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

Rice (Oryza sativa L.) fields are major sources of methane (CH4) 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, CH4 is also released from soil surface through ebullition and diffusion. However, little information is available for CH4 emission directly from soil surface (MDFS). In this study, in order to enlarge our understanding of CH4 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 CH4 emissions was not affected by temperature, fertilization, and rice straw inputs across the rice growing season. The mean total CH4 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 CH4 emission was about 1%. However, MDFS flux in the early rice season increased by rice straw input and MDFS accounted for 5% of total CH4 emission, probably due to increased CH4 production by rice straw inputs at higher levels than the capacity of aerenchyma tissue to intake and transport the CH4 produced in the early rice season with low tiller number. Our result indicate that MDFS may substantially contribute to the total CH4 emission in the early season of rice cultivation with organic inputs.Direct emission of methane from soil surface is less than 1% of the total emission but increases up to 5% with rice straw application.