Spectral Feature Characterizing and Nitrogen Content Prediction in a Soil with Different Particle Size and Moisture Content

摘要

Near-infrared reflectance (NIR) is a valuable fast and convenient technique able to quantify several soil properties. This research work was focused in to analyze the influence of moisture content, particle size, light source incidence angle and captator height on loamy mixed soil spectra. On the other hand, prediction models for Nitrogen (N) content at different moisture content and particle sizes were obtained, and the influence of these properties on N prediction was studied, as well as, the future applicability of NIR spectroscopy as a technique able to make prediction on site was analyzed. Captator height 100 mm and light source angle 45° were chosen as presenting sharpest spectra without apparent scatter effect above of the other heights and angles used. 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 vary from 0.5-1.0; 1.0-2.0 and 2.0-5 mm with r of 0.819; 0.815 and 0.818, respectively. Poor N prediction was obtained when the soil kept its natural moisture content with r of 0.575 and Standard Error of Prediction (SEP) of 3.275 on the contrary with the performance when it was dry with r of 0.815 and SEP of 2.425.