Research article

Higher soybean yield by inoculation with N-fixing and P-solubilizing bacteria

Department of Plant Sciences, Faculty of Biological Sciences, Quaid-i-Azam University Islamabad, Pakistan

^* Corresponding author: asgharibano@yahoo.com

Accepted: 25 September 2009

Abstract

Phosphorus availability for soybean growth is frequently low because P reacts with iron, aluminum and calcium in soil to form insoluble phosphates. The increasing price of phosphatic fertilizers is a major obstacle faced by farmers for application of recommended P doses. Low yield of soybean in Pakistan is also lowering adoption by farmers of this oilseed crop. These issues could be solved by inoculation of beneficial microorganisms that enhance the availability of N and P to the plant. Here, we tested the effect of inoculation of Bradyrhizobium or Pseudomonas, or both, in the presence and absence of P₂O₅ fertilizer, on soybean yield. Experiments were carried out in pots and the field during 2004 and 2005 under natural conditions. The bacterial strains were applied in broth culture in the pots at the seedling stage or as a seed treatment in the field. Our results showed that co-inoculation of Bradyrhizobium and Pseudomonas strains with the P₂O₅ treatment resulted in increased grain yield of 38% in pot experiments and 12% in the field experiment, compared with the P₂O₅ treatment alone. Bradyrhizobium japonicum strain TAL 377 produced 74.64 μg/mL indole acetic acid and 261.2 μg/mL gibberellic acid. Similarly, Pseudomonas strain 54RB produced 8.034 μg/mL indole acetic acid and 1766 μg/mL gibberellic acid. The survival efficiency of Bradyrhizobium was up to 46% higher due to co-inoculation and P₂O₅ as compared with its single inoculation. On the other hand, Pseudomonas survival efficiency was up to 33% higher with added P₂O₅ as compared with its single inoculation.