Effects of combined application of nitrogen and potassium on oil concentration and fatty acid component of oilseed rape (Brassica napus L.)

Context: Nutrient inputs significantly affect the quality of rapeseed, yet comprehensive research on combined nutrient applications is lacking.Objective: To investigate the effects of combined application of N and K on rapeseed traits, including N, K, oil, and protein concentrations, fatty acid component, seed yield and oil yield. Methods: A 2-year field experiment was conducted in the Yangtze River Basin involving the rapeseed cultivars H9 (low oil) and Z11 (high oil). Sixteen N and K fertilizer combinations encompassed four N rates (0, 90, 180, and 270 kg N ha- 1) and four K fertilizer rates (0, 60, 120, and 180 kg K2O ha-1).Results: The results revealed that the combined application of N and K significantly affected rapeseed oil and protein concentrations by modulating the nutrient concentrations. Specifically, applying N reduced the oil concentration while applying K increased the oil concentration. Each 1.0% rise in seed K concentration corresponded to a 14.9% average increase in oil concentration, counterbalancing a 2.8% increase in N concentration. Additionally, the higher oil concentration of Z11was closely linked to its seed K concentration. In contrast, protein concentration increased with the N application and decreased with the K application. Furthermore, applying N reduced palmitic (C16:0) and stearic (C18:0) acid content and increased oleic (C18:1) acid content, which further increased with K. Combining the K application with the N treatment resulted in higher seed yield and oil yield compared to a single N application, which particularly benefited the high oil cultivar Z11.Conclusion: Utilizing an N180K120 combination significantly improved rapeseed oil concentration, fatty acid composition, seed yield, and oil yield.Implications: This study details the effects of applying K at various N fertilizer rates on enhancing rapeseed quality and yield, emphasizing the importance of the N and K ration in oilseed rape production.