Effect of straw and biochar on soil organic carbon and carbon pool management index in purple soil under rape-maize rotation

In order to reveal the response of the organic carbon pool of purple soil to straw and biochar application in Southwest China, this experiment quantified the content of various forms of organic carbon and the carbon pool management index in rape-maize rotation systems in the national monitoring station for soil fertility and fertilizer efficiency of purple soils. There were five treatments, including no organic material (CK), straw (CS), biochar (BC), 50% straw+50% biochar (CS+BC), and straw+microorganisms (CS+D), which were repeated three times. The results showed that straw and biochar addition increased soil total organic carbon, microbial biomass carbon, particulate organic carbon, mineral-associated organic carbon, labile organic carbon, and carbon pool management index as compared with those of the CK treatment. The highest content of microbial biomass carbon, coarse particulate organic carbon, and soil microbial entropy were found in the CS+D treatment, with increases of 104.17%, 248.57%, and 66.61%, respectively. The content of microbial biomass carbon, coarse particulate organic carbon, and soil microbial entropy increased by 75.25%, 211.43%, and 51.38%, respectively, in the CS treatment. As compared with the CK treatment, carbon pool management index increased by 87.42 and 70.95 in the CS+D and CS treatments, respectively. The highest content of mineral-associated organic carbon was 13.14 g·kg-1 in the BC treatment. Overall, the activity and quality of soil organic carbon improved by the addition of straw and straw + microorganism, whereas the stability of soil organic carbon was improved by the addition of biochar, which is beneficial for the long-term stable fixation of soil organic carbon.