关键词: 稻油轮作, 氮肥用量, 产量稳定性, 氮素积累量, 氮素表观平衡, 氮素利用率

Abstract:

【Objective】By studying the effects of nitrogen fertilizer application rates on the annual crop yields, stability, and nitrogen uptake in the rice-rapeseed rotation system, this study explored the changing trends of the appropriate annual nitrogen fertilizer application rates for rice and rapeseed, so as to provide a theoretical basis for rational fertilization in the rice-rapeseed rotation in the middle reaches of the Yangtze River region.【Method】This locational trial was located in Wuxue City, Hubei Province, and was started in 2016. In this study, eight consecutive years of field locational trials were selected from 2016 to 2024. Five nitrogen fertilizer application rate gradients of 0, 90, 180, 270, and 360 kg N·hm^-2 were set up for both crops in the two seasons. The yields and their stability, nitrogen accumulation amounts, nitrogen fertilizer use efficiency, apparent nitrogen surplus, and the annual trends of appropriate nitrogen fertilizer application rates in the rice-rapeseed rotation system were analyzed. 【Result】Nitrogen fertilization significantly enhanced crop productivity in rice-rapeseed rotation systems. Compared with the nitrogen-free treatment, in each nitrogen-applied treatment, the average annual yield of rice increased by 1 035-1 769 kg·hm^-2, with an increase range of 19.4%-33.2%. The application of nitrogen fertilizer had a significant yield-increasing effect on winter rape; compared with the nitrogen-free treatment, the average annual winter rape yield increased by 1 041-2 208 kg·hm^-2, and the yield increased by 1.3-2.8 times. Aboveground nitrogen accumulation in rice and rapeseed increased progressively with elevated N inputs, averaging 36.8-108.2 kg·hm^-2 and 43.4-139.3 kg·hm^-2 higher than that under the zero-N control, respectively. Continuous observations indicated rising trends in both N accumulation and N recovery efficiency (NRE) for both crops under continuous rotation. During the rice season, with the increase in nitrogen fertilizer application rate, compared with the previous year, the average annual increase in nitrogen accumulation increased from 2.6% to 9.8%. In the rapeseed season, the increase in nitrogen accumulation in the nitrogen-free treatment was not significant among years. After applying nitrogen fertilizer, the nitrogen accumulation increased by an average of 3.4%-5.1% annually compared with the previous year. NRE in rice remained stable during the first three years but exhibited a parabolic rise starting from the fourth year. For rapeseed, NRE under 90-270 kg N·hm^-2 N rates increased by 5.6% annually, whereas no significant improvement occurred at 360 kg N·hm^-2. Apparent N balance in the zero-N treatment consistently showed deficits, while N-surplus in fertilized plots declined annually by 3.6%-8.3% (rice) and 2.4%-6.7% (rapeseed). Systematic analysis revealed an annual increase of 2.3% in optimal N rates for rice (annual mean: 146.8 kg N·hm^-2) and 0.9% for rapeseed (annual mean: 198.0 kg N·hm^-2).【Conclusion】In the continuous rice-rapeseed rotation planting mode, it was necessary to apply fertilizers with appropriate nitrogen application rates according to the nitrogen absorption characteristics of the crops in the rotation system, and to dynamically adjust the annual nitrogen allocation amount according to the soil nitrogen status.

Key words: rice-rapeseed rotation, nitrogen fertilizer application rates, yield stability, nitrogen accumulation, apparent nitrogen surplus, nitrogen use efficiency