Application of near infrared reflectance spectroscopy for the analysis of organic C, total N and pH in soils of Uruguay

摘要

Near infrared (NIR) reflectance spectroscopy was used to analyse samples (n = 332) from different soils from Uruguay (South America) for organic carbon (OC), total nitrogen (N) and pH. One set (n = 200) of samples randomly selected was used to develop the NIR calibrations while the remaining (n = 132) samples were used as the validation set. The samples were scanned in a small circular cup in reflectance mode (400-2500 nm), using a Foss NIRSystems 6500 (Silver Spring, MD, USA). Modified partial least squares (MPLS) was used to produce the calibration models and cross-validation was used to avoid collinearity effects among variables. Three mathematical treatments and four scatter corrections were also applied. The calibration coefficient of determination (R{sup}2{sub}(CAL)) and the standard error in cross-validation (SECV) were 0.94 (SECV: 1.9) for OC; 0.91 (SECV: 0.19) for total N in g kg{sup}(-1) and 0.93 (SECV: 0.18) for pH, respectively. The simple correlation coefficient of validation (r{sub}(VAL)) and the standard errors of prediction (SEP) were 0.74 and 5; 0.73 and 0.4; 0.84 and 0.28 for OC, total N and pH, respectively.