Green manure, a traditional practice of incorporating plant materials into soil, enhances soil fertility and structure. After a decline post-1990s, its use in China has rebounded due to green agriculture policies, reaching 3.71 million hectares by 2022. However, adoption on ecological farms remains limited (42.9%), often hampered by single-species use and suboptimal management. This study conducted a meta-analysis of 15 articles (183 effect sizes) to evaluate green manure's ecological benefits. Results show it generally increases subsequent crop yields (78.7% of data showed positive effects), with a mean increase of 13.8%. Benefits depend on species, crop type, and climate; legume green manures, for example, increased wheat yield by 5.1%, while non-legumes decreased it. Green manure consistently improved soil microorganisms (100% positive effects) and nutrient cycling (82.9% positive), boosting available nitrogen, phosphorus, and potassium. It also enhanced soil organic carbon (87.5% positive), sequestering carbon with a mean increase of 17.3%. Trade-offs exist: green manure can reduce soil moisture and increase greenhouse gas emissions by an average of 40.7%. In China, primary models include intercropping (e.g., in maize fields, tea plantations, orchards) and rotation (e.g., in rice-wheat systems). For ecological farms, which require multi-functional technologies, green manure supports soil health and nutrient management. Successful application requires selecting species suited to local conditions and integrating it with practices like fertilizer reduction. Challenges to wider adoption include insufficient evidence of direct economic benefits for farmers and a lack of strong policy support. Overcoming these requires better policy incentives, improved ecological compensation, and synergistic application with other sustainable practices to realize green manure's full potential in agriculture's green transformation.
Chaolin et al. (Wed,) studied this question.