Potential use of rock-phosphate-solubilizing bacteria associated with wild rice as inoculants for improved rice (Oryza sativa)

A study was conducted to isolate P-solubilizing bacteria from the rhizosphere of three wild rice species and to test their ability to mobilize P from rock phosphate (RP). Inoculated seeds or seedlings of eight different strains were grown in soils supplemented with a P fertilizer mixture (PFM) consisting triple super phosphate (TSP) and RP, each providing equal amounts of P2O5. Crop growth, NaHCO3-extractable P, crop P uptake and yield were compared with two uninoculated controls, with either TSP or PFM added. In the pot experiment, P availability varied from 20 to 48 mg P kg(-1) soil. Yields ranged between 4.8 and 6.6 g per pot and were not significantly different between treatments. In the field experiment, shoot P accumulation in inoculated and TSP-control treatments at the heading stage ranged between 79-129 mg and 219 mg per pot, respectively. Dual inoculants comprising Staphylococcus scirui, Bacillus pumilus, Bacillus subtilus and Bacillus cereus increased yield by about 29% over PFM-controls (324 g m(-2)) but those yields were 21% lower than TSP-controls (510 g m(-2)). Therefore, application of inoculants combined with PFM is not a viable alternative for TSP under the tested conditions because yield was limited by the P availability.