METHANE EMISSION FROM RICE FIELDS: THE EFFECT OF FLOODWATER MANAGEMENT

Rice fields emit methane and are important contributors to the increasing atmospheric CH4 concentration. Manipulation of rice floodwater may offer a means of mitigating methane emission from rice fields without reducing rice yields. To test methods for reducing methane emission, we applied four water management methods to rice fields planted on silty-clay soils near Beaumont, Texas. The four water treatments investigated were: normal permanent flood (46 days post planting), normal flood with mid season drainage aeration, normal flood with multiple drainage aeration, and late flood (76 days post planting). Methane emission rates varied markedly with water regime, showing the lowest seasonal total emission (1.2 g m(-2)) with a multiple-aeration treatment and the highest (14.9 g m(-2)) with a late flood. Although the multiple aeration water management treatment emitted 88% less methane than the normal irrigation treatment and did not reduce rice yields, the multiple-aeration treatment did require 2.7 times more water than the 202 mm required by the normal floodwater treatment. A comparison of measured methane emission and production rates obtained from incubated soil cores indicated that, depending on time of season and flood condition, from zero to over 90% of the methane produced was oxidized. The average amount of methane which was oxidized during times of high emission was 73.1 13.7 percent of that produced.