Meta-analysis shows the effect of straw return on soil organic carbon and total nitrogen in croplands

As an important agricultural management practice, straw return to field plays an important role in soil carbon and nitrogen cycling. However, there is still a lack of evaluations on the effects of straw biochemical properties and field return practices on soil organic carbon and total nitrogen contents in agricultural soils under straw field return. In this study, we combined Meta-analysis and enhanced regression tree (BRT) modeling with peer-reviewed articles up to March 2025, and synthesized 2 556 observations from 480 articles to quantitatively analyze the effects of straw return on soil organic carbon and total nitrogen in agricultural soils globally based on the biochemical properties of straw and other environmental factors. The results showed that the soil organic carbon and total nitrogen contents increased by 16.9% (P<0.001) and 17.1% (P<0.001), respectively, but the soil carbon to nitrogen ratio decreased by 0.1% (P>0.05). Based on the BRT model, it was found that the straw C∶N ratio and the amount of straw returned to the field were the core variables affecting the soil organic carbon and total nitrogen contents. The method of straw return and environmental factors significantly regulated the responses of soil organic carbon and total nitrogen content under straw return, and soil organic carbon increased significantly by 25.9% (P<0.001) under straw mulching, and soil total nitrogen increased significantly by 19.7% (P<0.01) under straw tilling and field return. In addition, temperate climate and wheat cropping system showed higher soil carbon sequestration efficiency, while continental climate and gramineous cropping system (wheat and rice) were more favorable for soil total N accumulation. Soil organic carbon increased significantly by 18.2% (P<0.001) under the long-term straw return experiment (≥15 years), and the effect of soil total nitrogen accumulation stabilized within 10−15 years. This study can provide a scientific basis for the scientific management of crop residues and the enhancement of soil carbon and nitrogen utilization efficiency in farmland.