Characterization of organic phosphorus in leachate from a grassland soil

The degree of eutrophication in fresh water ecosystems may be influenced by the forms of phosphorus (P) leached from agricultural systems. Physico-chemical fractionation of P in leachate from a grassland soil carried out over a two year period indicated that the majority of the P loss from the Lismore soil occurred in unreactive particulate (55-76%) P form S. P-31 nuclear magnetic resonance analysis of a selected leachate sample indicated that unreactive P was mainly comprised of monoester and diester forms of organic P. The presence of phosphomonoesterase (20 - 200 mug p nitrophenol l(-1) h(-1)) and phosphodiesterase (68 mug bis-p nitrophenol l(-1) h(-1)) activity in leachate resulted in hydrolysis of 10-21% of total unreactive P JUP), indicating that some of the monoesters and diesters can be eventually hydrolyzed into inorganic P forms during P transport. Enzyme hydrolysis showed that 23% of the TUP was present as labile monoester P (LMP), followed by 20% as mositol hexakisphosphate (IHP) and 14% as diesters (phospholipids and nucleic acids). The findings of this study suggest that LMP, IHP and diesters are an important component of organic P leaching from the grassland soil. (C) 2003 Elsevier Ltd. All rights reserved.