Crop-residue management is an important mitigation technology using biomass, vermi-compost etc. processed under aerobic conditions which is being utilised as a commercial option to reduce greenhouse gas emissions. Vermi-composting is a modified method of composting using earthworms to eat and digest farm waste and turn it into a high quality vermi-compost in two months or less. It is different from other composts due to the presence of worms such as earthworms, red wigglers, white worms etc. (Satavik, 2011).
Most byproducts of cereals, pulses, and oilseeds are useful as feed and fodder for livestock. Byproducts of other crops like cotton, maize, pigeon pea, castor, sunflower, and sugarcane are used as low calorie fuel or burnt to ashes or left in the open to decompose over time. Modest investments in decentralised facilities for aerobic digestion of agricultural residue through vermi-composting and biogas generation can meet the needs of energy-deficit rural areas.
Crop residue management is an important component of organic farming that helps the conservation of carbon in the rhizosphere thereby mitigating the emissions of GHG to the atmosphere. It includes leguminous cover crops grown as green manure to provide a cost-effective source of N to subsequent crops. Organic farming relies heavily on inputs of organic residues in the forms of green manure (i.e., cover crops), plant compost, and composted animal manures added to the soil along with integrated biological pest and weed management, crop rotation, and mechanical cultivation to sustain and enhance soil productivity and fertility without the use of synthetic N fertiliser and pesticides (figure 1). The handling of crop residues also has an impact on net carbon gains. Removal of straw or stover can result in significant loss of soil organic carbon (SOC). If they are used as bedding for livestock, then much of the carbon may be returned to the soil as manure (Lal et al., 1998).
Lack of availability of proper chipping and soil incorporation equipment to ensure that proper height of crop residue is cut, is one of the major reasons for the colossal wastage of agricultural biomass. Increased cost of labour and transport is another reason for lack of interest in utilising the crop-residue management technologies.
- When crop-residue is incorporated into soil, the soil’s physical properties and its water-holding capacity are enhanced.
- Organic residues and N fertilisers increase soil organic carbon and subsequently improve soil structure and aggregate stability. By stabilising soil aggregates, soil organic matter is more protected from microbial decay (Six et al., 1999). The use of organic residue management cover crops and manures can lead to soil organic carbon accumulation by improving aggregation as well as reducing the need for synthetic fertiliser application while providing crops with equally adequate amounts of nutrients.
- Addition of organic residue to the soil reduces environmental pollution potential while maximising the N-use efficiency and providing crops with sufficient N.
Co-benefits of organic amendments applied to soil are a reduced need for herbicides by reducing weed emergence and enhancing soil quality, which provides better habitat for beneficial soil fauna. For example, decomposers such as earthworms can help in organic amendments. The castings and the channels that earthworms create improve root growth, water infiltration, and the physical structure of the soil. Earthworms also stabilise soil organic matter and contribute to the formation of stable soil aggregates.
- The carbon and nitrogen mineralization rate of these manures and organic residues are relatively low for the recovery of N, which ranges between 5-18% of total N for manures and 8% for compost. Thus, these organic amendments would need to be applied in huge amounts in order to considerably increase the short term N supply, which would lead to higher costs.
Crop residue management through vermi-composting brings about 463 mg CO2e m-2 hr-1 compared to their anaerobic digestion value of 694 mg CO2e m–2 hr-1. The experiments done by Chan et al., (2011) in Australian cities clearly confirm the reduction in GHG emissions through crop residue and vermicompost management. There will be ample opportunity for farmers to reduce GHG emissions in vermicompost production by reducing the use of chemical fertilisers which generally initiate the emission of N2O and CH4.
Tschakert (2004) estimated the cost-effectiveness of crop residue (millet) based compost application for soil carbon sequestration in small-scale dry land farming systems for three resource-endowment groups at Old Peanut Basin, Senegal, for a 25-year project period (figure 2).
Chan K.Y., Conyers M.K., Li G.D., Helyar K.R., Poile G., Oats A. and Barchia I.M. (2011). Soil carbon dynamics under different cropping and pasture management in temperate Australia: Results of three long term experiments. Soil Research, 49, 320-328.
Dixit S., Prasad J.V.N.S., Raju B.M.K. and Venkateswarlu B. (2010): Towards a carbon-Neutral rural India. Part 1 challenges and opportunities in Agriculture. India Infrastructure Report, pp393-406, 2010.
Lal, R., Kimble, JM, Follet, RF, and Cole, CV. (1998): The Potential of U.S. Cropland to Sequester Carbon and Mitigate the Greenhouse Effect, Ann Arbor Press, Chelsea, Michigan, USA. Lal, R, Kimble JM, Follett RF, and Stewart BA. (1998c) Soil Processes and the Carbon Cycle. CRC Press LLC.
Satavik (2011): Vermicomposting. Available at <http://www.satavic.org/vermicomposting.htm>
Six, J., Elliott, E. T., and Paustian, K. (1999). Aggregate and soil organic matter dynamics under conventional and zero-tillage systems. Soil Sci. Soc. Am. J. 63, 1350–1358.
Tschakert, P. (2004): The costs of soil carbon sequestration: an economic analysis for small-scale farming systems in Senegal. Agricultural Systems, 81:227–253.