Tuesday, November 6, 2007
223-6

Quantification of Soil Total Phosphorus Using Mid-Infrared Spectroscopy.

Kimberly Epps, Soil and Water Science, University of Florida, PO Box 110290, Gainesville, FL 32611-0290, James B. Reeves III, USDA-ARS Environmental Management and Byproduct Utilization Laboratory, Bldg. 306, BARC-East, 10300 Baltimore Ave, Beltsville, MD 20705, and Nicholas Comerford, PO Box 110290, University of Florida, University of Florida, Soil & Water Science Department, Gainesville, FL 32611-0290.

Infrared-spectroscopy has already been used to successfully quantify total carbon and nitrogen in soils and plant residues. The aim of this work was to investigate the usefulness of mid-range diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in the determination of soil total phosphorus (TP) across a range of soil textures. A total of 138 surface soils (0-10 cm) from six study plots in southern Bahia presenting two land-uses (secondary forest and traditional cacao production) were used. The areas ranged in soil texture from 7-52% clay. Total phosphorus of air-dried, hand-ground soils was analyzed using the sulfuric-acid/ peroxide digestion method. Spectral data were obtained with a Digi-Lab FTS-7000 FTIR instrument and collected in the mid-infrared region (4000-400 cm-1). Measured total phosphorus values were correlated with scatter corrected, mean centered spectral data using partial-least squares regression to obtain prediction models. Calibration results validated using cross-validation of 25 randomly chosen subsets yielded an r2 of 0.85 and root mean square error of prediction (RMSEP) = 12% of the mean TP value. Predictions were improved within texture classes only for sandy soils (n = 48; 65-85% sand), for which r2 = 0.90 and RMSEP = 12% mean TP. DRIFTS is a promising approach for the rapid determination of total phosphorus with minimal sample pretreatment. Future work should test its efficacy on other forms of extractable phosphorus.