Determining Phosphorus Concentration using Spectral Reflectance of grass and soil samples

This study aimed to determine phosphorus (P) concentration using reflectance spectra of grass and soils in the Lake Okeechobee drainage basins, Florida. A total of 150 grass samples and 150 soil samples were collected from the three sites in the Lake Okeechobee drainage basins. The reflectance spectra of both fresh and dried samples for grass and soil were measured using UV, VIS, and NIR spectroscopy in 175-2550 nm with an interval of 1 nm. P concentrations of the samples were correlated with the reflectance of the same samples. Two third of both vegetation and soil samples were used for calibration and remaining one third of vegetation and soils were used for validation. Multiple stepwise linear regressions (MLR), and partial least squares (PLS) analyses were applied to the data sets in order to predict P concentrations for soil and grass. Tukey’s means test was performed in order to compare the means of P concentrations for three sites. Also, actual and predicted P concentration maps of the fields for vegetation and soil were plotted. Strong relationships (R=0.778, 0.869, and 0.92, PLS) for validation data sets were obtained between absorbance and P concentrations in soils. Spatial variation in actual and predicted maps showed that P variability could be represented using diffuse reflectance spectroscopy in UV, VIS, and NIR regions.