Effects of strong ionic polarization in the soil electric field on soil particle transport during rainfall

Self Cite

It is well known that humus markedly increases soil aggregate stability, but at the same time strongly decreases the flocculation of clay particles in suspension. These seemingly inconsistent observations suggest the need for a deeper understanding of the physical mechanisms that govern clay–humus interactions. In this research, soil samples from an Entisol were used to explore the role of cationic polarization in humus‐increased soil aggregate stability and sodium (Na+) and potassium (K+) ions were used to characterize weak and strong polarization, respectively. The results showed that strong cationic polarization has a critical role in increased soil aggregate stability in the presence of humus. We concluded that, without cationic polarization, the effects of humus alone on soil aggregate stability were weak in the presence of monovalent metal cations. When we compared the individual contributions of humus and strong cationic polarization, the latter proved much more important than humus in increasing soil aggregate stability. The strongest increase in soil aggregate stability occurred when strong cationic polarization was coupled with humus. The combined analysis of activation energy of soil flocculation in suspension and soil aggregate stability in the presence of humus indicated that humus increased the long‐range electrostatic repulsive force of soil particles, and increased the short‐range attractive force of soil particles. Consequently, humus decreased the flocculation of soil particles in suspension but increased soil aggregate stability; all effects were adjusted by the strength of cationic polarization. Highlights Elucidation of physical mechanisms of cation–surface interactions that determine clay–humus interactions. Cations at the particle surface of the clay–humus complex are strongly polarized. Cationic polarization has a critical role in humus‐increased soil aggregate stability. Without cationic polarization, the effect of humus alone on soil aggregate stability was weak.

Section: Resultsmentioning

confidence: 99%

Role of cationic polarization in humus‐increased soil aggregate stability

Huang

et al. 2016

Self Cite

“…Soil electrochemical properties determine important physical, chemical and biological reactions and processes that occur in soil (Antelo et al, ), such as the stability of soil aggregates (Li et al, a), transport of soil colloids or nanoparticles (Petosa, Brennan, Rajput, & Tufenkji, ), adsorption–desorption of contaminants (Juang & Wu, ) and immobilization and uptake of nutrients by plants (Kopittke, Blamey, Peng, & Menzies, ). Soil is the core of terrestrial ecosystems; therefore, studies on the electrochemical characteristics of soil and the interactions between charged particles in soil systems have practical advantages and benefits for agricultural production and environmental protection.…”

Section: Introductionmentioning

confidence: 99%

Characterizing surface electrochemical properties of simulated bulk soil in situ by streaming potential measurements

Liu

Wang

et al. 2019

To evaluate the feasibility of using streaming potential to characterize the surface electrochemical properties of soil in situ, a quartz sand‐packed column was used to mimic the porous structure and architecture of bulk soil. A laboratory‐made apparatus was developed to measure in situ the streaming potential of quartz grains in the packed column under environmentally relevant physicochemical conditions (e.g. electrolyte pH, Fe oxide coating on sand grains, transport of goethite and amorphous Al hydroxide colloids, and the presence of humic acid). The results showed a significant positive relation between the measured streaming potentials and zeta potentials of the quartz grains examined. With decreasing electrolyte pH, the streaming potential of the quartz grains became less negative because of the greater protonation effect. Similarly, when Fe oxide was adsorbed on to the quartz surfaces, the streaming potential of Fe oxide‐coated quartz grains was less negative than that of uncoated quartz grains as a result of charge neutralization between positively charged Fe oxide and negatively charged sand grains. However, the streaming potential of Fe oxide‐coated quartz grains became more negative when humic acid was added to the electrolyte solution because of increased adsorption of negatively charged humic acid. Interestingly, an obvious change of streaming potential in the processes of colloidal goethite and amorphous Al hydroxide transport in the sand‐packed column grains occurred. Given that the overall positive charge of the colloidal amorphous Al was greater than that of goethite colloids, transport of amorphous Al colloids was found to exert a stronger effect on the variation in streaming potential of quartz sand. Taken altogether, the in situ streaming potential results showed that streaming potential can be used as a powerful index to characterize directly the surface electrochemical properties of quartz grains representing bulk soil. Highlights The variation in surface electrochemical properties of bulk soil needs investigation. We measured the streaming potential produced by simulated bulk soil using a laboratory‐made apparatus. The streaming potential of bulk soil varied with the change in environmentally relevant conditions. Streaming potential is a powerful index characterizing the surface electrochemical properties of bulk soil.

“…During the drying process, non‐volatile electrolytes present in the soil water will be deposited on soil particle surfaces, resulting in a very small residual electrical surface charge. As wetting proceeds from rain or irrigation, forces of surface hydration arise and electrolytes dissolve and disperse, allowing the inherent electrical properties of the surface to express themselves, with the consequent development of electrical double layers (whose thicknesses will depend on the ionic strength of the soil water solution) (Li et al ., , ; Hu et al ., ). These forces give rise to swelling and breakdown of soil aggregates, and the release of microaggregates and primary soil particles.…”

Section: Introductionmentioning

confidence: 99%

Coupling effects of surface charges, adsorbed counterions and particle‐size distribution on soil water infiltration and transport

Gong

Tian

2018

Self Cite

Summary Soil pores are the channels for water transport. The surface charges, the non‐classic polarizabilities and concentrations of the adsorbed counterions in a soil determine soil particle interaction forces that affect soil pore status. Particle‐size distribution is another important factor that affects soil pore status. Therefore, surface charges, adsorbed counterions and particle‐size distribution would probably be coupled in soil water transport. In this study, two soils with different surface charge densities, different adsorbed counterions and different particle‐size distributions were used to study their coupling effects on soil water movement. The results showed that these factors were strongly coupled in soil water movement. When the soil electric field strength was strong (depending on surface charges, adsorbed counterion polarizabilities and concentrations), the net interaction forces of soil particles was repulsive, thus soil aggregates could be broken. The degree of aggregate breakdown coupled with particle‐size distribution determined soil water movement. For this case we found that (i) increasing attractive forces of soil particles could greatly improve soil water movement and (ii) water movement was slow when the soil had large clay or small silt or sand contents. When the soil electric field was weak, the net interaction force of soil particles was attractive, thus aggregates could not be broken. For this case we found that (i) further increasing the attractive forces of soil particles could not improve soil water movement and (ii) water movement was fast when the soil had large clay or small silt or sand contents. Highlights Coupling effects of particle size and particle interactions on soil water movement are not clear. Large clay contents can decrease or increase soil water movement depending on soil particle interaction forces. Fast water movement occurred in soil with strongly polarized cations and large clay content. Particle interaction forces and particle‐size distribution were strongly coupled in soil water movement.