Optimal Water Management Improves Irrigation Efficiency While Modulating Reactive Nitrogen Losses: A Global Meta‐Analysis

ABSTRACT Irrigation plays an essential role for crop production, but unreasonable irrigation is accelerating the depletion of water resources and exacerbating nitrogen (N) losses. Optimal water management (OWM) is critical for improving crop yield and decreasing N losses. However, few studies comprehensively estimate the effects of different OWM practices (i.e., optimal irrigation rate, time, and technology) on crop yield and N losses, and their water saving potentials. Here, we conducted a global meta‐analysis of 562 observations in 103 sites to estimate these effects. Under the current sample support, we found that OWM increased crop yield and irrigation water productivity (IWP) by 2.7% and 19.1%, respectively, while reducing irrigation water use (IWU) by 21.6%. OWM tended to reduce ammonia (NH 3 ) volatilization and nitrate (NO 3 − ) leaching in several crop‐indicator combinations, whereas some optimal irrigation rate and time practices increased nitrous oxide (N 2 O) emission. A simplified scenario analysis suggested that broader adoption of OWM could reduce IWU from 1372 to 1075 km 3 , corresponding to an illustrative water‐saving estimate of 297 km 3 . Our analysis could provide theoretical and technical support for water management in coordinating crop production and N losses.