Sodium adsorption

SAR Sodium Adsorption Ratio - this ratio expresses the relative activity of sodium ions in the exchange reactions with the soil. 

This is defined as the relative concentration of sodium to calcium plus magnesium, and is represented by a parameter known as the sodium adsorption ratio (SAR). The absolute concentration values of the different cations in irrigation water are not adequate for estimating probable hazards. An important consideration is the extent to which the exchangeable sodium percentage (ESP) of the soil will increase as a result of adsorption of sodium from the irrigation water. The higher the ratio, the... 

Soil structure. High salt concentrations, and high sodium adsorption ratios in particular, adversely affect the physical properties of the soil (Davidson Quirk, 1961), altering such parameters as particle size and hydraulic conductance. 

Handy, R. D. and Eddy, F. B. (1991). Effects of inorganic cations on sodium adsorption to the gill and body surface of rainbow trout, Oncorhynchus mykiss, in dilute solutions, Can. J. Fish. Aquat. Sci., 48, 1829-1837. 

Sodium Adsorption Ratio. Because of the swelling effects of Na+, the relative amount of sodium (sodicity) in the water quality especially in the irrigation water quality is an important measurement in soil science. Decreased permeability can interfer with the drainage required for normal salinity control and with the normal water supply and aeration required for plant growth. The relative sodium status of irrigation waters and soil solutions is often expressed by the sodium adsorption ratio (SAR)... 

The selectivity of the exchange between two cations is specific to saline snbsnr-face systems, described by the sodium adsorption ratio (SAR). Based on Na content in soil solutions, the U.S. Salinity Laboratory (U.S. Salinity Laboratory 1954) derived the equation... 

Fig. 8.26 Exchangeable sodium percentage (ESP) along a Burleson soil column, as a function of the sodium adsorption ratio (SAR) of irrigation water. The values were obtained by percolating the soil columns with sodic water (total electrolyte concentration of 11 meq/L). Each curve corresponds to a given applied volume of solution (Thomas and Yaron 1968)...

Panayiotopoulos KP, Barbayiannis N, Papatolios K (2004) Influence of electrolyte concentration, sodium adsorption ratio, and mechanical disturbance on dispersed clay particle size and critical flocculation concentration in alfisols. Comm Soil Sci Plant Anal 35 1415-1434... 

TABLE 10.1. Sodium Adsorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP) Values Associated with 20% Reduction in Saturated Hydraulic Conductivity (SHC) for Pembroke Soil (10- to 30-cm Incremental Depth) at Three pH Values... 

The sodium adsorption potentials of two humid soils are presented in some detail and the SAR-ESP data are shown in Figures 11.1-11.4. For comparison purposes, these figures also include the SAR-ESP relationship of salt-affected soils found in arid-region soils (western United States). Figures 11.1-11.4 show that for any given SAR, the ESP for either one of the two humid soils is greater than the ESP of the western U.S. soils. This indicates that the two humid soils adsorb sodium on their exchange complex more effectively than the western U.S. soils. 

Oster, J. D and G. Sposito. 1980. The Gapon coefficient and the exchangeable sodium percentage-sodium adsorption ratio relation. Soil Sci. Soc. Am. J. 44 258-260. 

Yadav, J. S. P. and I. K. Girdhar. 1980. The effects of different magnesium calcium ratios and sodium adsorption ratio values of leaching water on the properties of calcareous versus noncalcareous soils. Soil Sci. 131 194-198. 

The effect of using the sodium adsorption isotherm (equation 6) to determine the apparent diffusion coefficient can be seen by... 

Rundberg R.S., Albinsson Y, and Vannerberg K., Sodium adsorption onto goethite as a function of pH and ionic strength, Radiochim. Acta, 66/67, 333, 1994. 

The typical compositional range of exchange sites in soils, shown in Figure 8.4, reveals that sodic soils have higher than normal levels of exchangeable Na" ". The important ionic concentrations in soil solution that affect the level of exchangeable Na are [Na" ], [Ca " ], and [Mg +], The sodium adsorption ratio, or SAR, is a solution property defined by the equation... 

Figure 1. Na on Quartz Comparison of experimental (29) and simulated adsorption and zeta-potential data. Modeling parameters for surface ionization and sodium adsorption are given in Table I. Surface site concentration Z SOH = 7.06 x 10 M.

The [Ca2+ + Mg2"1-] tenn was necessary because many early water analyses did not distinguish between the two ions. The left side of Eq. 8.21 was termed the ESR (exchangeable sodium ratio). The solution concentration ratio on the right side was termed the SAR (sodium adsorption ratio). The SAR is written as [Na+]/([Ca2+ + Mg2+]/2)1/2 when the concentration units are millimoles of charge per liter. The reduced ratio (r) of the double-layer exchange equation (8.19) is equal to the SAR divided by (1000)1/2. 

Two parameters are used to measure and evaluate the effects of excess sodium in soils. These are the sodium adsorption ratio (SAR) and the exchangeable sodium percentage (ESP). SAR is a parameter used to describe the composition of irrigation water or existing soil solution and is used to predict the ESP. SAR is defined by the equation... 

Fig. 32. Sodium adsorption on Ni(llO). Close-packed columns of Na atoms (shaded) lie in every other trough of the nickel substrate. There is no positional correlation in placements of neighboring Na columns. The Na—Na spacing within each column is not related to the Ni—Ni spacing along the trough direction 166).

If the water used for irrigation contains plenty of Na and little of Ca, the cation exchange may result in saturation of the soil with the alkaU metal. Because of this the soil disintegrates into clay particles, which makes its agricultural properties worse. For evaluating the excess of sodium in these waters is often used the coefficient of sodium-adsorption ratio... 

For a given eroding fluid, the boundary between the flocculated and deflocculated states depends on the value of the sodium adsorption ratio. The sodium adsorption ratio, SAR, is used to quantify the role of sodium where free salts are present in the pore water and is defined as ... 

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