Figure 4: Visual assessment of partial least squares regression model results for soil total carbon ( ) prediction from subsets of (a) visible/near-infrared (VNIR) and (b) mid-infrared (MIR) diffuse reflectance spectra based on soil order. The parameters given are the coefficient of determination ( ), root mean squared error (RMSE, %), residual prediction deviation (RPD), and the ratio of performance to interquartile distance (RPIQ). The range of values reflects the results of 10 random iterations of the models. Results are also shown for full sample set models with no subsetting for comparison.