Determining irrigation amount and fertilization rate to simultaneously optimize grain yield, grain nitrogen accumulation and economic benefit of drip-fertigated spring maize in northwest China

Inappropriate water and fertilizer management can lead to unstable crop yield, and excessive irrigation and fertilization can potentially cause soil degradation and groundwater pollution. A two-year field experiment was conducted on drip-fertigated spring maize (Zea mays L.) in Ningxia of northwest China to explore the effects of four irrigation amounts (I75: 0.75ETc, I90: 0.90ETc, I105: 1.05ETc and I120: 1.20ETc, where ETc is the crop evapotranspiration) and four N-P2O5-K2O fertilization rates (F60-30-30, F120-60-60, F180-90-90 and F240-120-120 in 2016; F150-70-70, F225-110-110, F300-150-150 and F375-180-180 in 2017) on maize growth, grain yield, grain nitrogen accumulation, economic benefit and soil nitrate residue (NO3-N). Considering the goal of conserving both water and fertilizer while maintaining relatively high yields and minimizing soil NO3-N, a management strategy to optimize irrigation and fertilization regimes was developed based on the response surface methodology. The results showed that irrigation amount and fertilization rate significantly affected leaf area index, aboveground biomass, grain yield and harvest index. The irrigation-fertilization interaction significantly affected plant and grain nitrogen accumulation. In 2016 with lower fertilization range, grain yield and grain nitrogen accumulation were highest under I120F240-120-120, reaching 14,440 kg ha-1 and 184.50 kg ha-1, respectively. In 2017 with higher fertilization range, both grain yield and grain nitrogen accumulation initially increased and then decreased with increasing irrigation and fertilization regimes. Grain yield and grain nitrogen accumulation were highest under I90F300-150-150, reaching 16,884 kg ha-1 and 195.09 kg ha-1, respectively. Although plant nitrogen uptake was dramatically higher under I90F375-180-180 than those in the other treatments, grain yield was markedly lower under I90F300-150-150 and nitrogen harvest index was also lower. Soil NO3−-N increased with increasing fertilization rate, but it decreased with increasing irrigation amount. When irrigation amount and fertilization rate increased at the same time, the soil NO3−-N accumulation area moved deeper in the soil profile. Soil NO3--N content and distribution in the 60−100 cm soil layer showed an increasing trend, but this trend was less obvious than that in the 0−60 cm soil layer. When the irrigation amount was 447−452 mm and the N-P2O5-K2O fertilization rate ranged from 290−145-145 to-303−152-152 kg ha-1, grain yield, grain nitrogen accumulation and economic benefit (≥13,688 CNY ha-1) can reach 95 % confidence interval of their maximum values simultaneously. This study can provide a theoretical basis for high-efficient water and fertilizer utilization in sustainable spring maize (Zea mays L.) production in northwest China.