The Effect of Particle Size on Sensing Phosphorus by Raman Spectroscopy

The accurate sensing and determination of phosphorus (P) concentration in soil samples using spectral measurements are dependent upon the condition of soil sample, instrument and environment. The condition of soil sample includes soil type, particle size and moisture content. The variation in soil conditions reflects the variation in the intensity of scattering. The effect of particle size on soil spectrum in sensing phosphorus concentration using Raman spectroscopy was investigated. The soil samples were collected from the Okeechobee drainage basin. The samples were dried and graded into five particle sizes. A portable infield P sensor was used to measure the Raman spectra of soils. The spectral range for the measurement was between 340 and 3640 cm. The results show that soil particle size had an effect on Raman spectrum of soils. The predictions of P show that partial least squares analysis (PLS) produced higher coefficient of determinations for the estimations of P with the same particle size when compared to a combination of different particle sizes.