Textures of Soils

The texture of soil is determined from the relative proportion of sand, silt and clay. Two systems of soil texture classifications, as suggested by ISSS and USDA, are in common use. Both the system make use of an equilateral triangle whose area is divided into 12 compartments, each representing a textural class. The difference is primarily due to differences in size ranges of sand and silt fractions. The triangle based on ISSS size fraction is given in Fig. 2.2. For the... 

One of the questions that can be answered with the help of adsorption measurements concerns the microtexture of natural clay minerals. Several idealized models for the texture of soil clays (see [5]) have been considered, but rather than assuming one model a priori, one should try to gain useful information from experimental relationships between the size of clay particles and apparent density or surface area and internal porosity, as described in Sections 6.1 and 6.2.1. Experiments aiming at the evaluation of the microtextures of clay minerals were carried out by Ben Ohoud and van Damme [95], who studied kaolinite, sepiolite, palygorskite and 20 monoionic montmorillonite samples. The accessible surface area S of consecutive fractions of size r was measured by N2 adsorption using the classical BET method, whereas the open porosity P was measured from the amounts of adsorbed N2 at a relative vapor... 

The description of a soil in relation to the amount of mineral material, clay, silt and sand, is called the soil texture. There are large variations in the texture of soils found on farms. Soil texture can be analysed accurately in a laboratory but can also be assessed in the field using hand texturing. 

Humus The dark organic material in soils, produced by the decomposition of soils. The matter that remains after the bulk of detritus has beenconsumed (leaves, roots). Humus mixes with top layers of soil (rock particles), supplies some of the nutrients needed by plants -increases acidity of soil inorganic nutrients more soluble under acidic conditions, become more available, EX. wheat grows best at pH 5.5-7.0. Humus modifies soil texture, creates loose, crumbly texture, that allows water to soak in and nutrients retained permits air to be incorporated into soil. 

Easily observed physical properties of soils often are useful indexes of behavior. These index properties include texture and appearance, specific weight, moisture content, consistency, permeability, compressibility, and shearing strength [37,38]. 

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. 

P. F. White, Soil and plant factors relating to the poor growth of Lupinus species on fine-textured alkaline soils. Aust. J. Agric. Res. 4l il (1990). 

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

Texture, organic matter content, oxygen status and pH values of soil in use area(s) Amqlmts and timing of precipitation Temperature and solar irradiance in use area(s) (temperate vs. tropical vs. nordic)... 

Soil properties A Soil texture (sand, silt, clay), organic matter/carbon content, and pH Stones, roots, and hardpans must be largely absent to allow representative sampling of soil profile Soil properties should appear uniform over test site Soil texture data should be available at time of site selection. Soil properties must match study purpose. This can be realistic use conditions, realistic worst-case or worst-case in terms of agrochemical mobility and persistence Must ensure that the majority of samples can be taken from the deepest sampling horizon. Information about sub-soils can be obtained from soil maps, test coring and on-site interviews... 

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 size, and particularly the size distribution of the particles (or PSD, as particle size distribution is often abbreviated), which is closely related to the texture of the soil, is an important characteristic that determines many of the... 

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