Emissions of GHGs are affected by the amounts and types of fertilisers applied, so judicious choice of fertiliser application rates and fertiliser types can reduce emissions. Rice cultivation is responsible for 10% of GHG emissions from agriculture. In developing countries, the share of rice in GHG emissions from agriculture is even higher, e.g., it was 16% in 1994.
See 'Rice production technologies' for an overview of all climate change mitigation technologies related to rice cultivation.
The source, mode, and rate of application of mineral fertilisers influence CH4 production and emission from flooded rice paddies. CH4 emissions from rice fields were decreased by 18% due to chemical fertiliser amendments (Minami, 1995).
Increases in rice production in south Asia have been attributed to increased nitrogen use. Increased nitrogen use may also have an additional benefit of lowering methane emissions. Incorporating urea into soil has been shown to reduce methane emissions. However, surface-applied urea resulted in 20% more emissions compared to an unfertilised field. The use of sulfate-based fertiliser has also being linked to methane emission reductions. Metra-Corton et al., (2000) reported that ammonium sulfate reduced methane emissions by 25-36% in rice fields. Applying phospho-gypsum (calcium sulfate dihydride) in combination with urea reduced methane emissions by more than 70%. Application of sulfatecontaining fertilisers reduced methane emissions from flooded rice fields (Adhya et al., 1998). In contrast, incorporation of organic sources, for instance green manure and rice straw, in soils stimulates methane emission (Denier van der Gon and Neue, 1995).
Foliar application of nitrogenous fertiliser is another potential mitigation practice for reducing CH4 emissions from rice soils (Kimura et al., 1992). Adhya et al., (1998) demonstrated a large inhibition of CH4 production and emission by an application of single superphosphate and a smaller inhibition by an application of rock phosphate. They attributed this inhibitory effect to the high PO42- content of the P fertilisers. Nitrification inhibitors (thiourea, sodium thio sulphate and dicyandiamide) inhibited the CH4 emission activity of flooded rice field soil (Bronson and Mosier 1994).
Rath et al., (1999) found that the subsurface application of urea super granules was marginally effective in reducing the CH4 flux relative to that in untreated control plots. Bronson and Mosier (1994) reported that N fertilisers inhibit methanotrophic microorganisms in soils. Generally, fertilisers with an ammonical form of N (NH4+-N) increase CH4 emissions.
In principle, three different causes have been suggested for the inhibitory effect of nitrogenous fertilisers, especially NH4+-N fertilisers, on CH4 oxidation which results in increased emissions of CH4:
- An immediate inhibition of the methanotrophic enzyme system (Bedard and Knowles, 1989).
- Secondary inhibition through the NO2–production from methanotrophic NH4+ oxidation (Megraw and Knowles, 1987).
- Dynamic alteration of microbial communities of soil (Powlson et al., 1997).
Nitrogen fertiliser is commonly used worldwide. However, deliberate selection of the type of fertilisers to use based on GHG emissions potential is not commonly done. Site-specific research needs to be done to establish which fertilisers are cost effective with regard to both yield enhancement and GHG mitigation potential. This information also needs to be provided to growers.
- Crop growth and yields are stimulated while emissions are reduced compared to fertilisers without mitigation potential.
- Fertilisers with higher mitigation potential may cost more.
- Economics and mitigation potential.
According to Wassmann and Pathak (2007), rice production without organic amendments demonstrated the technical feasibility of reducing emissions at relatively low costs.
The addition of phosphogypsum is an efficient strategy to reduce emissions. Its actual costs varied from US$ 1.5 to 2.5 per t CO2e saved in the Philippines and China, respectively, and the reduction potential is approximately 1 t CO2e ha-1. However, the relative cost for phosphogypsum application in Haryana (India) was higher (US$5 per t CO2e saved), and the reduction potential was 0.29t CO2e ha-1.
Adhya T.K., Pathnaik P., Satpathy S.N., Kumarswamy S., and Sethunathan, N. (1998): Influence of phosphorus application on methane emission and production in flooded paddy soils. Soil. Biol Biochem 30: 177-181.
Bronson, K.F. and Mosier, A.R (1994): Suppression of methane oxidation in aerobic soil by nitrogen fertilisers, nitrification inhibitors and Urease inhibitors. Biol. Fertil. Soils 17: 263-268.
Denier van der Gon H.A.C. and Neue, H.U. (1995): Influence of organic matter incorporation in the methane emission from a wetland rice field. Global Biogeochem Cycles 9: 11-22.
Kimura, M., Asai, K. Watanabe A, Murase J and Kuwatsuka S (1992): Suppression of methane fluxes from flooded paddy soil with rice plants by foliar spray of nitrogen fertilisers. Soil Sci Plant Nutr 38:735-740.
Megraw, S.R. and Knowles, R. (1987): Methane consumption and production in a cultivated humisol. Biol Fertil Soils 5: 56-60.
Metra-Corton, T.M., Bajita, J.B., Grospe, F.S., Pamplona, R.R., Asis, C.A., Wassmann, R. and Lantin, R.S. (2000): Methane emission from irrigated and intensively managed rice fields in Central Luzon (Philippines), Nutrient Cycl. Agroecosys. 58, 37-53.
Minami, K. (1995): The effect of nitrogen fertiliser use and other practices on methane emission from flooded rice. Fertiliser Research. 40: 71-84.
Powlson, D.S., Goulding, K.W.T., Willison, T.W., Webster, C.P. and Hutsch, B.W. (1997): The effect of agriculture on methane oxidation in soil. Nutr Cycl Agroecosys 49:59-70.
Rath A.K., Swain, B., Ramakrishnan, B., Panda, D., Adhya, T.K., Rao, V.R. and Sethunathan, N. (1999): Influence of fertiliser management and water regime on methane emission from tropical rice fields. Agric Ecosyst Environ 76: 99-107.
Wassmann R and Pathak H. (2007): Introducing greenhouse gas mitigation as a development objective in rice-based agriculture: II. Cost- benefit assessment for different technologies, regions and scales. Agricultural Systems 94:826-840.