The effect of ionic strength variation and anion competition on the development of nitrate accumulations in variable charge subsoils

Soil Research ◽  
2005 ◽  
Vol 43 (1) ◽  
pp. 43 ◽  
Author(s):  
M. J. Donn ◽  
N. W. Menzies
Keyword(s):  
Ionic Strength ◽  
Charge Density ◽  
Soil Solution ◽  
Chemical Mechanism ◽  
Solution Ionic Strength ◽  
Adsorption Sites ◽  
Variable Charge ◽  
Profile Distribution ◽  
N Fertilisers ◽  
Anion Competition

The leaching of N fertilisers has led to the formation of nitrate (NO3) accumulations in deep subsoils (>5 m depth) of the Johnstone River catchment. This paper outlines the chemical mechanism by which these NO3 accumulations are formed and maintained. This was achieved via a series of column experiments designed to investigate NO3 leaching in relation to the soil charge chemistry and the competition of anions for exchange sites. The presence of variable charge minerals has led to the formation positive surface charge within these profiles. An increase in the soil solution ionic strength accompanying the fertiliser leaching front acts to increase the positive (and negative) charge density, thus providing adsorption sites for NO3. A decrease in the soil solution ionic strength occurs after the fertiliser pulse moves past a point in the profile, due to dilution with incoming rainwater. Nitrate is then released from the exchange back into the soil solution, thus buffering the decrease in the soil solution ionic strength. Since NO3 was adsorbed throughout the profile in this experiment it does not effectively explain the situation occurring in the field. Previous observations of the sulfate (SO4) profile distribution indicated that large SO4 accumulations in the upper profile may influence the NO3 distribution through competition for adsorption sites. A subsequent experiment investigating the effect of SO4 additions on NO3 leaching showed that NO3 adsorption was minimal in the upper profile. Adsorption of NO3 did occur, though only in the region of the profile where SO4 occupancy was low, i.e. in the lower profile. Therefore, the formation of the NO3 accumulations is dependent on the variable charge mineralogy, the variation of charge density with soil solution ionic strength, and the effects of SO4 competition for adsorption sites.

EFFECT OF IONIC STRENGTH AND SOLUTION pH ON P EXTRACTABILITY AND LEACHING IN COARSE-TEXTURED SOILS

1985 ◽  
Vol 65 (1) ◽  
pp. 101-108 ◽  
Author(s):  
A. EVANS Jr. ◽  
R. C. SORENSEN
Keyword(s):  
Organic Matter ◽  
Ionic Strength ◽  
Bulk Solution ◽  
Solution Ph ◽  
Adsorption Sites ◽  
Extractable P ◽  
Leaching Solution ◽  
Anion Competition ◽  
P Movement ◽  
P Distribution

A laboratory study was conducted using columns of Valentine loamy sand to determine the effect of ionic strength (I) and solution pH of a leaching solution on P distribution and extractability with depth. Solutions of KCl at concentrations of 1.0, 10−2, 10−4 and 10−6 mol∙L−1 with a pH of either 4.0, 6.0, or 8.0 were added to the column after the application of 0.3 g diammonium phosphate to the surface of each column. Approximately two pore volumes, 500 mL of solution, were added to the columns, after which they were sectioned and the amount of Bray extractable P in each section was measured. Increasing I resulted in an increase in the total amount of Bray extractable P per column while extractable P increased with column depth for decreasing I. The pH of the leaching solution did not influence the total amount of Bray extractable P per column, but appeared to influence P distribution for the I = 10−2 treatment. Dissolved organic carbon in the leachate was found to increase with decreasing I. Changes in the distribution of extractable P with depth were attributed to increased competition for P adsorption sites by various organic molecules, which were released into the bulk solution when the organic matter coatings underwent a transition from the spherocolloid to the linear flexible molecule configuration. Key words: Ionic strength, P movement, organic matter coatings, spherocolloid, anion competition

scholarly journals Short- and Long-Term Effects of Lime and Gypsum Applications on Acid Soils in a Water-Limited Environment: 3. Soil Solution Chemistry

Agronomy ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 826
Author(s):  
Geoffrey C. Anderson ◽  
Shahab Pathan ◽  
David J. M. Hall ◽  
Rajesh Sharma ◽  
James Easton
Keyword(s):  
Ionic Strength ◽  
Soil Solution ◽  
Soil Profile ◽  
Soil Layer ◽  
Solution Chemistry ◽  
Soil Solution Chemistry ◽  
Short Term ◽  
Solution Ionic Strength ◽  
Gypsum Application

Aluminum (Al) toxicity imposes a significant limitation to crop production in South Western Australia. This paper examines the impact of surface-applied lime and gypsum on soil solution chemistry in the short term (1 year) and the long-term (10 years) in water limited environments. In the experiments, we measured soil solution chemistry using a paste extract on soil profile samples collected to a depth of 50 cm. We then used the chemical equilibrium model MINTEQ to predict the presence and relative concentrations of Al species that are toxic to root growth (Al associated with Al3+ and AlOH2 or Toxic-Al) and less non-toxic forms of Al bound with sulfate, other hydroxide species and organic matter. A feature of the soils used in the experiment is that they have a low capacity to adsorb sulfate. In the short term, despite the low amount of rainfall (279 mm), sulfate derived from the surface gypsum application is rapidly leached into the soil profile. There was no self-liming effect, as evidenced by there being no change in soil solution pH. The application of gypsum, in the short term, increased soil solution ionic strength by 524–681% in the 0–10 cm soil layer declining to 75–109% in the 30–40 cm soil layer due to an increase in soil solution sulfate and calcium concentrations. Calcium from the gypsum application displaces Al from the exchange sites to increase soil solution Al activity in the gypsum treatments by 155–233% in the short term and by 70–196% in the long term to a depth of 40 cm. However, there was no effect on Toxic-Al due to Al sulfate precipitation. In the long term, sulfate leaching from the soil profile results in a decline in soil solution ionic strength. Application of lime results in leaching of alkalinity into the soil profile leading to a decreased Toxic-Al to a depth of 30 cm in the long term, but it did not affect Toxic-Al in the short term. Combining an application of lime with gypsum had the same impact on soil solution properties as gypsum alone in the short term and as lime alone in the long term.

scholarly journals Estimates of soil solution ionic strength and the determination of pH in West Australian soils

Soil Research ◽  
1985 ◽  
Vol 23 (2) ◽  
pp. 309 ◽  
Author(s):  
PJ Dolling ◽  
GSP Ritchie
Keyword(s):  
Ionic Strength ◽  
Soil Solution ◽  
Field Capacity ◽  
Deionized Water ◽  
Distilled Water ◽  
Ph Measurements ◽  
Solution Ionic Strength

The average ionic strength of 20 West Australian soils was found to be 0.0048. The effects of three electrolytes (deionized water, CaCl2 and KNO3), three ionic strengths (0.03, 0.005 and soil ionic strength at field capacity, Is) and two soil liquid ratios (1:5 and 1:10) on the pH of 15 soils were investigated. pH measurements in solutions of ionic strength 0.005 differed the least from measurements made at Is. The differences that occurred in comparisons with distilled water or CaCl2 of ionic strength 0.03 (0.01 M) were much greater (20.4 pH units). An extractant with an ionic strength of 0.005 may provide a more realistic measure of pH in the field than distilled water or 0.01 M CaCl2 for West Australian soils.

Effects of pH and ionic strength on the cation exchange capacity of soils with variable charge

Soil Research ◽  
1981 ◽  
Vol 19 (1) ◽  
pp. 93 ◽  
Author(s):  
GP Gillman
Keyword(s):  
Ionic Strength ◽  
Cation Exchange ◽  
Cation Exchange Capacity ◽  
Exchange Capacity ◽  
Surface Soils ◽  
Ph Values ◽  
Variable Charge ◽  
Effects Of Ph ◽  
Variable Charge Soils

The cation exchange capacity of six surface soils from north Queensland and Hawaii has been measured over a range of pH values (4-6) and ionic strength values (0.003-0.05). The results show that for variable charge soils, modest changes in electrolyte ionic strength are as important in their effect on caton exchange capacity as are changes in pH values.

Temperature-Regulated Fluorescence and Association of an Oligo(ethyleneglycol)methacrylate-Based Copolymer with a Conjugated Polyelectrolyte—The Effect of Solution Ionic Strength

2013 ◽  
Vol 117 (46) ◽  
pp. 14576-14587 ◽  
Author(s):  
Sahika Inal ◽  
Leonardo Chiappisi ◽  
Jonas D. Kölsch ◽  
Mario Kraft ◽  
Marie-Sousai Appavou ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Conjugated Polyelectrolyte ◽  
Solution Ionic Strength

Amelioration of subsurface acidity in sandy soils in low rainfall regions .2. Changes to soil solution composition following the surface application of gypsum and lime

Soil Research ◽  
1994 ◽  
Vol 32 (4) ◽  
pp. 847 ◽  
Author(s):  
CDA Mclay ◽  
GSP Ritchie ◽  
WM Porter ◽  
A Cruse
Keyword(s):  
Ionic Strength ◽  
Soil Solution ◽  
Ion Pairs ◽  
Chemical Properties ◽  
Sandy Soils ◽  
Soil Surface ◽  
Field Trials ◽  
Annual Rainfall ◽  
First Year ◽  
Solution Composition

Two field trials were sampled to investigate the changes to soil solution chemical properties of a yellow sandplain soil with an acidic subsoil following the application of gypsum and lime to the soil surface in 1989. The soils were sandy textured and located in a region of low annual rainfall (300-350 mm). Soil was sampled annually to a depth of 1 m and changes in soil solution composition were estimated by extraction of the soil with 0.005 M KCl. Gypsum leaching caused calcium (Ca), sulfate (SO4) and the ionic strength to increase substantially in both topsoil and subsoil by the end of the first year. Continued leaching in the second year caused these properties to decrease by approximately one-half in the topsoil. Gypsum appeared to have minimal effect on pH or total Al (Al-T), although the amount of Al present as toxic monomeric Al decreased and the amount present as non-toxic AlSO+4 ion pairs increased. Magnesium (Mg) was displaced from the topsoil by gypsum and leached to a lower depth in the subsoil. In contrast, lime caused pH to increase and Al to decrease substantially in the topsoil, but relatively little change to any soil solution properties was observed in the subsoil. There was an indication that more lime may have leached in the presence of gypsum in the first year after application at one site. Wheat yields were best related to the soil acidity index Al-T/EC (where EC is electrical conductivity of a 1:5 soil:water extract), although the depth at which the relationship was strongest in the subsoil varied between sites. The ratio Al-T/EC was strongly correlated with the activity of monomeric Al species (i.e. the sum of the activities of Al3+, AlOH2+ and Al(OH)+2 in the soil solution. An increase in the concentration of sulfate in the subsoil solution (which increased the ionic strength, thereby decreasing the activity of Al3+, and also increased the amount of Al present as the AlSO+4 ion pair) was probably the most important factor decreasing Al toxicity to wheat. The results indicated that gypsum could be used to increase wheat growth in aluminium toxic subsoils in sandy soils of low rainfall regions and that a simple soil test could be used to predict responses.

Ionic strength and polyelectrolyte molecular weight effects on floc formation and growth in Taylor–Couette flows

Soft Matter ◽  
2021 ◽  
Author(s):  
Athena E. Metaxas ◽  
Vishal Panwar ◽  
Ruth L. Olson ◽  
Cari S. Dutcher
Keyword(s):  
Molecular Weight ◽  
Ionic Strength ◽  
Solution Ionic Strength ◽  
Radial Injection ◽  
Couette Cell ◽  
Taylor Couette

A Taylor–Couette cell capable of radial injection was used to study the effects of varying solution ionic strength and polyelectrolyte molecular weight on the polyelectrolyte-driven flocculation of bentonite suspensions.

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