A record of N2O and CH4 emissions and underlying soil processes of Korean rice paddies as affected by different water management practices

Rice is staple food of half of mankind and paddy soils account for the largest anthropogenic wetlands on earth. Ample of research is being done to find cultivation methods under which the integrative greenhouse effect caused by emitted CH4 and N2O would be mitigated. Whereas most of the research focuses on quantifying such emissions, there is a lack of studies on the biogeochemistry of paddy soils. In order to deepen our mechanistic understanding of N2O and CH4 fluxes in rice paddies, we also determined NO3 (-) and N2O concentrations as well as N2O isotope abundances and presence of O-2 along soil profiles of paddies which underwent three different water managements during the rice growing season(s) in (2010 and) 2011 in Korea. Largest amounts of N2O (2 mmol m(-2)) and CH4 (14.5 mol m(-2)) degassed from the continuously flooded paddy, while paddies with less flooding showed 30-60 % less CH4 emissions and very low to negative N2O balances. In accordance, the global warming potential (GWP) was lowest for the Intermittent Irrigation paddy and highest for the Traditional Irrigation paddy. The N2O emissions could the best be explained (*P < 0.05) with the delta N-15 values and N2O concentrations in 40-50 cm soil depth, implying that major N2O production/consumption occurs there. No significant effect of NO3 (-) on N2O production has been found. Our study gives insight into the soil of a rice paddy and reveals areas along the soil profile where N2O is being produced. Thereby it contributes to our understanding of subsoil processes of paddy soils.