cereal crops of India viz., rice and wheat were recommended with 30-45 and 30-60 kg K 2O /ha, respectively considering soil type, K status, water regime, crop variety and soil test to attain maximum yield. Comparatively higher K recommendations were made for K exhaustive sugarcane in Andhra Pradesh, Karnataka and Maharashtra; and split application in Tamil Nadu. Wider K recommendations (30-160 kg/ha) were suggested for potato, another high K demanding crop grown in Punjab, Himachal Pradesh, Uttar Pradesh and West Bengal states. CONCLUSION The fertiliser nutrient use trend in majority of states in India is not sufficient and dominated by only NP fertilisation. This has lead to a negative balance of K in most of the soils across India and getting serious day by day. The balance sheet of K prepared based on K consumption mainly consists of fertiliser K in different crops as input and its removal by crop as output showed greater K mining in Indian agriculture, but it is off the reality because other sources of K contribution to soil-plantatmosphere system were not considered while preparing a

Table 22 – Critical levels of available (NH4OAc) K in different soils for different crops Crop Rice

Soil (State) Critical level Medium Black Soil (A.P.) Red Soils (A.P.) Dubba and Chalka Light Soils of Kodad (A.P.) Alluvial Soils (A.P.) Rarha Series, Alluvial Soils (U.P.) Uttari Series, Alluvial Soils (U.P.) Calcareous Soils (Bihar) Phondaghat Series, Lateritic Soils (Maharashtra) Udic Ustochrepts, Uttari Series (U.P.) Lateritic Soils, Kumbhave Series (Maharashtra) Fluventic Ustochrept (Orissa) Khatki Series Typic Haplustalf (U.P.) Wheat Belar Series, Vertic Haplaquept (West Bengal) Bankati Series, Aeric Ochraqualf (West Bengal) Uttari Series, Typic Ustrochrepts (U.P.) Rarha Series, Alluvial Soil (U.P.) Jagdishpur Bagha, Calcreous Soil (Bihar) Umendanda Soil Series (Bihar) Puto Series, Alfisol (Bihar) Khatki Series, Typic Haplustalf (U.P.) Maize Haplustalf (Rajasthan) Valuthalakudi Series (Tamil Nadu) Jagdishpur Bagha, Calcreous Soil (Bihar) Sorghum Islamnagar Series 3 & 4 (M.P) Typic Chromusterts (Maharashtra) Pearl Millet Medium Black Soil (A.P.) Black Calcareous Soils (Gujarat) Alluvial Soils (A.P.) Groundnut Light Soils of Kodad (A.P.) Black Calcareous Soils (Gujarat) Potato Sub Montane Soils (H.P.) Cotton Tulewal and Samana Series, Alluvial Soils (Punjab) Chickpea Rahra Series, Alluvial Soils (U.P.) Uttari Series, Typic Ustochrepts (U.P.)

(mg/kg) 100 75 67.5 190 117 120 58 76 110 86.6 64 71 112 110 100 95 60 50 48 71 47 71 81 240 335 95 60 160 60 65 120 50 137 105

Source: 55

Table 23 – Conditions for variable crop response to K application in low and high K soils Low soil available K but no crop response to K application ♦ ♦

Soil crop yields Sub-optimum NP application

♦

Micro nutrient deficiencies

♦

K contribution through irrigation water Leaf litter K contribution in legumes Sub-soil K contribution Relative low clay content and good % saturation Poor crop management Regular manure additions

♦ ♦ ♦ ♦ ♦

High soil available K but crops respond to K application ♦ High K demanding crops ♦ High yield levels with large K removals ♦ Low soil K release rates despite high soil K ♦ Balanced fertilisation ♦ Low % saturation ♦ No organic matter recycling ♦ Hybrids and HYVs ♦ Good crop management Indian Journal of Fertilisers, May 2014 75

balance sheet of K. Mining of K further go high if K budget of remaining states like North-East, Himachal Pradesh and Jammu & Kashmir are included. It is believed that about 12-13 mt of K is mined in Indian agriculture by considering fertiliser K as only input. However, by considering all the inputs of K, negative balance of K is 4 times lesser than the belief i.e., to the extent of 3 mt annually. Approaches were made to maintain K balance by increasing area under conservation agriculture (CA) practices, green leaf manuring and nonconventional K sources, which lead to further reduction in overall negative K balance in Indian agriculture (2.8 mt per annum). But, still total K mining in Indian agriculture is negative; therefore urgent notice is essential on K management for sustainable agriculture to meet food and fibre demand of India. Potassium management requires a thorough understanding of K forms in soil and their dynamics before recommendations. Nonexchangeable K has to be considered as it is a major K reserve in soil and contribute greatly to plant K uptake rather going only for NH 4 OAc-K expressed as exchangeable or readily available K. Nonexchangeable K contribution to crop K demand was ample to the extent of 90 percent, under K stress conditions. Measures of nonexchangeable K are sensitive to know the impacts due to cropping, K fertilisation and manuring as shown by the balance sheet of K under both short term and long term cropping systems and fertilisation. Soil ability to maintain the level of available K for easy uptake by crop plant depends on soil type, nature and intensity of cropping, the relative rate of removal and release of K from nonexchangeable source and the extent of fertiliser use. It is, therefore, advisable to regularly monitor the non-exchangeable K status of different soils and modify the current fertiliser practices to maintain soil fertility and to

Table 24 – Effect of suggested recommendations and response of K under different categories of exchangeable and non-exchangeable K Category Ex. K

Non Ex.K

No of districts 15

Suggested Recommendations

Response to K (Low/Medium/High)

I

Low

Low

II

Low

III

Low

IV

Medium Low

V

Medium Medium 115

VI

Medium High

172

Crops may not need immediate K additions.

VII

High

Low

1

VIII

High

Medium 24

IX

High

High

Long term cropping would need K additions after few years K application is not required immediately. K application is not required.

Reference

K fertilisation is must

High (Field crops) High (Brinjal) High (Potato) High (Mustard) High (Maize) High (Onion) High (Cabbage) High (Tomato) High (Potato) High (Finger millet) High (Groundnut, pearlmillet, maize, sunflower, sorghum)

33 24 15 23 11 7 47 22 36 3 54

Medium 18

K fertilisation is essential

High (Sunflower) High (Rice) High (Sugarcane)

51 5 4

High

2

K additions at critical stages Low (Rice) of crops improve yield levels. Low (Wheat) High (Cotton) High (Ginger)

44 44 64 40

58

Continuous cropping needs K addition at critical stages as nonexchangeable K fraction does not contribute to plant K nutrition substantially. Maintenance doses of K may be required for intensive cropping systems

High (Greengram) High (Banana)

55 2

High (Tobacco) High(Onion) High (Potato) Medium (Maize)

27 31 65 28

Low (Groundnut) Low (Chickpea) Medium (Sorghum) Low (Mustard) Low (Rice & wheat) High (Potato) Medium (Orange) Medium (Chilly) Medium (Soybean)

17 63 49 67 19 17 26 6 64

Low (Rice)

59

Low (Groundnut) Low (Maize) Low (Maize) Low (Rice) Low (Finger millet) Low (Maize) High (Banana) High (Banana)

17 17 17 59 17 17 37 8

129

Indian Journal of Fertilisers, May 2014 76

Table 25 – Contribution of irrigation water in crop K nutrition in different agro-ecosystems of India State/District

No of samples/Year

Punjab (Ferozepur) Tamil Nadu (Cauveri Delta) Gujarat (Bhavanagar) Uttar Pradesh (32 districts) West Bengal (Birbhum) Maharashtra (Nanded) Karnataka (Haveri) Karnataka (Kolar) Madhya Pradesh (Semli and Shyampura) Andhra Pradesh (ICRISAT, Patancheru) Rajasthan (Thana) Andhra Pradesh (Kothapalli) Rajasthan (Govardhanapura)

500 (2009) NA (2010) 220 (2013) 124 (2013) 142 (2013) 70 (2011) 13 (2006-08) 19 (2006-08) 12 (2006-08) 8 (2006-08) 11 (2006-08) 15 (2006-08) 8 (2006-08)

sustain the crop productivity. There is an urgent need for soil test calibration studies involving boiling nitric acid method of determining non-exchangeable K for arriving at fertiliser recommendations for crops on soils with different mineralogical composition. FUTURE LINE OF WORK 1. Characterisation of soils across different agro-ecological regions of country based on nonexchangeable K reserves to enable better K management under different cropping systems. 2. Studies related to K requirements of intensive cropping systems of different states to maintain K balance is essential. Information on K dynamics, its depletion or build up under intensive cropping systems is meager. This encourages urgent need to work out relationships between K uptake/ K recommendation/K supply.

Range of K concentration (mg/L)

K contribution (kg/ha) with 5 irrigations

K contribution (kg/ha) with 8 irrigations

Reference

1.9-96.3

3.8-192.6

6.1-308.2

43

1.0-9.5

2.0-19.0

3.2-30.4

10

0.0-54.6

0.0-109.2

0.0-174.7

38

2.0-13.0

4.0-26.0

6.4-41.6

47

0.5-2.5

1.0-5.0

1.6-8.0

0.1-0.6

0.20-1.2

0.32-1.9

21

0.9-1.2

1.8-2.4

2.9-3.8

54

4.2-5.1

8.4-10.2

13.4-16.3

1.0-4.2

2.0-8.4

3.2-13.4

1.73-7.05

3.5-14.1

5.4-22.6

6.0-9.0

12.0-18.0

19.2-28.8

0.14-0.97

0.28-1.9

0.45-3.1

4.2-7.4

8.4-14.8

13.4-23.7

3. Utilisation of the maps generated and districts identified in the present study in prioritizing regions for K fertiliser use. Need to link up these maps with predominant crops/cropping systems being followed in the different districts or regions, so that further fine tuning to K recommendations can be evolved. 4. Inclusion of new methodology for estimating non-exchangeable K in all soil testing laboratories situated across India. Continuous monitoring of both K fractions (exchangeable and nonexchangeable) in different soil types under predominant cropping systems is mandatory for better K management. 5. Preparation of balance sheets of soil K in different production systems and zones at least after every decade is required. For monitoring of K status/dynamics, and crop yield sustainability, new Indian Journal of Fertilisers, May 2014 77

long term fertiliser experiments may be initiated in each of nine categories of soils suggested in the present paper considering predominant soil types and cropping systems. REFERENCES 1. Agriculture Census. Dept. of Agriculture and Cooperation, Ministry of Agriculture, Government of India (2005-06). 2. Ahmad, F., Ashuman Kohli and Suraj Prakash. In International Symposium on Potassium Nutrition and Crop Quality. 4-5 March- 2014, Ranchi, Jharkhand (India) : pp. 8 (2014). 3. AICRPDA. All India Coordinated Research Project for Dryland Agriculture- Annual Report 201213. CRIDA, Hyderabad (2013). 4. Alam, M., Geeta Kumari, Sinha, S.K., Vipin Kumar and Khusboo Verma. International Symposium

Table 26 – General K recommendations for major crops in India Crop State Rice Andhra Pradesh Kerala Orissa Punjab Tamil Nadu West Bengal Wheat Bihar Haryana Punjab Uttar Pradesh West Bengal Sugarcane Andhra Pradesh Bihar Maharashtra Karnataka Tamil Nadu Uttar Pradesh Cotton Andhra Pradesh Gujarat Punjab Karnataka Potato Himachal Pradesh Punjab Uttar Pradesh West Bengal Tobacco Andhra Pradesh Gujarat Karnataka Tea Northeast South Coffee Karnataka Coconut Kerala Banana Maharashtra Tamil Nadu Grapes Karnataka Maharashtra Pineapple Assam Karnataka

General potash recommendation (Kg K2O/ ha)

30-45 in K-deficient and light soils 30-45 depending on variety and water regime 20-37 in Kharif, preferably in splits and 20-40 in Rabi depending on variety and soil fertility 30 38 for short duration varieties, 50 or medium-long duration varieties None to 60 depending on variety, season and soil test 25 for irrigated, timely sown crop 30-60 30-60 30 in absence of soil test. Split application One to 70 depending upon variety and soil test 112 in K-deficient soils 30 115-170 75-188 for planted or ratoon crop 112 in 3 splits to main planted crop 15-75 depending on region and soil fertility 40-50 in rice fallows and eastern irrigated zone 30-80 None 37.5 for irrigated, 30 rainfed 60 125 30-115 depending on region and soil test rating 60-160 depending on soil test rating 30-40 in heavy soils, 60-80 in light soils 30-40 75 for FCV, 25 for bidi tobacco 40-120 for mature tea 180 within year of pruning and 100-300 in other years depending upon yield level. Source of N also important in deciding K dose. 120 for bearing robusta yielding over 1 t/ha, 160 for bearing Arabica yielding over 1 t/ha 680 g/ adult palm for unirrigated tall, 1200 g/adult palm for irrigated tall and hybrids 600 g 330 g

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JainV. K. J. Potassium Res., 17: 98-100 (2001). 64. Vedhika Sahu, Goswami, R.G., and Chawhan Shaivalini, In International Symposium on Potassium Nutrition and Crop Quality. 4-5 March- 2014, Ranchi, Jharkhand (India). pp 115 (2014). 65. Yadav, L.M., Dwivedi, D.K. and Singh V.P. In International Symposium on Potassium Nutrition and Crop Quality. 4-5 March- 2014, Ranchi, Jharkhand (India). pp 84 (2014). 66. Yadav, S. R., Gaikwad, S. P. and Sardesai M. M., Rheedea 8 : 145 – 147 (1998). 67. Yadav, S.S., Abha Tikkoo and Singh J.P., J. Indian Soc. Soil Sci., 61 (2) : 107-111 (2013). 68. Yadav, S.S., Abha Tikkoo., Sultan Singh and Bikram Singh, J. Indian Soc. Soil Sci., 59 (2) : 164-168 (2011).

HANDBOOK ON FERTILISER USAGE NOVEMBER 2012 The last edition was published in 1994. Having realised the increasing need, the present edition has been brought out to provide updated information on various aspects of fertiliser use and crop nutrition. The wide ranges of topics covered in the hand book are : 14.Other Fertiliser Materials 15. Secondary Nutrients 16. Micronutrients 17. Soil Conditioners and Soil Amendments 18. Efficient Use of Fertilisers 19. Fertiliser and Water Management 20. Fertigation 21. Integrated Nutrient Supply System 22. Fertiliser Use and Crop Quality 23. Fertiliser Use and Environment 24. Climate Change and Agriculture 25. Economics of Fertiliser Use 26. Fertiliser Legislation and Quality Control

1. Fertilisers and Their Use 2. Plants Need Food 3. Understanding the Soil and Soils of India 4. Soil Fertility and its Maintenance 5. Organic Fertilisers 6. Bio-fertilisers 7. Fertilisers 8. Nitrogenous Fertilisers 9. Phosphatic Fertilisers 10. Potassic Fertilisers 11. Complex Fertilisers 12. Mixed Fertilisers 13. Specialty Fertilisers

Agricultural planners; extension staff of central and state governments, fertiliser industry, KVKs; scientists of ICAR/SAUs; agriculture students; farmers and staff of agencies involved in development of fertiliser and agriculture will find this revised edition very informative and useful.

Price per copy Rs. 400/- Outside India US $50 For your copies please write to:

THE FERTILISER ASSOCIATION OF INDIA FAI House, 10, Shaheed Jit Singh Marg, New Delhi-110067 Tel:011-46005211, 91-11-26567144 FAX: 91-11-26960052 Email: [email protected] Website: www.faidelhi.org Indian Journal of Fertilisers, May 2014 80

Indian J. Fert., Vol. 10 (5), pp.86-101 (16 pages)

Sulphur Management : Issues and Strategies I.Y.L.N. Murthy, A. Aziz Qureshi, S.N. Sudhakara Babu and K.S. Vara Prasad

Directorate of Oilseeds Research, Rajendranagar, Hyderabad 500 030

Sulphur is indispensible for higher agricultural production to meet the growing demands of food and nutrition. The large quantity requirement and removal of sulphur and its low use has caused widespread deficiencies and nutrient imbalance resulting in low use efficiencies of other nutrients and resources. The nature of sulphur element as anion and its involvement in various transformations affect its plant availability. Correct assessment of S status of soil of proper method and extractant is critical in attempting management to decide the source, method and time of application. Significant increases in yield and quality of crops are recorded due to S application. The residual effect of sulphur was significant and positive in wide range cropping systems and in ratoon crops of sugarcane. The build up soil S due to regular S application was cumulative that need consideration in S recommendations and management. Single super phosphate is the popular source of sulphur along with phosphorus besides gypsum, ammonium sulphate, ammonium phosphate sulphate and elemental sulphur. Organic matter maintenance, integrated use of S sources along with recommended N and P, use of Thiobacillus and PSM organisms can supplement meeting S requirement for sustainable S management. Newer sources of S like micronized S, liquified bentonite S with partial water solubility and slow release pattern would increase sulphur use efficiency, reduce its application with reduced cost and environmental impact. The synergistic and antagonistic responses of S with other nutrients need to be established for different soil types and critical concentrations in plant and soils. Long term effects of sulphur use in different soil types and cropping systems, assessing role of S in pest and disease management, remediation of heavy metal contaminations are the research priorities.

Introduction

S

ulphur (S) is becoming increasingly important in balanced nutrition of crops to meet the complete nutrient requirement resulting in higher use efficiency, reduction in cost and environmental impact (43). It provides a direct nutritive value to crops as essential plant nutrient; provides indirect nutritive value as soil amendments, especially for calcareous and saline alkali soils and improves the efficiency of other essential plant nutrients. S is best known for its role in forming amino acids methionine (21% S) and cysteine (27% S); synthesis of proteins and chlorophyll; oil content of the seeds and nutritive quality of forages (47,100). The nature of sulphur as plant nutrient, of its abundance in organic matter and the pressure of intensive crop cultivation under tropical and subtropical environment limits its natural supplying capacity (96). Adoption of high-yielding varieties and multiple cropping systems, higher fertiliser use is imperative to meet the nutrient needs of the growing population (77, 93). The demand projections of plant

nutrient needs for meeting the increased crop production is huge and the gap widens due to escalating costs and shortages, declining organic sources and crop residue returns. Broad discrepancies exist between global sulphur supply and demand leading to large stocks of sulphur are piling up at oil refineries around the world and the sulphur industry is engaged in enhancing its utility (65). Fertiliser industries consume large amounts of sulphur during manufacturing process. India and China being agriculture driven economies offer broad

opportunities for consumption of large quantities of sulphur in the form of sulphur-based fertilisers. The gap in sulphur fertiliser use to its crop removal is estimated to be more than 12 million tonnes (Figures 1 and 2) and Asia leads the table with highest requirement of sulphur (65,99). With high crop yields, S is removed in large amounts in quantities equal or more than P especially in crops and cropping systems involving oilseeds. Experience over the past four decades in India has shown that

Figure 1 – Plant Nutrient Sulphur Requirement and Deficit (Mt) Source : (65) Indian Journal of Fertilisers, May 2014 86

Figure 2 – Country wise sulphur deficit of plant nutrient sulphur

mismatch between crop production methods and resource characteristics has led to decline in soil fertility, increased soil losses, loss of biodiversity, disturbed ecological balance and build up of insect-pests and diseases (38). Balanced fertilisation has received considerable attention in recent years (4, 30, 31, 36). The information related to S management on issues and strategies too have been discussed in this paper. India is the third largest producer, second largest consumer, and largest importer of fertilisers in the world (108). The partial factor productivity for fertiliser (NPK) application has declined from 15kg food grain/kg fertiliser in 1974-79 to 6kg food grain/kg fertiliser in 2007-12 (Figure 3) mainly due to the nutrient imbalance due to the increasing deficiency of secondary and micronutrients. Sulphur has become a major nutrient after N and P limiting food production in India. Results of TSI-FAI-IFA study confirmed that sulphur deficiencies nation-wide are dramatic, and the S requirements are enormous. Amount of S needed to produce one tonne of seed is about 3-4 kg S for cereals (range 1-6); 8 kg S for legume crops (range 5-13); and 12 kg S for oil crops (range 5-20) (108). In

Source : (65)

intensive crop rotations, S uptake can be high, especially when the crop residue with economic produce is removed from the field (Table 1). This leads to large S depletion in soil if the similar amount of S is not applied through fertiliser. Owing to its widespread deficiency in most soil types, sulphur recommendation is evident for all crops (45, 46).

Significant crop responses to S application have been reported in different crops and regions (39). All the applied nutrients are not taken up by the crops and have inherent limitations as per the nature of element, soil reaction, availability of other nutrient elements, its reactivity and plant available form, crop, etc. The

Figure 3 – Declining factor productivity (fertiliser NPK) for food grains in India Source: (108) Indian Journal of Fertilisers, May 2014 87

Table 1 – Crop removals of sulphur and other nutrients in crop production Crop

Yield

Nitrogen

(t/ha)

(kg/ha)

Phosphorus Potassium Sulphur (kg/ha)

(kg/ha)

(kg/ha)

Rice

7 (grain)

150

25

150

20

Wheat

4 (grain)

168

34

110

25

Corn

9 (grain)

360

52

230

50

Soybean

2.5 (seed)

200

25

110

15

Rapeseed

2.0 (seed)

90

16

110

35

Groundnut

3.5 (pod)

250

22

110

28

Cotton

1.5 (lint)

140

37

85

30

Sunflower

2.0 (seed)

75

7

35

25

Sesa me

1.2 (seed)

62

24

64

20

Linseed

1.6 (seed)

96

13

72

9

Oil Palm

20 (FFB)

193

36

249

75

Source: (101)

general use efficiency of sulphur is only 8-12% (Table 2) (69) and thus proper management of the nutrient is essential. Bottlenecks and strategies for increasing nutrient use efficiency can be well understood by analyzing the pathways of nutrients reaching the plant roots and its uptake and incorporation in plant tissues. Both these processes can be delineated as the factors external to plant and the factors internal to plant (43). Large acreage under cultivation is suffering from hidden hunger for one or more nutrients and/or soil related problems limiting complete nutrient supply to crops. S deficiency is becoming widespread in tropical and Table 2 – Nutrient use efficiency in India Nutrient

Efficiency (%)

Nitrogen

30-50

Phosphorus

15-20

Potassium

70-80

Sulphur

8-12

Zinc

2-5

Iron

1-2

Copper

1-2

Source: (69)

subtropical climatic regions throughout the world and especially in India because of the high temperature based oxidation of soil organic matter, use of highanalysis low S fertilisers, low S returns through farmyard manure and crop residue, high S removal from high yielding varieties and intensive agriculture, declining use of S containing fungicides and reduced atmospheric input caused by stricter emission regulation. Sulphur Transformations and Availability to Crops Sulphur is the most abundant and widely distributed element in the nature and found both in free as well as combined states. Sulphur, like nitrogen is an essential element for all living systems. In the soil, S is in the organic form (S containing amino acids-cystine, methionine, proteins, polypeptides, biotin, thiamine etc) which is metabolized by soil microorganisms to make it available in an inorganic form (sulphur, sulphates, sulphite, thiosulphate, etc.) for plant nutrition. Of the total S present in soil only 10-15% is in the inorganic form (sulphate) and about 75-90 % is in organic form. Cycling of S is similar to that of nitrogen. Transformation/ cycling of S between organic and elemental Indian Journal of Fertilisers, May 2014 88

states and between oxidized and reduced states is brought about by various microorganisms, specially bacteria. Thus, the conversion of organically bound S to the inorganic state by microorganisms is termed as “mineralization of S”. The sulphur/ sulphate, thus released are absorbed by either the plants or escapes to the atmosphere in the form of oxides. Most soil sources of S are in the organic matter and are therefore concentrated in the topsoil or plough layer. Available S status correlated positively with organic carbon and negatively with the pH of the soils of Sirsa district under paddy-wheat cropping system (65). Elemental S and other forms as found in some fertilisers are not readily available to crops. They must be converted (oxidized) to the sulphate (SO 42- ) form to become available to the crop. This conversion is performed by soil microbes and therefore requires soil conditions that are warm, moist, and good drainage (aeration) to proceed rapidly. The sulphate form of S is an anion (negative charge), and therefore is leachable. As a rough rule-of-thumb, S can leach through the soil profile at about 50% as fast as nitrates (NO 3-). In soils with a significant and restrictive clay layer in the sub-soil, it is common to find that sulphate which has leached through the soil over time and become “perched” on the clay layer. This SO42- is available to crops when the roots reach this area of the soil. Various transformations of the S in soil results mainly due to microbial activity, although some chemical transformations are also possible (e.g. oxidation of iron sulphide) the major types of transformations involved in the cycling of S are: 1. Mineralisation : The decomposition of large organic S compounds to smaller units and their conversion into inorganic compounds (sulphates) by the microorganisms. The rate of S mineralization is about 1.0 to 10.0 per cent per year.

2. Immobilisation: Microbial conversion of inorganic S compounds to organic S compounds and incorporation into microbial biomass. 3. Oxidation: Oxidation of elemental S and inorganic S compounds (such as H 2S, sulphite and thiosulphate) to sulphate (SO 4 2- ) is brought about by chemoautotrophic and photosynthetic bacteria. When plant and animal proteins are degraded, the S is released from the amino acids and accumulates in the soil, which is then oxidized to sulphates in the presence of oxygen, and under anaerobic condition (water-logged soils) organic S is decomposed to produce hydrogen sulphide (H 2S). H2S can also accumulate during the reduction of sulphates under anaerobic conditions, which can be further oxidized to sulphates under aerobic conditions. Sometimes, sulphide injury to rice noticed under extreme situations of high H2S accumulation. During the process of oxidation of elemental S to sulphate (SO 4 2- ), sulphuric acid is released and it is beneficial in different ways: i) as it is the anion of strong mineral acid (H2SO4) can render alkali soils fit for cultivation by correcting soil pH ii) solubilize inorganic salts containing plant nutrients and thereby increase the level of soluble phosphate, potassium, calcium, magnesium etc. for plant nutrition. 4. Reduction of Sulphate: Sulphate in the soil is assimilated by plants and microorganisms and incorporated into proteins. This is known as “assimilatory sulphate reduction”. Sulphate can also be reduced to hydrogen sulphide (H2S) by sulphate reducing bacteria (e.g. Desulfovibrio and Desulfatomaculum) and may diminish the availability of S for plant nutrition known as “dissimilatory sulphate reduction” which is not desirable for soil fertility and agricultural productivity. Isotopic pool dilution using

35

S

offers a tool that may prove valuable in understanding and modelling soil S turnover. The rates of sulphur (S) released to and removed from the soil inorganic pool using the isotopic dilution technique were estimated (22) and concluded that 35 S recovery was inadequate prior to day 2 and remineralisation of immobilised 35 S occurred after day 8. Thus estimates of gross S transformation rates should be based on data sampled between days 2 and 8. Gross S mineralisation varied from 0.914.9 micro g S/g soil/d, whereas gross immobilisation only varied from 0.5 to 3.1 micro g S/g/d. Gross S immobilisation was strongly correlated to the C/S ratio of the plant material, whereas gross S mineralisation showed a weaker, but still significant, correlation with lignin content. The results indicate that immobilisation may predominantly have been a biological process in response to carbon addition while early mineralisation may have been dominated by the biochemical hydrolysis of organic sulphates in the residues.

uptake, removal by leaching, and the impact of environmental factors on the rate of mineralization of organic S. Fluctuation in amounts of soluble sulphate in subsoil horizons may also occur because of leaching. Soluble sulphate often increases with depth in the profile and in same soils.

Soil Sulphur

Soils of the arid and semi-arid regions of the state have low total reserves of sulphur because of low organic matter content and its rapid mineralization resulting in leaching losses of sulphur. Light textured soils suffer most from the problem of S deficiency. Crop rotations with high S requirement as of oilseeds and pulses, or of high yielding varieties and at sites away from industrial activity with low SO 2 emissions show S deficiency. More than 75% of agricultural land is deficient or likely deficient. With more and more soils tested for soil fertility, more is the glaring S deficiency. In India, 45, 40 and 15% of soil samples collected from 240 districts exhibited, respectively >40%, 20-40% and 1000ppm. Alluvial soils of Bihar show high S levels of around 500ppm. Though total S content shows high values the plant requiring organic and available S status is low in most parts of India. Organic S which constitutes up to 98% of total S dominantly controls the levels of plant available S. Water soluble, adsorbed on soil colloids and organic or humus held S forms labile pool of S and will be in dynamic equilibrium, the mobility modified by the soil solution and mass flow.

Sulphur deficiency in Indian soils has been on the increase since the adoption of intensive agricultural practices. The deficiency, which noticed many years ago only in few localized areas, has engulfed much larger areas in its fold today. Presently, the response to S fertilisation is seen not only in high S demanding oilseed, legume and pulse crops, but also in cereal, fodder, cash and plantation crops largely in intensively cultivated or coarse textured soil. In mid 1990s about 51 million hectares or about 30% of cultivated area in the country experienced varying degrees of S deficiency (102). Extensive soil surveys in India have revealed that S deficiency varies from 15 to 83% with an overall average of 46% (Table 3) (92). Most of the alluvial soils of the Indo-Gangetic Plains (IGP) were found deficient with respect to plant available S. Continuous mining of S from soils has led to widespread S deficiency and negative soil budget in IGP India. Low S levels in Indian soils is regularly the main reason for low yield of cereals, pulses, oilseeds and commercial crops due to its involvement in the assimilation of nitrogen, photosynthesis, in synthesis of proteins and Scontaining amino acids. The widespread S deficiency in Indian soils depends more on climate, vegetation, parent material, soil texture, and management practices (28). The addition of S to alkali soil decreased the pH value and improved the chemical properties of the soil besides improving the yield and its related characteristics (54).

Table 3 – Extent of sulphur deficiencies in different states of India State No. samples % Samples in category Andhra Pradesh

1880

low 56

Karnataka Tamil Nadu

1703 1716

43 26

32 41

25 33

Kerala Bihar

5990 600

81 26

18 30

1 44

Orissa Jharkhand

2261 809

21 51

24 31

55 18

West Bengal Madhya Pradesh

6438 2000

39 33

36 55

25 12

Chhattisgarh Gujarat

1492 3016

23 33

38 29

39 38

Maharashtra Rajasthan

1045 4921

39 65

27 18

34 17

Uttar Pradesh Uttarakhand

6250 1558

49 42

38 41

13 17

Haryana Punjab

1515 3750

38 15

36 19

26 66

2250 49194

84 46

16 30

0 24

Himachal Pradesh All India

low soil temperatures slow this process. ♦ Poor Drainage: The conversion

of various forms of S to the available sulphate (SO42-) form is a microbial process requiring oxygen, therefore saturated soil slow this process. Pollution: Soil that, over the years, has been subject to high levels of deposition from industrial sources of S. ♦

Factors Affecting S Availability ♦ Sand: S is leachable, sandy soils

♦ SO 42-:NH 4 applications: Added

♦ Soil Organic Matter: Organic

♦

NH 4 has been shown to appreciably enhance the uptake of SO42-

matter is a reservoir for S

Criterion for Sulphur Deficiency Delineation

Soil Temperature: The conversion of various forms of S to the available sulphate (SO 42-) form is a microbial process; therefore

The critical limits of S in soils differed in relation to variation in extraction capacities of different

♦

High 10

Source: (92)

Irrigation Water: Irrigation water may contain high levels of S, and excess irrigation of sands can leach S out of the root zone.

are typically low in OM, therefore these soils are often low in S.

Medium 34

Indian Journal of Fertilisers, May 2014 90

extractants (101). The lack of an accurate predictive test for sulphur deficiency will lead to the continuation of sulphur application in both situations where they are not needed and, in some cases, the lack of applications in situations where they are needed. Efficiencies of S utilization and recovery differ due to different S carriers and other aspects of S nutrition of crops. It has been shown that in a given soil and with a given extractant, critical levels are different for different crops and varieties. The critical limits of S in soils differed in relation to variation in extraction capacities of different extractants (105). The critical level of S varies from as low as 5 ppm to as high as 30ppm. Among the extractants, 0.15% CaCl 2 is most commonly used and the operational criterion for field assessment is considered as 10ppm below which the soil is considered as deficient. Broadly, about 16% of black soils, 26% of alluvial soils and 43% of red and lateritic soils were deficient in S. District wise S

deficiency has been delineated in the country (101). The sulphur status in West Bengal was delineated and expressed as Nutrient Index (NI) for S ratings (9). Intensive cultivation with S free fertilisers caused S deficiency. An improved model for the risk assessment of sulphur deficiency was showed (70) in winter wheat based on agronomic, pedologic and climatic criteria that explained 84% of yield variability in response to sulphur application. The malate test, which measures the malate: sulphate ratio in leaf tissue, was reported as more successful indication (14) of the likelihood of a significant yield response to a sulphur application than the soil S ppm test. The magnitude of response was high in soils with critical sulphur availability index 5.99 to predict field response of raya to applied S in the soils of wet temperate and humid subtropical zone of Himachal Pradesh (74). The critical level of S in plant varies with the age. In general, higher concentration of S is seen during vegetative stage. There was variability in S uptake efficiency among the genotypes. While the critical levels of S in most crops fall in the range of 0.24 to 0.35%, the sufficiency level for optimum yield and quality varies with the crops and varieties. Critical concentration of S in plants in India was reviewed (101). In general, the average S content in cruciferous oilseeds was 1.195 in seeds and 0.13% in straw; in sunflower/sesame, it was 0.34% and 0.22%,; in legumes, it was 0.24% and 0.20%, respectively in seed and straw. Most of the S monitoring studies consider the extractable soil S at the beginning of the experiment to use as an index of soil S status that bear little or no relationship to the S taken up by plants during the entire growing season. Soils with available S less than 10 ppm (NH4OAC extractable or 1% CaCl 2) responded significantly to added S irrespective of the soils and the

crops, the magnitude of response, however, differed according to crops being higher in pulses and oilseeds than in cereals. The changes in extractable soil S with time were investigated (32) and related these to changes in plant S uptake in six soils with different long-term fertiliser histories using carrier-free 35 SO 4 -S to predict plant-available S. These results suggest that plants take up S from soil from the labile pool of S the quantity determined/varied by the extraction method. The continued S uptake after 8 weeks despite the low labile S pool was originated directly from the mineralization of soil organic S from S pools other than those present in the extractable soil S forms. Nitrogen : Sulphur Ratio - As the response of S and N in plants are similar, monitoring of N:S ratio in plants gives better indication of magnitude of the problem. A proper N:S balance is important for crop production. When N is in excess (high N:S ratio), there is insufficient S to combine with the N to make protein, and thus nonprotein N accumulates. N:S ratios vary as per the crops and varieties. Soybean plants with an N:S ratio of 16.5 was critical while a N:S ratio of 10:1 or narrower is optimum for forage crops. In groundnut highest pod yields were realised with a N:S ratio of 10:1. The N:S ratio only indicates the relative proportions of N and S in the plant, and does not indicate their actual magnitudes. Even if crop tissue tests show an optimal N:S ratios, there are three possibilities: both N and S levels are optimal, excessive, or deficient. For precise management, tissue testing for S status should include several criteria to improve the reliability percent S greater than the critical level; N:S ratio of 10 or less; a sulphate: total S ratio greater than 0.38. Liming with calcium carbonate caused a distinct decrease in S-SO 4 content in the soil. (58). Phosphate:sulphur ratio of 1:2 was substantially effective with Indian Journal of Fertilisers, May 2014 91

respect to acidifying effect of S on rock phosphate dissolution and consequently the uptake of phosphorus and plant biomass. Further, the interactions between sources x phosphorus levels, sources x P:S ratios and P:S ratio x P levels were also found significant with respect to dry matter yield and P uptake (18). S fertiliser could be efficiently utilised by saving up to 25 kg S/ha due to the inoculation of S-oxidizing microorganisms (Aspergillus terreus, Myrothecium cinctum and Scolecobasidium constrictum, inoculated at a rate of 250 ml/pot) (85). Sulphur requirements nation-wide in India are dramatic, and conclusive almost all trials responded to sulphur fertiliser with crop yield increases from 14 percent to 60 percent; Optimum sulphur fertiliser dose varied between 30 and 45 kg/ha. Economic returns from sulphur fertiliser use were very attractive (109). Direct and Residual Effects of S in Cropping Systems Sulphur application can benefit more than one crop in a sequence and produce a significant residual response. In FAO S network trials conducted in India at several locations, spectacular direct and indirect responses to S application was observed in different cropping system. It was found that crops responded equally to direct applications and residual effects of S. It was observed that crops directly fertilised contributed 47 to 82 % to the rotational response, while crops raised on residual contributed 18 to 53% response (Table 4). Residual effect due to application of 40 kg S ha-1 either to chickpea and lentil crops was reported (7) to have almost doubled the grain yield of the following crop green gram. In a wheat-groundnut cropping system in alluvial soils, wheat was benefitted from residual S (22% yield increase) than did wheat after rice, where the yield increase was 7% (106). Sulphur

deficiency

can

be

Table 4 – Direct and rotational response to sulphur in cropping systems Crop receiving S

Succeeding crop

Rice Groundnut

Mustard Wheat

Groundnut Wheat

Groundnut Groundnut

kg/ha/year

Rotational response Direct Residual

1066 1186

82% 56%

18% 44%

299 933

47% 80%

53% 20%

Source: (11)

corrected by applying Scontaining materials and significant residual effects have also been reported at all levels of application. Thus, S does not need to be applied every season (19). S fertiliser, besides enhancing yield and quality of crops, enhances nutrient uptake and fertiliser use efficiency through interaction of S with other fertiliser nutrients, from 4 to 39.2% increases in N use efficiency and from 5.4 to 10.5% in P use efficiencies (66, 103). Field studies in Alfisols at Hyderabad evaluated the direct and residual response of sulphur through SSP on rice-sunflower and sunflower-groundnut cropping systems. The direct effect of sulphur through single superphosphate on hybrid rice

resulted a significant increase of 21% in grain yield with a S use efficiency of 13 kg grain/kg at 45 kg S/ha (Figure 4). The residual effect of this on succeeding sunflower crop resulted in 37% increase in seed yield and 45% increase in oil yield. The value cost ratio (VCR) for direct and residual effects were 35 and 23 with a cropping system VCR of 58. In sunflower – groundnut cropping system, the direct effect of sulphur through single superphosphate on hybrid sunflower resulted in significant increase of 34% in seed yield and 44% in oil yield with a S use efficiency of 8.6 kg seed/kg at 45 kg S/ha (Figure 5). The residual effect of this on succeeding groundnut crop resulted in 21% increase in pod yield and 26% increase in oil yield. The VCR for direct and

residual effects were 17 and 34 with a cropping system VCR of 52. (96, 97, 40, 98). The release of S from the compost was high in the first year after compost application and then declined in each subsequent year suggesting that an application frequency of once in every second year may be better than the once in every four year application strategy, especially with 100 t/ha application rate (112). Sulphur applied in sugarcane plant crop improved the yield of ratoon as well. An increase of 20.89% in ratoon yield was observed from 0 to 80 kg S/ha applied to plant crop (90). Changes and dynamics of available sulphur status in soil due to sulphur applications was studied in Alfisols in rice – sunflower and sunflower – groundnut cropping systems (97). There was significant negative balance of sulphur with each year of crop production in rice – sunflower cropping system without application of sulphur, while the build up was marginal at 15kg S/ha (Figure 6). At 30 and 45 kg S/ha, the build up was high over the study period of three years. Contrastingly, under

Figure 4 – Direct and Residual effect of sulphur (SSP) in Rice – Sunflower Cropping system in Alfisols Source: (97) Indian Journal of Fertilisers, May 2014 92

Figure 5 – Direct and residual effect of sulphur (SSP) in sunflower - grounndut cropping system in Alfisols Source: (97)

sunflower – groundnut cropping system, even without applying sulphur, there was no negative balance while the sulphur accumulation increased significantly with 15 to 45 kg S/ha (Figure 7). This is due to the fact that with groundnut crop leaving all its foliage biomass back in soil has caused to maintain critical

sulphur level in the soil while with rice – sunflower cropping system due to the complete removal of crop biomass (above ground), there was net negative balance. It was reported(112) that the release of N and S from the compost was high in the first year after compost application and then

declined in each subsequent year suggesting that an application frequency of once in every second year may be better than the once in every four year application strategy, especially with 100 t/ha application rate whereas, While the release of phosphorus from compost was steady throughout the four-year experimental time.

Figure 6 – Soil S balance due to S applications in rice-sunflower cropping system in Alfisols (2000 to 2002) Source: (97) Indian Journal of Fertilisers, May 2014 93

Figure 7 – Soil S balance due to S applications in sunflower – groundnut cropping system in Alfisols (2000 to 2002) Source: (97)

Sulphur and Nitrogen in Relation to Yield and Quality of Crops: Both S and N has central role in the synthesis of proteins, the supplies of these nutrients in plants are highly inter-related. Sulphur and nitrogen relationships were established in many studies (64, 1, 46, 45, 48) in terms of dry matter and yield in several crops. A shortage in the supply of S to the crops lowers the utilisation of the available soil nitrogen, thereby increasing nitrate-leaching (60). It has been established that for every 15 parts of N in protein there is 1 part of S, which implies that, the N: S ratio is fixed within a narrow range of 15:1. The N: S ratio in the whole plant in general is 20:1 (17). In wheat crop, the yield increased linearly in the S and N interaction study (78) with increased N application. It was further suggested that S concentration of 0.2% and a N/S ratio of 18 in the flag leaf is sufficient for obtaining higher yields. Demonstration in barley plants indicated that at the whole plant level the apparent matching of supply to demand is accompanied by an apparent linkage of SO42- to NO3- uptake (15). Sulphur and nitrogen both are required for the synthesis of protein, therefore, the ratio of total N to total S in plant tissue can

reflect the ability of N and S in protein synthesis (13). Thus, a change in the ratio of reduced-N to reduced-S (NR/SR), which is a reflection of the amount of S-amino acids, suggests that protein metabolism has been significantly altered and has important implications for protein quality (27). Balanced fertilisation for increasing nutritional quality in oilseeds was also reviewed (41). Increased bulb yield of onion due to sulphur along with nitrogen was showed when slow release ammonium sulphate was applied as N source over urea and normal ammonium sulphate (72). The optimum onion yield and quality was recorded when the nutrient solution contained N 16.0 mmol/L and S 3.4 mmol/L but the same began to decrease when the sulphur concentration reached to 6.69 mmol/L (56). When the supply of N was limiting, S applications increased the barley quality parameters but decreased grain N concentration due to a dilution effect as a result of increased grain yield. In some cases, S applications resulted in decreased grain size (113).

(44) linseed (110) Groundnut (48) and Soybean (46). Decrease of 30% in cysteine and methionine concentration in seeds of S deficient but N sufficient sunflower plants has bee reported(44). S response and requirements between alfalfa, rape and barley was compared (8). Barley was the most responsive to applied S, although it had the lowest concentration of S (0.15 mg S g-1 dry herbage) and highest plant N: S ratio (16) at its highest yield. Similarly, the N: S ratio of 15.6, 3.1, 14.8 and 7.1 in grain for maximum response to S in maize, mustard, groundnut and wheat, respectively was reported(20).

A strong interaction of S and N for seed yield was found in rapeseed and mustard (26, 25), sunflower

A positive role of sulphate in regulating nitrate reductase an enzyme that perform the rate

Indian Journal of Fertilisers, May 2014 94

Under S deficiency conditions S and N concentrations as well as the amounts of glucose and sucrose in shoots and nodules in peas (Pisum sativum L.) were significantly reduced. It was assessed that the reduced amounts of available photosynthate with suboptimal S supply could become limiting to energy production and as carbon skeletons for ammonia assimilation, and therefore cause a lower N 2 fixation and a reduced yield formation (82).

limiting step of the nitrate assimilation pathway has been postulated. The role of availability of sulphur in regulating nitrate reductase was shown (2) in addition to its role in regulating ATP-sulphurylase. Moreover, nitrogen availability has a role in regulating ATP-sulphurylase as well as in regulating nitrate reductase. The synthesis of cysteine because of the incorporation of sulphide moiety into oacetylserine appears to be the meeting point between N-and S metabolism. Naturally occurring thiol compounds viz., cysteine and glutathione were shown to influence nitrate reductase activity in wheat and Brassica (59). Application of elemental S gave the highest number of millable canes (102.00 per ha), cane length (244.8 cm), cane diameter (2.53 cm), cane weight (1138.8 g), cane yield (83.50 t/ha) and commercial cane sugar (9.96 t/ha). Single superphosphate gave the highest pol % juice (17.63) and juice purity (87.41%) while gypsum gave the highest germination (51.29%) (91) Sulphur Fertilisation Microbial Interaction

and

Sulphur application (40 kg/ha) with Rhizobium inoculation in green gram, increased the bacterial population significantly (67, 68). The mean total number of nodules and active nodules significantly increased with application of S only up to 20 Kg S ha -1 but beyond the 20 kgha -1, the mean nodule production reached a plateau and did not increase further (29). ). It has also been reported (48, 61) that S is specifically involved in nitrogen fixation in legumes and S additions significantly increased N2 fixation, nodule weight plant -1, nodule weight per unit weight of root and N 2 -fixation per unit weight nodule. S fertiliser could be efficiently utilised by saving up to 25 kg S/ha due to the inoculation of S-oxidizing microorganisms (mixed culture of S-oxidizing microorganisms - Aspergillus terreus, Myrothecium cinctum and

Scolecobasidium constrictum inoculated at 250ml/pot) in terms of S equivalence of groundnut yield (85). The application of sulphur and PSM significantly increased the yield attributes (number of nodules per plant, number of pods per plant, pod weight per plant and seed index) and yields of groundnut (phytomass, pod, haulm yields and harvest index) except the number of kernels per pod (71). Inoculation with Thiobacillus increased the yield and improved the quality and the nutritional status of sugarbeets (6). Sulphur Interactions in Soil Interactions of S with N, P, Zn, B and Mo were studied in Uttar Pradesh across the crop responses(105). Significant positive interaction was observed between N x S. Interaction between P x S was significantly negative. Increasing supply of S to soil caused significant decrease in Zn, B and Mo contents in plant tissues. The critical limits of S in soils differed in relation to variation in extraction capacities of different extractants. Sulphur and Nitrogen: Intensive agriculture coupled with the use of improved cultivars and high analysis fertilisation offers conditions of nutrients exhaustion resulting in nutrient imbalance in soils. The lack of S was reported to limit the efficiency of added N(26); therefore, S addition becomes necessary to achieve maximum efficiency of applied nitrogenous fertiliser. A high N: S ratio (produced by addition of N) was reported to result in a decrease rate of mineralization of S in the soil sample during incubation (57). The optimum ratio of available N to available S as 7:1 has been indicated in soil (49). Ratios below 7 gave the reduced seed yields. A rapeseed and mustard crop under field conditions recovered 27-31% of added S without N, but 37-38% with 60 kg N ha-1 (80). Significant S and N interaction in winter wheat Indian Journal of Fertilisers, May 2014 95

was noted (86) . The crop did not respond to S application when N was deficient of optimum, and S applied with excess N increased straw but not grain yield. Combined effect of S and N enhanced the growth, yield and quality of canola. Maximum seed yield and oil content were obtained when the crop was fertilised @ 40 kg ha-1 S and 120 kg ha-1 N (81). In two cultivars of oilseed rape (Brassica napus), Hyola 308 and application of nitrogen did affect biological yield positively but it did not affect grain weight. The increase in dry matter production or biological yield was 14% when the amount of nitrogen fertiliser increased from 150 to 300 kg/ha. Sulphur application affected neither dry matter production nor grain weight. Two cultivars were significantly different for oil contents. Nitrogen affected the oil content negatively and decreased it by 3.3%. Increasing the amount of sulphur fertiliser from zero to 200 kg ha-1 resulted in an increase in oil content (24). The sulphur contents are influenced not only by sulphur fertilisers, but nitrogen fertilisers as well. Due to the strong N-S relationships, fluctuations in protein contents also caused decreases/increases in the sulphur contents of the wheat grain. The NS relationship could be described by using a mathematical linear function. Annual applications of 100 kg/ha superphosphate, containing more than 10 kg sulphur, provide sufficient sulphur to produce a 5 t/ha grain yield of wheat (33). Sulphur and phosphorous: Legumes and pulses usually require almost equal amounts of P and S. When P and S are present below the critical level in soil, plant growth and quality of production are affected adversely (21). Sulphur oxidation through soil microbes lead to production of sulphuric acid (H 2SO 4) which solubilises P. The acidity generated on oxidation of pyrite can be coupled to

solubilisation of rock phosphate or to reclaim alkali soil (52). The solubilisation of mussoorie rocks phosphate on addition of elemental S and pyrite and on inoculation with S and Fe-oxidising bacteria in soil was studied (51, 16). Application of 40 kg S along with a 40 kg P 2O5 ha -1 resulted in higher grain yield than S alone in chickpea (87). The synergistic effect of phosphorus and sulphur was reported on number and weight of nodules plant-1 , N, P, S and protein content of cluster bean (111). Thus, P and S are reported to have synergistic effect on the productivity of pulse crops.

and selenate (SeO 42- ), their most chemically stable forms in aerated neutral and near-neutral soils. It was indicated that application of Se with increasing rate produced an antagonistic effect on S assimilation. An amount of 20 kg Se ha –1 drastically reduced the S content in onion bulbs as well as the S controlled biochemical quality parameters namely pungency, enzymatically released pyruvic acid and quercetin. On the other hand, with increased S levels, the Se concentration decreased significantly (73).

The contents of reducing sugar and non-reducing sugar, and the total sugar content in soybean increased with 40 and 80 mg S and these parameters, however, decreased with 120 mg S per pot (3).

Combined application of S and N resulted in increased oil accumulation in the taramira (Eruca sativa Mill.) seeds right from the initial stage (26). The maximum increase was observed, when S and N were applied in three splits. There was a strong positive correlation between S and oil content in the seeds. S and N application in three splits resulted in the increased oleic acid (18:1) content, while decreased erucic acid (22:1) content over other treatments. Reduction in 22:1/18:1 fatty acid ratio in the oil resulted in improved quality of oil. Whereas the quality of Indian mustard cv. Varuna, oil, glucosinolate and protein contents were higher at 60 kg P and S/ha and 30 kg Zn/ha in both years. On the contrary, oil constants, i.e. refractive index, iodine value and acid value, were significantly reduced by the application of P, S and Zn in both years (88). Application of S at 40 kg/ha had no significant effect on yield and other traits, including oil content of

Sulphur and Micronutrients: Application of sulphur showed synergistic interaction with zinc and improved crop growth parameters, biomass production, number of capsule, seed output and reproductive capacity with grain biological yield (10). Combined application of sulphur along with micronutrients (Zn and Fe) had significant influenced on the growth, yield and nutrient uptake by safflower. Application of 30 kg S per ha along with foliar spray of Fe + Zn recorded the highest growth, yield and nutrient uptake (76). The highest yield and nutrient uptake in groundnut were noticed when plants treated with sulphur (S) combined with foliar spraying with Zn + B (50) .Sulphur can, in some crops, effectively reduce the possibility of Copper toxicity by creating Cu-S complexes. Anions tend to compete with other anions in terms of availability and plant uptake. Therefore, excess sulphate-S (SO 42-) can reduce the uptake of some anions such as available form of molybdenum (MoO4-) and selenate (SeO42-). Interaction between S and Se (selenium) uptake and assimilation by plants is expected, particularly when anions of S and Se are present as SO4 2– (Sulphate)

Sulphur and Crop Quality

Brassica napus. Increased S uptake resulted in a significant enhancement of glucosinolate content (3%) (89). Sulphur deficiency decreases grain size and baking quality because of formation of disulfide bonds formed from the sulphydryl groups of cysteine and this effects the viscoelasticity of dough (33). Elemental S gave the highest CCS percentage while single superphosphate gave the highest Brix percentage, pol percentage and purity percentage. Gypsum gave the highest cane yield, number of millable canes and CCS (84). It has been reported in sugarcane (104) that green tops had significant positive correlation with sulphur content in the stem and negative association with juice sucrose content. Sulphur content in the stem was associated significantly and negatively with sucrose content and sugar yield. Cane yield and sugar yield significantly increased up to 40 kg S/ha in Madhya Pradesh. S at 60 kg/ ha enhanced the quality of juice, N and K contents of juice, and N and K uptake. S at 80 kg/ha resulted in higher P and S contents of juice, P and S uptake, and available soil S status (107). Significant crop responses to S, Zn and B application have been reported in different crops and regions ( 40). The benefit due to S application along with recommended NPK in hybrid rice (DRRH-1) is due to two pronged responses of reduction in chaff and increase in harvest index (Table 5) (97). The chaff percentage has reduced from 20.5 % to 12-13% and the harvest index increased

Table 5 – Direct effect of fertiliser sulphur on hybrid rice in Alfisols Treatment NPK NPK S NPK S15 NPK S30 45 CD (P=0.05)

Grain yield (kg/ha) 6699 7648 7790 8123 588

Percent response 14.2 16.3 21.3

Straw Percent yield response (kg/ha) 5900 6817 4.1 7088 7.9 7461 12.6 1148

Source: (97) Indian Journal of Fertilisers, May 2014 96

Chaff (%) 20.5 13.0 13.3 12.7

Harvest Index (%) 31 33 34 35

from 31% to 35%. The percentage of increase due to S application was higher for grain yield (14 to 21%) compared to the increase in straw yield ranging from 4 to 13%, due to application of S at 15 to 45 kg/ha over the recommended NPK. A significant and antagonistic interaction of Cd and S was observed in mustard plant wherein S could alleviate the Cd induced impairment of biochemical and anatomical features of the plant and the enhancement of nitrate accumulation in the leaves (5). Role of Sulphur Management

in

Pest

The effect of sulphur application on the infection of potato tubers with common scab (Streptomyces scabies [S. scabiei]) and stem canker (Rhizoctonia solani) revealed that the highest tuber yield was obtained with the application of 25 kg ha-1 in sulphate form and 50 kg ha -1 in elemental form. The tuber yield was negatively correlated with the infection of tubers by common scab and stem cancer. The application of sulphur (particularly in elemental form) decreased the reaction of soil (pH) and as a consequence decreased the infections of potato tubers by S. scabies and R. solani. The sulphur application increased the sulphur content in the dry mass of tubers and eventually increased potato resistance against infection of stem cancer (55). The interaction of sulphur dioxide (0.2 ppm) and seed gall nematode, Anguina tritici, (83) reported that none or few cockles were formed when nematode inoculated plants were exposed to SO 2 . The antagonistic interaction was observed between nematode and SO2 when both combined together. In field and greenhouse studies chicken manure alone or with sulphur at all tested rates was effective in reducing Orobanche growth and infestation early in the season in comparison with the control and significantly reduced the dry weight of Orobanche and increased aubergine and potato

yield compared with the control (34). Sclerotinia rot (S. sclerotiorum) on mustard (Brassica juncea cultivars Kranti and TERI M-21) disease incidence was reduced at 40 kg S/ ha in combination with 120 kg N/ ha (79). Bloem et al (2004) studies the mechanisms of this sulphurinduced resistance (SIR) are, however, not yet known. Volatile S compounds are thought to play an important role because H2S is toxic to fungi. S fertilisation significantly increased the contents of total S, sulphate, organic S, cysteine, and glutathione in the plants, but decreased LCD activity. Infection with P. brassicae increased cysteine and glutathione contents, as well as the activity of LCD. Therefore crops were able to react to a fungal infection with a greater potential to release H2S, which is reflected by an increasing LCD activity with fungal infection. Management of Sulphur in Coarse Textured Soils Coarse textured soils are found to be deficient in available sulphur because these soils are mostly low in organic matter and therefore marginal to low in available sulphur. Sulphate (SO 42-) is easily prone to leaching losses in coarse textured soils and therefore, could be another main reason for its deficiency. Coarse textured soils particularly low in clay content ( STCR > compared to RDF of castor – sorghum cropping system in rainfed Alfisols (75). The application of secondary and micronutrients through blending or fortification with macronutrient fertilisers is the best option to ensure the balanced and efficient use of nutrients. Customised fertilisers facilitate the application of the complete range of plant nutrients in the right proportion and to suit the specific requirements of a crop during its stages of growth. The Central Fertiliser Committee has included

customised fertilisers in the Fertiliser (Control) Order 1985, as a new category of fertilisers that are area/soil/crop specific. Depending on the soil test report, climate, water requirement, crop and seed chosen, a particular type of grade of fertiliser (customised fertiliser) is prescribed along with the recommended doses and time and method of application to get the best yield and maintain soil health.

all studies on assessing the response of crops and cropping systems to sulphur provide positive benefits, the next level of precision management issues for achieving higher use efficiency is the priority.

Due to the variations in soil texture, total, inorganic and organic forms of sulphur, the crops and cropping systems followed, the applied sulphur will show differential response to crops. Invariably the soil applied sulphur through elemental, gypsum or pyrites have long term benefits compared to water soluble sulphate sources. However, due to the leaching of sulphates to lower soil layers, the deep rooted crops will have advantage that too at later stages of their growth which directly increases the quality.

of sulphur fertilisers such as micronised S that have higher efficiency in terms of solubility and slow release with protection against fixations for reducing the quantity, cost and environmental protection. Modification of time of application in two or three splits is also encouraging and need more studies.

The Potential Benefit of S Use in Oilseeds With the use of sulphur at 15-30 kg/ha in oilseeds involving cropping systems on 76% of soils with potential S deficiency, oil yield can be increased by at least 3 million tonnes that could effectively save cultivation of oilseeds in additional 5 to 8 million ha and saving of about Rs.10,000 crores of foreign exchange annually for India (98). CONCLUSION FORWARD

AND

WAY

Sulphur need and deficiency is increasingly becoming one of the limiting factors to further sustainable increases in agricultural production. More than 75% of agricultural land is deficient or likely deficient; almost all trials responded to sulphur fertiliser with crop yield increases from 14 percent to 60 percent; Optimum sulphur fertiliser dose varied between 30 and 45 kg/ha; economic returns from sulphur fertiliser use were very attractive. While almost

Consider the soil reaction and all possible S transformations in deciding the source, quantity and time of S application. ♦

♦ Promote the use of new sources

♦ Assess nutrient interactions of S

with other nutrients of their synergism and antagonism on long term basis and incorporate into recommendations and decision support systems. ♦ Long term assessment of use of

each source of S – pyrtes, elemental S, SSP, gypsum, Ammonium sulphate, etc. in different soil types and cropping systems is required to understand the sulphur dynamics and crop productivity. ♦ Always assess the investment on

S application on cropping system basis to consider direct and significant residual effects and increased quality, increased use efficiencies of other factors/ resources. Crop factor plays a significant role. ♦ The S build up due to continuous

use of S in cropping systems and its management in terms of stopping S application after a certain critical S build up need to be studied in long term studies in different soil types. ♦ The utility of S should be assessed

from multiple angles beyond the plant nutrition, in terms of correcting soil alkalinity reaction, disease and pest reduction, quality Indian Journal of Fertilisers, May 2014 99

improvement, etc. Emphasis and adoption of integrated nutrient management with reliance on on-farm resources and organics is critical for sustainable S supply for realizing higher yield and quality of crops. ♦

♦ Role of sulphur in ameliorating

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Indian J. Fert., Vol. 10 (5), pp.104-115 (12 pages)

Boron Management in Indian Agriculture Issues and Strategies M.V. Singh

Indian Institute of Soil Science (ICAR), Bhopal 462 043 Email : [email protected]

and Virendra Goswami

Rio Tinto India Pvt. Ltd., 21st Floor, Tower A, Building No.5, Cyber Terrace, DLF Cyber City, DLF Phase III, Gurgaon, Haryana 122 002 Email : [email protected]

The paper summarises issues and strategies of boron (B) management for boosting agriculture production in India. Boron deficiency is increasing due to far lower consumption of B from external supply as against increased depletion of B by crops. Lack of awareness about benefits likely to be accrued from B fertilisation, ignorance of losses occurred from B deficiency, undue fear of B toxicity, lack of new B products, unawareness about preferential choice of applying B in a given cropping systems, residual fertility, lack of willingness for producing ample B fortified NP/NPK on mass scale, higher capital requirements for producing advanced boron sources and extensive problems faced in registration and production of new B sources due to government policy, are some of the important issues which need suitable strategies of B management to ensure balanced nutrition of crops. Systematic data compiled for 173719 surface soil samples till 2011-12 indicated B deficiency to the tune of 51.7% in Indian soils as against 2% reported in early seventies. Average boron deficiency ranged between 8.4 to 67% in various states. Its deficiency has been confirmed through biological response which revealed that B is the most important nutritional constraint restricting productivity of cereals, pulses, oilseeds, vegetables, horticultural and cash crops in Indian soils. Hidden hunger has been reported in several soils, crops, agroecological zones except areas having high B containing irrigation waters. Boron deficiency can profitably (B:C ratio Rs. 5.2:1 to 52.7:1) be corrected by soil or foliar sprays of either B fertilisers, but borax penta hydrate( granular or crystalline) and solubor were found better than borax decahydrate. Boron fortified (0.1-0.3% B) NP/NPK enhanced the crop yields and improves quality of produce and nutrient use efficiency of NPK. Thus, B fortified NPK is the best hope for supplying B judiciously to all crops and all fields in future. Boron toxicity in soils and crops in India is not common due to B fertilisation except few areas having “inherent geogenic B toxicities” which can be managed by growing B tolerant crops and cultivars and by adopting other ameliorative strategies.

Introduction

I

ndia has achieved record food grain production of 259 million tonnes with annual growth of 2.6% since independence. About 50% increase in food grain production is attributed to fertiliser consumption (9). Country has 141 m ha cultivated area of which 78 million ha area is rainfed. Being all, the green revolution has made India net exporter of food grains. To ensure national food security, country will need about 294 million tonnes of food grain production by 2020. This increased demand of food grain production has led to continuous depletion of soil micronutrient fertility (6,39). As a result a steady fall of nutrientuse– efficiency (NUE) is seen during this period, from 17.9 kg grain /kg NPK to 3.9 kg grain/kg NPK during past five decades (Table 1). The decline in NUE is partly attributed to the increased incidences of deficiencies of zinc (Zn) and boron (B) in many parts of the country.

Boron (B) is one of the essential micronutrients required for the completion of normal growth and reproductive cycle of plants. According to study of Sillanpaa (1990), deficiencies of B could be suspected in almost every country in the globe. Boron deficiency is the most widespread in China, Australia, United America, Brazil, Europe, Turkey, India, Nepal, Pakistan, Bangladesh, Malaysia;

Philippines, Sri Lanka, Thailand, Nigeria and Malawi etc. Besides India, B deficiency is prevalent in more than 80 countries of the world and it inhibits productivity of 132 crops (3, 10,30,33,50). Among micronutrients, boron deficiency has become the most crucial constraint limiting NUE and crop yields. In view of this, present paper focuses on the issues and strategies of systematic B management in

Table 1 – Food production, fertiliser consumption and nutrient use efficiency in India Period

Additional foodgrain Increase in NPK production (m t) consumption (m t)

NUE (Kg grain response / kg nutrient added)

1960-70

26.4

1.47

17.9

1970-80 1980-90

21.17 46.80

2.44 5.28

12.7 8.9

1990-00 2000-10

20.42 44.76

3.18 11.42

6.3 3.9

Source: (9) Indian Journal of Fertilisers, May 2014 104

Indian agriculture for ensuring food and nutritional security of the country. Importance of Boron in Plants Essentiality of B as micronutrient for higher plants was established by Warington (1923) primarily for maintaining the integrity of cell walls. Boron is also beneficial for the normal growth and reproduction in human and animals. Boron is involved in number of metabolic pathways in plants and forms very stable organic compounds with cis-diol configuration (13). Boron is neither a constituent of enzyme nor it affects directly any of the enzymatic activities in plants (2). Boron is essential in plants for ensuring cell differentiation and its development particularly of growing tips, xylems and phloem, flowering and development of pollen grains. Boron is essential for the synthesis and translocation of sugar by forming sugar borate complexes in the plants, more so to growing tips otherwise it ultimately leads to death of tips, movement of growth regulators within plants, acts as a precursor of lignin synthesis through polymerisation of phenolic compounds and it helps in uptake of calcium (Ca) and other nutrient use efficiency (NUE) through balance nutrient ratio (26,40). Boron plays an important role in pollen germination and growth of pollen tube and thereby affecting

grain sterility in most plants. Boron helps in cell membrane and concentration in cell wall reflects the differences in B requirements among various plant species. Boron plays an important role in transport of potash into guard cell, thus stomata opening increases with B deficiency leading to higher water evaporation. Boron affects drought tolerance of plant species in rainfed conditions. Several issues of boron management however, require attention which needs to be tackled as given below: Issues of Boron Management Precise delineation of boron deficient areas, georeference mapping, establishing hidden hunger of B through biological crop response and enhancing over all profitability are the important issues of efficient B management in Indian agriculture. Such information on the extent of B deficiency and development of georeferenced maps is very much lacking. Deficiency of B is quite severe in many soils of India (1,44,47,57). Among different states, extent of B-deficient samples varied from maximum of 68% in West Bengal (4) to minimum 8.3% in Haryana (27). In general, B deficiency is most wide spread (3968%) in red lateritic soils of Karnataka (67), leached and acidic and old alluvium soils of West Bengal (24), Orissa (15), and in Jharkhand (51) and in highly calcareous soils of Bihar (47). Boron

Percent nutrient deficiencies in soil in India

Figure 1 – Extent of nutrient deficiencies in Indian soils Indian Journal of Fertilisers, May 2014 105

deficiency is the most common problem in upland crops grown particularly on calcareous / alkaline soils. Its deficiency is most wide spread in acid soils of humid and sub humid regions (49). As far as magnitude of B deficiencies is concerned, its deficiency is as high as that of phosphorus, sulphur and zinc. During past five decades, B fertility status of Indian soils has shown much decline. The deficiencies of zinc, boron, iron, manganese, copper, molybdenum and sulphur have been reported to the tune of 48, 52, 12, 5, 4, 13 and 46% soils, respectively (Figure 1) (45,54). Tandon (2009) calculated annual depletion of B and Zn as 13519 tonnes and 15184 tonnes in India with an average removal of 94.5 g ha-1 and 111 g ha-1, respectively. The net negative balance (deficit) from supply and demand gap is 39000 t/ annum of B which is causing severe deficiencies leading to decline in yield or many instances or even entire failure of crops (61,64). Boron deficiency over the years has emerged as a serious nutritional problem in most of the crops due to continuous depletion of native soil B. The boron deficiency occurs in almost 52% soils of the country based on analysis of 173195 surface soil samples data compiled by Singh (2013) (Figure 1) as against of 24 % samples reported to be B deficient by 1990 (43) and as low as 2% B deficiency before onset of green revolution (11). On an

average 62% soil samples were found deficient in Karnataka state based on analysis of more than ninety thousands surface soil samples (67). Such increase in B deficiency in Indian soils has been reported with progress of time by several workers (1,5,15,45,47,54,). Both acid and calcareous soils showed extensive B deficiency ranging from 3-89% in different parts of India (47,48).

highly leached rice-growing red and other associated soils (Alfisols, Oxisols and Ultisols). Hidden hunger of B and Zn deficiency in many crops is quite prevalent than that of visual deficiency, causing much adverse effects on the growth, flowering, seed setting and improving quality of produce (21,35,49,54).

Boron deficiency occurs widely in several states more so in coarsetextured, calcareous (Entisols and Inceptisols) of Indo-Gangetic alluvial plains of North India (49), fine textured calcareous black soils (Vertisols) of Deccan Plateau, and

Information related to suitability of source, rate and method of its application in crops and cropping systems has been made available (36,41,57,59) which is quite important in maximising food grain productivity in several

Strategies Boron Management

agro-ecological conditions. Although several sources and methods of application have been developed for correction of B deficiency, still correction of B deficiency is full of challenges as given below: – Lack of awareness about wide spread hidden hunger of boron – Lack of awareness about benefits likely to be accrued from boron fertilisation – Undue fear of boron toxicity at the cost of correcting boron deficiency – Lack of choice to new generation boron products – Preference to crop for boron

Table 2 – Merits and demerits of various boron fertilisers in view of hydration and boron content Boron Source

Physical B% Form as per FCO

Borax Deca hydrate

White fine crystalline powder

10.5

Borax Penta hydrate

White granular product

Boric Acid

Disodium Octaboratetetra hydrate

Relative solubility

Relative efficacy

Moderate in normal water but soluble in hot water

Good

14.6 BO 4

Moderate in normal water but good in hot water

Excellent

667

White amorphous powder

17.0

Moderate in normal water but good in hot water

Moderate

706

White amorphous Powder

19.5

Very good in normal water

Very Good

1500

BO

BO

4

3

B2O 3

Cost of B (Rs./ kg B ) nutrient 667

Remarks

· Borax is commonly used B fertiliser for soil . Quickly soluble thus making boron prone to leaching in high rainfall or light soil. · It requires more storable area due to low B content and high hydration water · It is prone to adulteration due to high hydration · Fine powder creates problem in fertiliser application when B is needed in small quantities. · It is unsuitable for B fortification in NP/NPK, thus costs extra labour for separate application. · Granular form helps slow release and less prone to leaching/flushing in high rainfall or light soils · Slow release property helps the crops to get boron nutrition for longer period and thus more efficient. · It requires less storable area due to high B (14.6%) content and high hydration water. · It is free from adulteration due to special granule which helps in uniform application with bulk NP/NPK fertilisers. · Granules and high B content makes suitable for B fortification in NP/ NPK, thus costs less on labour due to combined application and transport. · Approved both as fertiliser in FCO and insecticide. · Not available freely due to higher price, better alternative products and import restrictions. · Being hydrophobic in nature and fine powder form not very friendly for application. · More suitable for foliar sprays than for soil. · Very fine powder approved in FCO with high B · Suitable for foliar application due to instant solubility. . Very common among farmers for foliar spray in vegetables, cotton, fruits and some field crops. · Requires less storable area but cost more

Indian Journal of Fertilisers, May 2014 106

fertilisation in cropping sequence – Narrow concentration range of boron deficiency and excess – lack of awareness of new techniques of application – Lack of willingness for fortifying boron in NP/NPK – Government regulations for approval of advanced new boron products – Higher capital requirements for new fertiliser production During eighties emerging B deficiency and its correction was well recognised (36).However, small doses of B were recommended either for direct application to soil or through B fortified single super phosphate (0.16-0.18% B) to achieve higher crop yields in many parts of the country (8). During that time B fertilisation either directly to soil or through foliar sprays or applied through B fortified formulations could not become popular despite higher response of crops due to low profits on account of higher raw material cost, lack of subsidy and govt. controlled pricing policy etc. But in recent years, the situation is entirely different as the deficiency of B in Indian soils has aggravated in more than 50% soils over the past five decades, and favourable government policy is leading B as important component of NFSM, RKVY, BGREI etc (53,55). Management of B in Indian agriculture has become full of challenges; therefore suitable strategies are required to overcome difficulties being faced by the manufacturers and farmers as given below: Boron Fertiliser Sources Realising the increase in B deficiencies in soils and crops, Government of India (GOI) brought out B under the Fertiliser (Control) Order (1985) and approved various type of Fertilisers like (i) Straight B fertilisers (ii) boron containing micronutrient mixtures, and (iii) B fortified fertilisers to mitigate the adverse impact of B deficiencies

on crop growth and yields and check deterioration in soil fertility. Straight Boron Fertilisers: Common straight B fertilisers approved in FCO are given below for their use in agriculture either directly to soil or through foliar sprays on standing crops. Merits and demerits of various boron fertilisers is given in Table 2. Di sodium tetra borate penta hydrate (Granubor, 14.6% B), disodium tetra borate penta hydrate (fertibor 14.6% B Crystalline) and borax (Na2B4O7.10H2O fine crystal 10.5% B) for soil application and boric acid (H 3 BO 3, 17% B) and disodium octa borate tetra hydrate (Solubor, Na 2B 8O 13 .4H 2 O powder 20.0% B for foliar sprays are quite efficient and are being frequently used by the farmers. In addition few fortified and customised fertilisers are also approved during 2007 which had small percentage of micronutrient content. Boron in Micronutrient Mixtures Boron absorption by plants is influenced by various soil-climateplant factors. Boron had

synergistic or antagonistic effect to different nutrients uptake in the various crops. Boron fertilisation showed inconsistent effect on increasing or decreasing uptake and interaction with B x N, B x S, B x Cu, B x P. The interaction was synergistic between B x K, B x Zn, B x Mo whereas antagonistic interactions have been recorded between B x Ca, B x Mg, B x Fe, B x Mn. On one hand, most scientists are afraid of recommending regular application of B to most of the crops and soils because of undue fear of B toxicity hazards and because of narrow concentration range. On the other hand, 72 multi nutrient mixtures have been approved under their patronage with specific recommendations to add B in 93% mixtures as component in the 16 states (Table 3). These showed contradictory views as on one hand B is recommended as essential component of mixtures, while on the other hand B fertilisation is merely recommended for direct application to the soils despite vast deficiencies. Boron in multi nutrient mixtures kept between 0.02 to 50% w/w considering that

Table 3 – Boron recommended in number of micronutrient mixtures in various states Name of state

No. of total No. of Range of B mixtures mixtures with B conc., ppm

Andhra Pradesh Assam Bihar Delhi Gujarat Haryana Himachal Pradesh Karnataka Madhya Pradesh Maharashtra Orissa Punjab Rajasthan Tamil Nadu Uttar Pradesh West Bengal All India

6 2 6 1 5 2 3 6 2 10 6 3 1 14 4 7 72

Indian Journal of Fertilisers, May 2014 107

3 2 6 1 5 2 3 6 2 10 6 0 1 14 2 7 67

0.5-2.0 2.5-50 1.0-20 0.50 0.02-0.06 0.25-1.5 1.0-1.5 0.3-0.75 0.05 0.03-0.5 0.2-1.0 0.00 0.50 0.05-3.15 0.50 0.5-1.0 0.00-50

% age of mixture contain B 50 100 100 100 100 100 100 100 100 100 100 00 100 100 50 100 93

B in mixture would help in better flowering and fruiting. Boron additions in mixtures showed a positive effect on increasing yields and benefits. In view of this, it is suggested that optimum dose of B for direct application to soil should also be recommended without undue fear of toxicity as its use through multi micronutrient mixtures to correct B deficiency in crops otherwise soil fertility would get depleted continuously. Similarly in many areas, multi nutrient deficiencies are emerging fast either of B+P, B+S, B+Zn, B+P+Zn, B+Zn+S, B+ Zn+Mo, B+S+Mo or B+S+Zn+Mo leading to low yields (50,16). In old alluvial soils of West Bengal, large deficiency of multi nutrients was reported by Bhattacharya et al. (1998) where foliar sprays of multi micronutrients like 0.25% borax + 0.5% zinc sulphate + 0.05% sodium molybdate solution at 3 weeks interval 2-3 times significantly increased the yield response of various crops viz. cabbage, cauliflower, potato, wheat, rapeseed by 368, 167, 50.3, 5.09 and 1.84 q/ha compared to yield response of 109, 50, 15.2, 2.11 and 1.08q /ha due to foliar sprays of B alone, respectively. Boron in Site Specific Nutrient Management In several Site Specific Nutrient Management (SSNM) trials, B was found to be the most important constraint in achieving high productivity of 14-16 t ha -1 yr-1 of rice-wheat sequence and 11-18 t ha -1year -1 of rice–rice sequence in several states (65,66). Boron as one of the Site Specific Nutrient gave higher benefits (BCR >2) to hybrid rice-wheat sequence in soils of Palampur in Himachal Pradesh; Ranchi in Jharkhand; Ludhiana in Punjab; Faizabad, Modipuram, Varanasi in Uttar Pradesh and Pantnagar in Uttarakhand as well as for hybrid rice-rice sequence in Maruteru in Andhra Pradesh, Jorhat in Assam and Karjat in Maharashtra. Thus, B fertilisation 0.5-1.0 kg ha -1 is must for high productivity of rice and wheat in

several states of India. Similarly, in 95 Site Specific field trials conducted by ICRISAT, integrated Zn, S and B application increased the yield of maize, castor, groundnut and green gram by 1945 kg (75%), 440 kg (52%), 390 kg (53%) and 530 kg (65%) per ha over the farmer practices in red soils and black clayey soils of India (32,35).

government has approved B fortification at the range of 0.10.3% in FCO depending upon nature of NP/NPK fertilisers. Fortified fertilisers approved in FCO are given in Table 4. Although boronated fertilisers are the hope of future but none of the product is so far manufactured for farm scale consumption due to certain constraints.

Thus, a large number of experiments have proved high magnitude of B deficiency and economic benefits likely accrued than expected so attitudinal change and better understanding of B deficiency and frequent B fertilisation is needed by considering to biological response, crop demands and soil B fertility to ensure food and nutritional security in India.

Use of boron fortified fertilisers had advantages of ease in application, uniform distribution in soil, correction of deficiency as well as soil enrichment, improved N, P, K efficiency, less chances of adulteration etc. Use of boronated NPK (14-35-15-0.3) was tried in different crops like mustard, wheat, lentil, potato and coriander in old alluvial acid soils. It gave high responses (2-66%) either B with NPK or blended as boronated NPK in acid soil of Jalpaiguri and 24 Pargana districts of West Bengal. Potato showed better response to NPKB and the sequence was: Potato >Wheat >Coriander >Mustard >Lentil. Thus blending of NPK with borax penta hydrate at 0.3% was found a better option for managing B deficiency problem in cereals, oilseeds, pulses and horticultural and vegetable crops (24, 58).

Boron Fortified Fertiliser – A Way Forward Precise application of B is necessary because of small B requirement of crops. Contrary inadvertent use of B would be uneconomical. Further, B toxicity due to B fertilisation is rarely seen as farmers either do not apply B or apply inadequate dose despite high benefits accrued by them due to lack of ample availability. To ensure B fertilisation among masses B fortified fertilisers were recommended. In the initial phase, boronated single super phosphate (SSP) with 0.18% B was approved under FCO but it could not catch up with the farmers widely as it failed to meet the B requirements of most crops or due to fear of undesired use (8). But after 50 years of cultivation, B deficiency is increasing so application of B is must. Now

Crop Responses Fertilisation

to

Boron

Average response of maize, wheat and rice to 1.0, 1.5 and 2.0 kg ha-1 B added was 480, 370 and 310 kg ha-1, respectively in several B deficient soils. Chickpea, pigeon pea, groundnut gave mean yield response of 430, 340, 370 kg ha-1 and sesame, mustard, linseed and sunflower 90, 210, 150 and 320 kg ha -1, respectively (50, 61). In trials on calcareous soils, response of

Table 4 – Percentage of nutrients (N: P 2O5 : K20 : B) in fortified fertilisers approved under FCO Boronated SSP 0 : 16 :00: 0.15-0.20 B

Boronated DAP

18 : 46: 0 : 0.3 B

Boronated NPK

12 : 32 : 16 : 0.3 B

Boronated NPK

15: 15 :15 : 0.2 B

Boronated NPK

10 : 26 : 26 : 0.3 B

Boronated NP

24: 24 : 0 : 0.2 B

Boronated CaNO 3 14.6 : 0 : 0 : 0.25 B Indian Journal of Fertilisers, May 2014 108

Figure 2 – Yield response of groundnut and maize in cropping cycles with increasing doses of boron in red soil of Tamil Nadu

chickpea, lentil, mustard was found 350, 750, 300 kg seed ha -1 , respectively. Response of onion was 5.3 t ha-1 and that of sugarcane was 8.70 t ha-1 to the application of 1-2 kg B ha -1 in highly calcareous soils (36, 44). Rice showed significant response to B fertilisation in Bihar, Assam, Orissa, Tamil Nadu, Karnataka, West Bengal, Uttarakhand etc. Application of 0.5-2.0 kg B ha -1 increased the rice yield by 460, 500, 570 and 270 kgha-1 in acid soils of Assam, Jharkhand, Orissa and West Bengal with corresponding increase of 320,570, 1500 and 320 kg ha-1 of wheat, respectively. The magnitude of above response ranged from 11-15% for rice and 14-55% for wheat over no B treatment; thus B application is found quite profitable in these states (37,49). Response of potato tuber to soaking in B solution prior to sowing was found highest in hill soils followed by black, red lateritic and alluvial soils 3.8, 2.2, 2.0 and 1.8 t ha -1 respectively (12). Boron leaves residual effect to subsequent crops, thus application of B may be omitted in subsequent cops depending upon the rate of B applied. The cumulative response of groundnut, maize and cumulative response of both crops in sequence during two cropping cycles is shown in Figure 2 which

clearly revealed that boron fertilisation is beneficial as it leaves residual effect to subsequent crops in rotation in red soil of Tamil Nadu (63). Efficiency and Crop Response to Borax penta Hydrate vs Borax deca Hydrate New generation products with change in physical or chemical forms like borax penta hydrate (granubor, 14.6% B), borax penta hydrate crystalline (fertibor, 14.6% B) has advantage with respect to slow releasing properties, better quality, less adulteration, less storage and transport cost and ease to apply over borax deca hydrate (10.5% B) commonly available in the market. Granubor application significantly increased the yield of crops more than borax. In view to assess their efficiency, 28 field trials were carried out at Ludhiana, Palampur, Coimbatore, Hyderabad, Anand, Pusa, Bhopal under ICAR- SAUs Granubor Network studies in India which indicated that application of 100% of the recommended dose of B through borax penta hydrate 14.6% ( granubor) gave higher yield response and benefits to the application to various crops like rice, wheat, lentil, chickpea, groundnut, cotton, cauliflower, etc (20, 38,46). In most of the cases the effect of borax penta hydrate was Indian Journal of Fertilisers, May 2014 109

higher in various crops in most of the places or at par to that of borax deca hydrates in Bihar. On an average benefit – cost ratio from granubor was found Rs.20.58: 1 compared to Rs.17.81: 1 for borax deca hydrate when applied on equivalent dose of boron costing at the rate of Rs. 686/kg B to various crops. Application of borax penta hydrate (granubor) gave Rs. 2.77 to Rs. 9.12 extra benefit over borax application which corresponds to 15.6% to 162% extra economic returns, respectively except some oilseed crops compared to commonly used borax deca hydrate (Table 5) (59). Boron application 0.5-1.50 kg ha -1 is found profitable in calcareous and acid soils of Bihar and other parts of the country. The response for cereals, oilseed, pulses and other crops is given Table 6 which clearly revealed that the response vary with crop species, location, soil type etc. (53). Crop Response to Boron Fortification in NPK Fertilisers Boronated NP/NPK fertilisation is the need of the day as they are helpful in ensuring balance nutrition to crops. The government of India has approved B fortification rate 0.1 to 0.3% to NPK (W/W) so as to supply optimum dose. Higher concentration of B is recommended to high analysis fertilisation say 0.1 to 0.2% for DAP and 0.2-0.3% B fortification in SSP and nitrophos etc. Field trials numbering 46, 45, 14, 30, 10, 91 and 10 and 91 aimed to evaluate efficiency of boronated NPK (0.3% B through fertibor) on paddy, wheat, maize, mustard, soybean, potato cabbage and sugarcane were carried out in divergent soils of Gujarat, Uttar Pradesh, Maharashtra and West Bengal which gave extra yield response of 492, 330, 402, 144, 500, 2165, 7850 and 2165 kg ha -1 over no B treatment (58). The benefit- cost ratio of respective crops was Rs.11.64:1 for paddy, Rs. 10.99:1 for wheat, Rs.12.42:1 for maize, Rs.14.2:1 for mustard, Rs.18.2:1 for

Table 5 – Relative efficiency of granubor vs borax in increasing crop response and benefits Crop No. of Produce Boron Yield Produce response B response, kg/ha trial rate Rs/kg added, kg/ha in to B added, kg/ha kg/ha B control Granubor Borax Granubor Borax @ Rs.100/ kg Rs.72/kg Cauliflower 7 10 1.00 17597 Paddy 2 15 0.75 5571 Wheat 2 15 0.75 3875 Soybean 1 35 0.75 742 Groundnut 7 35 1.00 1473 Sunflower 3 35 1.00 1909 lentil 1 35 1.00 1560 Gram 1 35 1.00 1460 Mustard 3 35 0.75 1312 Cotton seed 1 25 1.00 1965 Crop species wise benefits and response to Granubor and borax Cereals 4 15 0.75 3048 Pulses 2 35 1.00 1510 Oilseeds 14 35 0.75 1480 Cotton seed 1 25 1.00 1965 Vegetables 7 10 1.00 17597 Mean of all 28 -

3677 395 327 148 219 212 123 120 161 552

3052 277 222 68 255 240 70 47 203 415

52.68 10.53 8.55 9.08 10.19 9.83 5.28 5.13 9.97 19.15

43.55 7.09 5.48 3.63 12.03 11.26 2.58 1.40 12.83 14.15

235 122 200 552 3677 -

210 59 227 415 3052 -

9.54 5.21 9.99 19.15 52.68 20.58

6.28 1.99 10.75 14.12 43.55 17.81

Rate: 1 kg B equiv. Rs.685/ from Borax and granubor fertilisers , Source: Singh (2006,2013), Network on Granubor

soybean, Rs. 7.65:1 for potato, Rs.28:1 for cabbage, respectively (24, 58). Response of Cash Crops to Boron Fortification Studies on optimising B fortification rate to DAP at Hyderabad indicated that B fortification to NP fertilisers was found beneficial to cotton in swellshrink soils. It requires higher rate of B fortification up to 0.75% level (Figure 3). Maximum seed cotton yield was obtained between 0.60 to 0.75% B fortified to DAP and was

at par in swell-shrink soils in erstwhile Andhra Pradesh (5). The benefit- cost ratio of respective crops was Rs.14.18: 1 for sugarcane for boronated NPK (57). Experiment on cotton was initiated at PAU, Research farm, Ludhiana on B deficient loamy sand (Typic Haplustept) having HWS- B 0.40 mg/kg soil. Cotton (LH 1556) was grown with basal dose of 75 kg N and 27kg P 2O5 ha-1 added through urea and DAP, respectively. Boron was applied through granubor at the rate of 0, 0.10% to 0.75%, 0.3%

(30 DAS), 0.3% (45 DAS), 0.3% (50% at sowing & 50% at 30 DAS), 0.3% (50% at sowing, 25% at 30 DAS & 25% at 45 DAS) and 0.15% spray each at 30 and 45 DAS (Table 7). Results showed that application of 1kg B ha -1 fortified to DAP gave maximum yield of seed cotton 1822 kg ha -1 compared to 1587 kg ha -1 yield recorded in B control treatment. Thus, B fortification is found beneficial in loamy sand of Punjab whereas foliar sprays alone gave low yield than soil basal application.

Table 6 – Response of crops to boron in various states Groups Cereals Pulses

Oilseeds

Cash crops

Crops Paddy Wheat Maize Chickpea Pigeon pea Lentil Black gram Groundnut Sesame Mustard Linseed Sunflower Onion Yam bean Sweet potato Sugarcane Cotton

Bihar, kg/ha Range Average 280-1240 10-1190 60-990 170-890 150-550 120-310 250-280 310-420 10-140 80-300 40-310 320 2830-7950 1740 7000 10500 -

310 370 480 430 340 250 270 370 90 210 150 320 5250 1740 7000 10500

Indian Journal of Fertilisers, May 2014 110

Other states, kg/ha Range Average 0-1670 30-1190 170-1050 130-900 30-90 40-490 40-350 50-420 3870-5800 670-3000 1810 60-350

320 380 480 420 60 240 170 220 4620 1840 1810 231

Figure 3 – Effect of boron fortified DAP on seed cotton yield in a swell-shrink soil in Andhra Pradesh

In Haryana, despite moderate to high B status and low B deficiency (8.4%) in general, cotton and mustard showed significant responses to the application of B (Table 8). Application of 1 kg B/ha gave high response to cotton and mustard by 15.71 and 15.77% over the control, respectively which was significantly higher than 0.5kg B/ha. Foliar sprays gave low yield than soil application (14, 22). Preferential Application of Boron in Cropping System Boron applied to crops leaves residual effect to the succeeding crops. Study at Pusa showed that B applied in rice-wheat and maizemustard system gave maximum average yield increase of 39% in rice, 18% in wheat and 30% in maize (60). In general, three foliar sprays of 0.25% boric acid gave similar response as that of 8 kg borax/ha added at the time of planting. Data averaged for 5 years for 80 kg borax applied as 8 kg/ha to each crop or 16 kg/ha to either

rice or maize in rice-wheat and maize-mustard sequence indicated that 16 kg/ha borax to Kharif crop gave cumulative higher response than 8 kg /ha though residual effect of both the treatments was at par on Rabi crop(Table 9). Soil application was found superior to foliar sprays. Rice was found more efficient than maize and maize was more efficient than mustard in utilizing B for grain production. Thus, crop utilising more boron and giving higher use efficiency should preferably be fertilised with B in a given cropping sequence. Wide Gap Between Demand and Supply of Boron Continuous cropping removes on an average 90-350 g/ha of boron. To meet the crop demands consumption of B fertilisers remained very low even after six decades of green revolution. Takkar et al. (1997) estimated annual demand of B to be 39000 tonnes by the year 2025 considering 50% of the deficient

Table 7 – Effect of B application on seed cotton yield, plant height and number of balls plant in Punjab (*Average of five plants) B added as granubor (kg/ha) Seed cotton Plant height through fortification with DAP yield (kg/ha) (cm)* 0 0.5 1.0 1.5 2.25 3.00 3.75 CD (5%)

1587 1686 1822 1705 1640 1667 1692 143

132 139 140 136 134 144 137 6.0

No of balls per plant* 25.4 31.4 30.8 32.8 30.2 32.5 33.5 4.6

Indian Journal of Fertilisers, May 2014 111

soils would need B fertilisation. Singh (2013) reported that the deficiency of B has increased drastically in over past six decades from 33% to 52% so B requirement for agricultural areas would be 58450 t/yr. Since present consumption of total borax is 21800 t/yr in India including industrial demands, of which the share of agriculture is only 1550 t/ yr . Now the Government of India is creating enormous awareness and fund allocation made under NFSM, RKVY and NHM, ISOPAM for promotion of Zn and B, so their consumption in agriculture is estimated to increase to the tune of approximately that of 20,000 t/yr equivalent of borax after year 2010. Basal application of B is found best than foliar sprays or topdressing due to high boron demand at early growth and reproductive stages of crops so B fortification will ensure adequate and even supply of B than direct application without any fear of B toxicity. Boron Toxicity- Issues and Management Strategies Boron deficiency and toxicity both need proper management though much attention has been paid to manage B deficiency in crop plants. Question is difficult to answer whether B fertilisation causing toxicity to crop plants is a very serious nutrition constraint in India and 80 countries of the globe or B toxicity a Site Specific B problem as the case may be for iron etc. Boron toxicity due to boron fertiliser use: The chances of emergence of above toxicity (“Anthropogenic B toxicity”) are much less depending upon soil type, nature of crop or crop cultivars and fertiliser-crop management options. Undue fear of toxicity and thereby restricting B fertilisation recommendations are hampering the yield and over all food security. It leads to undesired depletion of soil B fertility. Crop specialists most often do not recommend even optimum dose of B considering

Table 8 – Response of cotton, and mustard to boron in moderately boron deficient soils Boron added, kg/ha

Cotton Seed cotton Percent yield, kg/ha response

Mustard Mustard seed Percent kg/ha response

0.0

1508

-

1786

-

0.5 1.0

1679 1745

11.33 15.71

2004 2070

12.08 15.77

0.20% Spray

1535

1.79

1872

4.70

precautionary measures of B toxicity. The fact is that more than 90% farmers do not apply B at all or apply far less dose of B fertilisers than recommended. Even by chance if scorching on crop foliage occurs due to high rate of B fertilisation or foliar sprays, it is of temporary nature and mitigates within 2-4 weeks. Singh (2008) observed visual necrosis on soybean leaves in swell-shrink soil when 60 to 80 kg borax/ha was top dressed once at 30 days of growth. Visual B toxicity appeared after 10-15 days after top dressing. The effect was however temporary in nature and plants recovered within 4-6 weeks prior to maturity. Severity of visual necrosis was observed in case of soybean first followed by mustard and later in cotton. The yield of all crops gradually decreased when B supply increased above 3.0 kg B/ha in black clay soils. Singh et al. (2006) also studied the effect of eight times higher levels of borax viz. 0, 8,16,32 and 64 kg borax/ha applied once to first crop with 0 and 5t/ha farm yard manure (FYM) under maize-lentil two cropping cycles in calcareous soil of Bihar on the crop yield, borax uptake, agronomic efficiency (AE) and nutrient use efficiency (NUE). Results showed that increasing levels of B enhanced the biomass yield of both crops in both the years (Figure 4). Interestingly, borax applied even six times higher rate 64 kg B/ha did not hamper the yield of either crop or cropping systems as that of 8 kg borax ha -1 recommended to first crop. Increasing levels of borax from 8 to 64 kg ha-1 alone enhanced the boron uptake by all the crops from 239 to 621 g/ha and from 431

to 862 g ha when borax plus FYM or borax alone was applied (Figure 4). Maize absorbed 3-5 times more B than lentil due to its higher biomass yield. -1

Geogenic Boron Toxicity: This type of toxicity aroused from “inherent Site Specific soil-water factors” such as continuous supply of B from irrigation of crops with high B containing ground waters, city sewage or sodicity/salinity in soils showed much adverse effect on normal crop growth performance and requires much attention due to recurring supply of B to soilwater-cropping system (17). Geogenic B toxicity causes much yield loss than temporary toxicity emerges from B fertilisation by chance due to higher rate of B application. Strategies of Boron Toxicity Management in Plants Geogenic B toxicity caused by “inherent Site Specific soil-water factors” happen to be severe and invites specific management strategies such as proper site characterisation and demarcation, development of digitised maps and level of toxicity, purpose of

reclamation and associated problems like salinity/sodicity or level of industrial pollution. Suitable agronomic practices may be adopted such as use of higher rate of N, P, K, Zn, use of soil amendments, cultivation of high B demanding cereals, oilseeds, horticultural or bio fuel plants, leaching in salt affected soils etc for raising higher crop yields. Contrary to this, yield losses incurred in case of B toxicities induced by over dose of B fertilisation was much less compared to loss incurred by inherent Site Specific B toxicity. Hence, much emphasis is given to optimize the rate of B fertilisation for soil test-crop specific recommendations. Further plants have been classified as B sensitive, moderate and tolerant to enable cultivation of B tolerant plants and reducing adverse effect of B toxicity (15, 36, 49). Some soils may contain HWS-B upto 100 mg kg -1 or more while normal soils contain average HWSB between 0.05 to 1.00 mg kg -1 . Excess accumulation of B above 3.0 mg B kg-1 soil induces leaf necrosis; reduces leaf area to the extent which significantly reduces the photo synthesis, yield, quality of produce of common crops (40). Proper management of phyto toxicity, as leaf necrosis, occurred when water-soluble B exceeded above 5 mg B kg-1soil. Main source of B toxicity is ground water irrigation. Upper critical

Figure 4 – Effect of borax and borax with 5 t/ha FYM on cummulative seed yield of two maize-lentil cropping cycles in calcareous soil of Pusa, Bihar Indian Journal of Fertilisers, May 2014 112

Table 9 – Direct and *residual effect of boron added to rice –wheat and maize-mustard sequence on yield of crops in five cycles in calcareous soils of Pusa, Bihar Borax rate kg/ha

Application frequency / Borax treatment

Average grain yield over 5 cropping sequence Rice Wheat Maize Mustard

0

0

3432

2842

2236

1296

16

8 kg /ha to both crop

4304

3330

2720

1582

16

16 kg /ha either to rice or maize

4768

3362*

2924

1530*

*Residual effect

concentration of B for safe drinking water is 2.0 µg ml-1 whereas for safe irrigation to avoid B toxicity and yield loss was reported to be less than 1.0 µg ml-1 for sunflower, 3-4 µg ml-1 for wheat and 4-6 µg ml-1 B for pea grown on sandy loam soil (7). Khandelwal and Lal (1991) reported safe limit of B concentration (µg ml-1) in irrigation water for growing wheat was : Loamy sand Sandy loam Sandy clay loam Clay loam

5.0 µg 7.5 µg 7.5µg 10 µg

B ml-1 Bml-1. B ml-1. B ml-1.

It is interesting to note that irrigations from water containing 2.5µg B ml-1 deliver 125 g B ha-1 to support crop growth. Generally 34 irrigation in cereals, 2-3 irrigations in oilseeds and 1-2 irrigations in pulses are recommended depending upon season and water availability. Such irrigation delivers 125 to 375 g B ha -1 , thereby meeting partial B requirements of crops in tube well irrigated areas. High B concentration is reported in some ground waters of Punjab, Rajasthan, Haryana, Gujarat, thereby these states had lower B deficiency in soils and crops. Cultivation of Tolerant Crops and Cultivars Various crop species and genotypes vary widely in B uptake and utilisation efficiency which influences the magnitude of crop response to B fertilisation and their relative B requirement. Monocotyledon or cereal crops generally require less B and yields well even in low B containing soils, whereas dicotyledons legume and crucifers have high B requirements, hence suffer more frequently to B deficiency. Thus,

sensitive crops need little doses of B for optimum therefore, suitable cultivars adapted depending deficiency/toxicity in soil 10).

higher yield, can be upon (Table

Areas of Future Research ♦ Information on effect of B in

countering physiological stress like seed filling and grain sterility, chaffy grain, drought tolerance in plants, reproductive physiology like flowering and fruiting disorders, yield and quality improvement and resistance to diseases and pest is very much lacking, hence such information is very much needed. ♦ Boron fertility of Indian soils is

depleting on faster rate due to intensive cropping of high yielding crop varieties; therefore depletion rate of B under different soil, crop, and management system needs to be studied to forecast emergence of B deficiencies. ♦ Systematic GIS based mapping

is very much needed. Effect of pedofactors on emergence of B deficiency needs to be studied. ♦ Boron requirement of crops

varied 190 to 450 g/ha / yr and B use efficiency ranged from 4-26% considering direct and cumulative residual effect. Studies on choice of suitable source, method and time of B application needs research for enhancing N,P,K,S,B use efficiency. ♦ Creating awareness to check

undue fear of B toxicity from B fertilisation as against of geogenic B toxicities occurring in few areas having high B in irrigation ground waters. ♦ Boron fertilisation practices and

choice of crop in different cropping systems need to be evaluated considering direct and residual effect and nutrient use efficiency. ♦ Boron in Indian agriculture needs to be promoted by favourable simplified government policy for registration of new products, boron fortification in NP/NPK and financial support.

Table 10 – Relative sensitivity of different crops to boron stress Less susceptible

Moderately susceptible

Highly susceptible

Wheat Inbred Rice

Maize, Hybrid rice Mustard , Groundnut,

Alfa alfa, berseem Cauliflower, Carrot,

Oats Barley Sorghum

Radish, Onion , Cabbage Spinach, Tomato, Potato Black gram, Green gram,

Sugar beet, Turnip Cotton Sunflower, Rapeseed, Chickpea

Pearl millet , Finger millet

Tobacco

Apples, Grapes

Soybean

Sugarcane , Tea

Olive

Beans , Pea, red gram Pomegranate, Peaches, Citrus Pine , Apple, Rubber Banana, Papaya, Coconut, Pear Indian Journal of Fertilisers, May 2014 113

Coffee Marigold, Chrysanthemum

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Ibrikci, Rolf Sommer, Emin Bulent Erenoglu 122:1-59 (2013) 34.Sahrawat, K.L.,Wani S.P. , Rego T.J., Pardhasaradhi G., and Murthy K.V.S., Current Science 93:1428-1432. 10 (2007) 35.Sahrawat, K.L . Micro-nutrient deficiencies and crop responses in dry land. “Brain storming workshop on Soil test based nutrients including boron and other micro nutrients” Organized by ICRISAT-Agril. Directorate, Karnataka-Rio Tinto India, at Bengaluru India Sept.22, 2012 (2012) 36.Sakal,R.; Singh A.P, Sinha R.B. and Bhogal N.S., Twenty Five Years of research on micro and secondary nutrients in soils and crops of Bihar RAU, Pusa, Bihar pp 134(1996) 37.Sakal,R., Nayyar V.K., and Singh M.V., Indian Soc. Soil Sci. : 49 (1997) 38. Sharma, S.P. Final report of Network on granubor as source of boron for correcting boron deficiency in crops of Himachal Pradesh. CSHPKV, Palampur pp 45 (2008) 39. Sharma, P.D. and Singh M.V., Paper presented in International conference on natural resource management, New Delhi , Indian Soc. Soil Science, New Delhi (2009) 40. Shorrocks,V.M. Plant Soil 193:121–148 (1997) 41. Shukla, A.K., Subbarao A. and Singh A.K., Micro and secondary nutrients recommendations in crops in different agro-ecological zones of India. AICRP Micronutrients, IISS, Bhopal : pp 1-61 (2012) 42. Sillanpaa, M. Micronutrients– An assessment at country level – An International study. FAO Soils Bulletin 63 : FAO Rome, pp 208 (1990) 43. Singh, M.V. Annual report, AICRP Micro and Secondary Nutrients and Pollutant Elements in Soils and Plants, IISS, Bhopal : pp 134 (1990) 44. Singh, M.V. Micronutrient management. In G.B.Singh and B.R. Sharma (eds), 50 yrs of natural resource management, ICAR New Delhi pp. 177-198 (1999) 45. Singh,M.V. Fertiliser News 46 (2) : 24–42 (2001) 46. Singh, M.V. Efficiency of granubor II for enhancing crop

productivity in boron deficient soils. AICRP Micro-nutrient, IISS, Bhopal. 3: 1-82 (2005) 47. Singh, M.V. Emerging boron deficiency in crops and soils in India and their management. World Soil Science Congress abstract. 3.3 Stress adaptation, No.19477: Session 3.3.Philadelphia, USA, Aug. 2006 (2006) 48. Singh M.V., Micro and secondary nutrient research in India. AICRP Micro and Secondray Nutrient and Pollutant elements in soils and Plants, IISS, Bhopal (2007) 49. Singh, M.V. Micro- and Secondary Nutrient deficiencies in acid soils and their management. Tech. bull. Acid soils in India and their management in (ed. Rattan,R.K.), Indian Soc.Soil Sci. Bull. 25:27-58 (2008a) 50. Singh, MV. Micronutrients in crops and in soils of India. In. Micronutrients for Global Crop Production. (Ed. B.J. Alloway), Springer. Business : pp 93-125 (2008b) 51. Singh, R.P. Georeferenced survey of micronutrient status in soils of Jharkhand. Proc. National seminar on micro and secondary nutrients. GAU, Anand-IISS, Bhopal (2008c) 52. Singh M.V., Progress report Granubor Network IISS Bhopal pp 66 (2008d) 53. Singh, M.V. Relative efficiency of different sources of boron on cauliflower yield in different agro

-ecological zones of India. IPNC, Sacramento, USA (2009) 54. Singh, M.V. Spread of micronutrient deficiencies specially boron in India and response of field crops. “Brain storming workshop on Soil test based nutrients including boron and other micro nutrients” Organized by ICRISATAgril. Directorate, Karnataka-Rio Tinto India, Bengaluru, India, Sept.22, 2012 (2012a) 55. Singh, M.V. Boron deficiency in crops and its correction in India. In National Seminar on micronutrient zinc and boron management. Organized by OUAT -Rio Tinto India, 27/9/2012 (2012b) 56. Singh, M.V. Boron nutrition of crops. Nutrient management in India (ed. R.Prasad). Indian Society of Agronomy (Accepted) (2013) 57. Singh, M.V. and Goswami Virendra, Efficiency of B fortified NPK fertilisers in correcting boron deficiency in some cereal and oilseeds crops in India. Boron 2013, Istanbul, Turkey (2013a) 58. Singh, M.V. and Virendra Goswami Response of vegetable and fruit crops to boron fortified NPK in India. Boron 2013, Istanbul Turkey (2013b). 59. Singh,M.V. and Wanjari R.H. , Indian J. Fertiliser. 9(8) : 62-74 (2013) 60. Singh, A.P., Singh M.V., Sakal R., and Choudhary K., Tech. Bull. IISS, Bhopal-RAU Pusa, Bihar. No. 9:170 (2006)

61. Singh,M.V., Patel K.P. and Ramani V.P., Fert. News 48(4) : 5568 (2003) 62. Srivastava, P.C. Annual report of AICRP Micronutrients, GBPUAT, Pantnagar pp 1-86 (2010). 63. Stalin et al Four decades of research on management of micro and secondary nutrient and pollutant elements in crops and soils of Gujarat. AICRP- Micro and secondary nutrients and pollutant elements in soils and plants, IISS, Bhopal, Res. Bull.7: 1-10 (2010) 64. Takkar, P.N, Singh M.V., and Ganeshmurthy A.N., A critical review of plant nutrient needs, efficiency and policy issues for Indian agriculture for the year 2000-2025-Micronutrients. In Kanwar, J. S. and Katyal J.C. (eds). Plant nutrient needs, supply, and efficiency and policy issues : 20002025, NAAS, New Delhi : 238-254 (1997) 65. Tandon,H.L.S. Micronutrient hand book, FDCO, New Delhi pp186 (2009) 66. Tiwari, K.N. et. al. PDCSR Modipuram –PPIC India program, Gurgaon, PP 92 (2006) 67. Wani, S.P., Sahrawat, K.L., Sarvesh, K.V., Baburao Mudbi and Krishnappa, K Soil Fertility Atlas for Karnataka, India. Patancheru 502324, Andhra Pradesh, India: ICRISAT. pp 312. ISBN 978-929066-543-4 Order code: BOE 055 (2011) 68. Warrington, K. Annals of Botany 27 : 696-672 (1923)

SPECIALITY FERTILISER STATISTICS DECEMBER 2013

The Fertiliser Association of India has released the 2nd edition of the publication Speciality Fertiliser Statistics in December 2013. The publication covers the details of fertility status of soil, nutrient uptake efficiency in particular reference to secondary and micro nutrients, policy guidelines, details of capacity, production, import, sale, consumption of specialty fertilisers including slow release, fortified/coated, water soluble and customized fertilisers. The book also presents comprehensive statistics of use, production and prices of various micro nutrients. Additional information on organic manure and bio fertilisers are also covered in the publication. A directory of selected companies dealing with speciality fertilisers and micro nutrients is also given in the publication. The price per copy of the publication Indian Foreign

: :

Rs.500 + 80 extra for packing, handling and postage US $100

For your copies please write to:

THE FERTILISER ASSOCIATION OF INDIA FAI House, 10, Shaheed Jit Singh Marg, New Delhi-110067 Tel:011-46005211, 91-11-26567144 FAX: 91-11-26960052 Email: [email protected] Indian Journal of Fertilisers, May 2014 115

Website: www.faidelhi.org

Indian J. Fert., Vol. 10 (5), pp.118-132 (15 pages)

Soil Carbon Management Issues and Strategies Muneshwar Singh, R.H. Wanjari, M.C. Manna, B.L. Lakaria, Pramod Jha Indian Institute of Soil Science, Nabibagh, Berasia Road, Bhopal

and Ch. Srinivasarao

Central Research Institute for Dryland Agriculture Santoshnagar, Hyderabad

The soil carbon (C) reservoir is an important component of the global carbon cycle (45). Similarly, soil carbon sequestration is the removal of atmospheric CO 2 through photosynthesis to form organic matter, which is ultimately stored in the soil as long-lived, stable forms of C. The global carbon cycle is made up of flows and pools of carbon in the Earth’s system. The important pools of carbon are terrestrial, atmospheric, ocean, and geological (45,63). Earth is major reservoir of C and the lithosphere comprises of 75,004 Eg (Exagram = 10 18 g) of C (99.94%) of the total terrestrial C stock while non geologic C component consists of 46.46 Eg (0.06%) of the total C stock and ocean consists of 42 Eg (0.05 %). and the entire atmospheric reservoir contains merely 0.8 Eg (0.001%) carbon. Thus, even small changes in soil C stock can have a major impact on the atmospheric concentration on CO 2. The soil C stock affects and moderates soil processes and functions. Physical, chemical, biological and ecological soil quality is strongly governed by SOC stock and its quality.

Introduction

S

oil C occurs in two distinct form i.e. soil organic carbon (SOC) and soil inorganic C (SIC). Moreover, world soils constitute the third largest global carbon pool, comprising of two distinct components: (i) SOC estimated at 1550 Pg and (ii) SIC pool estimated at 950 Pg both to 1 m depth. Other pools include the oceanic (38,400 Pg), geologic/fossil fuel (4500 Pg), biotic (620 Pg), and atmospheric (750 Pg) (26). The SOC component comprises of highly reactive humus, and relatively inert charcoal, both of which are collectively termed ‘soil organic matter ’ (SOM). The SOM comprises the sum of all organic substances in the soil, including a mixture of plant and animal residues at various stages of decomposition, of substances synthesized microbiologically and or chemically from the breakdown of products, and of the bodies of live microorganisms and small animals and their decomposing products (48). Humus, a dark brown and black amorphous substance, has a large surface area, high exchange capacity, and large affinity for water and ions. Therefore, reduction in SOC stock (as is the case with most agricultural soils in India) leads to drastic decline in soil

quality and its functions. In addition, SOC stock is a major source or sink of greenhouse gases (GHGs such as CO 2 and CH 4) and can strongly influence the atmospheric chemistry. Use of nitrogenous fertiliser, manure management and no till farming can accentuate emission of N 2 O from crop land soils (67). The SIC component comprises of elemental C and carbonatebearing minerals such as calcite, dolomite and gypsum. The SIC component is dominant, more so than the SOC, in soils of arid and semi-arid regions. It consists of primary and secondary carbonates. Primary or lithogenic carbonates are derived from the weathering of the parent material of carbonaceous rocks. In contrast, secondary or pedogenic carbonates are generated through the dissolution of atmospheric CO2 to form weak carbonic acid, and its reaction with Ca2+ and Mg2+ brought in from outside the ecosystem (10,19). Soils of India are severely depleted of their SOC stock. Therefore, enhancing and maintaining SOC concentration to above the critical threshold (~1.5% in the 0-20 cm depth) is essential to improve soil quality, use efficiency of degraded soil etc. Therefore we need to focus Indian Journal of Fertilisers, May 2014 118

on the issues too numerous to mention. However, some namely removal of crop residues, burning of stubbles, exposing of soil unnecessarily, soil erosion, erroneous water management, burning of fuel wood, non recycling of carbon waste, no provision of incentive for carbon management, crop diversification and inclusion of legume, imbalance nutrient use etc are highlighted here. In context to cope up with these issues we must pay attention to the strategies such as (i) Restorative cropping system (ii) Tillage management (iii) Conservation agriculture (iv) Crop residue management (v) Agroforestry (vi) Biochar application (vii) Integrated nutrient management and (viii) Best management practices. This paper is oriented to issues and strategies to maintain and improve soil carbon build up. SOC Potential in Different Soil Orders: The Indian Scenario Potential of stock of soil organic carbon varies from soil to soil. Most of the agricultural soils contain lower SOC pools than their counterparts under natural ecosystems. The reduction of SOM, during conversion of natural to agricultural ecosystems along with drainage of wetlands, intensive tillage of soils and

Table 1 – Organic carbon stock (at 0-30 cm depth) in different soil orders (India) Soil orders

Organic carbon (Pg)

Total carbon stock in India (%)

Alfisols Aridisols

4.22 7.67

20.0 36.5

Entisols Inceptisols

1.36 4.67

6.5 22.2

Mollisols Oxisols

0.12 0.19

0.6 0.9

Ultisols Vertisols

0.14 2.62

0.8 12.5

20.99

100

Total (Source: 32,68)

burning or removal of crop residues has reduced the soil carbon stock. Thus, conversion to a restorative land use and adoption of recommended management practices can enhance the SOC pool. In general, SOC sequestration rate can be up to 0.5 to 1.5 t ha-1 yr-1 in cool and humid climate and 0.05 to 0.5 t ha -1 yr-1 in warm conditions and in arid regions (26). The rate of decomposition of SOM is generally higher in tropical than in temperate climates. However, crop species also play an important role in maintaining SOC pools,

through the quality and quantity of the residues that are returned to the soil (31). Increasing the SOC pool by one Mg C ha -1 yr -1 can enhance agronomic production in developing countries by 32 and 11 million tonnes per year in case of cereals and food legumes, respectively (25,61). Soil organic carbon stock of Indian soils is 10-12% of the tropical regions and about 3% of the total carbon mass of the world (32). The SOC stocks for India in terms of each soil order is estimated at 0-

30 cm depths since such quantitative data reflect the kinds of soil with different amount of organic carbon (Table 1). Indian soils classified under Inceptisols, contribute about 22% of the total SOC stock. Entisols contribute nearly 7% of the total SOC stock. Vertisols are extensive in the central and southern part of India and contribute about 13% of the total SOC. Aridisols are in general poor in organic carbon due to their high rate of decomposition, low rate of plant growth and its contribution of SOC. The Indian Mollisols contribute nearly less than 1% of the total SOC stocks due to the fact that only a small portion of geographical area of the country is covered by these soils. Most of Alfisols occur in subhumid to humid regions of the country and contribute about 20% of the total SOC stocks. Oxisols occupying small area contributed less than 1% of the total SOC stock. Also poor accumulation of SOC in Oxisols is due to greater decomposition in tropical humid regions. Management Issues Maintaining and improving soil

Table 2 – Impact of imbalanced nutrient application on SOC (g kg-1) and crop productivity (kg ha-1) under intensive and irrigated experiments LTFE Centers/ Particulars Control 100% N 100% NP 100% NPK NPK+FYM NPK +Lime Barrackpore (Inceptisols) SOC Rice yield Wheat yield Jute yield Jabalpur (Vertisols) SOC Soybean yield Wheat yield Palampur (Alfisol) SOC Maize yield Wheat yield Bangalore (Alfisol) SOC Finger millet yield Maize yield (Source: 57)

5.5 2537 873 990

5.9 3506 2640 2090

6.4 3960 3197 2136

6.3 4299 3258 2513

8.2 4415 3770 2788

-

4.2 975 1503

5.3 1250 1909

6.7 1900 4644

7.7 2161 5703

9.9 2470 6191

-

8.2 605 725

9.0 0.0 0.0

9.7 2233 1258

10.0 4111 2041

13.6 5787 3284

10.6 5498 3116

5.3 710 1147

5.0 708 1193

4.8 846 1531

5.2 3194 5436

5.8 3781 6212

5.1 3143 5219

Indian Journal of Fertilisers, May 2014 119

carbon is crucial if agricultural productivity and environmental quality are to be sustained for future generations. Increased inputs and technologies in modern agricultural production system can often compensate for and mask losses in productivity associated with reductions in soil quality. Soil carbon serves as the energy source for microbial processes; respiration and nutrient storage and turnover are soil quality indicators vitally dependent on soil organic carbon (46). Some other important properties that could be linked to SOC are plant available water capacity, aggregate formation and stability, bulk density, soil strength, cation exchange capacity, soil enzymes etc. Important issues are discussed here under. Imbalanced Use of Nutrients The nutrients are needed to be applied as per soil test status. Balanced nutrition keeps soil healthy and productive. The imbalanced nutrition leads to low productivity and degrades the soil. It also leads to decline in soil organic carbon as evident from long term fertiliser experiments (Table 2). Moreover, Alfisols group of soils are more vulnerable with respect to

reduction in crop productivity due to imbalanced nutrient use. Therefore, balance and integrated nutrient application plays vital role in either maintaining or improving the organic carbon in soil. Rice-wheat cropping system is one of the dominant cropping systems in India. It is exhaustive and highly input demanding system including seed, fertiliser, agrochemicals, irrigation etc. These crops deplete macro and micronutrients extensively from the soil. Thus, it also results in decline in soil organic carbon to a great extent. In addition to this, nutrient application in imbalanced way has aggravated the nutrient depletion pattern as well as soil organic carbon content. From data (Table 3) it is evident that imbalance nutrient application has low carbon stock than balanced and integrated nutrient application (INM). The NPK+FYM indicated higher SOC stock across the cropping system and soil types (55, 56). Burning of Crop Residues Crop residues are not agricultural wastes rather these have potential for plant available nutrients. The scarcity of labour compels the

farmers to go for mechanical harvesting. The farmers burn the crop residues/stubbles for making crop sowing easy. Residue burning is a prevalent practice in many parts especially in the rainfed regions as it causes a lot of impediment during field operations. It is a quick, laboursaving practice to remove residue that is viewed as a nuisance by farmers. However, residue burning has several adverse environmental and ecological impacts. Crop residue burning not only results in loss of entire amount of carbon but also 80% of N, 25% of P, 50% of S and 20% of K present in straw is lost (59). Similarly, a field experiment conducted on Inceptisols (New Delhi) indicated that crop residue burning has stabilized the carbon with reduction in grain yield of both rice and wheat (Table 4) (41). On the contrary, residue incorporation recorded significantly higher organic C as well as crop productivity. Rice residue incorporation increased soil organic C by 10.6% after two cropping cycles over initial status (7.5 g kg -1 ). Therefore, the crop residues are needed to be incorporated and this practice has to be encouraged amongst farmers to maintain and improve soil health.

Table 3 – Gross total soil organic carbon and net change in SOC (Mg ha -1) in long term fertiliser experiments at 0-15 cm depth LTFE Centers/ Particulars

Control

100% N

100% NP

100% NPK

NPK+ FYM

Barrackpore (Inceptisols) Rice Wheat

0.256 0.068

0.444 0.268

0.521 0.352

0.577 0.309

0.665 0.325

Jute Total

0.129 0.452

0.212 0.895

0.279 1.114

0.300 1.145

0.413 4.646

Akola (Vertisols) Sorghum

0.338

2.042

2.743

3.263

4.710

Wheat Total

0.052 0.390

0.494 2.536

1.066 3.809

1.651 4.914

2.197 6.907

Raipur (Vertisol) Rice

0.272

0.466

0.578

0.564

0.613

Wheat Total

0.429 0.701

0.622 1.088

0.712 1.290

0.815 1.378

1.006 1.619

(Source : 55,56) Indian Journal of Fertilisers, May 2014 120

Table 4 – Impact of rice residue management on soil organic carbon (g kg -1) and crop productivity (kg ha -1) Treatments

Soil organic carbon

Grain yield Rice Wheat

Residue incorporation

8.3

3600

3900

Residue burning Residue removal

7.6 6.9

3300 3200

4000 3850

SE M (Source: 41)

0.2

115

120

Table 5 – Average loss of soil organic carbon and nutrients on silty clay-loam soil at 8% slope (Dehradun) Treatment

Soil loss (t ha -1)

Carbon

Nutrient loss (kg ha -1) N P K

Sunnhemp Jowar (fodder)

31.7 49.3

286 371

40 53

12 11

13 19

Maize Cultivated

76.1 291

538 2167

79 228

18 71

28 99

Likewise, crop residue burning also pollutes the atmosphere. If the crop residues are incorporated or retained, the soil will be enriched, particularly with organic carbon. The burning of dead plant material adds a considerable amount of CO2 and particulate matter to the atmosphere and can reduce the return of much needed C and other nutrients to the soil (8,41). The lack of a soil surface cover may also increase the loss of soil minerals via surface runoff/soil erosion. Crop residues returned to the soil maintain organic matter levels, and crop residues also provide substrates for soil microorganisms. As microbes decompose crop residues and soil organic matter, CO2 is given off as a by-product of soil respiration. Therefore, it is reasonable to believe that residue levels might affect soil surface CO 2 fluxes. As a result of this there could be detrimental impact on soil biological properties as well as greenhouse gases (GHG) emission. Burning residues emits a significant amount of GHGs. For example, 70, 7 and 0.66% of C present in rice straw is emitted as CO 2, CO and CH 4 , respectively, while 2.09% of N in straw is emitted as N2O upon burning.

Exposing of Soil to Erosion Soil erosion causes losses of natural resources in terms of soil, water and nutrients. As per estimates losses of SOC along with nutrients (N, P, K etc) are more in soil exposed due to intense tillage practices compared to covered or mulched soil (9). Legumes are considered as erosion-resistant crops primarily owing to root factor and quick canopy development. On the other hand cereals are considered as erosion-permitting crops because of manner in which they are cultivated especially Kharif cereals (maize, jowar, bajra etc) that widely spaced crops. Studies at Dehradun (4,9) have revealed that maize being a row crop recorded higher runoff, soil and nutrient losses as compared to sorghum for fodder or green manure of sunnhemp (Table 5). Therefore, focus has to be on minimizing erosion which eventually prevents the soil, water, nutrient and carbon loss for sustaining the SOC and soil health. A range of natural resource management strategies that reverse the degradation process have a large potential of C Indian Journal of Fertilisers, May 2014 121

sequestration of India. Arresting land degradation reduces the erosion and soil displacement. The predominant form of land degradation in arid and semi-arid regions of India is water erosion. Erosion displaces the fertile surface layer which contains relatively higher organic carbon. The displaced carbon eventually gets oxidized to CO2 and released in to the atmosphere. Lakaria et al. (2010) conducted a study on different canopy covers on soil and nutrients losses in red soil and reported that the highest runoff, soil and nutrient losses were recorded under cultivated fallow whereas cluster bean and sesame are effective for minimising runoff, soil and nutrients losses and these can ensure production even during poor rainy season with 413.8 mm (Table 6). Degradation of soil through soil erosion not only leads to soil organic carbon loss but also adversely affected the carbon sequestration phenomenon (Table 7). Other resultant factors like water logging, salinization, lowering of water table also causes degradation of soil and thereby there is potential loss of carbon. Although soils of the tropical regions have low C sequestration rate because of high temperatures, adoption of appropriate management practices can lead to higher C-sequestration rate particularly in high rainfall regions (61). The ecosystem C pool of cropping systems has two related but distinct components i.e. soil carbon and vegetation carbon. Tree-based systems can sequester substantial quantities of C into biomass in short period. Total potential of soil C sequestration in India is 39-49 Tg year-1 (27). This is inclusive of the potential of the restoration of degraded soils and ecosystems, which is estimated at 7-10 Tg year -1 (Table 7). The potential of adoption of recommended management practices (RMPs) on agricultural soils can lead to sequestration of an additional 6.7 to 10 Tg year -1 . In addition, there is also a potential

Table 6 – Average runoff, soil, SOC and nutrient loss under different canopy covers (Mean of 4 yrs) (Datia Dist, Bundelkhand region, MP) Canopy cover

Runoff (mm)

Soil loss (Mg ha -1)

Carbon

Nutrient loss (kg ha -1) N P

K

Cultivated fallow

253.0

8.58

72.9

9.7

2.8

7.9

Maize Caster

172.5 194.8

4.69 5.10

52.6 56.6

5.4 6.6

1.9 2.4

4.4 4.8

Caster+ Green gram Sesa me

153.3 168.7

3.69 4.26

42.2 45.8

4.5 5.2

1.7 2.0

3.2 4.7

Cluster bean Groundnut

163.0 129.8

3.96 3.63

44.3 41.2

5.0 4.4

1.7 1.3

3.6 3.1

of SIC sequestration estimated at 21.8-25.6 Tg year-1 (27). Soil erosion causes rapid fertility depletion, damages crops by sedimentation and raising stream beds/river channels by

siltation which causes flash floods and limits discharge capacity, irrigation and navigation. So, soil conservation measures (like mulching, plantation on contour) should always be a major consideration for sustainable

Table 7 – Impact on soil organic carbon sequestration potential in degraded soils Degradation process

Area (Mha)

SOC sequestration Total SOC rate (kg ha -1 year-1) sequestration potential (Tg C year -1)

Water erosion Wind erosion

32.8 10.8

80-120 40-60

2.62-3.94 0.43-0.65

Soil fertility decline Water logging

29.4 3.1

120-1250 40-60

3.53-4.41 0.12-0.19

4.1 0.2

120-150 40-60

0.49-0.62 0.01-0.012

Salinization Lowering of water table Total (Source: 27)

7.20-9.82

Table 8 – Effect of tillage and mulching on soil erosion in hill slope (5-15%) Treatment

Dry weight of eroded soil (t ha -1)

Mulch No Mulch Zero-tillage (dibble) Minimum tillage (furrow planting) Conventional tillage (Spading) Zero- tillage + Mulch Zero- tillage + No Mulch Minimum tillage + Mulch Minimum tillage + No Mulch Conventional tillage + Mulch Conventional tillage + No Mulch (Source: 33)

22.25 58.02 23.77 35.68 61.13 13.12 34.43 20.12 51.24 33.43 88.85 Indian Journal of Fertilisers, May 2014 122

agriculture especially in hilly areas (Table 8) (33). Water Availability Water is important component of agricultural system. It influences crop productivity as well as soil health to a great extent. For instance, irrigated and rain-fed system varies with respect to water availability and management. However, majority of area is under rainfed situation in India. Therefore, water which is a scarce resource influences all output and efficiency factors. The carbon sequestration is also influenced by the moisture availability in soil. The SOC sequestration found to be less in rainfed than the irrigated agricultural production system (Table 9). Lack of Crop Diversification/ Legumes in Crop Rotation Crop rotation is one of the components of conservation agriculture. It has been widely known that legume based crop rotation adds organic matter in the soil. It is due to addition of leaf litter, stubbles, decayed residues of microbes etc. On the contrary, cereal based crop rotation adds less biomass material compared to legume system. Legume based rotation has enhanced soil organic C (Table 10) compared to cereal based cropping (57). Now-a-days crop diversification

Table 9 – Soil organic carbon sequestration rates under irrigated and rainfed situation in India Location / Production SOC sequesManure/Organic system tration rate matter application (Mg ha -1 year-1) rate Rainfed Varanasi(Inceptisols) Solapur (Vertisols) Iriigated Barrackpore (Inceptisols) Akola (Vertisols)

Rice-lentil Rabi Sorghum

0.31 0.89

FYM (@ 3.55 t ha -1) Sorghum stover, Leucaena clippings (@ 3.40 t ha-1)

Rice-wheat –jute

3.67

FYM (@ 10 t ha -1)

Sorghum-wheat

1.91

FYM (@ 10 t ha -1)

(Source: 55,63)

Table 10 – Effect of crop rotation and nutrient management on SOC (g kg-1) at long term fertiliser experiments Location

Crop rotation

Akola (Vertisols) Coimbatore (Inceptisols) Jabalpur (Vertisols) Junagadh (Vertisols)

Sorghum-wheat

Control

N

NP

NPK

150% NPK

NPK+ FYM

2.9

4.5

4.9

5.3

6.6

7.9

Finger millet-Maize 3.7

4.4

5.0

5.3

5.6

6.3

Soybean-wheat

4.2

5.3

6.7

7.7

8.7

9.9

Groundnut-wheat

7.4

6.8

7.7

7.9

7.6

8.3

is coming in a great way to meet the current demand for food, fiber and fuel. It would enhance the economic status of farmers. However, crop diversification should not be at the cost of soil health i.e. over exploitation of soil resources. Legumes are integral part of cropping system to sustain soil health. Legumes add organic matter along with biological nitrogen fixation and plays important role in maintaining and improving soil organic carbon and soil physical, chemical and biological state of soil. Experiments showed that replacing the erosion permitting tobacco with drumstick and aonla in pure and agro-horticulture systems with cover crop green gram and high value small seed species cumin and fennel found remunerative and enhanced C stock in soil (58). Similarly, strip row intercropping with red gram and the other strip with soybean/ maize during Kharif and gram / mustard during Rabi were found to be successful in Vertisols of

Madhya Pradesh (43). Strategies for Management

Soil

Carbon

Soil carbon sequestration implies enhancing the concentration/pools of SOC and SIC as secondary carbonates through land use conversion and adoption of recommended management practices (RMPs) for restoration of soil health (44). There is wide range of degraded soils with a depleted SOC pool. Important amongst these are those degraded by erosion, nutrient depletion, acidification and leaching, structural decline and pollution due to contaminants (44). Grainger (1995) estimated that there are approximately 750 million ha of world’s degraded land in the tropics with potential for afforestration and soil quality enhancement. Identification and implementation of mitigation and adaptation strategies over large areas in agricultural ecosystems can be an important step Indian Journal of Fertilisers, May 2014 123

towards stabi lization sequestration of C in soils.

and

Some of the strategies for improvement of carbon sequestration potential are no-till farming with crop residue mulch and cover cropping (conservation agriculture), integrated nutrient management (INM) including use of compost and manure, and liberal use of bio-solids. A number of longterm experiments were initiated long back in the country to quantify the effect of best management practices on carbon sequestration and for improvement of productivity in various agroecoregions. There is a need to quantify the build up of soil carbon in these experiments from time to time and with a robust methodology so that the results are accurate, inter-comparable and verifiable (63). The objective of any carbon sequestration strategy are to enhance the carbon stocks in the vegetation in case of tree systems, to enhance SOC content and retain it for longer time in soil as well as improve depth wise distribution of SOC and to stabilize the SOC by encapsulating it within stable micro-aggregates so that carbon is protected from microbial processes. Adoption of appropriate land use coupled with best management practices are important elements of such a strategy. However, the exact sink capacity depends on the kind of land use and the antecedent level of SOM, climate, soil profile characteristics and the management practices adopted (26). In order to address the aforesaid issues the following strategies need to be adopted for soil carbon management. Cropping System Pulses are generally grown in neutral to alkaline soils. Pulse crops have the ability to reduce soil pH in the rhizosphere and make the microenvironment favourable to nutrient availability. The availability of nutrients in the fields cropped with pulses

increases after their harvest and their residual effects is widely observed in the following crops (2). Further, pulses leave substantial amounts of N in the soil after their harvest (60). An improvement in the N budget of soils measured by improved soil reserves of readily mineralizable organic N and microbial biomass C and N are widely reported. Increased N availability is considered one of the important factors responsible for the beneficial effects of pulses on the following non-legume crops (2). Management strategies that maintain or enhance SOC stock have the potential of improving soil resources. Leguminous crops (e.g., pulses) add significant amount of organic matter to the soil through leaf drop and root biomass. Hence, the need to reduce both the on-site and off-site impacts of cerealbased rotation is an important reason for introducing pulses into rainfed cropping systems. Both concentration and composition of organic matter input are important to soil quality. Despite the availability of voluminous literature, several question of practical importance remain unanswered. The amount of belowground biomass left in the soil depends on the species, soil type, and the residue retention. Increasing SOC concentration of cultivated soils is a major challenge. For sustainability of soil productivity in intensive agriculture, it is desirable that cropping system should be changed after few years but unfortunately the modern agriculture has ignored this concept especially in India. Rice is grown in wet and dry season as well. Most of the cropping systems are cereal-cereal (rice-wheat, maize-wheat, pearl millet-maize etc.) and very little area is under cereal-legume. The Indo-Gangetic plain which is said to be food security region of the country needs to be explored by introducing legume crop in the system. It may be exploited by introducing summer mung in between wheat-rice or by

Table 11 – Influence of cropping system on SOC (g kg -1) in soil under long-term fertiliser experiment after 34 years Treatments

Jabalpur Soybean-wheat

Pantnagar Rice -wheat

Barrackpore Rice-wheat

Control 100% N

5.8 5.0

4.5 8.0

3.9 4.7

100% NP 100% NPK

6.9 8.4

8.3 8.6

4.5 5.0

100% NPK + FYM LSD (P = 0.05)

9.9 1.3

15.4 1.2

6.0 0.8

Initial (1972)

5.7

14.8

7.1

replacing rice by Kharif pulse (Pigeon pea) or wheat by chickpea /pea. Several studies proved that legume based system improved SOC in short span of 5 years (50,52). Soybean-wheat cropping system under LTFE has resulted in improvement of organic carbon from 0.57% to 0.99% (11) at Jabalpur. Similarly, Kundu et al (2001) reported increase in SOC from 0.44 to 0.89% after 7 years in soybeanwheat system. Contrary to this cereal-cereal based system at Pantnagar and Barrackpore could not maintained initial SOC level (Table 11). Thus, review revealed that incorporation of legume into cropping system restores SOC and may help in maintaining higher SOC in soil. The C:N ratio and composition of other nutrients in crop residues of pulses is relatively high. Nutrient composition of lentil residues indicates that N concentration is almost three fold higher than that in cereal residues (i.e., rice, wheat). Similarly, higher concentrations of Ca, S and K are also reported in pulse residues, which are recycled upon incorporation into the soil. Optimal soil conditions like moisture and temperature regimes, pH, salinity/sodicity, calcareousness, SOC concentration, and stock are critically necessary for both irrigated and rainfed system. Moreover, legumes with deeper root system endures high C sequestrations in lower layers in addition to the fact that these can explore nutrients from deeper layers of the profiles and recycle to the surface layer through leaf litter. Indian Journal of Fertilisers, May 2014 124

Similarly, soil nutrients like phosphorus can be mobilised by growing chickpea through release of several organic acids in the rhizosphere. These crops add C to soil in the form of rhizodepostion also. Legume residues also provide large amounts of N, P, K, Ca, Mg, S, Zn and all other required nutrients besides biomass C (63). The C: N ratio of legume residues is narrower than those of cereal residues. Tillage Management Reducing tillage intensity is one of the important options for enhancing the soil carbon sequestration. The conventional tillage practices disrupt the soil aggregates and exposes the carbon resulting in loss of carbon. In recent years, zero tillage along with the conservation agricultural practices have been suggested for enhancing the soil carbon status. Upon conversion of plough tillage to no-till farming, the reported mean rate of SOC sequestration was 570+140 kg C ha -1 yr-1, which may lead to the new equilibrium SOC pool in 40-60 yrs (69). Similarly, Pacala and Socolow (2004) estimated, that conversion of plough tillage to no till farming on 1600 million ha of crop and along with adoption of conservation-effective measures could lead to sequestration of 0.5-1 Pg C per year by 2050. It is well documented that reduced tillage improves the SOC and availability of nutrient. However, a very little amount of crop residue

Table 12 – Effect of tillage management on SOC content (g kg -1) after six years of soybean-wheat cropping cycles in a Vertisol Depth (cm)

No tillage

Reduced tillage

Conventional tillage

LSD (P=0.05)

13.08 8.01

12.47 8.70

11.01 7.20

1.23 0.92

6.69

6.42

5.57

1.04

0-5 5-15 15-30 (source : 1)

is available for incorporation into soil after use for paper, packaging material and building material. In long term study of 45 year reduced tillage along with organic matter improved the physical condition of soil, available nutrient status (NPKs), carbon content and crop productivity (23). In India the work on tillage and SOC is very limited. Most of the studies are on short term basis. The results of 6 years old experiment conducted at IISS with reduced tillage and conventional tillage with soybeanwheat system revealed that reduced and no tillage maintained larger amount of SOC compared to conventional tillage (Table 12). Soil organic matter (SOM) is the substrate of soil biological activities and soil organic C is considered as important component of SOM. Moreover, microbial biomass C is one of the

indicators of soil health. The integrated effect of tillage and crop rotation has been favourable on organic C and microbial biomass C (Table 13). Conservation Agriculture Adoption of conservation agriculture (CA) is an emerging dimension for recycling biomass into soil system and improving SOC stock in the surface layer. It is gaining importance both in intensively irrigated and rainfed situation. A long-term study on sorghum and mung bean cropping system comprising tillage conventional tillage and reduced tillage and conjunctive nutrient use (fertilisers and low cost farmbased organics) treatments on Alfisol (Typic Haplustalf) indicated significant improvements in grain yields and sustainable yield index. To harness advantages of CA systems in semiarid tropics, it is

Table 13 – Total soil carbon and microbial bio-carbon under different crop rotations with (CT) and without tillage (NT) on an Oxisol Crop Rotations

Total C (mg g -1) CT NT

MBC (µgCg -a) CT NT

Soybean -wheat Maize-wheat

15.3 14.7

20.6 22.4

177 185

347 367

Cotton-wheat Depth: 5-10 cm

13.9

20.6

206

326

Soybean -wheat Maize-wheat

13.4 15.3

17.3 19.0

194 209

280 322

Cotton-wheat Depth: 10-20 cm

13.2

19.7

140

232

Soybean -wheat Maize-wheat

14.4 15.6

16.3 17.2

192 182

214 272

Cotton-wheat

13.8

16.2

163

204

Depth: 0-5 cm

(Source: 3) Indian Journal of Fertilisers, May 2014 125

essential to retain crop residues on the surface as mulch (27), although it is a major challenge in our country due to various competing demands of crop residues as fodder for livestock and other domestic uses. However, in rainfed condition the potential for CA exists in crops like maize, pigeon pea, castor, cotton, sunflower, etc., where crop residues are not used as feed and for other competing purposes. Conventional tillage leaves no land unploughed and leaves negligible residues in the field. In contrast, conservation tillage disturbs the soil to the minimum extent necessary and leaves at least 30% residues on the soil. Zero tillage, minimum/reduced tillage and stubble mulch tillage are the components of conservation tillage. Conservation tillage involves planting of seeds into soil that hasn’t been tilled after the harvest of the previous crop. The crop germinates on residual soil moisture left by the previous crop, saving up to low cost of cultivation, higher net returns, better water productivity and improved soil health through better management practices for sustaining crop production in the hill eco-system (37,54). Conservation tillage, in addition to time and cost effectiveness, matches well with the fragile agroecosystems and poor socioeconomic conditions of farmers. Conservation tillage to wheat with retention of the material at the surface produced grain yield either equivalent to or greater than incorporation of this material at sowing in conventional tillage in hills of North-West India (51). Reduced tillage can be successfully adopted in north-west hill without affecting productivity (54). It results in cost reduction, improved soil organic matter and water retention. Soybean-lentil and soybean-wheat are better options under reduced tillage (53). Zero tillage saved time as well as resources without sacrificing yield. Conservation tillage not only improved soil organic C but also

enhanced plant available water capacity, aggregation and soil water transmission in the ricewheat cropping system. The adoption of zero tillage increased soil organic C content over conventional tillage by approximately 300 kg C ha -1 year-1 in the 0-30 cm soil depth in the sandy clay loam soil of the Indian Himalayas. Soil disruption through conventional tillage caused a reduction in soil organic C concentration (5) in the surface soil layer (0-15 cm) (Table 14). Crop Residue Management Crop residues include any biomass left in the field after grains and other economic components have been harvested. The above ground components of crop residues include shoot, leaves, cobs, husk, etc. There are numerous ecosystem services of residue retention on cropland, especially if maintained as surface mulch. On-site, residues retention improves soil physical (e.g., structure, infiltration rate, plant available water capacity), chemical

(e.g., nutrient cycling, cation exchange capacity, soil reaction), and biological (e.g., SOC sequestration, microbial biomass C, activity and species diversity of soil biota) quality (45). Mulches are effective against soil erosion, and in decreasing losses of water by surface runoff and evaporation. Consequently, agronomic productivity and profitability are high with use of crop residues in conjunction with NT in CA. Positive impacts of crop residue retention on soil quality are partly due to nutrients recycled into the soil and increase in carbon content. On an average, crop residues contain around 0.8% N, 0.1% P and 1.3% K (44), and crop wise nutrient composition as reported by Srinivasarao et al (2011) is presented in Table 15. Consequently, the longterm impacts of residues retention on soil quality are both due to elemental cycling and through providing food (energy source) and habitat for soil biota, especially for micro-organisms and earthworms. Crop residues are also a principal source of C, which constitutes about 40% of the total biomass on dry

Table 14 – Soil organic C at rice and wheat harvest (after 4 years of cultivation) as affected by tillage at Almora Treatment 0-15 cm

Rice

Soil organic C (g kg -1) 15-30 cm

Wheat 0-15 cm 15-30 cm

Zero tillage Conventional tillage

6.71 6.23

6.03 6.05

6.78 6.35

6.09 6.12

LSD (P=0.05)

0.28

NS

0.30

NS

Table 15 – Nutrient (N, P and K) content (kg Mg-1) of crop residues Crops

N

Crop Residues P 2O 5 K2O

Total

weight basis. Moreover, increase in rate of application of biomass C increases the SOC pool. The magnitude of increase in SOC pool, however, depends on other management i nput used in combination with crop residues mulch. Components of the management packages may differ with increase in the rate of input of biomass C into the system. Because C is only one of the building blocks of stable humus and humic substances (which are enriched with N, P, S and other elements compared with crop residues), application of N and other elements can enhance the humification. Jacinthe et al. (2002) observed that fertilisation of wheat residues with N increased humification of biomass and enhanced the C sequestration rate of the soil in Central Ohio, USA. Recycling of crop residues and green manuring could also be one of the strategies to restore organic matter. Management of crop residues is either through removal, burning or incorporation into soil. Burning is a minor practice in India. In situ recycling of crop residues in rice-wheat rotation reduced grain yield of rice and wheat (65). Most of the farmers recycle the crop residues not by choice but due to use of combine harvesters. They also sometimes burn the residue causing loss of precious organic matter, plant nutrients along with environmental pollution. Experiments conducted in Punjab have shown that co-incorporation of green manure and crop residues of wheat and rice helped alleviate the adverse effects of unburned crop residues on crop yields (Table 16).

16.0

2.3

13.7

32.0

Agroforestry

5.2 8.0

1.8 2.1

13.5 9.3

20.5 19.4

4.5 12.9

1.6 3.6

11.4 16.4

17.5 32.9

Rice Sorghum

6.1 5.2

1.8 2.3

13.8 13.4

21.7 20.9

Sugarcane Wheat

4.0 4.8

1.8 1.6

12.8 11.8

18.6 18.2

Agroforestry, a land-use system that involves the deliberate introduction, retention of mixture of trees or other woody perennials with agricultural crops, pastures and/or livestock to exploit the ecological and economic interactions of different components for enhancing the productivity in unit area and time, often improves productivity of the

Groundnut Maize Oilseeds Pearl millet Pulses

(Source: 64) Indian Journal of Fertilisers, May 2014 126

Table 16 – Effects of incorporation of green manure and crop residue on grain yield of rice (t ha-1) Treatment 1988 1989 1990 1991 1992 1993 Control (No N)

4.0

4.6

3.7

4.3

150 kg N ha

-1

6.3

6.6

6.2

180 kg N ha-1

6.6

6.9

5.8

Green manuring

6.6

6.5

Green manuring + wheat straw

6.9

6.9

6.9

6.9

6.7

7.0

5.9

5.3

0.53 0.59

0.46

0.45

0.32

0.37

Green manuring + rice straw LSD (P = 0.05)

system while providing opportunities to create carbon sinks. The amount of C sequestered largely depends on the kind of agroforestry system, management practices adopted, soils and the climate of the region (40). The above ground carbon sequestration rates in some major agroforestry systems around the world vary from 0.29-15.21 Mg ha -1 yr -1 (34) and differs greatly depending on a number of factors, like the agro-climate region, the type of system, site quality, previous land use, management practices adopted, etc. in general agroforestry systems on the arid, semi-arid and degraded sites have a lower carbon sequestration potential than those on fertile humid sites. The temperate agroforestry systems have relatively lower sequestration potential compared with the tropical systems. The carbon sequestration rates in some of the predominant agroforestry systems in India are presented in (Table 17). In agroforestry systems, the carbon stored in soil ranges from 30 to 300 Mg C ha –1 up to one meter depth (34). Carbon sequestered in agroforestry systems depend on the quantity and quality of biomass added through trees and soil parameters such as soil structure and aggregation. In a poplar based system an increase in soil carbon to the extent of 6.07 t ha -1 yr-1 was observed in 0-30 cm depth in sandy clay soil compared to loamy sand. About 69% of soil carbon in the profile was confined to the upper 40 cm soil layer wherein carbon stock ranged from 8.5 to

4.1

3.4

6.5

5.7

5.6

6.7

NT

5.3

6.2

6.5

5.8

5.5

6.4

6.8

5.6

5.5

150.2 Mg C ha -1 . A mix of agroforestry with crop field is a promising option to enhance C sequestration in soils. Biochar Application The conversion of biomass carbon to bio-char leads to sequestration of about 50% of the initial carbon compared to the low amounts retained after burning (3%) and biological decomposition (less than 10-20 after 5-10 years) (28). The efficiency of conversion of biomass to bio-char is highly dependent on the type of feedstock, but is not significantly affected by the pyrolysis temperature (within 350-500 o C common for pyrolysis). According to Gaunt and Lehmann (2008), terra preta soils suggest that

bio-char can have carbon storage permanence in the soil for many hundreds to thousands of years. Large amounts of carbon in biochar may be sequestered in the soil for long-periods estimated to be hundreds to thousands of years (6,28,35,72). While biochar mineralizes in soils, a fraction of it remains in a very stable form (49); this property of biochar provides it the potential to be a major carbon sink. Compared with other terrestrial sequestration strategies, such as afforestation or reforestation, carbon sequestration through bio-char increases its storage time (35,70). The slash-and burn system cause significant degradation of the soil and release of greenhouse gases. However, it also provides opportunities for improvement by conversion of the slash-and-burn system to the slash-and-char system. About 12% of the total anthropogenic carbon emissions by land-use change (0.21 Pg C) can be offset annually in the soil, if the slash-and-burn system is replaced by the slash-and char system. The principal mechanisms operating in soils through which bio-char entering, the soil is stabilized and significantly increase its residence time in soil

Table 17 – Carbon sequestration rates in some of the predominant agroforestry systems in India System (Location)

Carbon sequestration (Mg C ha -1) Leucaena agri-silvi system (Chandigarh) 0.87 Anogeissus agri-silvi system (Jhansi, UP) 1.36 Leucaena silvi-pasture system (Jhansi, UP) 1.82 Terminalia silvi-pasture system (Jhansi, UP) 1.11 Albizia silvi-pasture system (Jhansi, UP) 2.01 Dalbergia sissoo silvi-pasture system (Jhansi, UP) 2.90 Casuarona agri-silvi system (Coimbatore, TN) 1.45 Leucaena agri-silvi system (Bhadrachalam, AP) 17.7 Eucalyptus agri-silvi system (Bhadrachalam, AP) 7.5 Prosopis silvi-pasture system (Karnal, Haryana) 2.36 Acacia silvi-pasture system (Karnal, Haryana) 1.29 Dalbergia sissoo silvi-pasture system (Karnal, Haryana) 5.68 Leucaena monoculture (Hyderabad, AP) 5.65 Eucalyptus monoculture (Dehradun, UP) 5.54 (Source: 63) Indian Journal of Fertilisers, May 2014 127

Table 18 – Soil organic C, aggregate stability and bulk density of soil as influenced by long-term cropping, fertiliser, lime and organic manure application (0-15 cm) Treatments

Soil organic C (kg ha -1)

Mean weight diameter (mm)

Water stable Bulk density macroaggregates (%) (Mg m -3)

Control

6900

0.59

42.7

1.36

100% N 100% NP

6600 7500

0.51 0.65

31.4 44.8

1.38 1.36

100% NPK 100% NPK + lime

8000 8200

0.74 0.85

49.8 55.6

1.33 1.30

100% NPK + FYM Average

8400 7600

0.91 0.71

55.6 47.2

1.30 1.33

are intrinsic recalcitrance, spatial separation of decomposers and substrate, and formation of interactions between mineral surfaces (71). In a fifteen weeks biochar carbon stability study, Purakayastha et al. (2013) reported that the carbon loss ranged from 2.34% in maize biochar to 4.49% in rice bio-char. Among the bio-chars, maize biochar showed lowest carbon mineralization suggesting its greater potential for long-term carbon sequestration. Application of biochar showed highest amount of carbon in soil under wheat-pearl millet cropping system. The findings of a recent modeling study (73) reported that biochar amendments to soil, when carried out sustainably, may annually sequester an amount of C equal to 12% of the current anthropogenic CO2 emissions. They estimated that the maximum sustainable technical potential for carbon abatement from biochar is 1-1.8 giga ton (Gt) C per year by 2050. Technical estimates of the potential for biomass pyrolysis coupled with soil storage to sequester carbon suggest the several hundred giga tons of carbon emissions could be sequestered or offset by 2100, which is a large fraction of the needed to mitigate global climate disruption. It is also easy to monitor carbon sequestration as a climate change mitigation measure for national carbon accounting (12,14,28,74). It can be done by using the income generated and the quantity of carbon that has been sequestered

(12). Production and application of biochar to farm soils can tackle many global and domestic policy issues. Nevertheless, the application of bio-char at the farm level is discouragingly slow, largely due to financial constraints. Integrated Nutrient Management (INM) Integrated nutrient management play an important role in maintaining soil fertility and in turn soil health by improving physical, chemical and biological state of the soil. Studies reported by Hati et al. (2008) in 34 years old experiment of LTFE at Ranchi revealed that integrated use of nutrient with FYM and lime resulted improvement in organic carbon which in turn improved the mean weight diameter, water stable aggregate and reduced the bulk density (Table 18). The change in physical properties has favourable effect on soil productivity. Integrated nutrient management (INM) is also essential to SOC sequestration. The humification process can be severely constrained by the lack of N, P, S and other building blocks of soil humus (44). The efficiency of C sequestration is reduced when C and N are not adequately balanced (38). Therefore the SOC sequestration rate is enhanced by an increase in the application of biomass C (7,20) and N (18). They observed that high N rate treatments increased SOC Indian Journal of Fertilisers, May 2014 128

sequestration rates by 1.0- 1.4 Mg C ha -1 yr -1 compared with unfertilised controls. In Victoria (Australia), Ridley et al (1990) observed that application of P and lime increased the SOC pool in the 0-10 cm layer at an average rate of 0.17 Mg C ha-1yr-1. Similarly nutrient management in a particular system/soil also affects the turnover rate of carbon. In LTFE balanced nutrient use of nutrients resulted decline in turnover (the period required to maintain/ restore initial state of SOC) of carbon from 66 to 40 years at Barrackpore (Inceptisols) in ricewheat-jute and from 67 to 10 years in sorghum- wheat cropping system at Akola (Vertisols) (Table 19) (55) and it has further shortened with integrated nutrient management to 5.4 and 8.1 years, respectively. It means with regular application of NPK + FYM at these location will take only 5.4 (Barrackpore) and 8.1 (Akola) years to bring back the soil to initial state of carbon. Best Management Practices The best management practices (BMP) are defined as those practices which have been proven in research and tested through farmer implementation to give optimum production potential, input efficiency and environmental protection (16,22,30). According to FDCO and FAO, the BMP are set of agronomic and other soil-crop management practices which lead to the best

Table 19 – Initial value steady-state value overall rate of loss, rate of addition, and period of turnover, soil biological activity in long-term fertiliser and manuring at Barrackpore and Akola Treatment

Initial Soil C (Mg ha -1)

Barrackpore (Rice-wheat-jute) Control N NP NPK NPK+FYM Akola (Sorghum-wheat) Control N NP NPK NPK+FYM

SOC after 29 years (Mg ha -1)

C loss rate Mg C ha-1Yr 1 /Mg C ha-1

Turn over period (Yr)

15.62 – – – –

11.2 12.3 12.5 15.8 19.6

0.015 0.020 0.025 0.020 0.187

66 50 40 50 5.4

10.12 – – – –

9.90 11.66 12.32 12.98 15.40

0.015 0.060 0.086 0.105 0.124

67 17 12 10 8.1

Table 20 – Impact of resource conservation technologies on carbon and microbial properties of soil in rice Treatment

Soil C (g kg -1)

Bacteria (x 10 7)

Fungi (x 104)

Actinomycetes (x 105)

MBC (µg g -1)

DSR

5.6

106.51

19.50

31.25

157.90

SRI Conventional

6.1 5.5

238.62 170.25

26.40 19.35

37.60 28.30

192.20 162.20

5.0 0.23

89.45 4.9

8.2 2.6

17.24 4.7

91.20 6.45

Control SEM (±)

possible use of applied inputs for crop production, resulting in minimal adverse effect on the environment. It is a prerequisite for efficient and environment friendly fertiliser use that is important for all soils crops and fertilisers (66). These practices aimed at managing the flow of nutrients in the course of producing affordable and healthy food in a sustainable manner that protect the environment and conserve natural resources at the same time profitable to produce. The basic principle behind these practices is simple, that is the 4 R’s. Using the right fertiliser source at the right rate, right time and right place which conveys how nutrient application can be managed to achieve economic, social and environmental goals. The adoption of these practices would also depend on the main objectives of the farmers and the society e.g. Increase profitability, improve yields and/or protect the environment. These practices

ultimately result in increasing crop productivity and nutrient use efficiency. One of the best management practices of rice cultivation i.e. SRI (system of rice intensification) was compared with direct seeded rice (DSR) and conventional rice cultivation in rice – wheat cropping system. The agronomic package for SRI method of cultivation involved soil amendment @ 10 t FYM per ha during final land preparation, transplanting of rice with 10 days old seedlings (@ 1 seedling per hill) and square planting (30 x 30 cm), applying irrigation at hair crack stage and three interculture operation with cano weeder (at 15, 30 and 45 days after transplanting of rice) to give proper aeration of soil (39). During initial years the magnitude of increase in SOC was non-significant but afterwards gradually increased (Table 20). The study also indicated that improvement of soil organic Indian Journal of Fertilisers, May 2014 129

carbon in rice-wheat cropping under resource conservation technologies (RCT) has resulted in increase in microbial population and microbial biomass carbon (MBC). FUTURE RESEARCH AREAS Soil carbon is not only important for performing soil functions but also essential to safeguard environment. Soil is a good sink for atmospheric CO 2 . So, all efforts should be made to sequester carbon in soil. In order to keep pace with soil sustainability and climate change following areas needs immediate attention. ♦ Research carried all over the

world proved that for sequestration of carbon due care should be given to the best nutrient management especially N, S and K that would help sequestering carbon as N and S are part of humus which are resistant to decay and also got long life.

♦ Due to non availability of

manpower and time crops are mechanically harvested. It leaves straw on surface and for easy sowing operation straw is burnt by the farmers. Researcher should pay attention to develop machinery to combat the problem encountered due to mechanical harvesting. This will increase soil carbon and at the same time mitigate environment hazards. ♦ Residue incorporation is one of

the ways to enhance soil carbon but it is not possible everywhere due to other competitive uses. Identify the residue which has less demand for other uses and develop technology to recycle and incorporate crop residues into the soil. Loss of soil carbon through erosion is one the major channels of loss particularly cereal-cereal system. Therefore a legume should be incorporated into cropping systems, which would not only conserve soil carbon but also retain nutrients and improve soil health. ♦

♦ No-till/minimum tillage and

conservation agriculture no doubt is well proven method to sequester carbon. However, due to practical difficulty like management of weed and residues, it is not gaining momentum. Therefore, it is urgent need to address issues related to weed management and sowing of next crop by developing machine in context to tillage practices on regional and soil type basis.

Increase the research and development support for development of innovative technology to accelerate total C sequestration. ♦

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