Response of winter wheat yield, nitrogen use efficiency and soil nitrogen balance to rainfall types and nitrogen application rate in dryland

Abstract

<p id="C3">To study the effects of nitrogen application rate on grain yield, nitrogen utilization, and soil nitrogen balance of dryland winter wheat fields under different rainfall types, we explored the optimal nitrogen input levels for stable yield and high efficiency of winter wheat in the Weibei highland of North China, which could provide a theoretical basis for efficient fertilization. Five nitrogen treatments including 0, 60, 120, 180, and 240 kg hm^-2 (designated as N0, N60, N120, N180, and N240, respectively) were arranged in Heyang County, Shaanxi Province from 2017 to 2020. The three-year <italic>in situ</italic> experiment were as follows: (1) Different rainfall types had significant impact on yield and economic profits of winter wheat. Compared with the normal and dry year, the yield of the humid year was increased by 33.6% and 113.3% and economic profits were increased by two to three times or more. Nitrogen fertilizer recycling and agronomic efficiency of winter wheat had similar change patterns with yield, and the nitrogen fertilizer recycling, and agronomic efficiency were increased by 4.7%, 0.6 kg kg^-1 (normal year), and 11.9%, 2.5 kg kg^-1 (dry year) in the humid year compared with the normal and dry year. (2) Regardless of the rainfall type, the yield and nitrogen fertilizer recycling and agronomic efficiency of winter wheat increase first and then decrease with the increase of N application. The highest values were found under N180 treatment in both humid and normal years, and the NO₃^--N accumulation in 0-100 cm layer after wheat harvest were 108.9 and 113.6 kg hm^-2, respectively. In dry year, the NO₃^--N accumulation under N120 treatment in 0-100 cm layer after wheat harvest was 100.8 kg hm^-2 reaching the highest value. (3) The threshold of nitrogen input was determined by the best economic benefit and the highest yield, the nitrogen application rates in humid year, dry year, and normal year were 158.9-166.5, 121.2-130.0, and 148.1-155.7 kg hm^-2, respectively; The threshold of nitrogen input was determined by the balance of soil nitrogen pool and the maximum nitrogen uptake, the nitrogen application rates in humid year, dry year, and normal year were 166.5-190.3, 109.6-147.7, and 153.5-198.9 kg hm^-2, respectively. Considering the high yield and high efficiency of winter wheat and low soil nitrogen loss, we concluded that when the nitrogen application rates in humid year, dry year, and normal year were 158.9-190.3, 109.6-147.7, and 148.1-198.9 kg hm^-2, respectively. It was the suitable nitrogen application rate for both high yield and good environmental benefits, which could be benefit for reference in the production of this region.