Base saturation

Acidification the decrease of acid neutralizing capacity in water or base saturation in soil caused by natural or anthropogenic processes. 

Mollisols Thick, dark A horizon with high base saturation Temperate grasslands... 

Alfisols Bt horizon with moderate base saturation Temperate deciduous forests... 

Ultisols Low base saturation and Bt horizon Tropical to temperate, often forested... 

Physico-chemical characteristics of the soils were summarized in Table 1. The values were comparable to that described in the previous reports about the SERS (Doi and Sakurai 2003 Doi et al. 2004 Sakurai et al. 1998). The one-way ANOVA indicated that most of the soil variables significantly reflected the land degradation with high values of bulk density, sand content and exchangeable acidity, and low values of moisture content, pH, OM, base (K, Ca, Mg) contents, EC, CEC, base saturation rate, TN and TC contents, available phosphorus and MPN on the glucose medium with no antibiotics. These results also told that the human activities induced several soil environmental gradients. 

Method 5.2. Cation exchange capacity, exchangeabie bases and base saturation... 

The TEB value may be obtained by either the sum of the individually measured cations or by evaporating and igniting a portion of the ammonium ethanoate leachate to convert the metallic cations to oxides and carbonates, followed by addition of excess acid (to convert carbonates to chlorides) and back-titration with alkali. The latter method is difficult if the soil is insufficiently base-rich to provide an adequate amount of bases for the titration. On the other hand, the calcium carbonate in calcareous soils may be partially leached by the ammonium ethanoate at pH 7.0 in addition to the exchangeable bases and thus give an exaggerated TEB value and a percentage base saturation in excess of 100%. The TEB by ignition/titration can serve as a check on the values from the summation method. 

If the percentage base saturation as defined above is 60%, this provides an indication of the need for estimation of exchangeable aluminium and hydrogen, in addition to calcium and magnesium, by the ECEC procedure. 

Stone, D.M., A.R. Harris, and W.C. Koskinen (1993). Leaching of soil-active herbicides in acid, low base saturated sands Worst-case conditions. Environ. Toxicol. Chem., 12 399-404. 

The insolubility of Al(OH)3 and the diffusion of C02 to the atmosphere drive this reaction to completion. Also, adsorption of cations onto the colloid complex raises the percentage base saturation (extent to which the colloidal complex is saturated with exchangeable cations other than hydrogen and aluminum, expressed as a percentage of the total cation exchange capacity) of the colloidal complex, increasing the pH of the soil solution accordingly. 

Bukowski R, Jeziorski B, Szalewicz K (1996) Basis set superposition problem in interaction energy calculations with explicitly correlated bases saturated second- and third-order energies for He2. J Chem Phys 104 3306-3319... 

Soil CEC is composed of two types of constituents (1) weak Lewis acid metals, commonly referred to as bases (e.g., Ca2+, Mg2+, K+, and Na+) and (2) relatively strong Lewis acid metals, H+, and heavy metals, depending on the nature of the sample, for example, geologic waste or natural soil (Al3+, H+, Fe2+, Fe3+, and Mn2+). The term percent base saturation is commonly used to describe the percent of the sum of exchangeable bases relative to the CEC near pH 7 or at pH 7 (CEC ). The equation for percent base saturation is given as... 

Figure 3.43. The relationship between soil suspension pH and percent base saturation (from Magdoff and Bartlett, 1985, with permission).

An empirical relationship between pH and percent base saturation is shown in Figure 3.43. This relationship appears to be linear, but this does not imply any mechanistic molecular meaning, because soils or clay minerals contain many different functional sites. The general behavior of these data, however, is of practical value. For example, a sample with base saturation of approximately 20% will exhibit a pH of approximately 5, while a pH of approximately 7 suggests a percent base saturation of 100%. 

Based on your calculations in problems 17 and 18, estimate the percent base saturation of the sample and discuss its practical significance. 

Soil pH buffering appears to play a major controlling role in NH3 volatilization. The potential of soil to buffer pH depends on mineralogical composition, percent base saturation, type of exchangeable cations, and CEC. An empirical formula for soil pH buffering, noted as B, is given by (Avnimelech and Laher, 1977)... 

Brpnsted theory, 23 Definition of Kb, 38 Lewis theory, 24 HSAB theory, 12 Base saturation (%), 163 Basic organic compounds, 356 Bicarbonate, 30-33 Biotite, 104, 108 Boltzmann equation, 143 Bonding, 6-12 Covalent, 7 Ionic, 7 Boron, 127 Buffer capacity, 86... 

The % base saturation is a measure of the amount of the CEC of a soil holding the major cations (also called exchangeable bases) Ca " ", Mg ", K+, andNa+. 

Worked example 5.9 - cation-exchange capacity and % base saturation One method to measure the CEC of a soil is to leach a column containing a known weight of soil with a solution of a salt so that the exchange sites are saturated with the cation (index ion). After washing out the excess salt solution, a different salt solution is leached through the column and the exchangeable ions displaced, collected in a known volume and their concentration measured. 

Soils vary greatly in composition and reactivity. Many complex and dynamic processes occur continuously in most soils composed primarily of mineral and organic matter, water, and air. The soil atmosphere is composed of oxygen, carbon dioxide, nitrogen, and several minor gases whereas the mineral fraction varies in amounts of sand, silt, and clay and in types and amounts of clay minerals. Moreover, hydration and base saturation of the clay minerals also vary considerably. The organic matter and mineral colloids present in the soil contribute directly and indirectly to the extremely active nature of pesticide-soil systems. Since soil water contains many soluble compounds, it serves as an essential medium for many chemical and physical processes. The extreme complexity of these soil systems has been the primary reason that so few fundamental studies have been undertaken involving the ultimate fate of pesticides in soils. 

Separation of an Asphalt—Method 2. Asphalt samples were separated into six fractions acids, bases, saturates, aromatics-1, aromatics-2, and aromatics-3. Acids were isolated using anion exchange resin, and bases were isolated using cation exchange resin. The remaining fraction (asphalt, less acids and bases) was separated on alumina using the same procedure as in Method 1 for the separation of maltenes. The separation scheme is shown in Figure 3. 

Studying chronosequences of pastures in Para and Mato Grosso, Falesi (1976) found that the pH, ECEC, and base saturation of the topsoil remained elevated in all pastures. The... 

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