Synergistic Nitrogen and Potassium Improvement in Winter Oilseed Rape ( Brassica Napus  L.)  Yield for Sustainable Nitrogen Management

Abstract

Synergistic application of nitrogen (N) and potassium (K) fertilizers is an effective measure to improve crop yield and reduce the environmental nitrogen footprint. However, due to the substantial loss of K from soils and the imbalance of nutrient supply with an emphasis on N fertilizer input while neglecting K, the imbalance of N and K is becoming an essential factor in aggravating N loss in intensive crop production systems. In this research, rapeseed ( Brassica napus  L.) plants were grown in a 3-year split-plot designed field experiment with two cultivars (H9 and Z11) in the Yangtze River Basin. Sixteen N and K fertilizer combinations were conducted to investigate the effects of i) seed yield and yield components, ii) N absorption and utilization efficiency, and iii) assessing the role of N and K synergistic in sustainable N management in rapeseed. Combining 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. Insufficient K supply seriously reduced seed yield and N uptake in rapeseed while exacerbating the soil N surplus with high environmental risk. On the contrary, the results demonstrate that K application, especially under high N input, can significantly increase N utilization efficiency and reduce N surplus by inducing high N uptake. In comparison to the treatment without N and K fertilization, the yield of H9 and Z11 increased by 153.2%-397.5% and 150.4%-322.9% after the combined N and K fertilization, which was significantly higher than N or K fertilization alone. Application of K decreases N input and apparent N surplus at the same target yield. Consequently, cooperative management of N and K fertilization was critical to improving seed yield and N use efficiency, minimizing the ecological footprint of nutrients.

Keywords: Seed yield, Nitrogen, Potassium, Nitrogen use efficiency, Apparent N surplus, Sustainable