Prediction of topsoil organic matter and clay content from measurements of spectral reflectance and electrical conductivity

Soil organic matter (SOM) and clay content of a soil characterized as a coarse sandy loam were modelled using hyperspectral reflectance data acquired with a spectrometer and soil electrical conductivity (SEC) data acquired with an EM38 instrument manufactured by Geonics Ltd. The partial least squares (PLS) regression method was applied and the results validated using cross validation. First, the models were calibrated using only spectral reflectance data; then EM38 data were included in the X-matrix of predictors. Although SEC is significantly correlated with clay content, the results showed that EM38 data did not improve model performance for the estimation of soil organic matter content and clay content, despite the fact that EM38 showed significant correlation with clay content.