Redox window with minimum global warming potential contribution from rice soils

Eight different rice (Oryza sativa L.) soils were incubated using a microcosm technique to study CO2, CH4, and N2O contribution to global warming potential (GWP) at different redox potential (ER) conditions. Cumulative GWP from these three greenhouse gases reached a minimum at a redox "window" of +180 to -150 mV. Within the redox window, CO2 production accounted for 86% of the cumulative GWP, because both N2O and CH4 production were low. When EH was higher than +180 mV, both CO2 and N2O production made a significant contribution to the cumulative GWP, whereas CH4 production was a dominant contributor when EH was lower than -150 mV. During the incubation, each soil exhibited a unique signature of developing such an optimum redox window with a minimum GWP. Multiple regressions showed that initial soil organic matter (OM) and S content might have a significant control (P = 0.02) on the time required for the soils to reach the redox window when the incubation started from aerobic conditions. The results of this integrated study on productions of the three greenhouse gases provide a theoretical base for abating soil GWP loading into the atmosphere by regulating soil EH conditions.