Physical Indicators and Mechanism of Vertisolization: A Case Study of the Cis-Caucasian Vertic Chernozem

Abstract

Vertisolization —the development of vertic properties and vertic horizons—is a widespread process leading to adverse physical and technological properties of chernozems.. There is still no generally accepted theory of the genesis of this phenomenon, although it is a priori clear that the physicochemical mechanisms of the interaction between fine particles and soil water in swell–shrink cycles are the underlying factors. Patterns of the dynamics of the main categories of soil porosity in dependence on the soil water content have been studied at a quantitative level in the genetic horizons of a Cis-Caucasian vertic leached chernozem (Luvic Chernozem (Epiloamic, Katoclayic, Aric, Novic, Bathyvertic)) in comparison with a chernozem without vertic properties. The physical state of vertic soils is represented by structural diagrams of porosity as a function of the specific volumes of various pore categories depending on the volumetric water content. The diagrams are constructed using the experimental data on the textural porosity of aggregates obtained by saturating individual aggregates with a nonpolar liquid (toluene) and humidification with hot water vapor and a fundamental ionic electrostatic model of the disjoining pressure. Vertisolization is characterized by a significant reduction in the textural porosity and a predominance of specific volumes of the external pore space (cracks and interaggregate voids) in the overall structure of the porous dispersed system. The most likely cause of vertisolization is a sharp (twofold) decrease in the effective width of the electrical double layer in the dispersed system with an increase in the particle interaction through stable layers of liquid phase (compaction effect). In turn, this brings about adverse technological properties of the vertic chernozems and lumpy fragmentation upon drying with the formation of large cracks, which complicates their tillage and agricultural activities in general.