Methane and nitrous oxide emissions from a rice field in relation to soil redox and microbiological processes

Paddy rice fields provide an environment for production of two important greenhouse gases, CH4 and N2O, because of variations in soil characteristics, moisture content, and microbial activity during the cropping season. Emissions of CH4 and N2O from a paddy rice field in northern China were measured in situ by static chamber technique during March to December in 1995 and 1996. Factors affecting gas emission, including soil temperature, pH, and redox potential (Eh), were measured as well. Emissions of CH4 and N2O were strongly correlated with changes in soil redox potential. Significant CH4 emission occurred only at soil redox potential lower than approximately -100 mV, while the emission of N2O was not significant below +200 mV. A significant inverse relationship between CH4 and N2O emissions was observed (r = -0.49, n = 16, 5% confidence level). The results suggest the possibility of using management practices to maintain the redox potential in a range where both N2O and CH4 emissions are low. The activities of six related bacteria groups (zymogenic bacteria, acetic acid and hydrogen-producers, methanogens, CH4 oxidizers, and nitrifiers and denitrifiers) in the soil were also measured in an effort to explain the relationship between gas emission and soil microbiological processes. Methane emission was significantly related to the logarithm number of zymogenic bacteria (r = 0.76, n = 12, 1% confidence level), as well as to soil redox potential (r = -0.72, n = 12, 1% confidence level). Both zymogenic bacteria number and soil redox potential appear to be predicators of CH4 emission potential.