Laboratory of Isotope Biogeochemistry

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 O₂ 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 δ¹⁵N 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.