Effect of rice straw application on CH4 emission in continuous and recently converted paddy fields

Management of rice straw is of environmental concern because it significantly affects methane (CH4) emissions from rice paddies. To evaluate straw-application effects on paddies those have different cultivation histories, we measured CH4 emissions in continuously cultivated rice paddy (CP) and recently converted paddy (RP) (from soybean cultivation) with rice straw treatments (+S). Further, we hypothesized that changes in i) soil Fe (III) reduction and ii) population dynamics of methanogens were responsible for the different responses of CH4 emissions due to straw application between CP and RP. Methane (CH4) emission from CP+S was 2-fold larger than that from RP+S, although relative enhancement was higher in later (492%) than the former (289%) compared with no straw application. Stoichiometric evaluation revealed that applied rice straw acted as an exogenous source of electron donor for CH4 production, especially in CP. Our results showed that the increase in CH4 emissions by straw application was much greater in continuous than short term paddy.