Impact of Phosphate Solubilizing Microorganisms on Mineral and Organic Forms of Phosphorus and its Availability in Soil under Maize (Zea mays L.) Cultivation

The present study was performed in order to investigate the effect of plant growth promoting microorganisms on distribution of phosphorus forms in a calcareous soil under maize (Zea mays L.) cultivation and to evaluate these forms relationship with soil microbial characteristics. The experiment was carried out as a completely randomized design including control (without microbial inoculation), soil inoculation with Staphylococcus hominis and Brevundimonas sp., Piriformospora indica and mixture of fungus and bacteria treatments at five replications under greenhouse conditions. Maize seeds were planted in 3 kg pots and different forms of mineral and organic phosphorus, some microbial characteristics (microbial biomass carbon and phosphorus and phosphatase activity) and the phosphorus uptake in the plant were measured after three months of cultivation. The results illustrated the influence of microbial inoculation on mineral and organic forms of phosphorus as well as phosphorus uptake in the plant. The decreasing order of phosphorus mineral components was as Ca10-P> Ca8-P> Ca2-P> Al-P> Olsen-P> Fe-P> OCC-P in the control soil and this trend obtained as Ca10-P> Ca2-P> Olsen-P> Al- P> Ca8-P> Fe-P> OCC-P in the soil containing a mixture of microbes. Available phosphorus components, including Olson-P, dicalcium phosphate, and relatively stable and unstable organic phosphorus had positive and significant correlation with phosphorus uptake by the plant. There was a positive correlation between extracted Olsen- phosphorus and microbial phosphorus and carbon biomass, and alkaline phosphatase activity. In general, the results showed the positive influence of microbial inoculation, especially fungal and bacterial mixture, on the enhancement of phosphorus availability for the plant. The highest values of extracted phosphorus by Olsen method and phosphorus uptake by plant were found at 34.02 mg kg-1 and 11.52 mg pot-1, respectively, in the mixture of fungi and bacteria treatment with significant difference (p ≤ 0.05) compared to other treatments.