Effects of irrigation and nitrogen fertilization management on crop yields and long-term dynamic characteristics of water and nitrogen transport at deep soil depths

Abstract

Appropriate irrigation and nitrogen (N) management practices should be implemented to obtain high grain yields while considering the influence of water and N leaching on groundwater in the intensively cropped winter wheat (Triticum aestivum)-maize (Zea mays L.) rotation system. The calibrated RZWQM2 model was used to explore long-term (1984–2017) effects of irrigation and N fertilization on crop yield, water and nitrogen use efficiency, deep percolation water (DPW), N leaching loss (NLL), and their effects on deep soil layers (2−30 m) in this rotation system in the Jinghui Canal irrigation area of the Guanzhong Plain in China. Results showed that crop yields increased with increasing N rate. The critical N application rates of 140 and 240 kg N ha−1 coupled with 75 and 90 mm of irrigation for maize and wheat, respectively, resulted in high yields (7535 and 8977 kg ha−1), water use efficiency (2.22, 2.07 kg m-3), and nitrogen use efficiency (44.56, 40.78 kg kg−1). The simulated DPW values were 69 and 110 mm for maize and wheat, respectively, and NLL values were 25.36 and 25.47 kg ha−1. Crop yield and NLL for wheat were more sensitive to N application timing than maize yield and NLL, indicating that split N applications of two application times and three application times for maize and wheat, respectively, could be a more effective way of applying N fertilizer. DPW fluxes increased from 0.021-0.024 (varied over the 2−30 m depth) to 0.107-0.110 mm d−1 for irrigation ranging from 60 to 135 mm. The response times for DPW to be observed at the groundwater depth of 30 m could range from one year to more than two years, with DPW velocities of 0.034 and 0.077 m d−1 for 60 and 135 mm irrigation application amounts, respectively. NLL flux increased with added irrigation and N application rate, while decreasing exponentially with soil depth. Annual recharge of NO3-N to the groundwater (0.15–6.2 kg N ha−1) with lower irrigation amounts (60−90 mm) could be neglected, but higher irrigations (≥105 mm) even with lower N application rates could cause groundwater contamination. Therefore, comprehensively considering the effects of irrigation and fertilization practices on grain yields and groundwater could improve the sustainability of the agro-hydrological environment and agricultural production.