effect of nitrogen on weed tolerance and competition indices of five wheat cultivars to weeds competition

breeding and cropping cultivars with high weed competitiveness have played an important role in the non-chemical weed management. this experiment was carried out in order to study the effect of nitrogen on weed tolerance and competition indices of five wheat cultivars at the research field of agricultural faculty, university of mohaghegh ardabili, during 2010-2011 growing season. experimental factors were three nitrogen rates (0, 75 and 150 kg ha-1) and five wheat cultivars (kasgozhen, sieson, gaspard, azar2 and mv-17) which grown under weedy and weed free conditions. results showed that cultivar and nitrogen had a significant effect on stress tolerance index (tol index). the lowest tol was observed in mv-17 cultivar. application of 150 kg n ha-1 increased tol index nearly two times. results also showed that three tolerance indices weed interference tolerance index (witi), mean productivity (mp) and harmonic (harm) had a same trend and these indices increased by increasing nitrogen rate in kasgozhen, sieson and gaspard cultivars. in contrary, these indices were reduced by increasing nitrogen in mv-17 cultivar. results showed that competitive index (ci) had a significant difference with tolerance indices. by increasing nitrogen rate ci decreased from 2.5 to 0.5 in azar2 cultivar. findings of this experiment indicate that weed tolerance and competitive ability of wheat cultivars are different and can be used for iwm at sustainable agriculture.