Methane emission from soil surface during rice growth season under different temperature, fertilization, and rice straw input conditions

Abstract

Rice (Oryza sativa L.) fields are major sources of methane (CH 4 ) which is the second most important greenhouse gas after carbon dioxide. Methane is known to be released mainly through aerenchyma tissues of rice plants; however, CH 4 is also released from soil surface through ebullition and diffusion. However, little information is available for CH 4 emission directly from soil surface (MDFS). In this study, in order to enlarge our understanding of CH 4 emission from rice paddy fields, we investigated MDFS under different rice growth conditions such as temperature, fertilization, and rice straw input. Rice was cultivated using pots with different fertilization regime (chemical fertilizer vs. organic fertilizer + manure compost) with or without rice straw input under ambient or elevated (+3°C) temperature. Methane emissions from rice plants (including MDFS) and MDFS alone without rice plants were measured three times before mid-season drainage (MSD), in the course of MSD, and after MSD. The MDFS flux and its contribution to the total CH 4 emissions was not affected by temperature, fertilization, and rice straw inputs across the rice growing season. The mean total CH 4 flux and MDFS flux were 20.7 mg m -2 hr -1 and 0.22 mg m -2 hr -1 , respectively, and thus the portion of MDFS to total CH 4 emission was about 1%. However, MDFS flux in the early rice season increased by rice straw input and MDFS accounted for 5% of total CH 4 emission, probably due to increased CH 4 production by rice straw inputs at higher levels than the capacity of aerenchyma tissue to intake and transport the CH 4 produced in the early rice season with low tiller number. Our result indicate that MDFS may substantially contribute to the total CH 4 emission in the early season of rice cultivation with organic inputs.