Resolving compactness index of pores and solid phase elements in sandy and silt loamy soils. - Maja Bryk (2018)
Soil structure is expressed by the size, shape, and arrangement of structural elements.Shape indices of pores and solid phase elements along with the physical soil parameters allowfor thorough evaluation of soil structure. Therefore, the aim of the research was the analysisof properties of an index of shape – a compactness index CMP = (16·area)/perimeter2 – ofpore (“pore c-s”) and solid phase element cross-sections (“solid c-s”) ≥ 100 pix2 (0.045 mm2)of 4 soils. CMP was calculated via image analysis of resin-impregnated soil blocks preparedfrom intact soil specimens. The morphometric parameters of the objects assigned to selectedCMP classes (≤ 0.2, the lowest compactness; 0.201–0.4; 0.401–0.6; 0.601–0.8; 0.801–1;1.001–1.2; > 1.2, the highest compactness) were compared via 2-way ANOVA for twohorizons (A, C) and two textures (sand, silt loam). The usability of CMP in the description ofsoil structure was then tested. Moreover, the relations of the morphometric parameters of theobjects in CMP classes and soil physical and chemical properties (total organic carbon TOC;bulk and particle density; texture; field water capacity FWC; field air capacity FAC; availablewater capacity AWC; air permeability at –15 kPa lgFAP; saturated hydraulic conductivitylgKS) were examined by way of single and multiple linear regressions. For pore and solid c-sof CMP > 0.2 their number, area, and average areas in CMP classes decreased with increasing CMP value. The distributions of pore and solid c-s among CMP classes depended on soiltexture and structure (aggregate, non-aggregate), allowing for the diagnosis of soil structurestatus and change. Number and area of objects in CMP classes showed numerous strongrelations (R2 > 0.7) to the soil physical and chemical parameters for the studied soil texturesand horizons. The relations differed for pore and solid c-s and depended also on the objectshape (spread, compact or very compact). The average areas of the compact and very compactpore and solid c-s increased with the increase of clay and silt content and the decrease of sandcontent. The number of pore c-s of CMP > 0.2 was related to the texture or particle density.On the other hand, the number of solid c-s of CMP > 0.2, and the average area of the mostspread solid c-s were related to TOC and bulk density. FWC and AWC increased with thedecrease of the number of mainly compact and very compact pore c-s by the decrease of theaverage area of the most spread solid c-s. Both water capacities increased with the increasingaverage areas of pore c-s of CMP > 0.2 and the average areas of the compact and verycompact solid c-s. FAC increased with the increase of the number of the compact and verycompact pore c-s. lgKS increased with the increase of the number and area of mostly compactand very compact pore c-s. lgFAP increased with the area and the average area of the majorityof pore classes and some of the relations were also controlled by the number of pore c-s andthe average area of the most spread solid c-s. The study showed moreover that CMP increasedwith the decreasing size of the objects when measured via computer-aided image analysis.Small cross-sections revealed usually larger CMP values, and large cross-sections were moreoften classified as irregular or spread. Therefore the analysis of shape of soil structuralelements should encompass a wide range of element sizes in relation to the image resolutionto obtain the unbiased shape distributions.
Keywords: Soil structure; Aggregate; Pore; Shape; Compactness index; Soil physical properties