Clay soils characteristics

For studies involving test substance application to soil, there may be a requirement for more soil information than for studies where applications are made to foliage of established crops. The study protocol should describe any specific requirements relative to soil type selection and how to confirm the soil characteristics for the study. Most studies simply require that the soil be identified by its name (e.g., Keystone silt loam) and composition (e.g., percent sand, silt, and clay). This information can typically be acquired from farm records, a soil survey of the local area, or a typical soil analysis by a local soil analysis laboratory. In some instances, a GLP compliant soil analysis must be completed. The study protocol must clearly define what is needed and how it is to be obtained. Unless specified in the protocol, non-GLP sources are adequate to identify the soil and its characteristics. The source of the soil information should be identified in the field trial record. 

Drainage class, tile drainage, soil characteristics, and initial SOC levels can also impact SOC maintenance requirements (Arrouays and Pelissier 1994 Zach et al. 2006 Clay et al. 2007). If the SOC maintenance requirement is related to the SOC level, then the range of values reported by Barber (1978), Wilts et al. (2004), Larson et al. (1972), and Frye and Blevins (1997) may be related to these differences. To assess the impact of SOC level on maintenance requirements, data from Barber (1978), Wilts et al. (2004), Larson et al. (1972), and Frye and Blevins (1997) were analyzed using the Clay et al. (2006) approach (Table 8.1). For these calculations, a common soil depth (0-15 cm) and root to shoot ratios suggested by Johnson et al. (2006) were used. Across the sites, located in the central USA, the analysis suggested that in plowed fields, 15.5% of the SOC contained in the surface 15 cm must be returned annually (Fig. 8.5). The 0-15 cm soil zone was selected because soil data from this zone are available in many studies. 

Absorption Derivation of a relationship with soil characteristics such as pH, organic matter content, clay content and CEC... 

Basic soil characteristics, horizonation, texture, clay, air, water, solids, organic matter, organisms, and fundamental chemical concepts essential to soil chemistry... 

Vary the parameters within the above ranges. How does the soil type affect the transport of solutes Modify the model so that the soil characteristics vary with depth, e.g., a sandy soil near the surface becoming clay deeper below the... 

Of the various equilibrium and non-equilibrium sorption isotherms or sorption characteristics models, the most popular are the Langmuir and Freundlich models. The correct modeling of an adsorbate undergoing both transport and adsorption through a clay soil-solid system necessitates the selection of an adsorption isotherm or characteristic model which best suits the given system. The use of an improper or inappropriate adsorption model will greatly affect the... 

Kahnt, G., Pfleiderer, H. and Hijazi, L.A. 1986. Effect of amelioration dosed of rock powder and rock sand on growth of agricultural plants and on physical characteristics of sandy and clay soil. Agronomy and Crop Science 157 169-180. 

A wide variety of soils and sludge have now been treated. Soil characteristics that can impact the SET chemistry include the general soil type, which is treated (loam, sand, silt, and clay), the presence of humic material, the pH value, the soil s cation exchange capacity, its particle size, the amount of water present, and the iron content. Processes have been engineered to accommodate this wide range of variables [7,8,34]. Some soils can be treated... 

Bouabid, R., M. Badraoui, and P. Bloom. 1991. Potassium fixation and charge characteristics of soil clays. Soil Sci. Soc. Am. J. 55 1493-1498. 

More complex covers may be comprised of several layers, each with different soil characteristics. A cover installed at the Bersbo site in Sweden included layers of fine-grained clay, coarse-grained aggregate material, and a protective layer of natural till (Lundgren, 2001). 

Bedcett and Davis [ 3 ]define the upper critical level of an element either in plant or in soil as the concentration at which yield is first reduced. According to the same investigators, phytotoxic effects of a potentially harmful element depend mainly of the concentration in the plant tissue, so that the upper critical level for a certain plant species would be a fixed content. On the other hand, due to changing soil characteristics (CEC, pH, % C, % clay ) affecting the availability of an element for different soil types, the upper critical level in the soil is a variable concentration. Determination of the upper critical level in the plant may be obtained by plotting the yield versus the concentration in the plant (Fig. 1) [ 4 ]. 

Use Research aid for studying water purification, calcium exchange in clays, detergency, surface wetting and other surface phenomena, calcium uptake and deposition in bone, soil characteristics as related to soil utilization of fertilizer and crop yield, diffusion of calcium in glass, etc. 

Technological characteristics of the soil. Clay soils are more cohesive, sticky, and thus mechanically more difficult to treat as compared to sandy soils [5]. 

The condition for uptake of the pesticide by the plant is given by its persistence or system characteristics. The most persistent pesticides are particularly organometallic (most of them organomercury) compounds or derivatives of chlorinated hydrocarbons. Depending on the concentration in the soil, they can be identified especially in root crops, carrot, radish, beet, potatoes and plants giving oil. The rate of uptake of these substances by plants are different even in the case of substances with a similar persistence [29, 30]. The uptake can also be different in the case of identical plants [31]. Solid pesticides penetrate more easily into agricultural products from sandy and clay soils [32]. 

Waterlogged mineral soils are those in which part or the whole soil profile is saturated for a sufficient period of time to create distinctive gley horizons in the profile. These soils can be sandy, loamy, or clay soils. The other most commonly referred term is flooded soils. We confine our discussion in this group primarily to mineral soils. The distinctive characteristics of these soils are... 

Restoration of the protective properties of artificial sorption screens created on the ways of radioactive nuclide naigration from accumulating ponds is no less an important problem. Usually, clay soils with high sorption ability and containing such minerals as smectite and illite are applied for constructing such screens. In addition, artificial protective screens made of other disperse soils (from sand to loam) are applied the sorption ability of such soils is artificially enhanced beforehand with strengthening compoundssuch as oxalic silica-alumina gel. These compounds decrease the filtration ability of the screen and raise its sorption characteristics. 

As noted in Table I, the term clay refers to that part of the soil that is composed of particle sizes less than 2 /u.m. However, the term clay also can refer to the clay mineral content of a soil regardless of the particle size. Finally, the term clay often is used to denote a soil mass that possesses properties similar to those of a pure clay even though only a relative small percentage of the overall soil mass consists of clay-sized particles and/or clay minerals. For example, mixtures of sand and bentonite, a high-swelling clay, containing 4-10% (w/w) of bentonite typically possess some properties that are characteristic of clay soils, even though 90% (w/w) or more of these mixtures is made up of sand. 

Grim (1952) distinguished two modes of swelling in clay soils, namely, intercrystalline and Intracrystalline swelling. Intercrystalline swelling takes place when the uptake of moisture is restricted to the external crystal surfaces and the void spaces between the crystals. Intracrystalline swelling, on the other hand, is characteristic of the smectite family of clay... 

Table 20.1 Comparative physical characteristics of sohd wastes generated from hazardous and non-hazardous sources over sand and clay soil... 

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