Meta-analysis of the effects of nitrogen and water input gradients on maize yield, nitrogen fertilizer productivity, and water use efficiency in northern China

This study was conducted to determine the overall performance of the effects of water, nitrogen, other environmental factors, and agronomic measures on maize (Zea mays) yield, nitrogen productivity (NP), and water use efficiency (WUE) under different environmental and climatic conditions. This study is based on 35 studies on the effects of nitrogen application and water input gradients on maize yield, NP, and WUE, using meta-analysis to explore the relevant factors affecting maize yield, NP, and WUE in northern China, and to quantitatively analyze the relationship between each influencing factor and maize yield, NP, and WUE. The results showed that the average maize yield was 9.19 t·ha⁻¹, and the average of NP and WUE were 55.66 kg·kg⁻¹ and 1.83 kg·m⁻³, respectively. Water and nitrogen had a significant interaction effect on maize yield. Compared with the control, water input and nitrogen application increased the overall maize yield by 13.43% (P < 0.01) and 10.69% (P < 0.01), respectively. As the input volume increased, water and nitrogen gradually became the main limiting factors for the increase in NP and WUE. In the regression analysis, the effects of water and nitrogen factors, soil organic carbon (SOC), planting density (PD), and available potassium (AK) on maize yield were positive, while that of the mean annual temperature (MAT) was negative. In the structural equation model (SEM), there was a strong positive correlation between SOC and maize yield, and its standardized path coefficient was 0.73. In summary, there is still room for improvement in the water use efficiency and nitrogen productivity of maize in northern China. Based on optimizing water and fertilizer measures, appropriate soil nutrient inputs could increase SOC and AK levels in the soil. Simultaneously, planting density can be increased appropriately, to achieve a win-win situation between high maize yield, water-use efficiency , and environmental protection.