Spectral Feature Characterization and Nitrogen Content Prediction in Soils with Different Particle Sizes and Moisture Contents

The objective of this research is to analyze the influences of light source incidence angle, fiber height, moisture content, and particle size on loamy mixed soil spectra. Nitrogen (N) content calibration and cross-validation models at different moisture contents and particle sizes were obtained using partial least squares (PLS) analysis. Spectral data were collected using a spectrophotometer. Fiber height of 100 mm and light source angle at 45° were chosen to obtain the sharpest spectra without apparent scattering effect. The results show that moisture content and particle size strongly influenced the absorbance of the spectra, and a better N prediction model was obtained when the particle sizes were in the ranges of 0.5