Effects of rice-straw and phosphorus application on production and emission of methane from tropical rice soil

Rice-straw amendment increased methane production by 3-fold over that of unamended control. Application of P as single superphosphate at 100 mu g (g soil)(-1) inhibited methane (CH4) production distinctly in flooded alluvial rice soil, in the absence more than in the presence of rice straw. CH4 emission from rice plants (cv. IR72) from alluvial soil treated with single superphosphate as basal application, in the presence and absence of rice straw, and held under non-flooded and flooded conditions showed distinct variations. CH4 emission from non-flooded soil amended with rice straw was high and almost similar to that of flooded soil without rice-straw amendment. The cumulative CH4 efflux was highest (1041 mg pot(-1)) in rice-straw-amended flooded soil. Appreciable methanogenic reactions in rice-straw-amended soils were evident under both flooded and non-flooded conditions. Rice-straw application substantially altered the balance between total aerobic and anaerobic microorganisms even in non-flooded soil. The mitigating effects of single-superphosphate application or low-moisture regime on CH4 production and emission were almost nullified due to enhanced activities of methanogenic archaea in the presence of rice straw.