effect of competition on nitrogen absorb and use efficiency of wheat (triticum aestivum l.) and wild oat (avena fatua l.) at vegetative growth stage

in order to study of nitrogen absorb and use efficiency of wheat (triticum aestivum) and wild oat (avena fatua) 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. the first factor was competition between wild oat (densities of 0, 2, 4, 6 and 8 plants per pot) and wheat (density of 8 plants per pot) and the second factor was five different levels of nitrogen (1, 4, 8, 12 and 16 mm). the experiment was finished at the end of vegetative growth stage of wheat and data were analyzed using regression analysis. results showed that nitrogen percentage (np), nitrogen absorb efficiency (nae) and nitrogen use efficiency (nue) in wheat and wild oat were affected by experimental factors. nitrogen content increased in wheat as well as wild oat when nitrogen level increased to reach to asymptote at 8 mm nitrogen. np was decreased in wheat (except at 1mm nitrogen) when weed density increased, but was not affected in wild oat by wheat competition. nae of wheat was decreased exponentially in all weed densities and was not affected by wild oat competition. nae of wild oat followed a positive significant linear relationship with adding of density. it indicated the growth up of nitrogen absorb of wild oat in competition situation. nue was similarly affected in wheat as well as wild oat.