SOIL REDOX WINDOW WITH MINIMUM NITROUS OXIDE AND METHANE PRODUCTION: ITS APPLICATION IN A RICE FIELD

摘要

In this paper, we present the results of (1) a laboratory experiment using a soil microcosm system to study nitrous oxide (N_2O) and methane (CH_4) production at different redox potential (Eh) conditions and their relative contributions to cumulative global warming potential (GWP), and (2) a field experiment under four different irrigation and organic matter (OM) managements to find a best management practice to mitigate cumulative GWP from CH_4 and N_2O emission in a irrigated rice field. In the laboratory study, we found a redox "window" of +180 to -150 mV where both N_2O and CH_4 productions were low. Soils in this redox window were reducing enough to favor a complete denitrification with nitrogen gas (N_2) as end product, but the reducing intensity was not enough to initiate significant methanogenesis. The field study showed that non-flooding conditions maintained by controlled irrigation effectively reduced CHt emission from the fields with (by 79%) and without (by 71%) OM addition. Strictly reducing zones (Eh < -150 mV) that were favorable for methanogenesis developed at the lower depths of the soil in the non-flooded fields, which facilitated less CHt production and more CH_4 oxidation through the soil surface. Stimulated N_2O emission in the non-flooded soils offset part of the CH_4 emission reduction, especially in the fields without OM addition. In conclusion, non-flooding treatment reduced the cumulative GWP by only 47% in the field without OM addition, but by 73% with OM addition. The best management practice proposed in this study is to keep the field non-flooded with OM addition. It shows a minimum GWP from the rice fields, and no decrease in rice yield.