Distribution of Phosphorus Forms in Calcareous Soils Inoculated with Phosphate-Solubilizing Fungi

Phosphorus (P) is one of nutrient elements for plant growth. In most soils P has complex behavior and forms sparingly soluble and insoluble compounds with soil particles. Determination of forms of soil phosphorus influenced the activity of phosphate-solubilizing microorganisms (PSM) is important in the evaluation of soil phosphorus status. To evaluate the effects of PSM on P fractions distribution in a calcareous soil, an experiment was conducted in a factorial based on completely randomized design. The factors were including incubation time (0, 7, 21, 45 days) and microorganisms (Fungal strains including: Aspergillus niger, Aspergillus terreus, Penicellium sp. and control (without microbial inoculation)). Soil samples were incubated at 28 ° C for a period of 45 days. Then, different forms of inorganic phosphorus, organic phosphorus and Olsen phosphorus were determined by sequential extraction method. The results showed that the fungal inoculation caused significant changes in the amount of phosphorus, organic phosphorus and mineral phosphorus. At the end of incubation, amount of available phosphorus, organic phosphorus, mineral forms (Ca2-P) and (Ca10-P) in fungal inoculation compared to control treatment increased 1.53, 1.39, 4.05 and 1.07 times, respectively. However, the (Ca8-P) and (Al-P) forms in the treatment of fungi were reduced 23.76 and 35.95%, respectively. The amount of phosphorus in different forms and treatment control to a Ca10-P> OP> Ca8-P> Olsen-P>Al-P> Ca2-P respectively.The fungal treatment was observed, a negative correlation (r= -0.81**) between phosphorus Olsen-P and Organic-P (O-P), Ca10-P and significant positive correlation (r=0.83**) with Ca2-P ،Fe-P and Al-P. In general, using phosphate-solubilizing fungi in calcareous soils provides useful information for evaluation of phosphorous status in soil and understanding of soil fertility that influence plant nutrition.