Effects of Nitrogen Fertilizer Rates and Planting Density on Yield,Quality and Nitrogen Fertilizer Use Efficiency of Rapeseed(Brassica napus L.) under Delayed Sowing Condition

In order to establish a high yield population structure suitable for mechanical harvest,the field experiments were conducted in Chengdu plain to study the effects of different nitrogen(N) fertilizer rates(0-360 kg/hm2 N) and planting density(15×104-45×104 plant/hm2) on the rapeseed(Brassica napus L.)under delayed sowing condition.The results showed that the plant height,height of the first branch,number of primary branches and number of pods per plant increased significantly with the increase of N fertilizer application rates.With the increase of planting density,height of the first branch increased obviously,and the number of primary branches and pods per plant decreased clearly,but only the plant height decreased slightly.Both pod number and yield per unit area increased obviously with the increase of N fertilizer application rates,but the agronomic N fertilizer use efficiency(ANUE,12.0-5.5 kg/kg N) and partial factor productivity of applied N fertilizer(PFPN,27.9-9.4 kg/kg N) decreased clearly.There was a tendency of the increase of nitrogen fertilizer contribution rate(NRC,42.9 %-57.8 %) to yield with the increase of N fertilizer application rates.The yield of planting density(30×104-45×104 plant/hm2)under delayed sowing condition in rapeseed was higher than that of conventional planting density(15×104 plant/hm2) under direct-sown rapeseed.With the increase of N fertilizer application rates,rapeseed protein content(%)enhanced obviously,while lenolenic acid(%)increased a little,but oil content(%),oleic acid(%) and linoleic acid(%)decreased.The effect of planting density on quality was small.In conclusion,higher planting density(30×104-45×104 plant/hm2)would be favorable to the rapeseed under delayed sowing condition,and reasonable N fertilizer application rate(180 kg/hm2 N) would be favorable to higher yield,higher nitrogen fertilizer use efficiency and good quality of direct-sown rapeseed.