Abstract:In order to determine the reasonable amount of irrigation and nitrogen fertilizer for winter oilseed rape ( Brassica napus L.) at stem elongation stage, which is significantly important for improving water and nitrogen use efficiency, increasing yield and quality and decreasing environmental pollution, a two-year (2012—2013 and 2013—2014) field experiment was conducted to evaluate the effects of different irrigation and nitrogen applications on aboveground dry biomass accumulation, nitrogen nutrition index ( N NI ), radiation use efficiency ( R UE ), yield, water use efficiency ( W UE ) and nitrogen partial factor productivity ( N PFP ) of winter oilseed rape in Yangling District of Shaanxi Province. There were three irrigation levels (I 0 : 0 mm; I 1 : 60 mm; I 2 : 120 mm, I 2 was approximately equal to local traditional irrigation amount) and three nitrogen levels (N 0 : 0 kg/hm 2 ; N 1 : 80 kg/hm 2 ; N 2 : 160 kg/hm 2 , N 2 was approximately equal to local traditional nitrogen application amount). The results showed that irrigation and nitrogen could obviously improve aboveground dry biomass, R UE and yield. Compared with I 1 N 2 , I 2 N 1 and I 2 N 2 , the aboveground dry biomass of I 1 N 1 was reduced by 0.80%, 9.18% and 11.12%, respectively. Under treatments of I 0 N 1 , I 0 N 2 , I 2 N 1 and I 2 N 2 , nitrogen deficiency of winter oilseed rape occurred at different days after irrigation and nitrogen treatments, which was unbeneficial for the growth of winter oilseed rape. While the N NI of I 1 N 1 and I 1 N 2 were always higher than 1 at different stages, and the N NI of I 1 N 1 was fluctuated around 1, which indicated nitrogen status was optimum, but the N NI of I 1 N 2 was much greater than 1, which indicated nitrogen was excess. Irrigation and nitrogen had significant interaction effects on R UE in two years ( P ＜0.05), and I 1 N 1 could significantly improve R UE of winter oilseed rape in both drought year (2012—2013) and rainy year (2013—2014). The promotion of R UE was not obvious or even presented a downward trend when excessive irrigation or nitrogen application was conducted. In 2012—2013, seed yield of I 1 N 1 was significantly lower than those of I 2 N 1 and I 2 N 2 （ P ＜0.05), and it was reduced by 6.02% and 4.76%, respectively. While in 2013—2014, no significant difference was found among I 1 N 1 , I 2 N 1 and I 2 N 2 （ P ＞0.05). In both years, irrigation and nitrogen had significant interaction effects on crop evapotranspiration ( ET ), W UE and N PFP （ P ＜0.05). In 2012—2013 and 2013—2014, yield of winter oilseed rape ranged from 1 534 kg/hm 2 to 3 024 kg/hm 2 and from 2 318 kg/hm 2 to 3 746 kg/hm 2 , ET ranged from 195 mm to 339 mm and from 318 mm to 426 mm, W UE ranged from 7.9 kg/(hm 2 ·mm) to 10.4 kg/(hm 2 ·mm) and from 7.2 kg/(hm 2 ·mm) to 9.4 kg/(hm 2 ·mm). Among all of the irrigation and nitrogen treatments, I 2 N 1 achieved the highest seed yield within two years, the average yield, ET and W UE of which were 3 385 kg/hm 2 , 374 mm and 9.1 kg/(hm 2 ·mm), respectively. While I 1 N 1 achieved the highest W UE in both years, the average W UE of which was 9.9 kg/(hm 2 ·mm), with average yield of 3 264 kg/hm 2 , average ET of 333 mm. Therefore, compared with I 2 N 1 , I 1 N 1 could save water amount of 42.5 mm, and improve W UE by 8.79% with yield just reducing by 3.57%. From the perspective of saving water and fertilizer, and simultaneously achieving the goal of increasing yield, the I 1 N 1 (irrigation amount was 60 mm and nitrogen application amount was 80 kg/hm 2 ) treatment was recommended as an appropriate irrigation and nitrogen fertilization schedule for winter oilseed rape at stem elongation stage.
