Soil Moisture between Rice-Growing Seasons Affects Methane Emission, Production, and Oxidation

Abstract

Methane (CH4) emissions from rice (Oryza sativa L.) fields are believed to contribute to the greenhouse effect. Earlier studies on CH4 emission were mostly focused on the rice-growing season. The objective of this study was to determine the effects of soil moisture during the non-rice growing season on CH4 emission, production, and oxidation within the subsequent rice-growing season. Five moisture levels ranging from air-dryness to flooding were established in pots during the non-rice growing season. The CH4 fluxes from rice soils in the pots were monitored in a closed chamber and dark incubation was performed to determine CH4 production and oxidation potentials. Both CH4 emission and production increased significantly as the soil got wetter except when it was air-dried. The CH4 oxidation potential was also stimulated by the previous higher soil water content, which therefore buffered emission of the gas as its production increased. Soil water content considerably affected the seasonal variation pattern of CH4 flux and soil redox potential (EH). The higher the soil water content, the quicker soil EH declined and the earlier CH4 emission initiated after rice transplantation. Previous soil water content significantly affected soil organic C content before rice transplantation. Within the rice-growing season both the mean CH4 flux and its production rate were significantly correlated with soil organic C content. Thus water-history-induced change of soil organic C content may have affected soil reduction rate, and then CH4 production and emission within the rice-growing season. The results demonstrate how water management between rice crops can regulate CH4 emission, production, and oxidation during the rice-growing season.