Quantification of freeze-thaw related structure in cultivated topsoils using X-ray computer tomography

The aim of this work was to test the utility of various CT procedures for the investigation of topsoil microstructural features formed under the influence of annual freeze thaw processes in an agricultural Orthic Gray Brown Luvisol. Assuming that various tillage systems have different propensity to develop and preserve these features, soil cores were collected, prior to spring tillage, from plots characterized by no-till, moldboard plow and disc tillage systems. Micromorphological characterization of CT imagery indicated that soils from no-till treatments exhibited clearly developed platy structures. However, for two of these treatments, quantitative determinations of porosity in binary imagery did not reveal the presence of fine planar mesovoids associated with platy structures. Semivariograms of attenuation, in the three orthogonal axes of the CT imagery, revealed a higher dissimilarity in the vertical direction than in either horizontal direction in all the treatments that were most affected by freeze thaw processes. The variability of the grayscale values along the soil vertical and horizontal directions were also employed to establish morphometric indices for the platy structure.