Impact of Rhizobium and phosphate solubilizing bacteria on soil phosphorus dynamics and enzyme activity in black gram (Vigna mungo L.)

The study aimed to investigate the impact of Rhizobium and phosphate solubilizing bacteria (PSB) on the transformation of soil phosphorus (P) fractions and the key soil enzymes involved in P cycling. A field experiment was conducted using black gram in a randomized block design (RBD) with 7 treatments consisting of control, recommended dose of fertilizer, Rhizobium bangladeshense and Pseudomonas sp. alone and combined inoculation with inorganic fertilizers. Each treatment was replicated thrice. The soil samples were collected to analyze P fractions (available P, soluble P, Al-P, Fe1-P, Ca-P, Fe2-P, residual P, labile organic P, moderately labile organic P and non-labile organic P) and soil biological activity using standard methods. Data were statistically analyzed to determine the treatment effects. Co-inoculation of Rhizobium bangladeshense at 10 mL kg-1 seed with Pseudomonas sp. at 10 mL kg-1 seed along with the application of 75 % nitrogen and phosphorus (NP) and 100 % potash (K) significantly enhanced the P fractions and soil biological property when compared with control and alone inoculation of Rhizobium bangladeshense and Pseudomonas sp. The combined inoculation of Rhizobium bangladeshense and Pseudomonas sp. (T7) significantly (p ≤ 0.05) increased soluble, Al-, Fe- and Ca-bound P fractions, microbial counts and enzymatic (dehydrogenase and phosphomonoesterase) activities compared to control and single inoculations. These significant enhancements indicate superior P mobilization and soil biological activity under dual inoculation treatment. The combined inoculation of Rhizobium and PSB effectively mobilized fixed P forms and enhanced enzymatic activity, leading to improved P availability in soil while saving 25 % of N and P fertilizers.