Yield performance response to field configuration of maize and soybean intercropping in China: A meta-analysis

Context: Intercropping of maize and soybean has proven to be a sustainable cropping system all over the world. In recent years, as imports of maize and soybean have increased, the Chinese government has strongly promoted the maize -soybeans intercropping to prevent a decline in maize production and to obtain an extra soybean harvest. Research question: It is not clear what the coupling relationship is between the intercropping model and the change in yield of maize and soybean across China. Methods: The research searched for articles that fulfilled the criteria related to maize-soybean intercropping in China since 2000. It investigated the yield change through meta-analysis, and analyzed the allocation path of yield increase based on the field configuration level using single factor analysis, multilevel model analysis and random forest analysis. Results: Compared to monoculture, the total yield of intercropping maize and soybean increased by approximately 12%, while the equivalent yield decreased by 8% and 40%, respectively. The proportion of maize area was crucial for the maize intercrop yield. The shading effect of maize on soybean was a key factor in soybean yield reduction. Increasing the distance between the maize and soybean strips lead to an elevation of soybean intercropping yields without compromising maize yield or the total yield. Huang-Huai-Hai Plain Summer Sowing region and Southwest Mountain region were more suitable for promotion. The yield of intercropping was beneficial in this suitable integrated region when the soybean strip width did not exceed 78 cm (soybean row spacing <= 3) and the distance between the maize and soybean strips >= 77 cm. Conclusions: Maize-soybean intercropping had great potential for yield improvement, the overall LER was 1.6. In the Huang-Huai-Hai Plain Summer Sowing and Southwest Mountain regions, the yield-advantaged field configurations were: (soybean strip-width <= 61 cm or soybean rows <= 3, distance between strips >= 65 cm) and (soybean strip-width <= 76 cm or soybean rows <= 3, distance between strips >= 73 cm), respectively. Each plantation regions still need to select the optimal distance based on the local farming facilities and traditional farming habits.