Yield–water trade-offs of deficit irrigation in wheat in China: A meta-analysis across irrigation-reduction intensities and production levels

Deficit irrigation is widely used to improve water productivity (WP) in wheat production, but its benefits may be offset by grain yield loss. We conducted a multilevel meta-analysis of 125 studies to quantify the effects of deficit irrigation on wheat grain yield, actual crop evapotranspiration (ETc act), WP, and yield components in China, and to evaluate yield–water trade-offs across production levels, irrigation-reduction timings, and tertile-based irrigation-reduction intensity classes. Compared with the corresponding reference irrigation treatment, deficit irrigation significantly reduced grain yield (−14.8%), ETc act (−18.3%), spike number (SN; −8.6%), grain number per spike (GNPS; −6.7%), and thousand-grain weight (TGW; −2.9%). WP showed only a slight and non-significant increase (+2.8%), indicating that reduced crop water consumption did not translate into a statistically robust WP improvement. Irrigation-reduction intensity was the main factor regulating yield–water responses. Within the tertile-based intensity classification used in this meta-analysis, low irrigation reduction maintained grain yield and improved WP, moderate irrigation reduction improved WP but caused significant yield loss, and high irrigation reduction caused the largest yield penalty without significantly improving WP. Meta-regression indicated that grain yield responses approached zero at approximately 27.3% irrigation reduction (95% CI: 22.1%–31.8%). Production level modified response patterns, but its effect was less consistent than that of irrigation-reduction intensity. Yield loss was jointly associated with reductions in SN, GNPS, and TGW, with SN making the largest average contribution. Overall, wheat deficit irrigation should be managed as a threshold-dependent, production-context-specific, and growth-stage-sensitive strategy to balance water saving and yield stability.