An ASAE/CSAE Meeting Presentation Paper Number: 043114 Spectral Signatures of Common Phosphates in Soils and Their Effect on Absorbance Spectra of Soil Samples with Different Phosphorus Concentrations Ismail Bogrekci, PhD Postdoctoral Research Associate, bogrekci@ufl.edu. Won Suk Lee, PhD Assistant Professor, wslee@ufl.edu. Agricultural and Biological Engineering, Frazier Rogers Hall, PO Box 110570, IFAS, University of Florida, Gainesville, FL 32611-0570 Written for presentation at the 2004 ASAE/CSAE Annual International Meeting Sponsored by ASAE/CSAE Fairmont Chateau Laurier, The Westin, Government Centre Ottawa, Ontario, Canada 1 - 4 August 2004 Abstract. Phosphorus in the environment is mostly bound with iron, magnesium, calcium, and aluminum (Fe, Mg, Ca, and Al, respectively). This study aimed to determine both spectral signatures of Fe, Mg, Ca, and Al associated phosphates and analyze their spectra with soil samples. Obtaining most common spectra of the phosphates and their spectral signatures within a soil sample can be used for determining soil inorganic phosphorus (P) concentration. Four different P-compounds (CaPO 4 , AlPO 4 , FePO 4 2H 2 O, Mg 3 (PO 4 ) 2 2H 2 O) at 0,12.5, 62.5, 175, 375, 750, and 1000 mg/kg were investigated. Reflectance spectra of the four individual phosphates and different concentrations of the compounds within leached sandy soil samples were measured using UV, VIS, and NIR spectroscopy in a range of 225-2525 nm with an interval of 1 nm. In order to build a calibration model and reduce the number of selected wavelengths, correlation coefficient, stepwise multiple linear regression, and stepwise discriminat analysis were applied to data set. With selected wavelengths, discriminant analysis was conducted to classify the types of phosphates in soils. Keywords. Reflectance, Sensor, Phosphorus, Phosphates, Lake Okeechobee, UV, VIS, NIR,Spectroscopy, P compounds. The authors are solely responsible for the content of this technical presentation. The technical presentation does not necessarily reflect the official position of ASAE or CSAE, and its printing and distribution does not constitute an endorsement of views which may be expressed. Technical presentations are not subject to the formal peer review process, therefore, they are not to be presented as refereed publications. Citation of this work should state that it is from an ASAE/CSAE meeting paper. EXAMPLE: Author's Last Name, Initials. 2004. Title of Presentation. ASAE/CSAE Meeting Paper No. 04xxxx. St. Joseph, Mich.: ASAE. For information about securing permission to reprint or reproduce a technical presentation, please contact ASAE at hq@asae.org or 269-429-0300 (2950 Niles Road, St. Joseph, MI 49085-9659 USA).