INTERACTION BETWEEN BARLEY AND MIXED CULTURES OF NITROGEN-FIXING AND PHOSPHATE-SOLUBILIZING BACTERIA

Pot experiments were carried out to investigate the effect of inoculation with pure and mixed cultures of nitrogen fixers Azospirillum lipoferum 137, Arthrobacter mysorens 7 and the phosphate-solubilizing strain Agrobacterium radiobacter 10 on growth and mineral nutrition of two barley cultivars. A significant positive effect on grain yield both of the studied barley cultivars was obtained after inoculation with mixtures of A. lipoferum 137 + A. radiobacter 10 and A. lipoferum 137 + A. mysorens 7 only. The acetylene reduction activity on roots or in batch culture was significantly higher when A. lipoferum 137 and A. radiobacter 10 were combined. Using N-15 isotope dilution technique it was established that these mixed cultures significantly increased the accumulation of nitrogen fertilizer in the plants. The strain A. radiobacter 10 promoted a better accumulation of phosphorus fertilizer by plants and A. mysorens 7 increased the total phosphorus content in plant tissues. The maximum positive effect of joint inoculation on plant development was observed when the combined nitrogen in soil was in short supply. It was concluded that inoculation with bacterial mixtures provided a more balanced nutrition for the plants and the improvement in root uptake of nitrogen and phosphorus was the major mechanism of interaction between plants and bacteria. The introduced bacteria were able to colonize actively the rhizoplane of barley. No interspecific competition or antagonism were established between components of the bacterial mixtures in the rhizoplane. The strains A. mysorens 7 and A. radiobacter 10 improved viability of A. lipoferum 137 when the plants were grown in acid soil. Field experiments carried out on 3 barley cultivars confirmed the assertion that inoculation with mixed cultures significantly increases the grain yield and nitrogenous nutrition of plants as compared with single cultures.