Agriculture Reference
In-Depth Information
the name taken from the concept that material from the surface falls to the
bottom of the cracks, resulting in inversion of the soil.
In the field when soil containing 2 : 1 clays become wet, they swell shut and
water movement through them is extremely slow. In a soil profile wetting
and swelling of this type of clay will prevent downward movement of water
and associated contaminants. For this reason swelling clays are used to seal
both landfills and ponds to prevent leaching or leaking.
The crystals of 2 : 1 swelling clays are typically smaller than either kaolinite
or fine grained mica and thus have higher adsorption and cation exchange
capacities. However, surface adsorption will be of the same chemistry as that
in the fine micas.
2.1.3.3
Amorphous Clays
In addition to the crystalline clays described above, there are some materials
that act like clays but do not have a crystalline structure. Amorphous clays do
not have a definite X-ray diffraction pattern and are differentiated from the
crystalline clays on this basis. They are composed of mixtures of aluminum,
silicon, and other oxides and generally have high sorptive and cation exchange
capacities. Few soils contain large amounts of amorphous clays [2].
2.1.4.
Soil Texture
Sand, silt, and clay are the three components of soil texture. Various relative
compositions, expressed on a percentage bases, are used to give soils a textural
name such as sandy loam, or loamy clay. For soils containing significant
amounts of silt, the term
loam
is used, although with high levels (>88% silt,
<20% sand, and 12% clay), the soil would be called
silt
. Thus, a soil contain-
ing high amounts of sand would be sand, sandy loam, loamy sand, or sandy
clay, and clay soils would be designated as clay, clay loam sandy clay, and silty
soils as silt loam, silty clay loam, and so on. The textural name of a soil is estab-
lished by determining the soil's relative percentage of sand, silt, and clay and
then finding this percentage on a textural triangle, included in all standard
texts on soils (see Reference 1 or 14), to find the name. The textural name of
a soil often accompanies the name, (e.g., Milton silt loam) or can be obtained
from a soil scientist familiar with an area's soils.
Sandy soils are easiest to extract and analyze, while clay soils are the
hardest. Drying, crushing, and sieving will aid in extraction and analysis,
although it may not be necessary to crush very sandy soils. Clayey soils may
retain small amounts of contamination even after extensive extraction. In all
cases extraction and analysis procedures must be robust enough to handle all
textures containing all clay types [3].
