EFFECTS OF FIELD DRAINAGE ON SOIL PARAMETERS RELATED TO METHANE PRODUCTION AND EMISSION FROM RICE PADDIES

Field drainage has been reported to effect a reduction in the amount o f methane emitted from rice paddies. In this study we monitored the re dox state, soil acetate concentration, and methane emissions in two fi eld sites and an outdoor potted rice experiment. The rate of methane p roduction was determined by in vitro soil incubations. We found field drainage to be an effective method of mitigating methane emissions fro m rice paddies, with a 64% reduction in seasonal emissions reported af ter a single midseason drainage at the Richmond, Texas, site. The decr eased methane emissions were in response to soil aeration, as indicate d by changes in the Eh and ferrous ion concentration of the soil. The mechanism for this response appears to be a reduction in the rate of m ethane production, as indicated by significantly reduced soil acetate concentrations and decreased methane production rates in anaerobic soi l incubations. Evidence of drainage-induced methanogenic substrate dep letion is presented. In addition, the duration and timing of field dra inage required for effective mitigation are discussed. We found no evi dence that field drainage adversely affected grain yield.