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Information on the chemical forms of organic phosphorus (P) in soil waters is fundamental to understanding the dynamics of soil organic P and its potential for transfer from soils to watercourses. Phosphatase enzymes were used to classify water-extractable molybdate-unreactive P (MUP) from five Australian pasture soils into compounds that could be hydrolysed by (i) alkaline phosphomonoesterase (comprising labile orthophosphate monoesters, such as sugar phosphates), (ii) a combination of phosphodiesterase and alkaline phosphomonoesterase (comprising labile orthophosphate monoesters and orthophosphate diesters, such as nucleic acids and phospholipids), and (iii) phytase (including inositol hexakisphosphate). The phosphomonoesterase and phosphodiesterase preparations were specific to the target substrates, but the phytase preparation hydrolysed all ester-P bonds. Air drying of soils increased the …