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 of methane emitted from rice paddies. In this study we monitored the redox state, soil acetate concentration, and methane emissions in two field sites and an outdoor potted rice experiment. The rate of methane production was determined by in vitro soil incubations. We found field drainage to be an effective method of mitigating methane emissions from rice paddies, with a 64% reduction in seasonal emissions reported after a single midseason drainage at the Richmond, Texas, site. The decreased methane emissions were in response to soil aeration, as indicated 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 methane production, as indicated by significantly reduced soil acetate concentrations and decreased methane production rates in anaerobic soil incubations. Evidence of drainage-induced methanogenic substrate depletion is presented. In addition, the duration and timing of field drainage required for effective mitigation are discussed. We found no evidence that field drainage adversely affected grain yield.