Prevalence and Potential Bioavailability of Water-Soluble Organic Phosphorus in Riparian Soils.

Water-soluble P forms are important from a crop nutrition and water quality perspective.  While the factors influencing inorganic P availability are well established, much less is known about the factors controlling organic P solubility and its potential bioavailability.  We measured water-extractable P concentrations and P hydrolyzed by phosphatase enzymes in a range of unfertilized floodplain soils from the Lake Champlain Basin, Vermont.  In a group of 14 Ap-horizons, organic P was the dominant form of water-extractable P (74%).  Across the soils, 17% of the total water-extractable organic P was hydrolyzed to inorganic P by the addition of alkaline phosphatase (reflecting labile sugar phosphates), while 31% was hydrolyzed by alkaline phosphatase plus phosphodiesterase (nucleic acids and phospholipids).  Water-soluble organic P also dominated in another set of Ap (71%) and C horizons (69%), and was significantly correlated with organic matter and soil water content. Results show that soil map unit properties (organic matter and drainage) influenced the nature and reactivity of the water-soluble P pool.