Phosphorus (P) in dairy manure is predominantly in an inorganic and water-extractable form.  Most of the inorganic P is partitioned into particulate solids and can be released to surface runoff after land application.  Limited information is available on the chemical composition of the manure inorganic P solid phases - macroscopic methods indicate that some calcium- (Ca) and/or magnesium- (Mg) type phosphates are probable.  Researchers have found it to be extremely difficult to unambiguously detect these inorganic phases in dairy manure using conventional microscopic/spectroscopic methods such as SEM and XRD.  Therefore, the primary objective of this study is to confirm the presence of the probable P phases in dairy manure using X-ray absorption near edge structure (XANES) technique.  With a combination of macroscopic and chemical equilibrium (Mineql+) modeling, we observed that dicalcium phosphate anhydrous (CaHPO₄, DCPA), dicalcium phosphate dihydrate (CaHPO₄.2H₂O, DCPD), octacalcium phosphate (Ca₄H(PO₄)₃.3H₂O, OCP), beta-tricalcium phosphate (Ca₃(PO₄)₂, b-TCP), and struvite (MgNH₄PO₄.6H₂O) were the probable P solid phases in dairy manure.  Phythate and pyrophosphates are known to be the major components of molybdate unreactive P in the manure.  Therefore, the following model compounds are being used in XANES: b-TCP, dicalcium pyrophosphate, DCPA, DCPD, hydroxylapatite, OCP, phytic acid (from corn), and struvite.  Manure samples (Total P= 0.54-1.16 %), including on-farm anaerobic digester influent and effluent, were collected from six WI dairy farms.  The dried samples and model compounds were scanned three times to acquire XANES spectra between 2100 and 2250 eV (step sizes= 1.00, 0.25, and 1.00 eV; time= 5 s/pt) at the Synchrotron Radiation Center, Stoughton, WI.  Principal component analysis of the data is currently being used to determine the specific contributions of the model compounds to the sample spectra.