Herbicide and nitrogen rate effects on weed suppression, N uptake, use efficiency and yield in winter oilseed rape (Brassica napus L.)

Improved weed management strategies are imperative in oilseed rape production. Herbicide and nitrogen (N) fertilization could be integrated into weed management as these are known to affect weed emergence and growth. In this study, two-factor designed field experiments were conducted to investigate the direct and/or interactive effects of herbicide application and N fertilization on weed suppression, crop N uptake, apparent N use efficiency (ANUE) and yield in weed infested winter oilseed rape. Oilseed rape were grown under herbicide-treated or herbicide-free conditions subjected to five N rates. The results demonstrated that herbicide exerted persistent weed suppression, and thereby improved oilseed rape growth. Increasing N supply enhanced the competition ability of oilseed rape against weeds, due to much higher sensibility to N supply. The interaction effects between herbicide and N application resulted in much greater enhancements in N uptake by oilseed rape over weeds in response to increasing N supply, when herbicide was applied. In contrast, weed N uptake in herbicide-free plots could be comparable to or even higher than that of oilseed rape, leading to significantly lower oilseed rape ANUE than in herbicide-treated plots. Oilseed rape yield increased significantly with increasing N rates, and such responses were more pronounced with herbicide application. Therefore, target yields could be fulfilled with substantially reduced N input, if herbicide was applied. In conclusion, effective use of herbicide in combination with optimum N fertilization would be a strategy to achieve weed suppression, yield increase and meanwhile to improve ANUE and reduce N input in winter oilseed rape.