Exploring the use of near infrared reflectance spectroscopy (NIRS) to predict trace minerals in legumes

The use of near infrared reflectance spectroscopy (NIRS) was explored to predict trace mineral concentrations in two legumes. Samples (332), composite of white clover (n=97) and lucerne (n=235), from different locations in Uruguay representing a wide range of soil types, were analysed for sodium (Na), sulphur (S), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), and boron (B). The samples were scanned in reflectance in a monochromator instrument (400–2500 nm). Calibration models (n=262) were developed using modified partial least squares regression (MPLS) based on cross-validation and tested using a validation set (n=70). Two mathematical treatments of the spectra were compared (first and second derivative). The highest coefficients of determination in calibration (RCAL2) and the lowest standard errors of cross-validation (SECV) were obtained using second derivative. The RCAL2 and SECV were 0.83 (SECV: 0.8) for Na and 0.86 (SECV: 2.5) for S in g kg−1 DM; 0.80 (SECV: 4.4), 0.80 (SECV: 10.6), 0.78 (SECV: 22.9), 0.76 (SECV: 0.83) and 0.57 (SECV 25.7) for B, Zn, Mn, Cu and Fe in mg kg−1 DM on a dry weight, respectively. Sulphur (SEP: 5.5), sodium (SEP: 1.2) and boron (SEP 4.2) were well predicted by NIRS on a validation set.