Methane flux from irrigated paddy and dryland rice fields, and from seasonally dry tropical forest and savanna soils

Abstract

Methane flux was measured from four tropical, Indian ecosystems: dryland, irrigated rice, seasonally dry forest and savanna. Flux from the irrigated rice paddies was in the range 2.14-8.23 mg CH₄ m⁻² h⁻¹ during the crop period. In contrast, the dryland rice soil consumed 0.12-0.90 mg CH₄ m⁻² h⁻¹. Application of wheat straw+fertilizer stimulated CH₄ production in irrigated rice soil while it reduced CH₄ consumption in dryland rice plots. CH₄ flux measurements from nutrient-poor, well-drained dry deciduous forest and savanna soils indicated heavy methane consumption. Maximum CH₄ consumption was observed during the winter season (0.46-0.95 mg CH₄ m⁻² h⁻¹) at all the sites and was lowest during the rainy season (0.17-0.32 mg CH₄ m⁻² h⁻¹). The results suggest that dryland rice soils and natural ecosystems are potential sinks of CH₄. Conservative extrapolation of the results indicates that to compensate for CH₄ production from 1 ha of irrigated rice about 2.4 ha of natural ecosystems are needed. Thus there is a need of further evaluation of the role of tropical dryland rice soils and naturally dry ecosystems in the global methane budget.