http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=240627 Technical Abstract: Inorganic and organic phosphates react strongly with soil constituents, resulting in relatively low concentrations of soluble P in the soil solution. Multiple competing reactions are operating to regulate the solution-phase concentration of P-containing organic substrates and the released phosphate for assimilation by microbes, plants, or dispersal in the environment. In intensive agrosystems, external inputs of commercial fertilizers are often required to attain sufficiency levels of plant-available P. In this chapter, we focus on the ligand exchange process involved in the solubilization of organic P, a forerunner process crucial to the function of extracellular phosphohydrolases in accessing the recalcitrant soil organic P pool. Plants and microorganisms have evolved and developed multiple strategies to obtain needed P. In these strategies, frequent interweaving of biophysical and biochemical processes are observed in the mineralization of organic P forms. A fundamental reassessment of the biogeochemistry of P in the soil-water systems is necessary to improve our understanding of the physical chemistry of charged surfaces and the role of organic ligands in the turnover of stabilized organic P. Practical solutions to constraints to phosphohydrolases" activity are needed to attain improved use efficiency of this non-renewable resource.