AGRICULTURE MANAGEMENT PRACTICES IN RELATION TO SOIL CARBON SEQUESTRATION: A REVIEW

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1 Agric. Rev., 30 (4) : , 2009 AGRICULTURAL RESEARCH COMMUNICATION CENTRE / indianjournals.com AGRICULTURE MANAGEMENT PRACTICES IN RELATION TO SOIL CARBON SEQUESTRATION: A REVIEW Shachi Shah and V.Venkatramanan* Department of Basic Science, College Of Forestry and Hill Agriculture G. B. Pant University of Agriculture and Technology, Hill Campus Ranichauri , India ABSTARCT Growing interest in the potential for agricultural soils to provide a sink for atmospheric carbon has prompted studies of effects of management on soil organic carbon (SOC) sequestration. Adding organic matter to land is good for soil quality and crop yields, both short-term and long-term. While mitigating climate change by off-setting fossil fuel emissions, it also improves quality of soil and water resources, and enhances agronomic productivity. Strategies to increase the soil carbon pool include reducing tillage intensity and frequency, eliminating tillage, changing crop rotations, using winter cover crops, eliminating summer fallow, improving fertilizer management, adjusting irrigation methods, changing grazing regimes, soil restoration and woodland regeneration, water conservation and harvesting, agroforestry practices, and growing energy crops on spare lands. Soil carbon sequestration is a natural, cost-effective, and environ-mentally-friendly process. Once sequestered, carbon remains in the soil as long as restorative land use and best management practices are followed. Creation of a market for reducing carbon emissions would enable farmers to benefit economically from the process. Key words: Atmospheric carbon, Soil organic carbon, Agricultural practices. Soil carbon sequestration is the process of transferring carbon dioxide from the atmosphere into the soil through crop residues and other organic solids, and in a form that is not immediately reemitted. This transfer or sequestering of carbon helps off-set emissions from fossil fuel combustion and other carbon-emitting activities while enhancing soil quality and long-term agronomic productivity (Sundermeier et al., 2005). Soil organic carbon is essential to maintain a good physical condition and to absorb, retain and supply water and nutrients to crops (Franzluebbers and Steiner, 2002; Stephen et al., 2004). Soils store a significant amount of carbon. Global soils contain approximately 1.53 to 1012 metric tons of carbon (Post and Kwon, 2000). The global soil organic carbon pool, 1550 Pg, is twice the atmospheric pool and three times the biotic pool (Lal, 1997). An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossil fuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions (Lal, 2004 (a) and Lal et al., 1995). * Indian Agriculture Research Institute, New Delhi , India.

2 302 AGRICUTURAL REVIEWS Factors affecting carbon sequestration on agriculture land Restoring soil carbon levels worldwide is important for a number of purposes, including reducing atmospheric CO 2 concentrations (Lal, 2004 (b)). Several key agricultural practices are primarily responsible for changes in agricultural soil C (Parton et al., 1988, 1987). The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management (West and Post, 2002; Lal, 2004 ). In cooler climates, decomposition happens more slowly, so the plant residue has a greater chance of becoming humus, which is a stable part of soil with high organic carbon content. Likewise poorly drained soil types have the capacity to store carbon more readily than others (Pendel et al, 2005). Crops like wheat and corn produce higher amounts of residue, i.e., more organic matter (and more carbon) is left after harvest. Warm season grasses in conservation buffers are more effective at storing carbon than cool season grasses. Making certain plant choices can help capture more carbon from the atmosphere and make it available to processes that may lead to longer-term storage (Doster et al., 1983; Klemme, 1996; Hopkins et al., 1996; Stephen et al., 1987). Agriculture management practices that sequester soil carbon Many promising practices for soil carbon sequestration have been identified (Kimble et al., 2002). Appropriate practices differ for different soil, crop, and climate conditions (Antle et al., 2002; 2003). A single land use or management practice will not be effective at sequestering C in all regions (Lal et al., 1998). Cole et al., (1996) estimated that globally, over the next century, agricultural soils could sequester 40 to 80 billion metric tons of Carbon. The changes in land management that enhance soil C storage include reducing tillage intensity and frequency, eliminating tillage, changing crop rotations, using winter cover crops, eliminating summer fallow, improving fertilizer management, adjusting irrigation methods, implementing buffer or conservation strips, and changing grazing regimes, soil restoration and woodland regeneration, manuring and sludge application, improved grazing, water conservation and harvesting, agroforestry practices, and growing energy crops on spare lands (Lal,1999; Powell et al., 2002; Follett et al., 2001; Lobell and Anser, 2003; Follett, 2006; Stephen, 2004; Halvorsone and Curtis, 2007 and Bricklemyer et al., 2006). CARBON STORED ON LANDS By management system Crop land Crop/grass land conversion Trees/wetland conversion Cultivation of organic soils By tillage system Intensive tillage Moderate tillage No till Source: Smith, P. et al., Tons of carbon stored / acre tons/acre tons/acre tons/acre tons /acre Tons of carbon stored / acre tons/acre tons/acre tons/acre

3 Vol. 30, No. 4, COMPARISON BETWEEN TRADITIONAL AND RECOMMENDED MANAGEMENT PRACTICES IN RELATION TO SOIL ORGANIC CARBON SEQUESTRATION Traditional methods Recommended management practices 1.Biomass burning and residue removal Residue returned as surface mulch 2. Conventional tillage and clean cultivation Conservation tillage, no till and mulch farming 3.Bare/idle fallow Growing cover crops during the off-season 4.Continuous monoculture Crop rotations with high diversity 5.Low input subsistence farming and soil Judicious use of off-farm input fertility mining 6.Intensive use of chemical fertilizers Integrated nutrient management with compost, biosolids andnutrient cycling, precision farming 7.Intensive cropping Integrating tress and livestock with crop production 8.Surface flood irrigation Drip, furrow or sub-irrigation 9.Indiscriminate use of pesticides Integrated pest management 10.Cultivating marginal soils Conservation reserve program, restoration of degraded soils through land use change Source: Lal, R (b). 1) Conservation tillage It is widely believed that soil disturbance by tillage was a primary cause of the historical loss of soil organic carbon (SOC) and that substantial SOC sequestration can be accomplished by changing from conventional plowing to less intensive methods known as conservation tillage (Baker et al., 2007).Over the past two decades, conservation tillage has evolved primarily for erosion control. While tillage and cultivation generally result in loss of soil C and nitrogen (Mann, 1986), conservation tillage has proved to have the potential for converting many soils from sources to sinks of atmospheric C (Kern and Johnson, 1993). Lal et al., (1998) estimated that widespread adoption of conservation tillage on some 400 million ha of cropland by the year 2020 may lead to total C sequestration of 1500 to 4900 Mg. 2) Reduced tillage /no till farming Soil tillage practices are of particular significance to the soil C status because they affect C dynamics directly and indirectly. Tillage practices, which invert or considerably disturb the surface soil, reduce SOC (Lal, 1984; 1989). Conversely, long-term NT or reduced tillage systems have shown to increase SOC content of the soil surface layer as a result of various interacting factors, such as increase residue return, less mixing and soil disturbance, higher soil moisture content, reduced surface soil temperature, proliferation of root growth and biological activity, and decreased risks of soil erosion (Lal, 1989; Blevins and Frie, 1993). Long-term NT or reduced tillage systems have shown to increase SOC content of the soil surface layer as a result of various interacting factors, such as increase residue return, less mixing and soil disturbance, higher soil moisture content, reduced surface soil temperature, proliferation of root growth and biological activity, and decreased risks of soil erosion (Lal, 1989; Standely et al.,1990 and Blevins and Frie, 1993).Compared to estimates of the potential for carbon sequestration of other carbon mitigation options, no-till agriculture shows nearly twice the potential of scenarios whereby soils are amended with organic materials (Smith et al., 1998 and Robertson et al., 2000).

4 304 AGRICUTURAL REVIEWS 3) Legumes and/or grasses in crop rotation Maximizes the amount of carbon pulled into plant matter per unit of land as well as planting legumes, as a cover crop is a good way to replenish nitrogen levels in the soil as well as adding carbon to the soil. There is clearly carbon storage benefic in using legume crops resulting from increased plant residue input and increased soil organic carbon content as compared to the application of inorganic fertilizers. The nutrient use efficiency of plants grown with chemical-n fertilizer is approximately 60% or lower. For a 5-year rotation with two hay crops per rotation cycle, total CO 2 -C emission that is avoided in a 75- year period is 30 tons. Over the same period, soil carbon storage increase with manure application of 2 tons of carbon per year is approximately 30 tons/ha, with a total manure carbon input of 150 tons/ha (Bricklemyer, et al., 2002). More importantly, the carbon emission savings from using legume plants is permanent while soil carbon content increase resulting from increased inputs need to be maintained continuously (Campbell, et al., 1992). The beneficial effect of growing cover crops on enhancing SOC pool has been reported from Hungary by Berzseny and Gyrffy (1997), U.K. by Fullen and Auerswald (1998) Sweden by Nilsson (1986), Netherlands by Van Dijk (1982) and Europe by Smith et al., (1997). 4. Nutrient management It will help ensure optimal plant growth, resulting in better yields and more plant residue available to become soil organic carbon. However, using nitrogen in excess of crop needs not only wastes a producer s resources, but also results in greater GHGs emissions. Studies are being conducted on how the fertilizer source (inorganic vs. manure) may impact carbon sequestration (Oldeman, 1994). It is important to note that most of the practices listed not only favor carbon storage, but also have other environmental and soil health benefits, such as reducing erosion and chemical runoff and improving soil fertility (Russel, 2006). Long-term manure applications increase the SOC pool and may improve aggregation (Sommerfeldt et al., 1988; Gilley and Risse, 2000) and the effects may persist for a century or longer (Compton and Boone, 2000). 5. Avoid use of fallow Continued use of a crop-fallow farming system, even with NT, may result in loss of SOC. Conversion from crop-fallow to more intensive cropping systems utilizing NT will be needed to have a positive impact on increasing C Sequestration from croplands (Halvorson and Curtis, 2007). Fallow significantly in carbon decomposition is approximately 2 to 2.5 times faster than in a crop year (Vanden Bygaart et al., 2004). 6. Irrigation Similar to the addition of fertilizers and manures in a nutrient-depleted soil, judicious application of irrigation water in a drought prone soil can enhance biomass production, increase the amount of above-ground and the root biomass returned to the soil and improve SOC concentration. In addition, enhancing irrigation efficiency can also decrease the hidden C cost (Sauerbeck, 2001). In Texas, Bordovsky et al., (1999) observed that surface SOC concentration in plots growing irrigated grain sorghum and wheat increased with time. Financial benefits of soil carbon sequestration Besides the benefits of greater health and productivity of the soil, farmers may have the opportunity to receive financial benefits for modifying their management practices to store carbon. It is possible that a private system of trading for carbon credits will be established, which could pay producers some attractive price per acre. A few utility companies have already begun buying or leasing carbon credits

5 in some cases, but this is not yet a widespread practice. It is also possible that the government will provide certain incentives for producers to sequester carbon. There are a couple scenarios on the horizon for direct monetary benefit. First, a producer could receive a small amount per acre for switching to management practices that are associated with improved carbon storage in the soil, similar to the current federal programs that provide incentive payments or cost-share to farmers engaging in approved conservation activities. Research priorities to enhance C sequestration Our research priorities should be focused on following points to increase soil carbon sequestration. Identification of microbiological processes that could be manipulated to reduce decomposition rates of soil organic matter, Vol. 30, No. 4, Production of a fertilizer that increases a soil s organic content and ability to retain water, protects its organic matter, and improves its texture so it can hold more carbon and that uses less energy and reduces carbon emissions. Exploration of the effect of using different kinds of fertilizers to see if certain types enhance yields and carbon sequestration without high NO2 emission rates. Genetically engineering of the plants to increase their carbon retention, to produce cellular structures more resistant to decomposition, increasing the lifetime of soil organic matter and thus sequestering more carbon in soils. Find ways to make carbon accumulate faster, increase the vegetation s carbon density, and use biomass carbon in long-lived structural materials and industrial products. REFERENCES Antle, J.M. et al., (2002). Environ. Poll. 116 : Antle, J.M. et al., (2003). J. Environ. Eco. and Manag. 46: Baker, et al., (2007). Agr. Eco. and Environ. 118:1 5. Berzseny, Z. and Gyrffy, B. (1997). Agrok. Mas. Talajtan. 46: Blevins, R. L and Frye, W. (1993). Adv. Agron. 51: Bordovsky, D.G. et al., (1999). Soil Sci. 164: Bricklemyer, R.S. et al., (2002). Agron. J. 14 (2): Bricklemyer, R.S. et al., (2006). J. Environ. Quality. 35: Campbell, C.A. et al., (1992). Can. J. Soil Sci.72: Cole, V.et al., (1996): In : Climate Change 1995: Impacts. Adaptations and Mitigation of Climate Change: Scientific-Technical Analyses. Contribution of Working Group II to the Second Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, pp Compton, J. E. and Boone, R.D. (2000). Ecology. 81: Doster, D. et al., (1983). J Soil and Water Conserv. 38: Follett, R.F. et al., (2001). In: The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect. Lewis Publishers, Washington, D.C.MI.pp56 Follett, R F. (2006). Ame Soc Agron Abstracts. 14: Franzluebbers, A. J. and Steiner J. L. (2002). In: Agricultural Practices and Policies for Carbon Sequestration in Soil. Pp121 Fullen, M. A. et al., (1998). Soil and Tillage Res. 46: Gilley, J. E. and Risse, L. M. (2000). Trans ASAE. 43: Halvorson, A. and Curtis, R. (2007). Fluid J. 15 (3): Hopkins, J. et al., (1996). Rev. Agri. Econ. 18:

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