Agriculture Reference
In-Depth Information
A
Granular/crumb
E
Platy
Bt1
Subangular/angular blocky
Bt2
Columnar/prismatic
Bt3
C
Figure 1.6.
Soil structure and its most common location in a soil profile. Platy structure can be
found in any horizon. Subangular and angular blocky structure can be found both higher and
lower in the profile than indicated.
from the bottom peds in Figure 1.7). Because of their effect on air, water, and
roots, peds help in determining a soil's chemistry.
Figure 1.7 shows actual peds isolated from a soil profile. Generally speak-
ing, structure, except for platy peds, is considered to be a positive component
in soil. Platy structure, however, can retard the movement of air and water
down through the soil profile and so is considered a negative component.
Because it restricts air and water movement, it may cause areas of water
saturation and thus reducing conditions.
Because large voids between peds allow ready movement of water down
through the soil profile, ped surfaces often become coated with material
carried in the water. The most common coating is clay and is called “clay skins.”
If there is rubbing between the peds, the skins will have a smeared surface
and will often be shiny. Under such conditions the surfaces are said to be
“slicken sides.” Less common are surface coatings of silt and organic matter
carried by leaching into the lower horizons. Silt coatings are common in
horizons from which clay particles have been translocated to lower horizons.
