Effects of planting density and nitrogen application rate on rapeseed yield and nitrogen use efficiency

For rapeseed mechanization production,effects of rape density and nitrogen(N) application rate on growth and N efficiency were investigated under field condition.Two planting density(15×104 and 45×104 plant per hectare) and four N rates(0,90,180 and 270kg per hectare) were applied to study the interaction between N and density on agronomic characteristics,yield,N efficiency and N fertilizer requirements for Zhongshuang 11.Results showed that plant height,branch number,effective siliques per plant and seeds per pod significantly decreased at higher density,but branch height and 1 000-seeds weight increased significantly.Under higher density,the plant-type was uniform and ideal for mechanized harvesting.Yield of high density rape was higher.Both yields on high and low density increased at 0 to 180kg/hm2 N rates.But when N rates were up to 270kg/hm2,both yields decreased.N efficiency decreased at higher N rates and lower density.It indicated that higher density could promote seed N accumulation,decrease N fertilizer requirement and improve the N efficiency.For the same targets yield(compared to the top economic yield at low density,the average yield of Hubei Province and that of China),the N fertilizer requirement significantly decreased by 22.9% to 30.6% after increasing planting density.