AGEN 2363 Chpt. 7 Notes. Soil Surveys as a Basis For Land Use Planning.
I. Soil Surveys.
a. Most counties have published soil surveys. Most were mapped in the 1960’s-80’s.
b. Soils were critiqued in the field by soil scientists using core tests and aerial photo’s.
c. Soil surveys contain more information than just maps of soils. Examples:
- county description, weather, land use, chemical and physical properties of the soils,
descriptions of the geology, soil associations, soil series, and soil phases, and soil
limitations and suitability for engineering, wildlife, woodland, agriculture, and
d. The USDA-NRCS is responsible for the research and publication of the soil surveys.
e. Other soil survey trivia:
- Hard copies of most county soil surveys are now out of print.
- Most county soil maps are now available on-line in GIS format.
- Soils usually have to be at least a half-acre in size to be delineated on a soil map.
- Many county soil maps are out of date.
- You’ll find two types of soil mapping unit coding: numbers or symbols.
- If symbols are used, they can be interpreted by:
GaC2 = soil mapping unit or soil phase
Ga = soil series (Grenada)
C = % slope category (A = 0-1, B = 1-3, C = 3-5, D = 5-8 …)
2 = erosion status:
nothing = none - slight erosion damage (>75% topsoil),
2 = moderate erosion damage (50-75% topsoil),
3 = severe (<50% topsoil left)
f. Types of soil surveys:
1. reconnaissance. Very general.
2. detailed. Soil boundaries are traced throughout their length. Most county
soil surveys are like this.
3. intensive. Usually performed by private, certified, and licensed soil mappers
for very detailed maps used by land managers, sub-division
planners, engineering firms needing soil data for EPA reports, etc.
Soils are delineated to as small as 10 m grids.
II. Soil hierarchy.
1. Soil association. General type of soils you’ll find on the landscape in a particular
area. Related to the geology and soil formation process.
EXAMPLE: Grenada – Calloway – Henry
2. Soil series. Sort of like the species. Soils that have similar profiles, parent material,
age, etc. EXAMPLE: Grenada silt loam.
3. Soil Phase (mapping unit). Sort of like the variety. A sub-unit of the soil series due
to factors such as % slope, erosion, flooding frequency, etc.
EXAMPLE: Grenada silt loam, 1-3% slope
4. Soil taxonomic class. The ‘scientific name’ of a soil series.
EXAMPLE ‘fine, silty, mixed, thermic Typic Fragiudalf ‘ (that is for Grenada)
5. Soil classification divisions:
1. Order (there are currently 12 soil Orders) Dominant soil orders in the
- Alfisols. Derived under forests.
- Ultisols. Older, weathered, acidic Alfisols.
- Entisols. Very young soils with no evidence of significant development.
- Inceptisols. A little older than Entisols. Show early signs of growth.
2. Sub-Order. EX. Udalf
3. Great Group. EX. Fragiudalf
4. Sub Group. EX Typic Fragiudalf
5. Family. EX. fine, silty, mixed, thermic Typic Fragiudalf
6. Series. EX. Grenada silt loam
III. Soil map interpretations.
A. USDA land capability class. See handout. Now the following highlights:
Class I. The best soil you can get for growing crops without much danger to the
environment or cost to improve or protect.
Class I – IV. Usually considered the only ones feasible for crops.
There are four sub-classes that will knock a soil out of class I:
e = erosion hazard
w = wetness or flooding hazard
s = soil limitation such as stoney, shallow, sodic, etc
c = climate limitation such as excessive dryness or cold.
IV. Uses of soil surveys.
A. Land appraisals. Based on value of land for crops. EX. land with >% class I more
B. Design of tile drainage systems.
C. Nutrient management plans.
D. Sub-surface sewage disposal fields.
E. Delineation of best land for woodland, wetland, wildlife, crops, pasture, homes,
sub-divisions, AND suitable plants.
F. Planning and zoning by cities.
G. Land use plans, best management practices plans, etc.
H. EPA statements.
I. Recreational planning, pond construction, etc.