Synergistic effect of nitrogen and potassium on seed yield and nitrogen use efficiency in winter oilseed rape (Brassica napus L.)

The imbalance of nitrogen (N) and potassium (K) is becoming a crucial element in exacerbating N loss in intensive crop production systems. It is urgent to optimize N and K nutrient management to improve crop yield while reducing environmental risks. The purpose of this study was to investigate the effects of N and K co -application on seed yield, N accumulation, and sustainable N management in rapeseed. Different rapeseed cultivars of Huayouza No. 9 (H9) and Zhongshuang No. 11 (Z11) were treated with various N and K application rates, and the seed yield, yield components, N accumulation, N surplus, and N use efficiency (NUE) were examined in a 3-year split-plot field experiment. The co-application of N and K was a prerequisite for achieving high seed yield, and the contribution of N fertilizer to seed yield was in response to K nutritional status. Inad-equate K supplies reduced seed yield significantly by reducing the number of branches and pods per plant. In addition, K deficiency inhibits N absorption by rapeseed, exacerbating soil N surplus, especially under high N conditions. On the contrary, N application followed by K fertilizer promoted N absorption, raised NUE, and considerably decreased N surplus under high N supply. In comparison to the treatment without N and K fertil-ization, the yields of H9 and Z11 increased by 153.2-397.5% and 150.4-322.9%, respectively, after the com-bined N and K fertilization, which were significantly higher than N or K fertilization alone. High seed yield and sustainable N management in rapeseed can be achieved with the co-application of 180 kg hm-2 of N and 120 kg hm-2 of K2O. As a result, cooperative N and K fertilization management was critical to increasing seed yield and NUE. In practice, besides paying more attention to N fertilization, K fertilizer input should also be strengthened to further achieve a higher seed yield while minimizing the ecological footprint of nutrients.