Co-inoculation with phosphate-solubilzing and nitrogen-fixing bacteria on solubilization of rock phosphate and their effect on growth promotion and nutrient uptake by walnut

The aim of this work was to evaluate effects of co-inoculation with phosphate-solubilizing bacteria (PSB) and nitrogen-fixing bacteria (NFB) on solubilization of rock phosphate (RP) and their effect on growth promotion and nutrient uptake by walnut seedlings. Two PSB strains, Pseudomonas chlororaphis and Bacillus megaterium, and two NFB strains, Arthrobacter pascens and Burkholderia cepacia, were selected to investigate interaction between PSB and NFB in liquid medium. The maximum concentration of soluble phosphorus (P) was determined in the mixing culture of P. chlororaphis and A. pascens. A strong correlation was found between pH and soluble P concentration, as well as the total organic acid production and P solubilization. Co-inoculation with P. chlororaphis and A. pascens amendment with RP resulted in the highest plant height, shoot and root dry weight, P and nitrogen (N) uptake of walnut seedlings, and the maximum amounts of available P and N in soils under shade house conditions. However, mixed inoculation with B. megaterium and A. pascens failed to increase these parameters. The results demonstrated that co-inoculation with PSB and NFB amendment with RP could be a promising and alternative option for utilizing this potent source as P fertilizer in walnut plants and maintaining greater nutrient availability in soils. (C) 2012 Elsevier Masson SAS. All rights reserved.