Micromorphological and X-ray µCT study of Orthic Humic Gleysols under different management conditions

The aim of this study was to evaluate the spatial distribution of different void types and Fe–Mn oxide segregations in the A and B horizons of three Orthic Humic Gleysols from an uncultivated area and two long-time experimental plots – an unfertilized continuous maize plot and a fertilized maize–oats–alfalfa–alfalfa rotation plot – from Woodslee, Ontario. In view of the fact that numerous X-ray CT studies have obtained diverse results, in principal because of a different resolution of the analyzed CT imagery, the utilization of standardized classes in the quantification of similar features (e.g. soil pores) seems necessary in order to obtain comparable results. This X-ray study, performed on polished blocks, is an example of how µCT quantitative results related to volume and area of pores and Fe–Mn oxide segregations can be interpreted in connection with micromorphological characterizations of thin sections of the same samples, using typical micromorphological classes separated based on size and shapes of the analyzed features. Maximum pore volume values, noticed in the Ah horizon of the uncultivated soil and in the Bg horizon of the soil from the rotation plot, were considered an indication of a more favourable aero-hydric regime in these soils compared to the soil from the continuous maize plot. The lowest volumes of Fe–Mn oxides were found in the same horizons. Porosity and pore morphology have a clear influence in the evolution of redox processes and, implicitly, in the formation of typical redoximorphic pedofeatures in Gleysols. The thin-section analysis revealed that Fe–Mn nodules and concretions, as well as Fe depletion areas, were more frequent and better developed in the soil from the continuous maize plot than in the other soils. It was concluded that the examination of the soil features from the perspective of defined size and shape groups may represent a basis for a standardized spatial characterization of soil and for the interpretation of certain pedogenetic processes.