Impact of Organic Food Production on Soil Quality

Conservation Agriculture for Advancing Food Security in Changing Climate, Vol. 1

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Conservation Agriculture for Advancing Food Security in Changing Climate Vol. 1 (2018) : 409-418 Editors : Anup Das, KP Mohapatra, SV Ngachan, AS Panwar, DJ Rajkhowa, Ramkrushna GI and Jayanta Layek Today & Tomorrow’s Printers and Publishers, New Delhi - 110 002, India

Impact of Organic Food Production on Soil Quality RK Avasthe*, Subhash Babu, Raghavendra Singh and SK Das ICAR Research Complex for NEH Region, Sikkim Centre, Tadong, Gangtok, Sikkim (ICAR-National Organic Farming Research Institute) *e-mail: [email protected]

Introduction In agriculture, soil fertility declines over time due to continuous extraction of nutrients with crop harvest, soil acidification and other faulty anthropogenic activities. It is estimated that Global fertilizer use increased to 208.0 mt. by 2020 (Byrnes and Bumb, 1998). However, despite use of new and improved crop varieties and chemical fertilizers, crop yield began to slow down in the later part of the 20th century. The world’s annual cereal yield growth rate has declined from an average of 2.2 per cent in the 1970s to 1.1 per cent in the 1990s (Gruhn et al., 2000). Thus, nutrient management through organic farming helps stabilizing soil fertility via improving nitrogen fixation and reducing nutrient leaching. Recently, soil condition has also been affected by climate change and an increase in the prevalence of severe weather events.There is a need for innovative farming elucidations to improve soil health so that food production resilience may be ensured. The following have been identified as the main threats to soil management. Soil organic matter decline reduces soil quality, affecting fertility, structure, water retention capacity, soil biodiversity and carbon storage. Soil erosion can be accelerated by soil cultivation, leading to the loss of soil due to the action of water, tillage or wind. Compaction by farm machinery leads to a decline in a soil’s capacity to retain water and supply oxygen to roots. This can lead to soil erosion,

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increased water runoff and GHG emissions. Soil sealing occurs where soil is permanently covered by concrete or tarmac etc. It is caused by urban and industrial sprawl, leading to a long-term loss of fertile soils. Biodiversity decline (e.g. soil microbes and soil animals) is affected by all of the above and also climate change. Soil microbes benefit crop production because they decompose organic matter, release nutrients in a plant available form (e.g. nitrogen mineralization), stabilize soil structure and can control soil-borne pests and diseases. Soil contamination with chemicals or pests and pathogens, results when hazardous substances are either spilled or buried directly in the soil, or migrate to the soil from elsewhere. How can soil quality be improved? To improve the fertility of soil, a number of interventions are often made (e.g. the use of organic fertilizers and conservation tillage), which can also affect soil properties such as nutrient status, pH, organic matter content and physical properties. Such interventions can, however, be detrimental to other ecosystem services, leading to conflicting management options for agricultural soils. The following practices can be adopted by farmers to improve agricultural soils, (e.g. the organic matter content, climate change mitigation potential, physical properties and water holding capacity of soil): Adding organic material to help preserve the structural integrity of soils, e.g. crop residues, animal manures and the targeted use of legumes. Reduced tillage practices (where soil is no longer turned over before sowing) can benefit soil structure, fertility, rates of root growth, water infiltration, reduce rates of erosion and possibly reduce GHG emissions. Precision agriculture to deliver targeted nutrient and herbicide applications, based upon variability within the field. Intercropping where at least two or more crop species are grown on the same plot of land. The species use nutrients, water and light differently, so that they do not compete. Intercropping with legumes can introduce N into the soil, whilst deep-rooted plants can make nutrients in the subsoil available. Contour ploughing across a slope following elevation contour lines, forms a natural barrier to water flow down the slope, reducing run-off. Contour


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ploughing can become dangerous if the slope is too steep. Diversification of production types including perennial food crops, nuts and fruit, using whole-system oriented approaches, such as those found in crop rotations and permaculture. Paradigm shifts in agriculture Before 20th century traditional farming practices generally regarded as ‘organic’ but the introduction of synthetic farm inputs such as urea and DDT to increase crop yield over the traditional practices enhanced use of chemicals in agriculture. Organic food attained a special identity in 1960s but identification of organic sources, standardization of production methodology and its application in agricultural field received serious concern only after a long gap. Sir Albert Howard, referred to as the father of modern organic agriculture documented traditional Indian farming practices as superior to the conventional agriculture. During the 1st quarter of 20th century, Rudolf Steiner’s approaches biodynamic agriculture was probably the first comprehensive document on organic farming system. In 1909, American agronomist F.H. King after visiting China, Korea, and Japan for studying traditional fertilization, tillage, and general farming practices, published a book i.e. ‘‘Farmers of Forty Centuries’’. In the later years his book became an important reference for the introduction of new and improved methods (Paull, 2006). Masanobu Fukuoka devoted his 60 years for developing a radical no-till organic method for growing grain and other crops, now commonly known as nature farming or Fukuoka farming. The international campaign of Green Revolution launched in Mexico in 1944 with private funding from the US encouraged the development and use of hybrid plants, chemical controls, large-scale irrigation, and heavy mechanization in agriculture around the world. Rachel Carson’s Silent Spring, which appeared in 1942, chronicling the effects of DDT and other pesticides on the environment (Paull, 2007) is considered to be a basic driver in the US government’s banning of DDT. The International Federation of Organic Agriculture Movements (IFOAM) was founded in 1972 at Versailles, France, to exchange information on the principles and practices of organic agriculture across national and linguistic boundaries. Fukuoka’s first book, The One-Straw Revolution, appeared in 1975 advocates for a meticulous balance of local farming system and minimum human interference. The key characteristics include protecting the long-term fertility of soils by maintaining organic matter levels, fostering soil biological activity, careful mechanical intervention, nitrogen selfsufficiency through the use of legumes and biological nitrogen fixation,

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effective recycling of organic materials including crop residues and livestock wastes and weed, and diseases and pest control relying primarily on crop rotations, natural predators, diversity, organic manuring, and resistant varieties. Countless emphasis is placed to maintain the soil fertility by returning all the wastes to it chiefly through compost to minimize the gap between NPK addition and removal from the soil. The prolonged and overusage of chemicals has, however, resulted in human and soil health hazards along with environmental pollution. Farmers in the developed countries are, therefore, being encouraged to convert their existing farms into organic farm. The key factors affecting consumer demand for organic food is the health consciousness and the willingness of the public to pay for the high-priced produce. In general, consumers of organic products are an affluent, educated and health conscious group spurred by strong consumer demand, generous price premium, and concerns about the environment. Because of these hidden benefits, conventional growers are turning to organic farming. As mentioned in Arthashastra, farmers in the Vedic period possessed a fair knowledge of soil fertility, seed selection, plant protection, sowing seasons, and sustainability of crops in different lands. The farmers of ancient India adhered to the natural laws and this helped in maintaining the soil fertility over are latively longer period of time. Effect of organic food production on soil quality Agriculture intensification and anthropogenic activities affect the soil quality at all levels, including the structure and function of soil microbial communities. Farming management systems alter the soil microbial community structure through changes in carbon availability, pH (Cookson et al., 2007), nutrient availability or other chemical parameters. During past few years, conventionally managed agricultural system has used synthetic fertilizer and pesticides to improve crop productivity. This intensive use of agrochemicals will definitely reduce the biodiversity, increase irreversible erosion of soil and reduce soil organic matter (Schiavon et al., 1995). For sustainable organic food production, we have to apply organic manure to maintain soil health. An organically applied fertilizer affects both the chemical and physical properties of the soil and its overall health. Properties influenced by organic fertilizers include: soil structure; moisture holding capacity; diversity and activity of soil organisms, both those that are beneficial and harmful to crop production; and nutrient availability. An organic fertilizer influences the physical conditions of a soil in several ways. Plant residues that cover the soil surface protect the soil from sealing and crusting by raindrop impact, thereby, enhancing


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rainwater infiltration and reducing runoff. Increased organic matter contributes indirectly to soil porosity. Fresh organic matter stimulates the activity of macrofauna such as earthworms, which create burrows lined with the glue-like secretion from their bodies and are intermittently filled with worm cast material. Increased levels of organic matter and associated soil fauna lead to greater pore space with the immediate result that water infiltrates more readily and can be held in the soil. The less the soil is covered with vegetation, mulches, crop residues, etc., the more the soil is exposed to the impact of rain drops. Increased soil cover can result in reduced soil erosion rates close to the regeneration rate of the soil or even lower. Soil erosion fills surface water reservoirs with sediment, reducing their water storage capacity. When the soil is protected with mulch, more water infiltrates into the soil rather than running off the surface. This causes streams to be fed more by subsurface flow rather than by surface runoff. Organic sources of nutrients At present, most optimistic estimates show that about 25–30 percent of nutrient needs of Indian agriculture can be met by various organic sources (Yadav et al., 2013). Supplementation of entire N through FYM sustains crop productivity more than the use of conventional N fertilizers. FYM, compost, crop residue, non-edible oil cakes, green manuring, intercropping with legumes, biofertilizers and by products of agro industries are the major sources of plant nutrients. These organic sources besides supplying N, P, and K also make unavailable sources of elemental nitrogen, bound phosphates, micronutrients, and decomposed plant residues into an available form to facilitate the plants to absorb the nutrients. The farmers can in turn, get good remuneration from organically produced crops and if included in high value crop rotations, that is, aromatic rice due to their heavy demands in domestic, national, and international markets. Nutrient concentrations in FYM are usually small and vary greatly depending upon source, conditions, and duration of storage. The N, P, and K contents of fresh FYM range widely from 0.01 to 1.9 per cent on dry weight basis due to variable nature of manure production and storage. The rural and urban composts on an average contain about 0.5 to 1.0 per cent N, 0.4 to 0.8 per cent P2O5 and 0.8 to 0.12 per cent K2O. The average nutrient content in various crop residues is 0.5, 0.6 and 1.5 per cent N, P 2O5 and K2 O, respectively. With regards to green manuring, nitrogen content on dry weight basis in green manure crops ranges from 2.0 to 3.0 per cent. However, nutrients content in green leaf manure crops ranges from 1.5 to 2.5 per cent on dry weight basis. Besides, these sources, biofertilizers and vermicompost also valuable source of organic nutrients. It is estimated

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that the Rhizobia, Cyanobacteria, and Azospirillum can fix nitrogen in the range of 25-300, 15-25 and 10-30 kg/ha/annuum, respectively. On an average nutrient content in vermicompost ranges between 1.5 – 2.5 per cent nitrogen, 0.9 – 1.7 per cent phosphorus, 1.5 – 2.4 per cent potash, 0.5 – 1.0 per cent Calcium, 0.2 – 0.3 per cent magnesium and 0.4 - 0.5 per cent sulphur. Organic production systems and soil physical parameters Crop rotation as an indispensable component of organic production system is a cultural practice whose application varies in dependence of type of production and soil fertility. Unlike the conventional production systems in which crop rotation is not always carefully followed, the organic agriculture applies strict different crops with legumes. Besides that organic fertility inputs improves soil physical properties by lowering bulk density, increasing water-holding capacity, and improving infiltration rates (Sadanandan and Hamza, 2006). Lower bulk density implies greater pore space and improved aeration, creating a more favorable environment for biological activity (Werner, 1997). Tester (1990) also found that amending soil with compost significantly decreased bulk density and increased soil water content. Organic matter is the major component that stimulates the formation and stabilization of granular and crumb type of aggregates (Brady, 1996). As organic residue decompose organic acids, sugars, mucilaginous substances, and other viscous microbial byproducts are released, which along with associated fungi and bacteria, encourage the crumb formation and net effect of these activities will decrease bulk density and increase porosity as reported by Loganathan (1990). Higher organic matter addition could increase organic carbon content of the soil which resulted in an increased water holding capacity of the soil. The humus can absorb water two to six times its own weight. Soil organic matter is responsible to a great extent, directly or indirectly for making the physical environment of the soil suitable for the growth of crops. It exerted this benefit largely through its effect on improving soil aggregation and porosity, which in turn influenced soil structure, water infiltration, moisture conservation, drainage, aeration, temperature, and microbial activities. Organic production systems and soil chemical properties In organic farming entire crop nutrient demand supply though organic manures, which contents very high amount of organic carbon. Organic farming increases soil organic matter (SOM) content (Goh et al., 2001; Bhat and Sujatha, 2006; Yadav et al., 2013a) and humic substances (Nardi et al., 2002). During the transition years from conventional to organic


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systems, most soils show a slow but steady increase in SOM (Clark et al., 1998). Wander et al. (1994) proposed that the quality of SOM may even be more important than the quantity of SOM present in farming systems that use cover crops and other organic inputs and those that do not. Clark et al. (1998) found that SOM levels in the 0-30 cm depth had increased in the organic and low-input treatments by 19% after four years of organic practice. Alvarez et al. (1988) found a positive correlation between SOM content and available Ca, K, Mg, Na, and P. The higher availability of N, P, K, Ca, Mg, Mn, Zn and Cu under organic nutrient supply systems was reported by Pankajam and Devi (2009). They also observed pH increment of acidic soils due to the suppression of the activity of Fe and Al oxides and hydroxides, which played a vital role in protonation - deprotonation mechanism, controlling H+ ion concentration in soil solution. A typical value of CEC of humic colloids is of the order of 200-250 cmol (p+) kg-1 (Sanyal, 2002). Organic manure with higher amount of active humic fraction having high CEC had thus resulted in maximum enhancement of this parameter. Organic production systems and soil-biological properties Soil microbes are among the most important components to regulate SOM decomposition and nutrient cycling. An acre of living topsoil contains approximately 900 pounds of earthworms, 2,400 pounds of fungi, 1,500 pounds of bacteria, 133 pounds of protozoa, 890 pounds of arthropods and algae, and even small mammals in some cases (Pimentel et al., 2005). Microbial biomass in natural soils ranges between 90 and 2300 μg per gram of dry soil. However, active microbial biomass in agricultural soils range between 75 and 272 μg per gram of dry soil indicating that much of soil microbial biomass may be present in a dormant state (Bae et al., 2002). A balanced ratio of microbial biomass and activity is needed to consistently release nutrients for plant and microbial growth. Scientific research has demonstrated that organic agriculture significantly increases the density and species of soil’s life. Suitable conditions for soil fauna and flora as well as soil forming and conditioning and nutrient cycling are encouraged by organic practices. Organic supplements are easily colonized by microbes and increase other soil properties maintaining fertility stability. Organically managed soil has higher soil microbial activity and biological processes (Petersen et al., 1999; Yadav et al., 2013b; Singh et al., 2015).Enzymatic activities especially dehydrogenase activity commonly used as indicator of biological activity in soils because of its occurrence only within living cells, unlike other enzymes which can occur in an extra cellular state. Higher

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enzymatic activities under organic management systems as compared to its counterpart (conventional production systems) have been reported by several workers (Kremer and Li, 2003, Melero et al., 2006; Masto et al., 2006; Yadav et al., 2013b; Babu et al., 2015). Although, organic amendments can often contain enzymes, the increase in the activity of soils amended with organic residues is likely due to the stimulation of microbial activity rather than the direct addition of enzymes from organic sources (Martens et al., 1992). Conclusion Organic production systems have improved soil physico-chemical properties over modern chemical farming systems. The organic production system also encourages soil microbes in their ecological niche as help to facilitate the process of mobilization of nutrients. This enhanced population of microbes in would therefore, enhance the soil fertility in the years to come without application of hazardous chemicals. References Alvarez, C.E., Garcia, C. and Carracedo, A.E. 1988. Soil fertility and mineral nutrition of an organic banana plantation in Tenerife. Biol. Agri. Hort. (5): 313-323. Babu, S., Rana, D.S., Yadav, G.S., Singh, R., and Chettri, T.K. 2015. Effect of sunflower stover and nutrients management on soil biological properties and available nitrogen and phosphorus at different stage of pigeonpea growth under pigeonpea-sunflower cropping system. African J. Plant Sci. 9(6): 264-273. Bae, Y-S., Knudsen, G.R. and Dandurand, L.M.C. 2002. Influence of soil microbial biomass on growth and biocontrol efficacy of Trichoderma harzianum. Plant Path. J. (18): 30-35. Bhat, R. and Sujatha. S. 2006. Soil fertility status of ultisols as influenced by arecanut based cropping system and nutrient management through organic matter recycling. 18 th World Congress of Soil Sci. Philadelphia, PA. USA. Brady, N.C.1996. The nature and properties of soils. Tenth edition. Prentice Hall of India Pvt.Ltd. Agron. J. (54): 464-465. Byrnes, B.H. and Bumb, B.L. 1998. Population growth, food production and nutrient requirement. J. Crop Prod. (1): 1-7. Clark, M.S., Horwath, W.R., Shennan, C. and Scow, K.M. 1998.Changes in soil chemical properties resulting from organic and low-input farming practices. Agron. J. 90: 662-671. Cookson, W., Osman, M., Marschner, P., Abaye, D., Clark, I. and Murphy, D. 2007. Controls on soil nitrogen cycling and microbial community composition across land use and incubation temperature. Soil Biol. Biochem. (39)(3): 744–756. Goh, K.M., Pearson, D.R. and Daly, M.J. 2001. Effects of apple orchard production systems


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