Co-inoculation of Phosphorus Solubilizing Bacteria with Bradyrhizobium japonicum to Increase Phosphate Availability to Rainfed Soybean on Vertisol

In a field experiment (1991 and 1992), co-inoculation of Bradyrhizobium japonicum and phosphate solubilizing bacteria Pseudomonas striata alone and with superphosphate and rock phosphate increased the nodulation, shoot weight, N content at 60 days, N₂-fixation, total P content, seed yield and phosphorus use efficiency (PUE). Application of 60 kg P₂O₅ ha⁻¹ as superphosphate alongwith co-inoculation improved all the parameters, but it was at par with 60 kg P₂O₅ ha_-1 as rock phosphate and co-inoculation for nodule number planr, total P content and seed yield. However, maximum PUE (62.7 kg ha⁻¹) was recorded with 30 kg PP~ ha_-1 as rock phosphate and co-inoculation. Quantum of N₂-fixation ranged from 76.1 to 137.6 kg ha⁻¹ Correlations among nodules and their weight, viz., shoot weight and yield were significant. Inoculation with P. striata also enhanced the availability coefficient ratio, relative agronomic effectiveness and relative economic effectiveness of the rock phosphate.