effect of nitrogen on competition between wild oat (avena fatua) and wheat (triticum aestivum) at vegetative growth stage

in order to study the effect of nitrogen on competition between wild oat (avena fatua) and wheat (triticum aestivum) at vegetative growth stage, a factorial experiment was conducted based on completely randomized block design with three replications in research greenhouse of faculty of agriculture, at ferdowsi university of mashhad in 2008. first factor was five densities (0, 2, 4, 6 and 8 plants per pot) of wild oat in pure stand and competition with wheat (at constant density of 8 plants per pot). the second factor was consisted of five levels of nitrogen (1, 4, 8, 12 and 16 mm). the experiment was finished at the end of vegetative growth stage of wheat based on monoculture treatment at 8 mm of nitrogen. results showed the significant effects of nitrogen and wild oat’s densities on number of tiller and leaf area index of wheat. the number of tiller per plant in both plants increased when the nitrogen levels increased and/or the weed densities decreased. the interaction effect of wild oat densities and nitrogen levels on leaf area index of wheat was significant.the intraction effect was not affected by nitrogen in high levels of wild oat densities and by wild oat densities in low levels of nitrogen. it may demonstrate the dominance of wheat in the low nitrogen levels and wild oat in high densities when they compete each other in early stages of growth. comparison of relative biomass of wheat at different levels of nitrogen supported this hypothesis. results showed increasing the amount of nitrogen during the vegetative growth stage, can increase competitiveness of wild oat with wheat