Nonpoint source P pollution is a major concern in the Mid-Atlantic region due to the land application of animal manures and biosolids, which usually provide P in excess of crop needs. While macroscopic research has provided important information on the effects of land application of organic P sources on soil, these techniques cannot provide specific information about the species of P in manures, biosolids, or amended soils. Direct characterization techniques can provide specific information regarding the forms of P in organic P amendments. In-situ x-ray absorption near edge structure spectroscopy (XANES) was used to determine the primary species of P in dairy manure and several biosolids samples. Phosphorus K-edge XANES spectra from biosolids and manure samples were compared, using linear combination fitting, to spectra collected from synthesized or purchased mineral Fe-, Al-, and Ca-phosphates, phosphates sorbed to oxide minerals, and organic compounds likely to exist in manures and municipal biosolids. Preliminary results suggest that the predominant forms of P in these materials include P sorbed on Fe (hydr-) oxides in biosolids treated with Fe, and hydroxyapatite type Ca phosphate in lime stabilized biosolids. Knowledge of the major chemical species of P present in manures and biosolids will ultimately allow for better prediction of the long-term fate, and potential water quality impacts, of P in soils amended with organic by-products.