Abstract— In this study, soil samples were collected from two locations: Samawa and Rumetha in southern Iraq. The samples from each location were split into two datasets: calibration set and validation set. VNIR reflectance (350-2500 nm) and GIS-Kriging were used in combination with Partial Least Square (PLS) to predict total N. only two regions reported higher determination coefficient R2 and lower Root Mean Square Error (RMSE) than the other wavelength regions. PLS calibration models yielded an R2 of 0.96 and 0.97 for Rumetha and 0.87 and 0.94 for Samawa location in bands at 500-600 and 800-1000 nm, respectively. The potential of VNIR-based and GIS-Kriging models to predict new unknown soil samples were assessed by using validation datasets from both studied locations. The cross-validation of GIS-Kriging models were unsatisfactory predicted with an Q2 of 0.28 between laboratory-measured and predicted total N values for Rumetha and 0.43 for Samawa location. While VNIR- based validation models achieved highly predictive power with an R2v of 0.84 between laboratory-measured and predicted total N values for Rumetha and 0.85 for Samawa location. These results reveal extremely decreasing in model predictive ability when shifting from VNIR Spectroscopy method to GIS-Kriging.
Keywords— GIS, Kriging, Spectroradiometer, Total Nitrogen.
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