Seed rate and nitrogen fertilizer effects on wild mustard (Sinapis arvensis L.) and winter wheat (Triticum aestivum L.) competition

In order to evaluate wild mustard competitive effect on winter wheat, an additive series experiment was conducted in 2000-2001 at Agricultural Research Station of Mashhad University.The experiment had 3 factor: wheat seed rate (175, 215 and 255 kg/ha), nitrogen rate (150 and 225 kg/ha), and a range of wild mustard densities. Hyperbolic functions was used to describe yield-weed density relationship. Increasing wild mustard density had a negative, asymptotic – type effect on wheat biomass and grain yield. By increasing wheat seed rate, in optimum nitrogen rate, maximum wheat biomas loss has reduced about 51 %. Maximum yield loss has increased from 42.1 % to 50.4 %, as nitrogen rate incrased from optimum to upper optimum rate of wheat. By increasing of wheat seed rate from 175 to 255 kg/ha, maximum tiller number reduction due to high densities of wild mustard, has decreased by 54 %. Reduction of fertile tiller number was mostly occurred at presence of high nitrogen level, thus, reduction of fertile tiller number compared to control in N1 was 18%, while in N2 has increased to 30%. Wild mustard competition has reduced wheat seed number per ear 30% in compare to weed free control. Results show that wheat 1000 seed weight was more affected by nitrogen rate than plant densities. Apparently, in competition with wheat, wild mustard was better able to utilize the added nitrogen and thus gained a competitive adventage over the wheat.