Soil texture mineral matter

Soils also display a wide range of physico-chemical characteristics that influence the bioavailability of toxic metals to microorganisms, fauna, and plant roots. These characteristics include soil texture, organic matter, cation and anion type, pH, or alkalinity. The presence of colloidal clay minerals in soils greatly increases the... 

Indicates the pore space available for water and roots influenced by soil composition (mineral content, mineral type, and organic matter) and soil texture Affects adsorption of the chemical Affects the surface area where adsorption can take place Influences partitioning and availability of chemicals Affects ability of a soil to transmit water or air Dictates the porosity of the soil Affects the form, reactivity, solubility, availability, and toxicity of some contaminants Affects the toxicity of some substances (mainly heavy metals) with binding or antagonistic mechanisms, for example, by alkaline-earth metals and aluminum Organic matter content, type, and % carbon Influences soil sorption properties for heavy metals and... 

The most important master variables of soils which control element availability can be generalized as follows pH and redox potential texture organic matter (quantity and quality) mineral composition temperature and water regimen. Interactions... 

Soil is a complex matrix consisting of air pockets, water, mineral matter and organic matter. It can vary enormously in its composition and texture and consists of various layers with different properties. The upper layer, which is more directly involved in the input of chemical substances and where distribution and fate processes are more complex, is the so-called vadose or unsaturated zone. This means that the pore spaces in the soil materials are not fully filled with water. Below the vadose zone, there is the saturated zone, where pore spaces are completely filled with water. The top of the saturated zone is the water table, corresponding to the level to which water will rise at atmospheric pressure in a hole dug in the earth. 

When soluble copper salts are added to organic soils most of the copper is fixed in the zone of placement. For this reason toxicity is seldom observed in such soils even where hundreds of pounds per acre are added (Gilbert, 1952). Most medium-textured mineral soils can also fix copper but in much smaller amounts. The higher the percentage of organic matter in mineral soils the greater is the capacity for fixation of copper. 

If mechanically analysing a soil, the organic matter, stones and gravel are first removed. The rest of the mineral fraction is separated using sieving and sedimentation techniques. This gives an accurate measurement of the amount of elay, silt and sand particles present. The particle size for eaeh mineral fraetion is shown in Table 3.1. Because these mineral eomponents have very different properties it is important to know the relative amount of each, hence the importance of knowing the soil texture. Soil texture is classified into 11 textural elasses in the UK (see Appendix 1). 

Soil is a relatively thin layer of unconsolidated matter on the surface of the earth, in which there is biological activity. The bulk of most soil consists of a mixture of extremely small, loose particles of minerals and organic matter the mineral particles are derived from the weathering of rocks the organic matter from the dead remains of living organisms (Rowell 1994 Limbrey 1975). The composition and texture of the soil are altered by human habitation humans change the natural flora and fauna of entire areas, their activ-... 

The clay fraction, which has long been considered as a very important and chemically active component of most solid surfaces (i.e., soil, sediment, and suspended matter) has both textural and mineral definitions [22]. In its textural definition, clay generally is the mineral fraction of the solids which is smaller than about 0.002 mm in diameter. The small size of clay particles imparts a large surface area for a given mass of material. This large surface area of the clay textural fraction in the solids defines its importance in processes involving interfacial phenomena such as sorption/desorption or surface catalysis [ 17,23]. In its mineral definition, clay is composed of secondary minerals such as layered silicates with various oxides. Layer silicates are perhaps the most important component of the clay mineral fraction. Figure 2 shows structural examples of the common clay solid phase minerals. 

Nickel is strongly adsorbed by soil, although to a lesser degree than lead, copper, and zinc (Rai and Zachara 1984). There are many adsorbing species in soil, and many factors affect the extent to which nickel is adsorbed, so the adsorption of nickel by soil is site specific. Soil properties such as texture, bulk density, pH, organic matter, the type and amount of clay minerals, and certain hydroxides influence the retention and release of metals by soil (Richter and Theis 1980). 

The affinity of DOM with soil was very low with an average DOM sorption percentage of about 22.4 4.8% to 31.2 +5.2% only at an initial DOC concentration of 100 mg/1 and 200 mg/1, respectively, for the live selected DOMs (Table 10.3). This result was supported by the small slope m of 0.11 to 0.24 and Kd of 0.47 to 1.23 ml/g obtained from the IM isotherms. Liang et al. (1996), who worked on a variety of soils with clay contents ranging from 3 to 54%, showed that the adsorption of the DOC by soils increased as the clay, organic matter contents, and the surface areas of the soils increased. The coarse texture of the selected calcareous soil and the characteristics of the selected DOM itself can explain the lower affinity of DOM with soil observed in the present study. In addition, the acidic soil with higher Fe-oxide and Mn-oxide content exhibited much higher DOC adsorption ability than calcareous soil rich in 2 1 minerals. 

The sum of exchangeable Ca2+, Mg2+, K+, Na+, and Al3+ generally equals, for practical puiposes, the soil s cation exchange capacity (CEC). The CEC varies from 10 mmol(+) kg-1 for coarse-textured soils to 500 to 600 mmol(-f) kg-1 for line-textured soils containing large amounts of 2 1 layer silicate minerals and organic matter. 

Adsorption of Mo to hydrous Fe and A1 oxides is pH-dependent (Reisenauer, Tabikh, and Stout, 1962), and the rate of adsorption is highest at acidic pH. It decreases with increases in pH from 4.45 to 7.5. Compared with acid soils, alkaline soils are high in soluble or available Mo (Davis, 1956). As in any other soil, in alkaline soil the availability of Mo is also influenced by several other factors. The relative Mo content of the parent rock, the process of soil evolution, and the physicochemical attributes of the soil (pH, calcareousness, organic-matter content, cation-exchange capacity, texture, moisture, relative concentrations of other mineral elements) all influence the availability of Mo. 

Organic matter may, therefore, play either a beneficial or an inhibitory role in copper nutrition depending on the soil, the copper source, and the amount applied. Fresh crop residues added to mineral soils will furnish available copper that the crop can feed on before it is inactivated in the soil. Organic matter in coarse-textured soils will also tend to reduce losses of added copper salts by leaching. Although organic matter can adsorb... 

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