Soil base saturation

Forest Soil base saturation of 20% or higher (i.e., the percent of available cations in the soil that are bases) Calcium to aluminum molar ratio in the soil solution of 1.0 or greater... 

The RAINS Lake Model RLM (Kam and Posch, 1987) assumes that only a few reactions between the soil and soil solution need to be considered to describe surface water chemistry. These include relationships between soil base saturation and soil solution pH and between the soUd and liquid phases of aluminium. The change in base cations and therefore base saturation is determined by the movements of acids and bases into and out of the soil. This change is defined as ... 

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

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. 

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. 

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. 

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%. 

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)... 

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. 

Alfisols Soils possessing Bt horizons with >35% base saturation commonly Pleistocene aged... 

Mollisols Soils possessing a relatively dark and high C and base saturation surface horizon commonly occur in... 

Many approaches to the study of paleosols are unlike those of soil science, and more like soil geochemistry prior to the earlier part of the twentieth century (Thaer, 1857 Marbut, 1935). Such measures of soil fertility as cation exchange capacity and base saturation that are used for characterizing surface soils (Buol et al, 1997) are... 

In 1993 epoxy- lysulphide based coatings were used to coat two 250 MW thermal power projects at Dhanu, about 100 km north of Bombay. The site is on the coast, less than 1 km from the sea and as such the nature of the local atmosphere is highly corrosive, with continuous sea breezes, and the soil is saturated with marine salt. The coating has shown satisfactory performance (Figure 10.7) (Morton International, undated c). This project was constructed under the control of Bombay Suburban Electricity Supply Co. Ltd (BSES). 

Mollisol. A soil consisting of a relatively thick, dark-colored surface horizon that contains at least 0.58% organic carbon, has a base saturation of more than 50% (pH 7), and is predominantly saturated with bivalent cations. 

In the plains, Cambisols place the most drainage areas. These soils occupy the hilly plains and low mountain belts up to the 500-700 m elevation, where they coincide with the Broadleaf and Coniferous-Broadleaf Forest ecosystem types. In the most continental parts the oak forests are dominant. For instance, at the slopes of the Sikhote-Alin range Cedar-Broadleaf Forest and in Korean peninsula, the Oak-Maple Forest ecosystems are predominant. In Japan Beech Forest ecosystems are the most abundant. Heavy precipitation rates during wet season (up to 1000-1200 mm with P PE equal to 1) favor the increasing base saturation in the Luvic Cambisols. These ecosystems are characterized by a moderate rate of organic matter turnover with mean values of Cb equal to 2.5 C, is 0.67 and Cbr is 1.7. Such moderate rates are favorable to soil acidification with deposition input of sulfur and nitrogen acid forming compounds (NIES, 1996, Bashkin and Park, 1998). This process can be especially enhanced in... 

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