Soil nitrate-N distribution, leaching loss and nitrogen uptake and utilization of maize under drip irrigation in different precipitation years

To improve crop yield, excessive nitrogen usage in agricultural production has become increasingly important in recent years. Excessive nitrogen use increases soil nitrate-N accumulation and water pollution, and nitrogen leaching loss varies with precipitation year. It is of great significance to clarify the scientific fertilization model in different precipitation year types under drip irrigation in Ningxia to alleviate the problems of resource waste, water quality decline in the Yellow River, and groundwater pollution caused by unreasonable nitrogen usage. In this study, a 3-year nitrogen gradient experiment was carried out in the Pingjipu Farm, Ningxia Hui Autonomous Region, with five nitrogen application treatments: 360 kg∙hm⁻² (N4), 270 kg∙hm⁻² (N3), 180 kg∙hm⁻² (N2), 90 kg∙hm⁻² (N1), and 0 kg∙hm⁻² (N0), to analyze the effects of different nitrogen fertilization treatments on soil nitrate-N residues and leaching amounts, as well as on nitrogen uptake, utilization, and yield of maize under drip irrigation in rainy and dry years. The results showed that the peak value of soil nitrate-N content was closely related to precipitation; the peak value of nitrate-N residue was in the 40–60 cm soil layer in the rainy year (2018), and in the 20–40 cm soil layer in the dry years (2019 and 2020). In different precipitation years, soil nitrate-N residues, and leaching increased with the increased nitrogen usage and reached the maximum value under the N4 treatment. Precipitation significantly affected nitrate leaching, and in rainy years, the nitrate-N leaching loss caused by precipitation accounted for 50.62% of the total leaching loss, while in the dry year accounted for 34.82% of the total leaching loss. The regression analysis showed that maize yield initially increased and then decreased by the application rate of nitrogen in different precipitation years. The maximum yield was found under 270 kg∙hm⁻² (N3) in different precipitation years, and the yield and nitrogen uptake under the N3 treatment did not differ from 360 kg∙hm⁻² (N4). In rainy year, compared with N4, the utilization rate, agronomic utilization rate, and partial nitrogen fertilizer productivity increased by 11.38%, 6.16 kg∙kg⁻¹, and 13.85 kg∙kg⁻¹; and in dry years, they were increased by 12.10%, 5.06 kg∙kg⁻¹, and 15.00 kg∙kg⁻¹, respectively. In summary, when the nitrogen application rate was 270 kg∙hm⁻², the yield, nitrogen uptake, and utilization of maize in rainy and dry years were maintained at a high level, and the amount of nitrate leaching was also within an acceptable range. It is recommended that 270 kg∙hm⁻² is the appropriate nitrogen application rate for maize under different precipitation patterns in the Ningxia Yellow River irrigation area. The maximum threshold of nitrogen usage in the rainy year is 275.59 kg∙hm⁻², and that in the dry year is 320.20 kg∙hm⁻². The results from this study can provide a theoretical basis for the decision of scientific nitrogen application in different precipitation years of drip-irrigated maize in the Ningxia Hui Autonomous Region.