Methane production, oxidation, and emission from Indian rice soils

Abstract

Experiments were conducted to investigate methane (CH₄) production, oxidation, and emission from flooded rice soils. Incorporation of green manure (Sesbania rostrata) into rice fields led to a several-fold increase in CH₄ emission. A stimulatory effect of organic sources on CH₄ production in soil samples 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 samples at 35 d, as compared with a threefold increase in rice straw-amended soil over that in unamended soil under flooded conditions. In a study involving two experimental field sites differing in water regimes but planted to the 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) emitted distinctly more CH₄ than did the plots with continuous water depth of 3-6 cm (site II). Likewise, in another incubation study, CH₄ production in flooded soil samples increased with a progressive increase in standing water column from 5 mm to 20 mm. Application of carbamate insecticide, carbofuran, at 2 kg ai ha^-1 to rice fields retarded CH₄ emission through enhanced CH₄ oxidation. Hexachlorocyclohexane was found to inhibit CH₄ emission. The results suggest the need for extensive research efforts to develop technologies with dual objectives of environmental protection and crop productivity.