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

As an important agricultural management practice, straw return plays an important role in soil carbon and nitrogen cycling. However, there is still a lack of evaluation studies about straw biochemical properties and the effects of straw return practices on soil organic carbon and total nitrogen content in agricultural soils. In this study, we combined meta-analysis and boosted regression tree (BRT) model for the peer-reviewed articles published before 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 straw return increased the soil organic carbon and total nitrogen content by 16.9% (P<0.001) and 17.1% (P<0.001), respectively, while decreasing the soil carbon to nitrogen ratio by 0.1% (P>0.05). The analysis based on the BRT mode indicated 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 content. The methods of straw return and environmental factors significantly regulated the responses of soil organic carbon and total nitrogen content under straw return. Specifically, soil organic carbon increased by 25.9% (P<0.001) under straw mulching, and soil total nitrogen increased by 19.7% (P<0.001) under straw incorporation. In addition, temperate climate and wheat cropping systems showed higher soil carbon sequestration efficiency, while continental climate and gramineous cropping systems (wheat and rice) were more favorable for soil total nitrogen accumulation. Soil organic carbon increased 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 straw and the enhancement of soil carbon and nitrogen utilization efficiency in cropland.