METHANE SOURCES AND SINKS IN PADDY RICE SOILS - RELATIONSHIP TO EMISSIONS

Methane sources and sinks in a Louisiana rice soil and how they relate to atmospheric emissions were quantified. Total methane emission from the plant-soil system was compared with methane emission from surface soil between drill rows of rice (Oryza sativa L.), Results showed that over 95% of methane emitted to the atmosphere was through the rice plant. Average emission through the plant-soil system was 300 mg CH4 m(-2) day(-1) and 826 mg CH4 m(-2) day(-1) for the first and ratoon crops, respectively. By comparison average methane emission from soil between drill rows was 2.1 mg CH4 m(-2) day(-1) for the first crop and 12.7 mg CH4 m(-2) day(-1) for the ratoon crop. Significant methane oxidation was measured in the surface oxidized layer in the soil profile between drill rows. Treatment with methylfluoride inhibitor showed that methane emission from the soil would be five to ten times greater if oxidation did not occur in the surface layer. Laboratory studies of methane oxidation (also using methylfluoride) showed that approximately 30% of the methane in the rice root rhizosphere was being oxidized by methanotrophs. Results showed that methane oxidation in the surface oxidized soil layer and in the root rhizosphere play an important role on limiting atmospheric methane emissions from Louisiana paddy soils.