[Spectral characterization and N content prediction of soil with different particle size and moisture content]

The present work was focused on analyzing the influence of moisture content, particle size, light source incidence angle and observation height on a loamy mixed soil spectra Meanwhile, prediction models for N content with different moisture and particle sizes were obtained, and the influence of these properties on N prediction was studied. The future applicability of NIR spectroscopy as a technique able to make prediction on the spot was analyzed. Observation height 100 mm and light source angle 45 degrees were chosen to present a sharpest spectra. Moisture content and particle size were found to affect strongly the absorbance of the spectra, and an accurate N prediction was obtained when the particle sizes varied from 0. 5-1. 0, 1. 0-2.0 and 2-5 mm with r of 0. 82, 0. 81 and 0. 81, respectively. Poor N prediction was obtained when the soil kept its natural moisture with r of 0. 57 and SECV of 3. 06 compared with the performance when it was dry with r of 0. 81 and SECV of 2. 40.