[Effects of rice straw returning mode on rice grain yield and soil carbon pool management index in double...

A 2-year field experiment was conducted to study the effects of different rice straw returning modes on the rice grain yield and soil carbon pool management index (CPMI) in a double rice-cropping system. Four treatments were installed, including balanced mineral fertilization (NPK), NPK plus cut rice straw returning (SNPK), NPK plus incinerated rice straw returning (SINPK), and no fertilization (CK). In treatments SNPK and SINPK, the 2 years average grain yield of early rice and late rice was basically the same, and much higher than that in treatment NPK, with an increment of 5.7%-7.3%. As compared with treatments NPK and SINPK, treatment SNPK increased the grain yield of early rice significantly by 3.8%-8.8%, and enhanced the contents of various soil carbon forms and the soil CPMI, with the soil total organic carbon, active carbon, mineralized carbon contents, and the soil CPMI increased by 1.8%-2.0%, 5.9%-6.5%, 16.0%-41.6%, and 7.3%-7.8%, respectively. There was a significant parabolic correlation between soil CPMI and rice grain yield (r = 0.999 and r = 0.980 in early- and late-rice season, respectively). Treatment SNPK also increased the grain yield, the contents of various soil carbon forms, and the soil CPMI in the next early rice season.