POTENTIALITY OF LABORATORY VISIBLE AND NEAR INFRARED SPECTROSCOPY FOR DETERMINING CLAY CONTENT IN FOREST SOILS: A CASE STUDY FROM HIGH FOREST BEECH (FAGUS SYLVATICA) IN CALABRIA (SOUTHERN ITALY)

Clay content is the most important textural fraction because affects soil fertility and productivity. Reflectance spectroscopy in the visible and near infrared (Vis-NIR, 350-2500 nm) spectral region could be an alternative to laboratory standard methods. This paper was aimed to develop a calibration model with laboratory-based soil Vis-NIR spectra for clay content determination and mapping clay content using a geostatistical approach. Soil samples were collected at 235 locations in a forest area of southern Italy and analyzed in laboratory for clay content and Vis-NIR spectroscopic measurements. Partial least squared regression (PLSR) was applied to establish a relationships between reflectance and clay content. Calibration model was developed using only 175 samples, while the remaining 60 samples were used for testing the model. The results of PLSR were satisfactory and ordinary kriging was used for spatial interpolation of clay content determined both using conventional method and the PLSR model.