Optimizing water and nitrogen inputs for sustainable wheat yields and minimal environmental impacts

Context: Northern China still has great potential to increase wheat productivity. Studies have shown that the improper wheat management of water and fertilizer aggravates the risk of yield instability and environmental pollution in this region. Optimizing water and N management can increase wheat yield, improve nitrogen (N) use efficiency (NUE) and water-use-efficiency (WUE), and reduce nutrient loss and environmental pollution. Therefore, the potential benefits of water and N management measures for wheat productivity in Northern China require further quantification. Objective: We quantified the effects of different N fertilizers, water, and integrated water and N management strategies on wheat yield, NUE, WUE, and greenhouse gas emissions and comprehensively evaluated the potential benefits of integrated water and N management in wheat-producing areas in Northern China. Methods: Using a meta-analysis approach, we quantified and compared the effects of four water and N management strategies (optimal N management [ONM], optimal water management [OWM], integrated water and N management [IWNM], and traditional farmers' practices [FP]) on winter wheat yield, NUE and WUE, and related environmental effects in Northern China. Results and conclusions: The results showed that, compared to those in FP, the N fertilizer application rate was 35% lower in ONM, irrigation water was 39% lower in OWM, and the N fertilizer application rate and irrigation water rate decreased by 45% and 42% in IWNM, respectively. Water and N management strategies had positive effects on yield and partial factor productivity of applied N (PFP-N), with ONM, OWM, and IWNM with 7%, 10%, and 11% higher yields and 64%, 10%, and 103% higher PFP-N than those in FP, respectively. The management practices had a positive impact on gas emission reduction, i.e., NH3 3 volatilization decreased by 48%, 58%, and 72%, and N2O 2 O emissions were reduced by 29%, 32%, and 57% for ONM, OWM, and IWNM, respectively, compared to those in FP. In addition, the WUEs of OWM and IWNM were 16% and 31% higher than those of FP, respectively. The results of the meta-analysis showed that, compared with ONM and OWM, IWNM could achieve higher wheat yields and lower greenhouse gas emissions based on less fertilizer and water consumption. Significance: Water and N are important for sustaining crop productivity in China. Focusing on exploring and optimizing the relationship and interaction between fertilization and water management can increase wheat yield, reduce environmental impacts, ensure NUE and WUE, and provide a theoretical basis for ensuring food security.