Understanding the effects of tree-crop intercropping systems on crop production in China by combining field experiments with a meta-analysis

Tree-crop intercropping (TCI) systems have many environmental benefits in addition to providing direct economic benefits from trees and crops. An increasing number of field experiments have provided rich basic data on crop production in TCI systems in China. However, there are fewer quantitative analysis studies on a national scale. The purpose of this study was to investigate the effects of TCI systems on crop production in China by combining field experiments with a meta-analysis, and to understand whether the results of the field experiments and the national scale meta-analysis are consistent. This study consists of field experiments and a national-scale meta-analysis. In the field experiments, three TCI systems were designed with different tree species configurations in Dafeng District, Yancheng city, Jiangsu Province, China, to investigate their effects on the crop yield when compared with a sole cropping system. Furthermore, we conducted a meta-analysis of 36 studies with 94 comparisons in Chinese fields to examine the effects of TCI systems on crop yields and to explore how climatic conditions, crop species, tree species, and tree characteristics affect crop yields in TCI systems. In the field experiments, TCI systems had negative effects on crop yield, and understory crop yield was affected by the tree species in the TCI systems; the crop yield in the three TCI systems was 18.9–32.2% lower than that in the sole cropping system. The meta-analysis results were consistent with those of the field experiments. In the national scale meta-analysis, TCI systems had negative effects on crop yields in China (effect size = −0.488, 95% CIs = −0.576 to −0.401), and the TCI systems decreased crop yields by 38.6% overall when compared with sole cropping systems. Furthermore, the effects of TCI systems on crop yields were different among regions, climatic conditions, crop species, tree species, and tree characteristics. TCI systems should be designed carefully considering local climates, crop species, tree species, and tree characteristics to maximize agronomic and environmental benefits. This study has the potential to enhance our understanding of TCI systems in China by integrating field experiments and meta-analysis. These results can inform the development of more effective and sustainable agricultural practices.