An 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 CH 4 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, CO 2 , CH 4 , and Fe(II) were measured to understand soil organic matter decomposition and iron (Fe) reduction. Available N (N ava ) was also measured at the end of incubation. The results showed that decomposable C and reducible Fe are two key parameters that regulate soil CH 4 production (P CH4 ). There was a significant relationship between decomposable C and available N (N ava ) ( r 2 = 0.975**). Except for a sandy soil sample, a significant relationship between total Fe (Fe total ) and reducible Fe was found. From this experiment, a simple model of soil CH 4 production was developed: P CH4 = 1.593N ava – 2.460Fe total /1000 (each unit was mg kg −1 soil). After simulated CH 4 production by two soil chemical properties as above, there was a significant consistency between model simulation and actual measurement ( r 2 = 0.831**).