Empirical Model of Soil Chemical Properties that Regulate Methane Production in Japanese Rice Paddy Soils

To understand which soil chemical properties are the best predictors of CH4 production in rice paddy soils, a model was developed with empirical data from nine types of rice soils collected around Japan and anaerobically incubated at 30°C for 16 wk in laboratory conditions. After 1, 2, 4, 8, and 16 wk of incubation, CO2, CH4, and Fe(II) were measured to understand soil organic matter decomposition and iron (Fe) reduction. Available N (Nava) was also measured at the end of incubation. The results showed that decomposable C and reducible Fe are two key parameters that regulate soil CH4 production (PCH4). There was a significant relationship between decomposable C and available N (Nava) (r2 = 0.975**). Except for a sandy soil sample, a significant relationship between total Fe (Fetotal) and reducible Fe was found. From this experiment, a simple model of soil CH4 production was developed: PCH4 = 1.593Nava- 2.460Fetotal/1000 (each unit was mg kg-1 soil). After simulated CH4 production by two soil chemical properties as above, there was a significant consistency between model simulation and actual measurement (r2 = 0.831**).