Macrostructure of diagnostic B horizons relative to underlying BC and C horizons in Podzols, Luvisol, Cambisol, and Arenosol evaluated by image analysis

摘要

Five soils: Albic Ortsteinic Podzol, Albic Podzol, and Dystric Brunic Arenosol developed from sand, and Haplic Luvisol and Eutric Cambisol developed from loess were studied to evaluate morphometric features and selected physico-chemical properties of B horizons in relation to BC and C horizons. By standard laboratory methods soil texture, total organic carbon, the amount of carbonates, pH, particle and bulk density, total porosity were measured. Samples with preserved structure were used to produce for each tested layer 16 resin-impregnated 8 x 9 cm in size opaque soil blocks for qualitative and quantitative soil structure analysis. Utilizing the scanned images of the opaque blocks, the following morphometric parameters were measured: the relative area of pore cross-section (macroporosity), the relative length of pore cross-sections' perimeter, the relative number of pore and solid phase element cross-sections, the mean area of pore and solid phase element cross-section, and fraction of number of horizontally, diagonally and vertically oriented pore cross-sections. The numerical characteristics of each soil structure revealed that the layers of the B horizons differed from the underlying layers, representing BC, C and Ck horizons, in an ambiguous way, depending on soil genesis. The obtained morphometric parameters and morphological analysis showed that in the B horizons the original structure of sand or loess obliterated due to the processes of enrichment of the B horizons in organic substances, Al and Fe, and the soil fauna and flora activity, and consequently the development of aggregate structure or pores cutting the soil groundmass. The morphometric parameters measured by image analysis corresponded logically with basic soil properties. Namely, the organic carbon content and total porosity increased, and the bulk density decreased while the morphometric parameters grew showing the development of more loose soil arrangement No characteristic differences in view of the measured morphometric parameters were found between Bhs, Bs and Bt horizons (illuvial accumulation) and Bwo and Bw horizons (their genesis driven by in situ accumulation). The BC horizons were much more similar than the B horizons to the parent material with respect to the values of morphometric parameters. It should be stressed that the quantitative image analysis exposed visible in the opaque blocks qualitative dissimilarities between soil layers but due to the innate for soil especially a forest one high heterogeneity of structure the observed differences between the average values of morphometric parameters for the layers were not always validated through statistical tests. The orientation analysis provided no characteristic description of soil structure status, it helped however to interpret other morphometric parameters. Our study demonstrated that the quantitative macrostructure analysis could be an indirect method for evaluation of pedogenesis intensity because physico-chemical properties of the developed B horizons controlled the occurrence and extent of abiotic and biotic factors regulating soil structure. (C) 2015 Elsevier B.V. All rights reserved.