Organic fertilizers are important in agroecosystems, but the fate of specific forms of added phosphorus (P) in the long-term is not well understood. We studied the effects of 62 years of application of three organic fertilizers (dairy manure, compost and dried sewage sludge) on organic P forms in the topsoil as characterized by solution 31P NMR spectroscopy and enzyme additions in a field experiment on a slightly acidic