Effect of green manure on soil water and crop yield in the Loess Plateau of China: A Meta-analysis

Planting green manure is a long-established planting pattern in the dryland cropping areas across the Loess Plateau of China. However, due to limited precipitation, planting green manure may reduce soil water content and affect the succeeding crop yield. By combining data from 46 peer-reviewed publications, a Meta-analysis was carried out to assess the effect of green manure on precipitation storage efficiency (PSE) during the fallow period, soil water storage at succeeding crop planting (SWSP), succeeding crop yields, evapotranspiration (ET), and water use efficiency (WUE) in the Loess Plateau of China. Compared to fallow areas without green manure, area with green manure decreased PSE, SWSP and ET by 28.28% (P<0.05), 4.93% (P<0.05) and 2.51% (P<0.05), respectively, however, it increased succeeding crop yield and WUE by 2.37% and 8.97% (P<0.05), respectively. Green manure effect on soil water, crop yield, and soil water use varied with the interval between green manure termination and planting of succeeding crop, green manure biomass, and climatic conditions. Strong polynomial relationship was found between the response ratios (RRs) of PSE, SWSP and the interval between legume green manure termination and succeeding crop planting. Both PSE and SWSP maximized at an interval of 13 d. The RRs of crop yield and WUE were also correlated with legume green manure biomass in a polynomial way. Succeeding crop yield and WUE maximized when the legume green manure biomass was 2200 and 3100 kg∙hm⁻², respectively. Overall, introducing green manure during fallow period reduced soil water but enhanced succeeding crop production and water use in the Loess Plateau. Leaving a 12–14 d interval between legume green manure termination at a biomass of 2200–3100 kg∙hm⁻², succeeding crop planting can be a reliable practice to mitigate soil water consumption in such dryland areas.