A global synthetic analysis of the effects of reclaimed water irrigation on crop yield and water use efficiency

To quantitatively evaluate the effect of RW irrigation on yield, WUE, and IWUE, and identify aqueous, edaphic, and management factors that favor improved yield, WUE, and IWUE compared to control practices, a meta-analysis was conducted. The results indicated that RW irrigation is beneficial for improving crop yields, WUE, and IWUE (16.8, 23.8, and 18.7%, respectively). However, its effectiveness is highly dependent on the aqueous, edaphic, and management factors of the studies evaluated. Greater responses were found in practices using RW with a pH < 7 or a nitrogen content <100 mg/L. The soils with a pH ≥ 7, electrical conductivity between 2 and 4 dS/m, bulk density <1.35 g/cm3, and/or initial nitrogen content between 200 and 2,000 mg/kg produced the highest effect size. Furthermore, using a surface drip irrigation system, with a nitrogen fertilizer rate <1,000 kg/ha and irrigation level at 100% crop evapotranspiration are effective ways to use RW. Our findings highlight the potential of RW irrigation to improve crop yield, WUE, and IWUE and identify the conditions under which these results can be achieved. These results can provide a better understanding of RW irrigation and guide the practice of RW utilization in the future.