interrelationships among oilseed rape (brassica napus l.) grain yield and weed growth under different nitrogen levels

management of nitrogen fertilization in crops is one of the most important components of integrated weed management. a two-year field experiment was conducted to determine the direct effects of wild mustard aboveground biomass and n content of wild mustard on oilseed rape yield. a set of factorial treatments was arranged in a randomized complete block design with four replications. treatments were various wild mustard densities (0, 10, 20, 30, and 40 plant m-2) and nitrogen (n) rates (0, 50, 100, 150, and 200 kg n ha-1). increased wild mustard densities from 10 wild mustard m-2 caused a decrease of 27 % in oilseed rape n content of shoot. increase in nitrogen fertilizer caused an increase in n content of oilseed rape shoot up to 150 kg n ha-1, but no significant difference was found between 150 (0.88 %) and 200 (0.89%) kg n ha-1. correlation analysis showed that there was a negative significant correlation between oilseed rape grain yield and weed biomass (r=-0.60, p≤0.05) and weed nitrogen content (r=-0.81, p≤0.01). path analysis showed a highly negative significant direct effect (direct path: -0.88, p≤0.01) between weed biomass and oilseed rape grain yield.  correlation and path analyses indicated that the main factor which could cause oilseed rape yield loss was weed biomass and the second factor was n content in wild mustard.