Yield response of wheat and barley to inoculation of plant growth promoting rhizobacteria at various levels of nitrogen fertilization

The yield response of a wheat (Kirik) and a barley (Tokak 157/37) cultivar to inoculation with Azospirillum brasilense Sp246 and Bacillus sp. OSU-142 was studied in relation to three levels of N fertilization (0, 40, and 80 kg ha(-1)) under field conditions in Erzurum, Turkey, in 1999 and 2000. Seed inoculation with A. brasilense Sp246 significantly affected yield and yield components, both in wheat and barley. On average of years and N doses, inoculation with A. brasilense Sp246 increased spike number per m(2), grain number per spike, grain yield, and crude protein content by 7.2, 5.9, 14.7, and 4.1% in wheat and by 6.6, 8.1, 17.5, and 5.1% in barley, respectively, as compared to control. Inoculation with Bacillus sp. OSU-142 significantly increased kernel number per spike in wheat, but no significant effect was determined in the other characteristics. Grain yields and yield components were also higher at all levels of nitrogen fertilizer in the inoculated plots as compared to the control. However, these increases diminished at high fertilizer levels. These results suggest that application of the growth promoting bacteria A. brasilense Sp246 may have the potential to be used as a biofertilizer for spring wheat and barley cultivation in organic and low-N input agriculture.