Organic Matter Fraction As Affected By Long-Term Application of Rice Straw-Compost in Paddy Soil.

Soil organic matter (SOM) has been recognized as an important material in soil fertility and crop productivity as well as the carbon sink. In order to investigate the effect of long-term application of rice straw-compost on the amount of organic matter in paddy soil, density fraction has been utilited to separate mineral-linked organic matter from non-linked organic matter. The contents of C and N of the Light fraction (LF) and Heavy fraction (HF) of three different treatments were examed; no fertilizer (control), chemical fertilizer (NPK), and chemical fertilizer with rice straw-compost (NPK-Com). NPK-Com plot had the highest contents of C and N in both fractions (LF and HF) and control plot had the lowest contents. The amount of soil organic C (SOC) in LF and in HF ranged 6.77 to 8.23 g kg^-1 and 8.66 to 17.26 g kg^-1, respectively. The amount of soil organic N (SON) in LF and in HF ranged 0.76 to 0.85 g kg^-1 and 1.28 to 2.25 g kg^-1, respectively. Light fractions in all plots had higher C/N ratio than HF; 8.91 to 9.59 in LF and 6.60 to 7.21 in HF. The total carbon and the C/N ratio were highly positively correlated with LF, HF and LH+HF in long-term rice straw-compost application plot. These results indicate that long-term application of rice straw-compost in paddy soil increased stable SOM pool (associated with clay fraction) as well as labile SOM pool. Long-term rice straw application could be an efficient strategy to promote productivity and sustainability of agricultural system.