Optimising the effect of nitrogen on winter oilseed rape grain yield in China: A meta-analysis

Winter oilseed rape is a nitrogen-sensitive oilseed crop with a crucial role in the Chinese edible oil market. However, there is a lack of systematic analysis of the effect of nitrogen (N) on the grain yield of winter oilseed rape. In this study, the response of the winter oilseed rape grain yield to N application was quantified and the key factors were identified, and we modeled the winter oilseed rape grain yield and economic benefits as functions of the N application rate. We found that the effects of N application on winter oilseed rape are sensitive to envi-ronmental factors and most agronomic management practices. Fertilizer management was the most important factor for improving the effectiveness of N application. We recommend two types of N management practices for winter oilseed rape production comprising basal application of controlled-release urea or combination appli-cation of basal and topdressing normal urea. In the latter case, the frequency of topdressing should be increased while ensuring that adequate basal fertilizer is applied. Other agronomic management practices such as direct seeding and increasing planting density may be important for further improving the effects of N application. The suitable N application levels for basal application of normal urea in the three production regions in northwest China, southwest China, and middle and lower reaches of the Yangtze River are 155.16-227.65 kg N ha-1, 219.15-225 kg N ha-1, and 259.38-284.36 kg N ha-1, respectively.