Abstract:

【Objective】 Cropping system and nitrogen rate are important factors affecting the growth and yield formation of oilseed (Brassica napus L.). To investigate the effect of nitrogen application on yield formation and nutrient utilization of oilseed under different cropping system. 【Method】 a field experiment was carried out in Huanggang, Hubei province. A oilseed variety “Zhongyouza19” was used as the material, setting with two cropping system (rice-oil rotation, RO; soybean-oil rotation, SO) and four nitrogen rate (N0, 0; N1, 90 kg·hm^-2; N2, 180 kg·hm^-2; N3, 270 kg·hm^-2) in this study. Yield and its components, dry matter accumulation, agronomic traits, nitrogen content and seeds quality were measured. 【Result】(1) the seed yield of SO was significantly higher than that of RO, and the pods per plant, seeds per pod and 1000-seeds weight of oilseed in different cropping system all tended to increase significantly by increasing the amount of nitrogen. Compared with N0, the seed yield of RO increased by 176.68%, 436.49% and 835.40% under N1, N2 and N3 treatments, respectively, while that of SO increased by 123.96%, 344.46% and 547.25%. And the seed yield increased by 62.09%, 31.33%, 71.79% and 12.21% under N0, N1, N2 and N3 treatments, respectively, in SO compared to RO；(2) The root crown diameter, plant height, first effective branch height and branch number of SO rape were significantly higher than those of RO at maturity stage, and the increase in each agronomic trait index were significant under different cropping system with the increase in nitrogen application; the root biomass and above-ground biomass of SO were significantly higher than those of RO at all growth stages, but the root shoot ratio was lower than that of RO. the root shoot ratio decreased significantly after seedling stage in both cropping system with increasing nitrogen application. (3) Nitrogen content and nitrogen accumulation in the root, pod shell, stalk and seeds of SO were higher than those in RO, and the increase in nitrogen content and nitrogen accumulation in each part were significant with the increase in nitrogen application; the apparent nitrogen recovery efficiency under SO were higher than those under RO, and the apparent nitrogen recovery efficiency under RO increased with the increase in nitrogen application. (4) Compared with the RO, the soluble sugar content of pod shell under SO was lower, while the amino acid content and amino acid /soluble sugar content were higher with the same nitrogen application. The soluble sugar content decreased, but the amino acid content and amino acid/soluble sugar content increased with the increase of nitrogen application. Therefore, the oil content of oilseed in SO was lower than that in RO due to the limitation of fatty acid synthesis substrate, and the oil content of seeds decreased significantly with the increase of nitrogen application in cropping system. Oil yield was maximum in both cropping system at 270 kg·hm^-2 nitrogen application level, 1 678.60 kg·hm^-2 and 1 665.33 kg·hm^-2 for RO and 1 684.03 kg·hm^-2 and 1 687.10 kg·hm^-2 for SO respectively, but the difference in oil yield between 180 kg·hm^-2 and 270 kg·hm^-2 nitrogen application for SO was not significant. 【Conclusion】In conclusion, the nitrogen rate for RO can be controlled at about 270 kg·hm^-2, but the nitrogen rate for SO can be controlled at about 180 kg·hm^-2 to ensure higher nitrogen use efficiency and higher oil yield.

Key words: oilseed , (Brassica napus , L.),  , cropping system,  , nitrogen rate,  , yield,  , nitrogen use efficiency