study of beneficial levels and effect of azotobacter spp. and azospirillium spp.

in order to evaluate the effects of beneficial free living bacteria (azotobacter chroococcum and azospirillum brasilense) compared to different nitrogen fertilizer levels on yield and yield components of barley (hordeum vulgare cv reyhan) a field experiment was conducted at research station college of agriculture, ferdowsi university of mashhad in 2007-2008. the experiment was arranged in a randomized complete block design with three replications. fertilizer treatments were biological fertilizer (combine of azotobacter and azospirillum) and six nitrogen fertilizer levels (0, 20, 40, 60, 80 and 100 kg/ha). the plant characteristics were studied in terms of leaf area index, crop growth rate, total dry weight, shoot and root dry matter per plant and seed yield. the results showed that the effect of different nitrogen fertilizer levels imposed a significant effect on all plant characteristics. the difference between biological fertilizers, 60 and 80kg nitrogen fertilizer levels in shoot dry weight were not significant. additionally, in root dry weight and root/shoot ratio there were significant difference between biological fertilizer and all nitrogen fertilizer levels. there was no significant difference between biological fertilizer, 80 and 100 kg nitrogen fertilizer levels in terms of seed yield. there was no significant difference among biological fertilizer, 40, 60 and 80kg nitrogen fertilizer levels in leaf area index at three finally samples. it seems that, in this experiment biological fertilizer could be provide plant nitrogen requirements the same as 40-80kg nitrogen per hectare.