Empirical model of soil chemical properties that regulte methane production in Japanese rice paddy soils

Abstract

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