SPECTRORADIOMETRIC AND VISUAL COLOR MEASUREMENTS OF DISTURBED AND UNDISTURBED SOIL SAMPLES

We tested a new spectroradiometric method of color measurement in soil samples and found that the main advantage of this method is that it d etermines reliably the color of undisturbed soil fragments. To standar dize the process, and to compare the accuracy of the spectroradiometri c measurements with the results of visual determinations, we measured color in natural soil aggregates and in ground-homogenized samples and represented the results in the CIE 1976 (La*b*) color space. Variabi lity in colors in a given aggregate was evaluated with the parameter < Delta E(ab)> and was, on average, 10-fold greater than for ground sam ples. Grinding and homogenization of soil materials resulted in signif icant changes in color (18.3 CIELAB units in average), 89% of this col or difference being attributable to an increase in lightness. Visual m easurements of color with standard soil color charts showed an interob server variability very similar for disturbed and undisturbed samples. However, color differences between the instrumental measurements of s oil samples and the average visual judgments were 4.41 and 10.19 CIELA B units for disturbed and undisturbed samples, respectively, with the greatest errors fn the estimation of the L coordinates in both cases.