Nutrient Efficiency of Winter Oilseed Rape in an Intensive Cropping System: A Regional Analysis

Fertilization is essential for oilseed rape because it is sensitivity to nutrient deficiency, especially for winter oilseed rape (Brassica napus L.). To investigate regional nutrient efficiency and nutrient uptake-yield relationship of winter oilseed rape in an intensive cropping system, this study used data from 619 site-year on-farm experiments carried out in the winter oilseed rape planting area of the Yangtze River Basin, China from 2005 to 2010, with large yield in the range of 179-4 470 kg ha−1. Currently recommended application rates of N, P and K fertilizers increased rapeseed yield at different levels of soil indigenous nutrient supply (INS) in this region. Boundary values of plant nutrient uptake were established to analyze the nutrient uptake-yield relationship of winter oilseed rape (internal nutrient efficiency), i.e., 128 kg N ha−1, 24 kg P ha−1, and 122 kg K ha−1. The internal nutrient efficiency declined by 48.2%-64.1% when nutrient uptake exceeded the boundary value, resulting in excessive nutrient uptake (i.e., low yield response with high nutrient uptake), especially for K. In the intensive cropping system, agronomic efficiencies of N, P, and K were 5.9, 3.4, and 3.6 kg kg−1, and recovery efficiencies of N, P, and K were 35.6%, 24.1%, and 36.8%, respectively. These findings showed that the fertilization rate should be optimized by considering INS, nutrient status, and nutrient efficiency of winter oilseed rape. In this study, considering the lower yield improvement to high K uptake levels and low K fertilizer efficiency, application rate of K fertilizer should be reduced since soil K deficiency has already been mitigated.