Legumes can increase the yield of subsequent wheat with or without grain harvesting compared to Gramineae crops: A meta-analysis

Legumecereal crop rotation is considered a sustainable intensive rotation model that can reduce nitrogen (N) inputs, improve soil quality, increase biodiversity and reduce environmental pollution risks. However, compared with Gramineaecereal rotations, quantitative assessment of the effects of legumecereal rotations on grain yield and N use of subsequent cereal crops are lacking. There is also no comprehensive analysis of factors explaining the change in yield effects of subsequent cereal crops, or the differences in these effects, depending on whether the grains of the legume crops are harvested. Here, a meta-analysis of the effects of legumewheat (LW) and Gramineaewheat (GW) rotations on wheat yield and N use was conducted based on 453 observations from 62 studies published worldwide. Our results suggested that compared with GW rotations, LW rotations had a positive effect on wheat yields. Wheat yield was significantly increased by 21.28 % and 31.71 % (P < 0.05) under legume-harvested grainwheat (LHGW) rotation and legume that non-harvested grainwheat (LNHGW) rotation systems, respectively. The positive benefits of legume crops on wheat yield were reduced to some extent by their harvest. The main factors affecting wheat yield were fertilization rates and climate and soil types, with weight ratios of 0.32, 0.21 and 0.16, respectively. For fertilization rates, wheat yield benefits decreased with increases in N fertilizer inputs, and we identified significant positive benefits in temperate, subtropical and Mediterranean climates (P < 0.05). For soil types, sandy and loamy sand soils with low clay contents generally had the best wheat yield benefits. Furthermore, compared with GW rotations, LW rotations increased N use efficiency by 8.57 % on average, which was significantly affected by N inputs (P < 0.05). Therefore, the introduction of legume crops into the GW rotation system can increase wheat yields and reduce N applications regardless of whether legume grains are harvested. Moreover, legume crops have the best wheat yield benefits under low N input conditions, which can make an important contribution to the sustainable intensification of global wheat production.