Low Exchangeable Sodium Percentage Research Articles

Effect of drop energy and soil and water chemistry on infiltration and erosion

The effect of water salinity, soil sodicity, and raindrop energy on final infiltration rate, wash erosion, and soil particle splash of two kaolinitic soils (ustochrepts and paleudalf) was studied. Final infiltration rate decreased with the increase in soil sodicity and drop energy and increased with the increase of water salinity. Wash erosion and splash increased with the increase in soil sodicity and drop energy and decreased with the increase in water salinity. Infiltration was very sensitive to relatively low drop energy. The major decrease in final infiltration rate was already achieved at drop energies lower than 10 J mm−1 m−2. Wash erosion increased exponentially with the increase in drop energy compared to a linear increase of the splash. Soil splash was approximately 2–3 times higher than wash erosion for any given drop energy. The threshold energy for soil splash initiation was 4–6 J mm−1 m−2, while for wash erosion (low exchangeable sodium percentage (ESP)) it was 2–4 J mm−1 m−2, and for the high ESP it was beyond the lowest energy we used (2.1 J mm−1 m−2).

Adsorption of Polyacrylamide and Polysaccharide Polymers on Soil Materials

Knowledge of adsorptive behavior of polymers is useful in predicting their mobility in soil, depth of effective treatment, and other factors related to soil physical conditions. Adsorption isotherms were determined by batch technique for six tritium labeled polymers on three soils, one of which was pretreated to create a high exchangeable sodium percentage (ESP) of 34, and on washed quartz sand of three size fractions. The three anionic polyacrylamide (PAM) compounds had negative charge density of 40J > 21J > 2J, and the three polysaccharide compounds (guar) had a higher positive charge (T-4141), a lower positive charge (CP-14), and a negative charge (T-4246). Adsorption of CP-14, 21J, and T-4246 was measured on montmorillonitic clay extracted from one soil and a specimen sample of montmorillonite clay. Adsorption of a given polymer on the low ESP soils was not significantly different, but was significantly higher on the high ESP soil. The adsorption isotherms were T-4141 ≥ 21J > CP-14 ≫ 40J ≥ 2J > T-4246, and adsorption on sand was only a little less than on soil. The adsorption on clay was CP-14 ≫ T-4246 > 21J. The data suggest that the PAM and guar polymers studied do not penetrate the aggregates, because adsorption was approximately the same for all soils of similar aggregate sizes. Molecular size, molecular conformation, and electrostatic charge each significantly affected the adsorption isotherms.

Flocculation of Reference Clays and Arid‐Zone Soil Clays

AbstractThe effect of electrolyte concentration, exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR), and pH on the flocculation‐dispersion behavior of reference kaolinite, reference montmorillonite, reference illite, and the clay fraction of three arid‐zone soils was investigated. The clay mineralogy of the soils was dominated by either montmorillonite, kaolinite, or illite. The clays were Na‐ or Ca‐saturated and freeze‐dried before use. Critical coagulation concentrations (CCCs) were investigated in the range of pH 5.5 to 9.5, ESP of (here equated with percent Na clay) 0, 5, 10, 20, 40, 60, 80, and 100, SAR of 0, 5, 10, 20, 40, 60, 80, and ∞, and using electrolyte concentrations of 0 to 500 mmolc L−1. The CCC values increased with increasing ESP, increasing SAR, and increasing pH. The pH dependence of kaolinite and illite was greater than that of montmorillonite at all ESPs and SARs. The CCC behavior of the soil clays resembled that of illite, especially in its pH dependence at ESP 100 and SAR ∞. The CCC values of the soil clays, kaolinite, and illite showed a sharp increase at high ESP and SAR, whereas montmorillonite showed a sharp increase in CCC at low ESP and SAR. The CCCs for all soil clays were similar in magnitude, despite their differing clay mineralogies. The CCCs for the reference clays were much lower than those for the soil clays, indicating that extrapolation from reference‐clay results is not possible, and that additional factors such as organic‐matter content and Al‐ and Fe‐oxide content may influence the dispersion of soil clays.

Effect of Clay Charge Density and Adsorbed Ions on the Rheology of Montmorillonite Suspension

AbstractThe rheological characteristics of montmorillonite suspension as a function of exchangeable sodium percentage (ESP), (when the complementary cation is either Ca2+ or Mg2+) and specific electrostatic charge density were studied in aqueous media at a clay concentration of 25 g kg−1, at pH 7 and temperature of 25 °C. The suspension showed a Newtonian rheology when the clay was saturated by either Ca2+ or Mg2+, but the differential viscosity (the derivative of shear stress with respect to shear rate at a given shear rate) of Mg‐clay (2.3 mPa s) was higher than that of Ca‐clay (1.5 mPa s). The higher value for the Mg‐clay suspension is due to the smaller average number of platelets in a tactoid of Mg‐montmorillonite than in the Ca‐montmorillonite suspensions. Introducing Na+ at a low percentage (10%) into the exchange complex of Mg tactoid was enough to break down some of the tactoids to smaller ones, whereas the Ca tactoids remained stable. The differential viscosity at high shear stresses increases with increases in ESP, showing higher values for Na/Mg systems at a low ESP range. At higher ESPs, no difference in differential viscosity between Ca and Mg systems was observed. The higher extrapolated shear stress values for Na/Mg‐montmorillonite suspensions suggest that the number of linkages between clay particles per unit weight of clay is higher than that found in Na/Ca‐montmorillonite for the same ESP and clay concentrations. The differential viscosity and the extrapolated shear stress values for the various smectites (the electric charge density varied between 0.91 and 1.22 molc kg−1) suggest that the extent of particle‐particle interaction in clay suspension decreases with increases in electrostatic charge density of smectites.

Effects of exchangeable sodium on crusting behavior of a sandy loam soil

Field and greenhouse studies were conducted at the Central Soil Salinity Research Institute, Karnal, India, to evaluate the effect of exchangeable sodium (ES), amount of water applied, and evaporation and temperature conditions at drying on the crusting behaviour of a sandy loam soil. The exchangeable sodium percentage (ESP) ranged from 5.8 to 30.7 in the field and from 6 to 60 in the greenhouse studies. Soil crusting behaviour was evaluated in terms of crust strength measured by a simulated seedling emergence technique. Water was applied as natural or simulated rainfall. Crust strength increased with ESP, amount of water applied, and temperature, but decreased with increasing evaporation demand. This change in crust strength was steep above ESP 30. Although drying of the crust increased its strength, beyond a certain degree of dryness the disappearance of water films surrounding the soil particles reduced strength for low ESP soils.

Corrigenda - Effects of exchangeable sodium on crusting behavior of a sandy loam soil

Field and greenhouse studies were conducted at the Central Soil Salinity Research Institute, Karnal, India, to evaluate the effect of exchangeable sodium (ES), amount of water applied, and evaporation and temperature conditions at drying on the crusting behaviour of a sandy loam soil. The exchangeable sodium percentage (ESP) ranged from 5.8 to 30.7 in the field and from 6 to 60 in the greenhouse studies. Soil crusting behaviour was evaluated in terms of crust strength measured by a simulated seedling emergence technique. Water was applied as natural or simulated rainfall. Crust strength increased with ESP, amount of water applied, and temperature, but decreased with increasing evaporation demand. This change in crust strength was steep above ESP 30. Although drying of the crust increased its strength, beyond a certain degree of dryness the disappearance of water films surrounding the soil particles reduced strength for low ESP soils.

Effect of soil texture and CaCO3 content on water infiltration in crusted soil as related to water salinity

The effect of soil texture and CaCO3 content on water infiltration rate in crusted soil was studied with the use of a rain simulator. Two types of soils with low exchangeable sodium percentage (ESP 400 mm winter rain. Soil samples with clay percentages between 3 and 60 were collected in each region. Distilled water (simulating rainfall) and saline water (simulating irrigation water) were sprinkled on the soil. The soils were exposed to ‘rain’ until steady state infiltration and corresponding crust formation were obtained. For both types of soils and for both types of applied water, soils with ∼ 20% clay were found to be the most sensitive to crust formation and have the lowest infiltration rate. With increasing percentage of clay, the soil structure was more stable and the formation of crust was diminished. In soils with lower clay content (< 20%), there was a limited amount of clay to disperse and, as a result, undeveloped crust was formed. Silt and CaCO3 had no effect on the final infiltration rate for either type of applied water, whereas with saline water, increasing the silt content increased the rate of crust formation.

Effect of exchangeable sodium and phosphogypsum on the hydraulic properties of several South African soils

The susceptibility of soils to the deleterious effects of sodicity was assessed for samples which varied with respect to physical, mineralogical and other properties. For this purpose soil samples were collected from different locations in South Africa. The effect of electrolyte concentration and sodium adsorption ratio (SAR) on hydraulic conductivity (HC) was determined with permeameters, while the combined effects of raindrop impact energy and low electrolyte concentration of rain on infiltration rate (IR) were assessed using a rainfall simulator. Soils proved to be either stable or susceptible to the effects of sodicity as indicated by modulus of rupture, air-water permeability ratio, HC and IR measurements. Sesquioxides and organic matter promoted stability. Final IR was always less than HC due to crust formation even at low exchangeable sodium percentage (ESP) levels as a result of the dispersive effects of both mechanical impact (physical disruption) of rain drops and low electrolyte concentration (chemical dispersion). When the chemical effect was reduced (ESP>1 or higher electrolyte concentration as a result of surface gypsum application), final IR was higher. S. Afr. J. Plant Soil 1985, 2: 179–186

Response of soils to sodic and saline conditions

The interaction between soil particles and the soil solution depends on the types and amounts of soil clays. Montmorillonite is the most reactive clay. Ca-clay forms tactoids (quasi crystals) and has limited swelling and dispersion. Na-clay forms single platelets and disperses freely. In a mixed Na/Ca system, “demixing” of the cations occurs as the Na ions concentrate on the external and the Ca ions on the internal surfaces of the tactoids. The demixing explains why a small percentage of exchangeable Na sharply increases the zeta potential and dispersion of montmorillonite clay. The hydraulic conductivity of a soil depends on both Na and the total salt concentration of the percolating solution. High hydraulic conductivity may be maintained, even at high exchangeable sodium percentage (ESP) values, if the solution concentration is above a critical (threshold) level. When waters of very low salt content are used, decreases in hydraulic conductivity and clay dispersion occur even in soils with low ESP values (<10). The main mechanism for hydraulic conductivity reduction in waters of medium to high salinity (replacecodegt0.5 dS/m) is clay swelling. High content of expansible clays increases the susceptibility of soils to intermediate (10<ESP<20) sodicity. The effect of low sodicity (ESP < 10) on clay swelling is minimal and the hydraulic conductivity of these soils is maintained at high values. When waters having low salt concentrations (salt concentration below the flocculation value of the clay) are used, clay dispersion, movement, and lodgement in the conducting pores comprise the main mechanism responsible for hydraulic conductivity reduction. These results occur even at low ESP. The most important soil property which determines its susceptibility to sodic conditions, when the soil is leached with rain or snow water, is the potential of the soil to release electrolytes from primary minerals and/or CaCO3 dissolution. Soils which release sufficient electrolytes to maintain the concentration of the soil solution above the flocculation value of the clay will not disperse, and thus will not be sensitive to low sodicity.

Effects of zero tillage and stubble retention on some properties of a cracking clay

Soil chemical and physical properties of a black cracking clay were measured after five years under a zero tillage and stubble retention trial. Stubble retention slightly increased the organic carbon content of the 0-10 cm layer, and the dispersion ratio of the 0-4 cm layer. Stubble retention increased dry aggregate size in the 0-4 cm layer of the zero tilled treatments, apparently due to a reduction in the rate of drying of the surface after rain. Changes in the distribution of cations in the surface soil developed in the absence of tillage, with lower exchangeable sodium percentage (ESP) and higher exchangeable potassium percentage in the 0-4 cm layer under zero tillage. The reduction in ESP in the 0-4 cm layer under zero tillage also reduced dispersion ratios. The ratio CEC : % clay for the 0-4 cm layer was reduced by zero tillage. Chloride profiles gave evidence for increased deep infiltration under zero tillage. This is attributed to the presence of cracks that were not closed by tillage.

EXCHANGEABLE SODIUM AND SOIL WATER BEHAVIOR UNDER FIELD CONDITIONS

The effect of exchangeable sodium on soil water behavior under field conditions was investigated in five differentially gypsum treated plots of a highly sodic soil. The soil is representative of the sodic soils of the Indo-gangetic plains in northern India. The soil texture is sandy loam in the surface 0–15 cm and the clay fraction is dominantly illitic. Exchangeable sodium percentage (ESP) varied from 4 to 38 in 0–15 cm and 28 to 88 in the 15–30-cm layer. Basic intake rate of the soil increased from 8.7 mm per day in soil of highest ESP to about 25 mm per day in soil of lowest ESP. Higher basic intake rate and increased retention at low suctions resulted in greater profile water storage. Soil water diffusivity values (D) calculated from the water distribution following evaporation showed that at a water content of 0.22 cm3/cm3 while D (cm2/day) decreased from 34 to 26 when ESP increased from 4 to 11, the D value sharply decreased to 8 with a further rise in ESP to 16. Improvement in transmission characteristic resulting from lowered ESP was reflected in the drying pattern of soils. The first stage of drying was delayed in low ESP treatments compared to the high ESP treatment because of regular movement of water from lower layers to the surface to meet the evaporation demand. The effect of treatments on water movement was noticeable to a depth of 90 cm studied in these experiments, although the improvement in layers below 15 cm was very small in treatments receiving lower doses of gypsum.

Emergence response of subterranean clover to dissolved gypsum in relation to soil properties and evaporative conditions

Using small plots set in the earthen floor of an open glasshouse, the emergence response of subterranean clover to dissolved gypsum has been determined on 10 soils covering a range of clay and exchangeable sodium levels. The response on a loam soil of low exchangeable sodium percentage (E.S.P.) has been examined at three times of differing evaporative potential. For loams and clay loams, the appearance of a response depends on the severity of evaporative conditions as well as on the E.S.P. On clay soils not naturally self mulching, some response is probably always obtained but, in general, the higher the clay content and the higher the E.S.P. and evaporative potential, the more likely is an emergence response to dissolved gypsum. Emergence was found to be highly correlated with the matric potential of the surface 1/2 in. at the time emergence began. From a consideration of the relationships between emergence and moisture status, the most significant effect of the gypsum treatment seems to be the delay of several days it causes in the air drying of the surface soil, probably because of improved transmission of moisture from beneath. Parallel effects on surface soil temperature to those on moisture can be explained in terms of differences in amount of evaporative cooling. Relationships found between emergence and emergence response to gypsum on the one hand and clay content and E.S.P. on the other are presumably a reflection of the relationship of these soil properties to porosity and moisture transmission.