Abstract
ABSTRACT While long‐term film mulching has consistently increased crop yields, it has also contributed to land degradation, prompting adjustments in straw returning rates. However, the responses of soil organic carbon (SOC) and structure to optimal straw returning rates are in need of a deeper understanding. Here, we examined the effects of soil structure, SOC dynamics, and maize productivity under long‐term film mulching with varying straw return rates (0, 6000, 12,000, and 18,000 kg ha −1 ) in semi‐arid farmland. The SOC and particulate organic carbon (POC) content both reduced after long‐term film mulching. The varying changes of soil aggregation processes caused by different straw returning rates, which in turn affect the distribution of soil aggregates, particularly the proportion of > 0.25 mm aggregates. The effects of different straw return rates on crop yield were mainly driven by changes in organic carbon pools (microbial biomass and dissolved organic carbon), resulting from nutrient inputs that stimulated microbial growth. Higher straw return rates have promoted the stratification of SOC and modified the proportional distribution of organic carbon fractions. These changes have directly and indirectly increased maize yield by 21% and economic benefits by 15%. Based on the total application of straw in dryland farming systems, increasing the straw application rate to 18,000 kg ha −1 resulted in a synergistic improvement in SOC content, soil structure and economic benefits.