Soil Texture and Structure

To promote the use of poor quality water for irrigation, a field research study was conducted in three semi-arid regions with water scarceness in Syria in order to define, under field conditions, the wheat yield response function to irrigation water salinity, the effect of soil texture and structural characteristics on the irrigation water salinity threshold, and to compare this value with the conventional threshold value. 

The results of this research study indicate that wheat tolerance for irrigation with saline water is affected by various real in-field conditions, including soil texture and structure, climate, irrigation water management and agricultural practices. 

J. Hassink, Effects of soil texture and structure on carbon and nitrogen mineralisation in grassland soils. Biology and Fertility of Soils I4 26 (1992). 

Changes in soil consistence are a useful surrogate measure for identifying restrictive layers because soil texture and structure are often difficult to measure consistently by inexperienced operators and because root abun-... 

Soil can be made of different percentages of clay, sand or silt particles that combine to give soil its texture. Clay particles are smaller than sand particles which are smaller than silt particles. It is difficult to alter the composition of soil particles, whereas it is possible to operate on aggregates that soil particles form to create the soil structure. Soil texture and structure have a strong impact on microbial colony formation a sandy, dry and well-aerated soil encourages fungal colonisation, whereas a poorly aerated clay compact soil hosts facultative aerobic or microaerophilic bacterial colonies. 

In addition to soil factors such as texture and structure controlling water movement within a given soil, other factors include temperature, water content, and salt composition and concentration. For example, the data in Figure 10.1 show that as temperature increases, hydraulic conductivity also increases, perhaps because of increasing water fluidity. Furthermore, hydraulic conductivity increases as water content increases. The data in Figure 10.2 demonstrate that as salt concentration increases, hydraulic conductivity also increases, a phenomenon linked to the electric double layer (Chapters 3 and 9). 

ASSESSMENT OF SOIL STRUCTURE (SOIL TEXTURE). The Structure of the soil is important for the water content, air content and thermal metabolism of the soil. It has determinative effects on plant growth and on root penetra-... 

The texture and structure of a soil also affect plant response to nitrogen additions through effects on root development and depth of penetration. A restricted root system limits the ability of the plant to assimilate nutrients and also limits its uptake of water. Since the movement of water through soils by capillarity is slow and limited, the plant roots must literally go after it. A deep root system, therefore, assures that a much greater proportion of the supply in the soil is available to the plant. In addition, soil compaction limits the absorption of the rainfall. Such unfavorable conditions do of course lower the efficiency of applied nitrogen. 

The properties of a soil are a function of both its texture and structure, and the chemical and mineralogical composition of its particles. Some of these properties are its capacity to adsorb water, its plasticity and cohesion, and its changes in mechanical behavior due to variations in environmental conditions and time, such as its compressibility, permeability, strength, and stress transmission. The sediments together with fossils can also provide data needed for the reconstruction of the geological processes that have formed the soil. 

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. 

The technical factors that must be considered include (1) volatility of pollutants, (2) lateral and vertical concentration of VOCs, (3) soil types and properties (e.g., structure, texture, permeability, stratification, and moisture content), (4) emission control requirement, (5) schedule for cleanup, (6) position and length of screened interval, (7) blower type, and (8) site factors (e.g., depth and contaminated extension area, depth to water table). 

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