Water productivity of irrigated maize production systems in Northern China: A meta-analysis

Understanding water productivity (WP) on a regional scale is useful for identifying and managing inefficiencies in irrigated crop production systems. However, relevant WP analyses are not available for maize production systems in China. A meta-analysis was conducted of maize WP in Northern China that included 2354 observations from 282 articles published between January 2000 and March 2018. Our goal was to quantify the current WP and its constraining factors, and estimate the boundary function for WP in the different maize agro-ecological zones of Northern China. The Northern China average WP across the large set of field experiments was 22.3 kg ha(-1)mm(-1), with Northeast China (NE, 25.8 kg ha(-1)mm(-1)) > North China Plain (NCP, 22.3 kg ha (-1)mm(-1)) Northwest China (NW, 21.6 kg ha(-1)mm(-1)). The boundary function for WP had slopes of 42.5, 36.8 and 40.4 kg ha(-1)mm(-1) for NW, NCP and NE, respectively. The WP was significantly correlated with latitude, vapor pressure deficit, N application rate, seasonal average temperature, experimental regions and years. WP was increased by optimal irrigation, soil surface with plastic mulch, deep tillage, straw incorporation into the soil, ridge planting, and the application of super absorbent polymer. In this study, we provided both reference WP values, recommendations to achieve higher WP and identification of regions with opportunities for improvement.