Nitrogen Rate and Planting Density Effects on Yield and Nitrogen Utilization Efficiency of Direct Seeded Rape (Brassica napus)

The high yield of crops mainly depends on the interaction between nitrogen (N) fertilization and planting density. The present study evaluated the influence of different N application rates and planting density on the yield and N utilization efficiency of direct seeded rape during the 2016–2017 and 2017–2018 growing seasons. The three N application rates including 108 kg N ha−1, 144 kg N ha−1 and 180 kg N ha−1 were laid out into main plots while planting density including 15.0 × 104, 22.5 × 104, 30.0 × 104 and 37.5 × 104 plants ha−1 respectively into sub-plots. The results showed that suitable planting density was the premise to gain high rapeseed yield and the contribution of planting density to rapeseed yield was small when it surpassed a certain value. The highest yield in the two growing seasons was achieved at 144 kg N ha−1 with planting density of 30.0 × 104 plants ha−1. The rapeseed yield increased linearly as N uptake of the seed part increased, but at high planting density, there was no increase in yield with the increase N uptake of non-seed parts (stem + husk) when rapeseed yield exceeded a certain value. High planting densities raised shoot N uptake and N transfer to rapeseed seeds with the increase of density and N utilization efficiency was also improved. The too much N application resulted in more N accumulation in non-seed parts without increasing production. Under the same target yield, the increased planting density can save 32.4–65.7% of N fertilization compared with the conventional planting density. The combination of different N fertilization rates and planting densities is helpful to increase rapeseed yield. The best N management strategy is to achieve high yield and reduce the environmental risk to reduce the N fertilization at suitable high density. © 2022 Friends Science Publishers