Fig. 4: Legume pre-crop effect on main crop yield as a function of yield level and among global regions.

a The log yield response ratio (yield of crops following legumes vs. non-legumes) decreased with increasing yield level with a more pronounced pre-crop effect at low N fertilizer rate. b Legume pre-crop effect on main crop yield across global regions. The dashed horizontal and vertical lines in a were drawn at lnRR = 0 and averaged grain yield (standardized grain yield = 0), respectively. Standardized grain yields were calculated by observed values minus mean and divided by one standard deviation. The solid line and shading area in a represent the smoothed conditional average response and the 95% confidence interval (CI) fitted by local weighted regression using “loess” function in R. Dots and error bars in b represent overall effect sizes from a meta-analysis and 95% CIs. For each region, the numbers denote the total observations with the number of studies in parentheses. Yield benefits differ significantly among global regions, as indicated by non-overlapping CIs.