Soil color value

The use of organic components increases the discrimination in soils that are otherwise similar. For example, soils that have identical Munsell color values could be discriminated by subtractive FTIR. A new ancillary method using thermal gravimetric analysis in addition to IR analysis on samples prior to and after pyrolysis has been applied to soils and could give additional valuable information for the discrimination of soils (Thermo electron corporation application note 50862). 

The tolerance to high pHs is important in particular for industrial processes using reactive azo dyes, which are usually performed under alkaline conditions. A strain of C. bifermentans selected from a contaminated soil was tested for the ability to decolorize Reactive Red 3B-A at pHs from 5 to 12 while no decolorization was observed at pH 5, the dye was nearly completely decolorized across a broad range of pH values (6-12) after 48 h of incubation in this study a previous analysis of UV/Vis spectra of Reactive Red 3B-A, Reactive Black 5, and Reactive Yellow 3G-P after 0, 12, 24, and 36 h incubation was carried out, showing different decolorization rates for the three dyes, with no change in color content in the abiotic control [5]. 

Interestingly, the pH value of soil will alter the color of certain flowers. 

Alkalinity has to be measured in the field because C02 is often pressurized in groundwater (due to addition of C02 from soil and other underground sources). Upon exposure to the atmosphere some C02 may leave the water, causing part of the HCO3 to break down. For these reasons it is highly recommended that alkalinity be determined in the field. Field-measured alkalinity values are needed for water-rock saturation calculations. Various setups are available for alkalinity measurements in the field by titration of the sample with an acid and pH coloring indicator. 

Except for extracts with anhydrous EDA, data in Table 4 were obtained for humic substances isolated from an air-dried H+-exchanged humic histosol soil. For extractions with pyridine, A,A-dimethylformamide (DMF), di-methylsulfoxide (DMSO), and sulfolane, soils (60 g) were thoroughly mixed with the appropriate solvent (250 cm ). After centrifugation the residues were repeatedly extracted with water until the supernatants were only faintly colored. Supernatants for each of the solvent systems were combined and the pH values of the solutions were adjusted to 1.0 using 5M hydrochloric acid. Humic and fulvic acids were separated by centrifugation. 

Data for the tropical soils provide information about differences in the behavior of DMSO (Table 9). The adsorbance values show, as would be predicted, that sodium hydroxide extracted most organic materials from the H -exchanged soils, and that 0.1 A/ base was generally better than 0.5M base. exchanging had little influence, as might be predicted, and excess salt suppressed solubilization. Again, the addition of acid to DMSO increased solubilization of the colored humic substances. Furthermore, the addition of acid dispenses with the need to H+-exchange the soils prior to extraction with the solvent. 

Suppose that in a particular soil solution all indicators with EX values above + 200 millivolts converted to their reduced forms (which tend to be colorless), but all indicators with EX below -f 200 millivolts remained in the oxidized (colored) form. The Eh of the solution must then have been very near +200 millivolts. Methylene blue, which is intensely colored in the oxidized state, has been used as an indicator of the onset of strongly reducing conditions in soil solutions. It becomes colorless at an Eh of about +11 millivolts, assuming a pH of 7 (see Table 7.2). 

Humic acids - the fraction otf humic substances that is not soluble in water under acidic conditions (pH < 2) but is sol uble at higher pH values. They can be extracted from soil by various reagents and which is insoluble in dilute acid. Humic acids are the major extractable component of soiL humic substances. They are dark brown to black in color. 

Sodic (black alkali) soils are a particularly difficult management problem. The water permeability of these soils to water is very slow. The pH of sodic soils is commonly greater than 9 or 9,5, and the clay and organic fractions are dispersed. Dispersed organic matter accumulates at the surface of poorly drained areas as water evaporates and imparts a black color to the surface, hence the name black alkali. Sodic soils are found in many parts of the western United States. In some locations they occur in small patches, slick spots, less than 0.5 ha in extent. Such patches occupy slight depressions, which become accentuated as surface soil particles disperse and are blown away by wind erosion. The percolation of insufficient water to satisfy plants and to control salinity is the main problem associated with sodic soils. In addition, their relatively low soluble-salt concentrations and high pH values can result in direct Na toxicities to the most sensitive plants. 

Such simple models need validation and for this reason ETAD is conducting in a field study to investigate some representative dyes (at manufacturing sites and dyehouses) under a project termed Pathways of Colorants to the Environment. The environmental risk posed by a colorant is a function of both its inherent ecotoxicity and the concentrations attained in the environmental compartments. Unlike other substances eg, household detergents) which are emitted continuously, dyes releases result mainly from batch processes and result in spatial and temporal peak emissions. Obviously, short-time concentrations should be compared with acute data on ecotoxicity, whereas long-tom residual concentrations need to be cranpared with chronic effect levels. Because, data on chronic effects are not often available, empirical information serves as a basis for the effects assessment, ie, the extrapolation to a Predicted No Effect Concentration (PNEC). This PNEC value is to be compared with the so-called Predicted Environmental Concentration (PEC) in order to estimate safe levels of residual dye in the environment. Since it is the dissolved state in which a dyes may become biologically available, it is the aquatic environmental compartment which is primarily addressed here. Nonetheless, some consideration of the impact of dyes on sewage and soil is also included. 

Humic and fulvic acids are defined on the basis of the procedures used in their isolation. Humic acid is the colored organic material which is extracted from soils by a strong alkaline solution and which is insoluble in aqueous solutions of pH values less than about two. Fulvic acid, however, is the colored organic material which is soluble in basic and acidic solutions. 

Dark Surface. For use in LRRs N, P, R, S, T, U, V, and Z. A layer 10 cm (4 in.) or more thick starting within the upper 15 cm (6 in.) of the soil surface with a matrix value 3 or less and chroma 1 or less. At least 70% of the visible soil particles mnst be covered, coated, or similarly masked with organic material. The matrix color of the layer immediately below the dark layer must have chroma 2 or less. 

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