Exploring the use of near infrared reflectance spectroscopy to study physical properties and microelements in soils

Near infrared (NIR) reflectance spectroscopy was used to predict the content of silt, sand, clay, iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn) in soil. A total of 332 samples from agricultural soils (0-15 cm depth) in Uruguay (South America) were used. The samples were scanned in a monochromator instrument (NIRSystems 6500, Silver Spring, MD, USA). Two mathematical treatments (first and second derivative) with SNVD (scatter normal variate and detrend) and without scatter correction were studied. Modified partial least squares (mPLS) was used to develop the calibration models. The coefficient of determination in calibration (R-cal(2)) and the standard error in calibration (SEC) using the second derivative were 0.81 (SEC: 5.1), 0.83 (SEC: 5.3), 0.92 (SEC: 2.6) for percent sand, silt and clay, respectively. The R-cal(2) and standard error of cross-validation (SECV) were for Cu 0.87 (SEC: 0.7), for Fe 0.92 (SEC: 21.7), for Mn 0.72 (SEC: 83.0) and for Zn 0.72 (SEC: 1.2) on mg kg(-1) dry matter. It was concluded that NIR reflectance spectroscopy has a great potential as an analytical method for routine analysis of soil texture, Fe, Zn and Cu due the speed and low cost of analysis.