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

Abstract

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. Inadequate 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 fertilization, the yields of H9 and Z11 increased by 153.2–397.5% and 150.4–322.9%, respectively, after the combined 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.