Field experiments were conducted during 2008-2010 to investigate the ef- fects of NPK fertilization on seed yield and economic benefit of a new hybrid cultivar of winter oilseed rape (Brassica napus L.) - Xiangzayou763, and to determine the optimum NPK ratio and dose in Hunan, China. The results showed that NPK ratio (1:0.50:0.50) with 180 kg/hm2 N, 90 kg/hm2 P2O5 and 90 kg/hm2 K20 was the optimum combination for the highest seed yield (2 231.13 kg/hm2) and economic benefit (9 816.97 Yuan/hm2), of which 1 641.23 Yuan/hm2 being set for fertilizer in- vestment (VCR=4.11). Besides, the effects of N, P and K fertilizers on seed yield and oil production of winter oilseed rape were not identical. N had the greatest ef- fect on plant growth of winter oilseed rape, followed by P and K. Total leaf number, green leaf number, leaf length and width, rhizome diameter, branch number, dry weight per plant and other agronomic characters in high N treatments were higher than those in low N treatments. By correlation and path analysis of yield components, the contribution rate to seed yield was found: effective silique number per plant〉seed number per silique〉l 000-seed weight.
[Objective] This assay was to explore the contribution of enzymes ac- counting for nitrogen reutilization in two Brassica napus varieties No.6 (low nitrogen use efficiency) and No.2 (high nitrogen use efficiency). [Method] We measured the yield, transportation and accumulation of grain nitrogen, loss of leaf nitrogen and ni- trogen use efficiency (NUE) in the two rape varieties, by inhibiting proteolytic en- zyme (PE), glutamine synthetase (GS) and glutamate synthetase (GOGAT) and la- beling with lSN. [Result] Under GOGAT inhibitor treatment, both of the two varieties presented minimum NUE, yield and nitrogen transportation in grain and maximum ni- trogen loss in leaf. The effect of PE inhibitor was the second greatest, and that of GS inhibitor was the lowest. Moreover, 80% of the nitrogen that had been accumu- lated in leaf was transported out during late growth stage, and 50% to 70% of the grain nitrogen derived from the nitrogen in vegetative organs. The two varieties ex- hibited the same tendency. Rape variety No.2 had higher yield, grain nitrogen accu- mulation and lower nitrogen loss compared with No.6. [Conclusion] GOGAT has the greatest effect on the accumulation of grain nitrogen, yield and nitrogen reutilization in rape. Different enzyme activity may be the major factor resulting in different nitro- gen rautilization in the two rape varieties. Nitrogen stored in leaf during early growth stage is mainly used for nitrogen remobilization. A large proportion of grain nitrogen derives from vegetative tissues.