Abstract
Soil phosphate (P) sorption is a mechanism that removes P from the soil solution. Since many soil microorganisms can produce organic acids capable of desorbing soil P, they could be used as one means of increasing the supply of plant available P. An experiment was conducted to determine the capacity of a soil fungus to desorb P from the surfaces of seven Hawaiian soils with varying mineralogy and P-sorption capacity. The soils were unfertilized, or fertilized with three doses of KH2PO4 to achieve four initial concentrations of solution P (original, 0.05, 0.1, and 0.2 mg L-1). The soils were either inoculated or not inoculated with Mortierella sp., a phosphate-solubilizing fungus (PSF). Inoculation significantly increased soil solution P by desorbing P from a vertisol at all solution P concentrations tested, whereas in the Molokai soil desorption occurred only at the two higher solution P concentrations and at the three higher solution P concentrations in the Wahiawa soil. In soils that had higher soil P sorption capacities, P desorption did not occur. Microbial desorption of P was evidently controlled by soil P sorption capacity and the level of adsorbed P.
