Microbial utilization and transformation of phosphate adsorbed by variable charge minerals

We examined the microbial transformation and utilization of P adsorbed on the surfaces of some variable charge minerals, which are dominant in Chinese red soils, in order to evaluate the feasibility of enhancing the availability of soil P to plants through biological approaches. Under laboratory conditions, microorganisms utilized adsorbed P very efficiently. The utilization of the added adsorbed P by microorganisms after a 3-week incubation was 42-43% for kaolinite-P, 42-46% for goethite-P and 38-43% for amorphous Al-oxide-P, which was about 4-8 times higher than the utilization of applied soluble fertilizer P by crops within a growing season. Of the adsorbed P transformed by microbes, 17-34% was water-soluble and 0.5 M NaHCO3-extractable P, and 23-37% was incorporated into microbial biomass, with the amounts of water-soluble and NaHCO3-extractable inorganic P of the microbial medium and the control being similar for the three variable charge mineral-P complexes. The efficient utilization and transformation of adsorbed P could have been resulted from the increased solubility of Fe, Al and Si from (i) the minerals because of the decrease in pH of the culture medium, (ii) the possible complexation by low molecular weight organic acids, and (iii) the increased desorption of adsorbed P through ligand exchange by the organic anions from microbial activities. These results showed that microorganisms have a great potential to enhance the availability of soil P to plants by transforming soil-bound P into a more water-soluble P pool in soils. (C) 1998 Elsevier Science Ltd. All rights reserved.