Saturated extract

Table 3.1. The major ion composition of dispersed soil solutions and saturation extracts from selected soils in California, U.S. 

Solution/Solid Phase Solution phase (water soluble, saturation extracts) > Solid phase... 

Plant Soil pH DTPA Extract Saturation extract Shoots/leaf Yeild... 

Element USa,b Total mg/kg Southern California0 Total Saturation extract mg/kg mg/L Israeld Total mg/kg... 

Mahler R.J., Bingham F.T., Sposito G., Page A.L. Cadmium-enriched sewage sludge application to acid and calcareous soils Relation between treatment, cadmium in saturation extracts, and cadmium uptake. J Environ Qual 1980 9 359-364. 

The major ion composition of dispersed soil solutions and saturation extracts from selected soils in California, U.S. Concentrations of trace elements in soil solutions of the California soils that received sludge applications. Concentrations of trace elements in soil solutions extracted by saturated paste from two metal salt-spiked Israeli soils incubated at saturated regime. 

Fio, J.L. and Fujii, R. (1990) Selenium speciation methods and application to soil saturation extracts from San Joaquin Valley, California. Soil Sci. Soc. Am. J., 54, 363-369. 

HPLC Dilute with H20, Na carbonate added to saturation, extract with ether, centrifuge... 

The immediate source of nutrient elements for plants is the soil solution but there is a paucity of information concerning its composition especially for micronutrients. A number of practical problems arise in studying the soil solution and the first is actually getting a sample of it. The soil solution can be removed for analysis by centrifugation or direct suction. Some workers prefer a saturation extract , when the soil is allowed to equilibrate with water which is then extracted by mild suction. The solutions extracted by these techniques are very dilute and consequently not stable chemically. They present considerable analytical problems although these have eased in recent years now that very sensitive flameless atomic absorption methods have become widely available. 

The soil solution is dominated by the major cations calcium, magnesium, potassium and sodium whose solution concentrations are typically up to 2 to 3 mmol L"1. In contrast, the concentrations of microntrients tend to be at the micromolar level. For example, in saturation extracts of Californian soils the following concentrations were measured Co = 1.0, Cu = 0.6, Fe = 0.9, Mn = 3.1, Mo = 7.6 and Zn = 1.1 pmol L-1, respectively (Bradford et al 1971). 

These methods were selected for different reasons, but mainly for their flexibility and novelty. Rhizon samplers represent the current equivalent of porous cups, widely used in the recent past centrifugation is possibly the current most widely used method because of the ease and the ready availability of the requisite equipment in most laboratories squeezing is a novel alternative, since it has been used on soils recently (Di Bonito, 2005) and has the potential to access water contained in small pores soil suspension or saturation extracts constitute a valid alternative, especially when batch experiments are carried out (Degryse et al., 2003). Furthermore, these methods are capable to perform fractionated extraction on the soil, whereby a combination of the methods can be used to provide soil water originating from a wider range of pores, which can present a variety of interactions with the soil matrix and possibly different chemistry. 

TABLE 11.2. Crop Sensitivity to Salts, Based on the Saturation Extract Test... 

Distribution of metals and ligands (% of total) in saturation extracts of some sewage sludge amended soils... 

Figure 11.1. Cd uptake by com shoots against molar concentrations of CdCl+ and Cd in saturation extracts of soils. (Redrawn from Sposito and Bingham, 1981 copyright 1981, Taylor Francis, Ltd., www.tandf.co.uk/joumals.)...

For soil classification purpose the conductivity of saturation extracts of soils is required. However, extraction of solution from a saturated paste is very difficult process. As an approximation, the conductivity of the water extracts from a 1 2.5 soikwater suspension is determined and the conductivity of the saturation extract is calculated as EC (saturation extract) = E.C (1 2.5 extract) x 250/saturation percentage. 

This does not hold good for soil containing gypsum for which saturation extract must be obtained. 

FIG. 2.4 Extraction is initiated with the aqueous hydrotrope solution at A, saturation extraction at B. The total composition along BC when water is added. The extracted compound, saturated with water, is separated E, while the aqueous solution changes along BD. Evaporation of water gives DF and the process is repeated. 

Textural analysis was conducted using temperature-controlled water baths and the Bouyoucos hydrometer method ( 8) with 2 modifications. First, soil samples were agitated for 20 seconds with plastic plungers instead of mixing the soil by inverting the container, and second, the clay suspension was not washed and sieved to determine fractional sizes. Organic matter percentages were determined with a dichromate reduction method (9). Electrical conductivity (ec) and pH were measured from the saturation extract of... 

Procedures based on extraction with deionised water, dilute calcium chloride (0.01 M CaCl2) potassium chloride (1M KC1), saturated sodium fluoride (NaF) and hydrogen peroxide (H202) have been described. All procedures (except for H202 which ideally uses field-moist soil) are based on the use of air-dry soil of <2 mm particle size. No correction for water content is made when reporting pH results. The soil/solution ratio and the temperature of measurement should be noted on the report, as other soil/solution ratios are often used. These include saturation extracts and soil/solution ratios of 1 1 and 1 2.5. 

From analyses of saturation extracts and exchangeable cation concentrations for a large number of soils from the western United States, the statistical relation of ESR... 

FIGURE 11.3. The steady-state profile of soil salinity, expressed as the electrical conductivity of the saturation extract, in lysimeters. The irrigation water has EC values of 2 (solid lines) and 4 (dashed lines) dS m "1. Numbers on the figure are the respective leaching fractions. 

More recently salinity has been measur ed in terms of tire electrical conductivity (EC) of a solution. In addition to overcoming some of the ambiguities of TDS measurements, the EC measurement is quicker and sufficiently accurate for most purposes. To determine the EC, the solution is placed between two electrodes of constant geometry, including constant distance of separation. When an electrical potential is imposed, the electrical current varies directly with the total concentration of dissolved salts. The current is inversely proportional to the solution s resistance and can be measured with a resistance bridge. Conductance is the reciprocal of resistance and has units of reciprocal ohms or siemens (formerly mhos). The EC of the saturation extract of the soil measures the salinity of the soil. 

FIGURE 11.4. Influences of adjusted SAR of the Irrigation water upon the SAR of saturation extracts from Pakistani soils after three years of cropping. (From R. S. Ayers and D. W. Westcot. 1976. Water Quality for Agriculture. Food and Agriculture Organization of the UN, Rome.)... 

The traditional classification of salt-affected soils in the United States has been based on the soluble salt (EC) concentrations of extracted soil solutions and on the exchangeable sodium percentage of the assodated soil. The dividing line between saline and nonsaline soils was established at 4 dS m-1 for water extracts from saturated soil pastes. Salt-sensitive plants, however, can be affected in soil whose saturation extracts have ECs of 2 to 4 dS m l. The Terminology Committee of the Soil Science Sodety of America has recommended lowering the boundary between saline and nonsaline soils to 2 dS m-1 in the saturation extract. 

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