Soil texture assessment

Soil moisture can have a significant effect on decomposition (Swift et al. 1979). This is due, in part, to the fact that soil moisture can affect the metabolism of decomposer microorganisms. This effect can be modified by soil texture because bioavailable moisture is determined, in part, by the suction with which water is held between soil particles (matric potential). Thus, the calibration of soils to a known matric potential can lead to the assessment of the effect of bioavailability of moisture in soil (Hillel 1982) and allow for the comparison of process rates between soils at the same matric potential (Orchard and Cook 1983). 

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-... 

Based on the mineralogy controlling weathering and soil development, sensitivity of ecosystem to acid deposition is assessed with a comprehensive consideration on the effect of temperature, soil texture, land use and precipitation. The results show that the most sensitive area to acid deposition in China is Podzolic soil zone in the Northeast, then followed by Latosol, Dark Brown Forest soil and Black soil zones. The less sensitive area is Ferralsol and Yellow-Brown Earth zone in the Southeast, and the least sensitive areas are mainly referred to as Xerosol zone in the Northwest,... 

Alpine soil zone in the Tibet Platean, and Dark Loessial soil and Chernozem soil zone in central China. These regional different soil sensitivities to acid deposition can be attribnted to the differences in temperature, humidity and soil texture (Hao et al, 1998). It has been shown that the assessment of ecosystem sensitivity to acidic loading depends strongly on the calculation of chemical weathering of soil base cations due to an input of proton with depositions. 

Based on the mineralogy controlling weathering and soil development, sensitivity of ecosystems to acid deposition is assessed with the comprehensive consideration on the effect of temperature, soil texture, land use and precipitation. The results show... 

The texture of the soil refers to the amount of sand, silt, and clay contained in a soil sample. The distribution of particle sizes determines the soil texture, which can be assessed in the field or by an accurate particle-size analysis in the laboratory. The classification of the particle size according to Wentworth is provided in Table 14.9. 

A soil profile is a section taken vertically through the soil. In some cases this may consist only of a shallow surface soil of 10-15 cm on top of rock such as chalk or limestone. In deeper well-developed soils there are usually three or more definite layers (or horizons) which vary in colour, texture and stmcture (Fig. 3.1). The soil profile can be examined by digging a pit or by taking ont cores of soil from various depths using a soil auger. A careful examination of the layers can be useful for assessing soil texture, stmcture and eompaction as well as the soil cropping potential. The colour of the soil in the various horizons will indicate whether the soil is well or poorly drained. 

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. 

With practice, it is possible to become reasonably skilled at assessing soil texture by feeling the soil in the following way ... 

Electrical conductivity (or its mathematical inverse, resistivity) of a soil solution is strongly correlated with total salt content. Therefore, laboratory methods involving solution or saturated paste conductivity are often used to assess soil salinity. Electrical conductivity measurements of bulk soil (designated as ECa for apparent electrical conductivity) were also first used to assess salinity. Resistivity and conductivity measurements are also useful for estimating other soil properties, as reviewed by and. Factors that influence ECa include soil salinity, clay content and cation exchange capacity (CEC), clay mineralogy, soil pore size and distribution, soil moisture content, and temperature. ° For saline soils, most of the variation in ECa can be related to salt concentration. In non-saline soils, conductivity variations are primarily a function of soil texture, moisture content, bulk density, and CEC. The theoretical basis for the relationship between ECa and soil physical properties has been described by a model where ECa was a function of soil water content (both the mobile and immobile fractions), the electrical conductivity of the soil water, soil bulk density, and the electrical conductivity of the soil solid phase.Later, this model was used to predict the expected correlation structure between ECa data and multiple soil properties. ... 

Carefully moisten a handful of stone-free soil until the particles cling together (avoid excess water). Work it well in the hand until the stmcture breaks down mb a small amount between the thrrmb and fingers to assess the texture according to how gritty, silky or sticky the sample feels. The handful of moist soil can also be assessed by the amount of polish it will take, and the ease or difficulty of moulding it into a ball and other shapes. 

The above textural groups are used in advisoiy work for making recommendations on dose rates for soil-acting hetbicides and for assessing available-water capacity, suitability for mole drainage, woikability and stabiUty of soils. 

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