Rice cultivation is responsible for 10% of GHG emissions from agriculture (Figure 1). In developing countries, the share of rice in GHG emissions from agriculture is even higher, e.g., it was 16% in 1994. A variety of technologies are presented on ClimateTechWiki for reducing emissions from rice cultivation.
The following rice-related mitigation technologies are described on ClimateTechWiki:
- Fertiliser, manure and straw management 
- Water management: mid-season drainage 
- Water management: alternate wetting and drying 
- Potassium fertiliser application 
- Agricultural biotechnology 
- Reduced tillage 
- Direct seeding 
- Chemical fertiliser amendment 
- Electron acceptors 
This differs per technology. See the individual technology articles for more information.
Optimising irrigation patterns by adding drainage periods in the field, or early mid season drainage reduced CH4 emissions by 7-80% compared to flooded conditions. Using composted rather than fresh rice straw reduced emissions by 58-63%. Such large reductions and relative ease of implementation suggest that these are the best methane mitigation technologies for farmers (Wassman et al. 2000). The reductions of 16-22% in CH4 emissions suggest it would also be a good practice if associated yield reductions can be overcome by higher seeding rates or other means. Compared to prilled urea as the sole N source, ammonium sulphate could reduce CH4 emissions by 10-67%. Methane can be reduced by fallow incorporation (11%) and mulching (11%) of rice straw as well as addition of phosphogypsum (9-73%) in all rice ecosystems. Nitrification inhibitors can repress methane emissions from flooded soils (Bronson and Mosier, 1991). Methane emissions were lowest in plots treated with a mixture of prilled urea and Nimin, a nitrification inhibitor which inhibits the autotrophic oxidation of NH4+ to NO2– (Sahrawat and Parmar, 1975). Removal of a surface peat layer (soil with a high percentage of organic material) of soil before irrigation reduces the emission of methane significantly. This practice (peat soil technology) has been recently reported by the Russian scientists (Sirin et al. 2010).
Incorporation of rice straw in soil generally increases CH4 emissions. However, it can be a disposal problem, and compared to burning it, incorporation of rice straw before a wheat crop in Haryana (India) or vegetable crops in the Philippines and China resulted in significant reductions of approximately 0.4 t CE ha-1 in methane emissions (Wassmann and Pathak, 2007). However, the field operations and its detrimental effects on upland crops make this option costly. Mixing of straw in construction material or feeding it to animals is additional options.
Mitigation potential exists through the use of new rice cultivars with lower emissions, but they have a higher seed cost (Pathak and Wassmann, 2007). The use of such cultivars is only promising under conditions where the existing methane emissions are high, i.e., in China and the Philippines. The challenge for rice research is to develop technologies that increase rice productivity and at the same time reduce GHG emissions.
The costs vary widely per technology. See the individual technology pages for detailed price information.
Bronson, K.F. and Mosier, A.R. (1991): Effect of encapsulated calcium carbide on dinitrogen, nitrous oxidem methane and carbon dioxide emissions from flooded rice, Biol. Fertil. Soils. 11.
Kasterine, A. and Vanzetti, D. (2010): The effectiveness, efficiency and equity of market-based instruments to mitigate GHG emission from the agri-food sector, in UNCTAD Trade and Environment Review 2009/2010, Geneva. Available at http://www.intracen.org/uploadedFiles/intracenorg/Content/Exporters/Sect... .
Pathak, H. and Wassmann, R. (2007): Introducing greenhouse gas mitigation as a development objective in rice-based agriculture: I. Generation of technical coefficients. Agricultural Systems 94 (2007) 807-825.
Sahrawat, K.L. and Parmar, B.S. (1975): Alcohol extract of neem (Azadirachta indica L) seed as a nitrification inhibitor. J Indian Soc Soil Sci 23:131-134.
Sirin, A., Chistotin, M., Suvorov, G., Glagolev, M., Kravchenko, I., and Minaeva, T. (2010): Drained peatlands used for extraction and agriculture: biogeochemical status with special attention to greenhouse gas fluxes and rewetting. Geophysical Research Abstracts Vol. 12, EGU2010-11623, 2010. EGU General Assembly 2010.
Wassman, R., Lantin, R.S., Neue, H. U., Buendia, L.V., Corton, T.M. and Lu, Y.(2000): Characterization of methane emissions from rice fields in Asia. III. Mitigation options and future research needs. Nutrient Cycling in Agroecosystems 58: 23–36.