The significance of the threshold and turbidity concentrations in relation to sodicity and microstructure

Soil Research ◽  
2001 ◽  
Vol 39 (6) ◽  
pp. 1185 ◽  
Author(s):  
J. P. Quirk
Keyword(s):  
Electrolyte Concentration ◽  
Sandy Loam ◽  
Infiltration Rate ◽  
Threshold Concentration ◽  
Diffuse Double Layer ◽  
Soil Permeability ◽  
Soil Microstructure ◽  
Discernible Effect ◽  
Irrigation Practice ◽  
The Stability

Quirk and Schofield (1955) in their paper on the effect of electrolyte concentration on soil permeability in relation to sodicity designated 2 concentrations: the threshold concentration, which related to the first discernible effect on soil structure; and the turbidity concentration, at which the dismantling of the soil microstructure is indicated by the appearance of dispersed particles in the percolate—this occurs when the electrolyte concentration is about one-quarter of the threshold concentration. This behaviour is explained in terms of clay domains, which are assemblages of many clay particles in parallel alignment. Within a clay domain, slit-shaped pores with surface separations about equal to the thickness of clay crystals exist. When calcium is the dominant exchangeable ion the clay domains are stable because where contiguous crystals overlap the surfaces reside in a potential well as a result of strong attractive forces. These attractive forces are similar to those responsible for the stability of Camontmorillonite and Ca-vermiculite crystals. A model of 3 clay crystals is used to illustrate how crystal interaction within a clay domain, in terms of classical repulsive diffuse double-layer forces and modern attractive forces, affect domain stability. Attention is drawn to a misconception, now prevalent in the literature, which does not recognise the basic significance of the turbidity concentration with respect to microstructure and wrongly contends that the concentration of electrolyte required to effect the dispersion to flocculation transition in soil suspensions can be used for predicting the level of electrolyte required to sustain soil permeability or infiltration rate in irrigation practice. It is shown that the flocculation concentration is almost 8 times the turbidity concentration. The application of the threshold concentration concept in irrigation practice is discussed. It is demonstrated that the threshold and turbidity concentration comfortably explain the behaviour of a heavy clay soil subjected to border-check irrigation and Cajon sandy loam in Arizona.

Soil permeability in relation to sodicity and salinity

1986 ◽  
Vol 316 (1537) ◽  
pp. 297-317 ◽  
Keyword(s):  
Irrigation Water ◽  
Soil Structure ◽  
Particle Interaction ◽  
Threshold Concentration ◽  
Double Layers ◽  
Soil Permeability ◽  
Clay Particles ◽  
Irrigation Practice ◽  
Repulsive Forces ◽  
Soil Colloids

Difficulties encountered in the irrigation of sodium-affected soils or in the reclamation of sodic—saline soils can be circumvented by controlling the electrolyte level in the irrigation water, which prevents deterioration of the soil structure. The threshold concentration concept simply expresses the minimum level of electrolyte required to maintain the soil in a permeable condition for a given degree of sodium saturation of the soil colloids. It is shown that decreases in permeability at concentrations below the threshold concentration are occasioned by increased clay-particle interaction owing to the extensive development of diffuse double layers which give rise to enhanced swelling. Mechanical failure is associated with this swelling and deflocculation of clay particles. This behaviour of sodium-affected soils is considered in relation to the operation of van der Waals forces, hydration forces and osmotic repulsive forces arising from the development of diffuse double layers on particle surfaces. Considerations of ion-exchange equilibria between particle surfaces and the soil solution (irrigation water) are discussed in relation to the threshold concentration concept, and the application of the concept in irrigation practice is illustrated by reference to several case histories.

Structural stability of Chernozemic soils as affected by exchangeable sodium and electrolyte concentration

1994 ◽  
Vol 74 (2) ◽  
pp. 157-164 ◽  
Author(s):  
D. Curtin ◽  
H. Steppuhn ◽  
F. Selles
Keyword(s):  
Electrolyte Concentration ◽  
Clay Content ◽  
Threshold Concentration ◽  
Prairie Soils ◽  
Structural Deterioration ◽  
Soil Clays ◽  
Low Salt ◽  
Leaching Solution ◽  
The Stability ◽  
General Response

The stability of soil structure in the presence of exchangeable Na is an important factor determining the success of irrigation developments using sodic waters. Our objective was to determine the effects of sodium adsorption ratio [SAR = Na/((Ca + Mg)/2)0.5, where concentrations are expressed in mmolc L−1] and electrolyte concentration on saturated hydraulic conductivity (K) and on macroscopic swelling in a range of Brown Chernozemic soils from southern Saskatchewan. All soils showed the same general response to sodicity (SAR) and electrolyte concentration of the leaching solution, i.e., K decreased as SAR increased and as salt concentration decreased. However, major differences existed between the soils in their susceptibility to Na-induced structural deterioration. For example, at SAR 20, the electrolyte concentration needed to maintain stable structure ranged from about 5 to 30 mmolc L−1. Our results indicated that use of a generalized threshold concentration curve to partition stable from unstable structure would not be satisfactory for all irrigated prairie soils. Texture was a major source of variation between soils; the limits on acceptable irrigation water SAR should generally be decreased as clay content increases. Swelling and dispersion of soil clays both contributed to sodicity-induced K decline. Soil clays swelled appreciably when soil exchangeable Na percentage exceeded about 10. In contrast to swelling, which was relatively insensitive to electrolyte concentration, clay dispersion was only observed at low salt concentrations (≤ 20 mmolc L−1. In implementing irrigation water:soil compatibility guidelines, it will be necessary to identify soils which deviate substantially from general or average behavior because of their propensity to disperse or swell. Key words: Sodicity hazard, threshold concentration curves, clay swelling

scholarly journals Influence of Living and Dead Roots of Gansu Poplar on Water Infiltration and Distribution in Soil

2020 ◽  
Vol 10 (10) ◽  
pp. 3593 ◽  
Author(s):  
Dashuai Zhang ◽  
Yao Dai ◽  
Lingli Wang ◽  
Liang Chen
Keyword(s):  
Preferential Flow ◽  
Storage Capacity ◽  
Water Storage ◽  
Infiltration Rate ◽  
Water Infiltration ◽  
Soil Porosity ◽  
Soil Permeability ◽  
Rapid Urbanization ◽  
Water Storage Capacity ◽  
Porosity And Permeability

During rapid urbanization, it is necessary to increase soil permeability and soil porosity for reducing urban runoff and waterlogging risk. Woody plants are known to increase soil porosity and preferential flow in soil via living roots growth and dead roots decay. However, the primary results of dead woody plant roots on soil porosity and permeability have been discussed based only on the hypotheses or assumptions of different researchers. In this study, living and dead roots (decayed under natural conditions for more than 5 years) of Gansu poplar trees (Populus gansuensis) were selected. They were selected to compare the influence between living and dead roots on water infiltration rate and soil porosity in a cylindrical container (diameter = 20 cm, height = 66 cm) under laboratory conditions. Results indicated that the steady-state water fluxes at the bottom of the containers without roots (control), with living roots, and with dead roots were 54.75 ± 0.80, 61.31 ± 0.61, and 55.97 ± 0.59 cm d−1, respectively. Both living roots and dead roots increased the water infiltration rates in soil and also increased the water storage capacity of soil. The water storage capacities of soil without roots, with living roots, and with dead roots were 0.279, 0.317, and 0.322 cm3 cm−3, respectively. The results from SEM indicated that smaller pores (30–50 μm) were in living roots and larger pores (100–1000 μm) were in dead roots. The soil permeability was increased by living roots possibly due to the larger channels generated on the surface of the roots; however, water absorbed into the dead roots resulted in greater water storage capacity.

scholarly journals Electrophoretic Deposition of Copper(II)–Chitosan Complexes for Antibacterial Coatings

2020 ◽  
Vol 21 (7) ◽  
pp. 2637 ◽  
Author(s):  
Muhammad Asim Akhtar ◽  
Kanwal Ilyas ◽  
Ivo Dlouhý ◽  
Filip Siska ◽  
Aldo R. Boccaccini
Keyword(s):  
Electrophoretic Deposition ◽  
Mechanical Stability ◽  
Metallic Copper ◽  
Antibacterial Properties ◽  
Threshold Concentration ◽  
X Ray Diffraction ◽  
X Ray ◽  
Antibacterial Coatings ◽  
Elemental Analyses ◽  
The Stability

Bacterial infection associated with medical implants is a major threat to healthcare. This work reports the fabrication of Copper(II)–Chitosan (Cu(II)–CS) complex coatings deposited by electrophoretic deposition (EPD) as potential antibacterial candidate to combat microorganisms to reduce implant related infections. The successful deposition of Cu(II)–CS complex coatings on stainless steel was confirmed by physicochemical characterizations. Morphological and elemental analyses by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy verified the uniform distribution of copper in the Chitosan (CS) matrix. Moreover, homogeneous coatings without precipitation of metallic copper were confirmed by X-ray diffraction (XRD) spectroscopy and SEM micrographs. Controlled swelling behavior depicted the chelation of copper with polysaccharide chains that is key to the stability of Cu(II)–CS coatings. All investigated systems exhibited stable degradation rate in phosphate buffered saline (PBS)–lysozyme solution within seven days of incubation. The coatings presented higher mechanical properties with the increase in Cu(II) concentration. The crack-free coatings showed mildly hydrophobic behavior. Antibacterial assays were performed using both Gram-positive and Gram-negative bacteria. Outstanding antibacterial properties of the coatings were confirmed. After 24 h of incubation, cell studies of coatings confirms that up to a certain threshold concentration of Cu(II) were not cytotoxic to human osteoblast-like cells. Overall, our results show that uniform and homogeneous Cu(II)–CS coatings with good antibacterial and enhanced mechanical stability could be successfully deposited by EPD. Such antibiotic-free antibacterial coatings are potential candidates for biomedical implants.

Influence of sodium adsorption ratio on sodium and calcium breakthrough curves and hydraulic conductivity in soil columns

Soil Research ◽  
2007 ◽  
Vol 45 (8) ◽  
pp. 586 ◽  
Author(s):  
Oagile Dikinya ◽  
Christoph Hinz ◽  
Graham Aylmore
Keyword(s):  
Hydraulic Conductivity ◽  
Electrolyte Concentration ◽  
Soil Aggregates ◽  
Breakthrough Curves ◽  
Sodium Adsorption Ratio ◽  
Threshold Concentration ◽  
Critical Threshold ◽  
Soil Columns ◽  
Clay Particles ◽  
The Matrix

The paper examines the effects of electrolyte concentration and sodium adsorption ratio (SAR) on the relative saturated hydraulic conductivity (RHC) and the ionic behaviour of calcium (Ca) and sodium (Na) ions in the Na–Ca exchange complex. Batch binary exchange and saturated column transport experiments were carried out to quantify these effects using an agricultural Balkuling soil and a mining residue. Generally, RHC has been found to decrease with time, with increasing SAR, and with decreasing electrolyte concentration. The more rapid decrease in RHC in the mining residue, particularly at the lowest concentration (1 mmol/L), was consistent at all SAR values. The decreases in RHC were likely to be caused by partial blocking of pores by dispersed clay particles, as evidenced by the appearance of suspended clay particles in the effluent during leaching. Significant differences in RHC were observed in the passage of fronts of decreasing electrolyte concentrations for CaCl2 and SAR 15 solutions through the soil columns. These differences were attributable to structural alterations (slaking) of the media and the nature of the particles released and mobilised within the porous structure at any given point in the column. Measurements at the critical threshold concentration and turbidity concentration at SAR 15 revealed structural breakdown of the pore matrix system as evidenced by decreased RHC. The increase in SAR to 15 is initially accompanied by erratic RHC, presumably due to the break up of soil aggregates under the increased swelling forces. The less coherent mining residue soil was substantially more vulnerable to blockage of pores than the Balkuling soil in which clay particles are likely to be more readily mobilised, and hence available to re-deposit and occlude the matrix pores.

The stability of soil aggregates as affected by organic materials, microbial activity and physical disruption

Soil Research ◽  
1978 ◽  
Vol 16 (1) ◽  
pp. 9 ◽  
Author(s):  
JM Tisdall ◽  
B Cockroft ◽  
NC Uren
Keyword(s):  
Microbial Activity ◽  
Organic Materials ◽  
Sandy Loam ◽  
Soil Aggregates ◽  
Moist Soil ◽  
Severe Restriction ◽  
Wetting And Drying ◽  
Fine Sandy Loam ◽  
The Stability

On moist incubation the equivalent of 50 t ha-1 or more of ground, readily decomposable organic materials greatly increased the proportion of stable aggregates of Shepparton fine sandy loam within 1-4 weeks; the aggregates remained stable for up to 32 weeks if left undisturbed. Severe restriction of microbial activity in aggregates of Shepparton fine sandy loam by sterilization or dryness increased the effect of physical disruption associated with intermittent wetting and drying, and simulated cultivation. The results suggest that microorganisms in non-sterile moist soil can produce bonding substances which compensate partially for those bonds broken physically.

scholarly journals Analysis Of Geoelectrical And Soil Test Data To Determine Subsurface Conditions In Makassar City, South Sulawesi

Khazanah ◽  
2020 ◽  
Vol 12 (2) ◽  
Author(s):  
Jefri nainggolan ◽  
◽  
Muhammad Fajar ◽  
Keyword(s):  
Water Content ◽  
Sandy Loam ◽  
Standard Penetration Test ◽  
Special Treatment ◽  
Test Results ◽  
Penetration Test ◽  
Resistivity Tomography ◽  
South Sulawesi ◽  
Laboratory Test Results ◽  
The Stability

Research has been carried out to determine subsurface conditions. The research objective was to determine the physical properties of the soil in order to evaluate and provide recommendations for solving foundation problems. The methods are the resistivity geoelectric and IP geoelectric method (induced polarization) with ERT (Electrical Resistivity Tomography), SPT (Standard Penetration Test) and laboratory test results. The results of the resistivity values obtained varied in the range from 17.0 - 172.0 ohm m with a depth of 0 m - 2.87 m, most of which were interpreted as alluvium soil, namely sandy loam. This is reinforced by the results of the IP method where the low chargebility value is around 0.130 - 4.70 msec. In addition, it was found that from the SPT test, it was obtained that the variation of blows from 14 to 21 N at a depth of 0 - 5.50 meters and >60 N from a depth of 5.50 - 20 m which stated that most of them consisted of clay and sandstones. Then based on laboratory tests, it was found that at a depth of 3 - 3.5 meters it consisted of 86.47% clay with a plastic limit of 37.07% and the water content was 39.41%, while at a depth of 9 -9.5 meters it consisted of sandstones which the characteristic is non- plastic with a water content of up to 72.04%. It is concluded that the surface soil is conductive, it is necessary to hold special treatment for this type of soil in order to avoid erosion when it is saturated with water and it is hoped that the stability of the soil will be better. One of two ways is by mixing high density soil and making a "chicken claw" foundation to strengthen the foundation with a depth of more than 5.0 meters. Keywords: Geoelectric, Standard Penetration Test, Resistivity, Chargebility, Foundation.

scholarly journals INFLUÊNCIA DA APLICAÇÃO DE VINHAÇA NA CAPACIDADE DE INFILTRAÇÃO DE UM SOLO DE TEXTURA FRANCO ARENOSA

Irriga ◽  
2010 ◽  
Vol 15 (4) ◽  
pp. 344-352 ◽  
Author(s):  
Alexandre Barcellos Dalri ◽  
Glauco Eduardo Pereira Cortez ◽  
Luis Guilherme Senarese Riul ◽  
Jairo Augusto Campos Araújo ◽  
Raimundo Leite Cruz
Keyword(s):  
Soil Erosion ◽  
Sandy Loam ◽  
Infiltration Rate ◽  
Water Infiltration ◽  
Infiltration Capacity ◽  
Rate Estimate ◽  
Erosion Risk ◽  
Soil Water Infiltration ◽  
Loam Soil ◽  
Horton Model

Este trabalho teve como objetivo estudar o efeito da aplicação de diferentes lâminas de vinhaça na infiltração de água no solo e verificar a adequação dos modelos de Horton e Kostiakov-Lewis na estimativa da taxa de infiltração. Os tratamentos corresponderam à aplicação de cinco doses de vinhaça (0, 200, 250, 300 e 350 m3.ha-1). A aplicação de vinhaça propiciou uma redução da taxa de infiltração básica do respectivo solo em estudo, causando efeito negativo para essa característica, pois, eleva o risco de erosão do solo e majora a possibilidade do escoamento superficial. O modelo de Horton propiciou o melhor ajuste sobre os dados observados, e o modelo de Kostiakov-Lewis superestimou os valores da taxa de infiltração.   UNITERMOS: vinhaça, infiltração, solo.     DALRI, A.B.; CORTEZ, G.E.P.; RIUL, L.G.S.; ARAÚJO, J.A.C.; CRUZ, R.L. VINASSE APPLICATION INFLUENCE ON INFILTRATION CAPACITY OF SANDY LOAM SOIL     2 ABSTRACT   The objective of this study was to analyze effects in different depth in soil water infiltration and to verify the Horton and Kostiakov-Lewis models adequacy in infiltration rate estimate. The treatments were five doses of vinasse (0, 200, 250, 300 and 350 m³.ha¹). The vinasse application reduced the soil erosion risk increasing the possibility of runoff. The Horton model had the best adjustment on the observed data, and the Kostiakov-Lewis model overestimated the infiltration rate values.   KEYWORDS: vinasse, infiltration, soil.

scholarly journals Different resource allocation in a Bacillus subtilis population displaying bimodal motility

2021 ◽  
Author(s):  
Leendert W. Hamoen ◽  
Biwen Wang ◽  
Jojet Staal ◽  
Yongqiang Gao ◽  
Remco Kort ◽  
...  
Keyword(s):  
Bacillus Subtilis ◽  
Exponential Growth ◽  
Microscopic Analysis ◽  
Feedback Regulation ◽  
Ribosomal Gene ◽  
Threshold Concentration ◽  
Negative Feedback Regulation ◽  
Continuous Increase ◽  
Motile Cells ◽  
The Stability

To cope with sudden changes in their environment, bacteria can use a bet-hedging strategy by dividing the population into cells with different properties. This so-called bimodal or bistable cellular differentiation is generally controlled by positive feedback regulation of transcriptional activators. Due to the continuous increase in cell volume, it is difficult for these activators to reach an activation threshold concentration when cells are growing exponentially. This is one reason why bimodal differentiation is primarily observed from the onset of the stationary phase when exponential growth ceases. An exception is the bimodal induction of motility in Bacillus subtilis, which occurs early during exponential growth. Several mechanisms have been put forward to explain this, including double negative-feedback regulation and the stability of the mRNA molecules involved. In this study, we used fluorescence-assisted cell sorting to compare the transcriptome of motile and non-motile cells and noted that expression of ribosomal genes is lower in motile cells. This was confirmed using an unstable GFP reporter fused to the strong ribosomal rpsD promoter. We propose that the reduction in ribosomal gene expression in motile cells is the result of a diversion of cellular resources to the synthesis of the chemotaxis and motility systems. In agreement, single-cell microscopic analysis showed that motile cells are slightly shorter than non-motile cells, an indication of slower growth. We speculate that this growth rate reduction can contribute to the bimodal induction of motility during exponential growth.

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