Quantifying the impacts of agricultural management practices on the water use efficiency for sustainable production in the Loess Plateau region: A meta-analysis

The lack of water resources limits sustainable agricultural production in the Loess Plateau region of China, and optimizing field management practices to improve crop water use efficiency (WUE) is a key strategy to solve this problem. However, there is no consensus among researchers on the most appropriate field management practices regarding WUE, which requires further integrated quantitative analysis. We conducted a meta-analysis by computing 1338 effect sizes from 171 publications to quantify the effect of agricultural practices (nitrogen (N) fertilizer management, mulching management, water-saving irrigation, straw return and conservation tillage) on crop WUE. Our results showed that N fertilizer management (51.83% increase, P < 0.05) is the most effective practice for improving the crop WUE, followed by mulching management (17.44% increase, P < 0.05), water-saving irrigation (15.97% increase, P < 0.05), straw return (10.00% increase, P < 0.05), and conservation tillage (5.09% increase, P < 0.05). This study also identified the key drivers (including climatic factors, soil factors, and human intervention factors) that affect the crop WUE under various field management practices. For example, the mean annual precipitation, annual evaporation, soil type, pH, soil total nitrogen content, N application frequency, N fertilizer type, and N application rate were identified as the key factors that affect the crop WUE under N fertilizer management practices. In addition, we quantified the effects of the different drivers on the crop WUE under various field management practices by subgroup analysis, and then the drivers level with the best improvement effect of WUE was determined. Specifically, when the N application rate is 150-225 kg ha-1, the N fertilizer type is controlled release urea, the soil covering ratio is more than 0.5, the irrigation method is drip irrigation, the amount and length of straw returning is 10,001-15,000 kg ha-1 and less than 0.5 cm, etc., the improvement effect of crop WUE was the best. In a word, our results provide references for determining appropriate integrated agricultural management strategies to ensure efficient water use and sus-tainable production in the Loess Plateau region.