Chapter 4 Flashcards
soil series
group of soils originating from the same parent material and having similar soil horizons in the soil profile, with the primary difference between them being their soil texture
Each soil series is named for a nearby geographic feature (e.g. town name)
divided into “phases” based upon their difference in texture, and the name of a soil phase indicates a feature that affects managemen
who provides soil maps?
Through the USDA, the NRCS (National Resources Conservation Service)
can be used to determine the soil series found at a specific site
If more detailed information (including soil chemistry) is required, the landscape architect can commission a soil survey for a site
Soil horizon
layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath.
defined by obvious physical features such as color and textur
Soil profile
vertical section of the soil through all its horizons and extending into the parent material
Sand
largest particle size, with soil particles between 0.05 and 2.0 millimeters in diameter
Silt
Fine soil particles between 0.05 and 0.002 millimeter in diameter that can be picked up by air or water and deposited as sediment
Clay
smallest particle size, with soil particles smaller than 0.002 millimeters in diameter
loam
soil that is primarily composed of sand and silt, with a small amount of clay particles
equal parts sand and silt in a loam soil, and most sources list loam as being composed of 40% sand, 40% silt and 20% clay.
why is soil texture important
important in determining a soil’s water-holding capacity, permeability and workability
influence upon the plant communities found in a soil class
friable soil
texture in which large clumps are easily broken apart by hand, but which cannot easily be broken apart into (undesirably) small particles
ideal for agriculture and for the growth of most plants
Porosity
void size between particles within a soil and can be expressed as the percentage of void space in a soil
has a direct relationship with soil permeability (
Well-graded soil
wide range and even distribution of soil particle sizes, in which the small soil particles fill the voids created by the larger grains
Gap-graded soil
contains various particle sizes, but in which gradation between sizes is broken by the absence of some particle sizes
Uniformly graded soil
soil that consists of a single range of particle size
Permeability
rate at which water moves through soil
Infiltration rate
rate at which water flows into soil through small pores
Percolation
the downward movement of water in a soil.
what to do when soils not draining
can be amended with sand and/or gravel to increase their permeability
to reduce soil permeability
adding clay to sandy soils can reduce permeability, as can the addition of peat moss or other highly absorbent organic materials.
hydric soils
Soils with low permeability in areas subject to regular moisture
characterized by being heavily saturated with water for prolonged periods of time
this prolonged saturation renders the soils anaerobic and generally results in the soils being bluish in color.
soils and septic systems in rural areas
Soils with a slow rate of percolation cannot accommodate septic systems
these areas often preclude the development of housing or other uses that might require a septic system (where a municipal sewer system is not present)
Bearing capacity
measure of a soil to decrease in volume under the pressure of a given weight
Angle of repose
maximum slope at which a loose material can be piled while remaining stable
Soil elasticity
ability of a soil to return to its original shape after being subjected to a load condition
Soil plasticity
ability of a soil to be deformed under pressure without breaking apart
Liquid limit
minimum moisture content at which a soil will flow under its own weight.
clay-heavy soils
a soil with a uniform particle size or those that shrink and expand through wetting and drying cycles
factors that effect erosion
precipitation patterns, topography (slope), soil disturbance and site location (e.g., coastal sites often experience erosion from storm events), natural disasters
hydrophobic soils
wildfires - the soil in burn areas exhibits water repellence. decreased, thereby increasing erosion
Soil erosion
not only removes fertile topsoil, it introduces high concentrations of sediment into watersheds, thereby reducing water quality and causing aggradation (the filling in of stream channels with sediment), among other issues.
best practices to reduce soil erosion
-Preserve existing vegetation
*Reduce the total area of land disturbance
*Stabilize excavated areas with seeding, sodding, matting or mulching and divert runoff away from these areas
*Minimizing disturbance to steep slopes
*Schedule clearing and grading activities during the dry season and suspend them prior to and during precipitation events
*Locate non-point pollution sources (e.g. construction access roads) in areas that do not drain directly into water bodies
*Introduce erosion control fencing, blankets and stabilize drainage channels with erosion-resistant materials (e.g. riprap)
Gully erosion
widening, deepening, and headcutting of small channels and waterways due to erosion
Rill erosion
removal of soil by running water with formation of shallow channels that can be smoothed out completely by normal cultivation.
