Abstract
The unreasonable application of nitrogen (N) fertilizer leads to high nutrient losses and severe potential of agricultural non-point source contamination, which threatens water quality in the upper Yellow River Basin. Therefore, the aim of this study is to explore the effects of N application rates and various control measures on rice yield and N leaching in paddy fields in the Yellow River irrigation area. Four treatments were employed in this study, CK (no N fertilizer application, 0 kg N∙ha(-1)), CRU (controlled-release urea application, 180 kg N∙ha(-1)), OPT (optimal N fertilizer application, 210 kg N∙ha(-1)), and FP (N fertilizer application based on farmer experience, 240 kg N∙ha(-1)), to examine paddy yield, N use efficiency (NUE), N concentrations in leaching water at various soil depths, and N contents along the 0-100 cm depth of the soil profile. The results indicated that the amount of TN leached was 25.14-48.04 kg∙ha(-1) after different N applications, and the TN leaching coefficients of FP, OPT, and CRU were 10.88%, 11.27%, and 7.07%. Compared to FP and OPT, the CRU significantly reduced the concentrations of TN, ammonium N (NH(4)(+)-N), and nitrate N (NO(3)(-)-N) in the surface and soil water, with average TN leaching decreasing by 31.55% and 27.35% in the years 2022 and 2023, respectively. NO(3)(-)-N was identified as the primary form of N leached from the paddy fields. Compared to FP and OPT treatments, the CRU treatment increased the average paddy yield by 19.99-20.66% and improved the average NUE by 19.04-16.38%. This study revealed that the application of high amounts of N positively affected soil N leaching, and controlled-release urea demonstrates superior efficacy compared to conventional fertilization. The application of controlled-release urea at a rate of 180 kg N∙ha(-1) not only ensures a good paddy yield but also reduce N losses, which should be recommended to local farmers.