To refine estimates of source strengths from agricultural wetlands and to study the process of methane production and emission, this study was carried out in rice fields at the Texas A&M University Agricultural Research and Extension Center, Beaumont, Texas, during the summer of 1989. It focussed on two fields on different soil types (Lake Charles clay and Beaumont clay) and spanned a period from shortly after permanent field flooding (June 6, 1989) until field draining prior to harvest (August 28, 1989). Integrated methane emission over 75 days ranged from 4.5 to 15.9 g m(-2) . Aboveground biomass, net primary production, and root biomass were determined. Methane emission was strongly related to aboveground biomass in one of two fields studied. Laboratory incubations of soil cores show that methane production by soil bacteria is highest near the soil surface in the rice row and decreases with depth and distance from the plant. Much of the seasonal increase in total methane production is due to increasing activity at intermediate depths and distances from the plants. The temporal and spatial distribution of methane production was found to be related to root biomass. Seasonally integrated emission was 42% of methane production in both fields. Soil pore water methane and plant stem gas composition are related to the distribution in the soil of methane production and root biomass. Methane production ceased with field draining prior to harvest, even following prolonged anaerobic incubation. Methanogenesis rapidly resumed with added acetate substrate.
