Methane production, oxidation, and emission from Indian rice soils

Experiments were conducted to investigate methane (CH4) production, oxidati on, and emission from flooded rice soils. Incorporation of green manure (Se sbania rostrata) into rice fields led to a several-fold increase in CH4 emi ssion. A stimulatory effect of organic sources on CH4 production in soil sa mples was noticed even under nonflooded conditions. Addition of rice straw at 1% (w/w) to nonflooded soil samples held at -1.5 MPa effected a 230-fold increase in CH4 production over that in corresponding unamended soil sampl es at 35 d, as compared with a threefold increase in rice straw-amended soi l over that in unamended soil under flooded conditions. In a study involvin g two experimental field sites differing in water regimes but planted to th e same rice cultivar (cv Gayatri) and fertilized with prilled urea at 60 kg N ha(-1), the field plots with deep submergence of around 30 cm (site I) e mitted distinctly more CH4 than did the plots with continuous water depth o f 3-6 cm (site II). Likewise, in another incubation study, CH4 production i n flooded soil samples increased with a progressive increase in standing wa ter column from 5 mm to 20 mm. Application of carbamate insecticide, carbof uran, at 2 kg ai ha(-1) to rice fields retarded CH4 emission through enhanc ed CH4 oxidation. Hexachlorocyclohexane was found to inhibit CH4 emission. The results suggest the need for extensive research efforts to develop tech nologies with dual objectives of environmental protection and crop producti vity.