Meta-analysis of green manure effects on soil properties and crop yield in northern China

The application of green manure is a traditional and valuable practice for agroecosystem management. In northern China, the effects of green manure on production of the region's major crops have been extensively investigated, but the inconsistent conclusions that these case studies have yielded cannot provide effective guidance for practical local agricultural production. Here, we conducted a meta-analysis to generate a comprehensive evaluation of the effects of green manure on soil properties and crop yield in this region. Our results shown that green manure improves soil quality effectively, decreasing soil bulk density by ∼ 5.6 %, increasing microbial biomass carbon by 28 %, and improving the activities of soil enzymes by 14 % ∼ 39 %. Among the different types of green manure, legume green manure more markedly increased both nitrate and hydrolysable nitrogen, while non-legume green manure more markedly increased available potassium. Soil gravimetric water content was decreased under green manure treatment. Maize yield was significantly increased under green manure by 11 % on the whole, while effects of green manure on wheat and potato were inconsistent. In summary, the application of green manure in northern China can improve soil quality significantly, and proper green manure use can improve cash crop yields.