Combined System of Organic Substrate and Straw-Degrading Microbial Agents Improved Soil Organic Matter Levels and Microbial Abundance in a Rice–Wheat Rotation

Rice–wheat rotation is one of the most intensive agricultural planting modes in China and is pivotal to develop optimized straw-returning management in situ to improve soil fertility and productivity in agricultural ecosystems. Previous studies have mainly focused on the effects of straw return with a single application of organic fertilizers. The integrated management of different fertilizers in improving the management of straw return in situ is not well known. In this study, a field experiment was conducted from 2017 to 2019 to explore the effects of a combined system of modified organic substrate (MOS) and straw-degrading compound microbial agent (CMA) on soil physiochemical properties, labile organic carbon, microbial activities, and soil microbial community composition under the background of direct crop straw return and chemical fertilizer utilization. Four treatments were designed: (1) control check; (2) CMA; (3) MOS; and (4) MOS + CMA. The results showed that the MOS + CMA treatment had the combined advantages of soil organic matter (SOM) accumulation, soil nutrient increase and soil microbial community alteration, which may be more suitable for improving the quality and fertility of sandy loam soil. This study provides novel insights for further understanding the effects of organic substrates and composite microbial agents on SOM changes and microbial community composition and function in the field, which has important implications for sustainable crop production and agricultural development.