Heterogeneity of pore space properties at the pedon scale of the Phaeozems humus horizon

The variability of soil parameters depends on the chosen method of measurements, the genesis and type of soil land use, and the level of hierarchy of soil structure organization. Computed tomography of soils is an actively growing method of soil structure study, for which many methodological issues remain relevant. The aim of this work was to examine the variability of the main parameters of the pore space (total porosity, number and average pore size) by the example of the humic horizon of a Phaeozem soil. For this purpose, an excessive number (15 microcores of 2 × 3 cm volume) was sampled from soil profile. Based on statistical evaluation of parameter variation, the objective was to determine the optimal number of replicates allowing full characterization of the soil pore space microstructure at the pedon scale. The smallest difference in heterogeneity between pedon and representative elementary volume REV was observed for total porosity (~12 times), while this ratio is larger (~14 times) for number and average pore size. On average, the threshold level, at which the dispersion of properties stopped decreasing, was 7.3 ± 0.6 monoliths for total porosity, 6.5 ± 0.6 monoliths for pore number, and 7.5 ± 0.4 monoliths for LT. Thus, minimal number of replicates necessary for full characteristic of soil structure is 7 monoliths. Sampling and analysis of microcores in 3 repetitions allows to describe the heterogeneity of the structure of the upper pedon horizon only by 25–30%.