Solubilization of Araxá natural phosphate and decomposition of plant residues by bacterial isolates

ABSTRACT Brazil imports most of the phosphate fertilizers used in agriculture, however, it has national deposits in its territory that can supply part of the domestic market demand. In order of these to be used effectively, it is necessary to identify techniques to accelerate the release of phosphorus (P) from these rocks. The objective was to evaluate the influence of inoculation with phosphate solubilizing bacterial isolates (PSB) and decomposition of different plant residues in the solubilization of Araxá natural phosphate (ANP). Two experiments were carried out in a completely randomized design in a 5 x 4 factorial scheme, with four replicates. The first experiment evaluated the solubilization of ANP by PSB in culture medium with four different sources of carbon: glucose, saccharose, cellulose, and pectin. The treatments were incubated for seven days and then were analyzed the P concentration and pH values. In the second experiment, the ANP was applied in 300 cm3 of soil, placed in incubation chambers, with six grams of dry and crushed plant material of white oat, brachiaria, crotalaria, lupine, and the inoculation of PSB. Decomposition was evaluated weekly by quantifying the carbon of the CO2-C released and, after 42 days was analyzed the concentration of P in the soil. It was observed that the carbon source directly influences the solubilization of ANP by PSB, especially the genus Burkholderia. Treatments containing crotalaria and lupine residues showed higher CO2-C values, and the ones containing plant residues associated with BSF inoculation obtained the highest levels of P in the soil.