Microstructural strength of tidal soils – a rheometric approach to develop pedotransfer functions

Abstract

Differences in soil stability, especially in visually comparable soils can occur due to microstructural processes and interactions. By investigating these microstructural processes with rheological investigations, it is possible to achieve a better understanding of soil behaviour from the mesoscale (soil aggregates) to macroscale (bulk soil). In this paper, a rheological investigation of the factors influencing microstructural stability of riparian soils was conducted. Homogenized samples of Marshland soils from the riparian zone of the Elbe River (North Germany) were analyzed with amplitude sweeps (AS) under controlled shear deformation in a modular compact rheometer MCR 300 (Anton Paar, Germany) at different matric potentials. A range physicochemical parameters were determined (texture, pH, organic matter, CaCO 3 etc.) and these factors were used to parameterize pedotransfer functions.The results indicate a clear dependence of microstructural elasticity on texture and water content. Although the influence of individual physicochemical factors varies depending on texture, the relevant features were identified taking combined effects into account. Thus, stabilizing factors are: organic matter, calcium ions, CaCO 3 and pedogenic iron oxides; whereas sodium ions and water content represent structurally unfavorable factors. Based on the determined statistical relationships between rheological and physicochemical parameters, pedotransfer functions (PTF) have been developed.

Rheological evaluation of soil aggregate microstructure and stability across a forested catena

“…To this end, the integral z parameter may be the most useful indicator of micro-structural stability. This term effectively quantifies the excess of elastic to plastic deformation across a range of soil strain Stoppe andHorn, 2018). It therefore encompasses the other rheological parameters included in this study (i.e., γL, γf, Gʹ0, Gʺ0).…”

“…There are a couple of possible mechanisms that may explain these results. For one, in some soils SOC can increase particle dispersion if bound to positively charged functional groups on clay minerals (Stoppe and Horn, 2018). For another, soils with high organic matter content can have relatively high saturated water contents and relatively low bulk densities (Pértile et al, 2016), both of which factors can reduce soil strength to shear stress (Ghezzehei and Or, 2001;Stoppe and Horn, 2018).…”

“…For further comparison of the quasi-elastic range (tan δ < 1), the dimensionless area parameter integral z is defined according to Stoppe and Horn (2018):…”

“…Besides, this approach has been used to study the microstructural changes and stiffness degradation in Oxisols and Vertisols in Brazil (Markgraf and Horn, 2007) and Fluvisols in Germany and Spain (Markgraf et al, 2012;Stoppe and Horn, 2018).…”

Possibilities of using rheological parameters as physical indicators of soil structural changes

“…Реологическое поведение почв, как отражение их физико-механических свойств и структурных особенностей, зависит одновременно от большого количества физических, химических и биологических параметров, таких как мине-ралогический и гранулометрический состав, качественное и количественное содержание катионов и анионов почвенного раствора, рН среды, содержание и состав органического вещества, экссудаты микроорганизмов и растений и т. д. (Хайдапова и др., 2016; Хитров, Хайдапова, 2019; Холопов и др., 2018; Holthusen et al, 2017;Stoppe, Horn, 2018). Поэтому изменение того или иного параметра в результате естественных природных процессов или антропогенной нагрузки прямо или косвенно влечет за собой закономерное изменение реологического поведения почв в различных природных зонах и системах землепользования.…”