Classification of Soils
Introduction to Agriculture
What will we learn today?
How do we classify soils?
What is a soil profile?
What is a land capability class?
What is the Soil Classification System?
Soil Profile
A soil profile is a crosssectional view of a soil
showing its many layers
Each layer in the soil is called
a horizon
Shows many characteristics
of each layer:
Thickness
Color
Texture
Structure
Soil Horizons
A Horizon – TOPSOIL
1” to 3’ deep depending on region
Rich in humus, soil organisms, plant roots
B Horizon – SUBSOIL
Fine particles of clay, little organic matter
Water drainage and root penetration
C Horizon – PARENT MATERIAL
Not true soil, weathered parent material
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Quic kTime™ and a
TIFF ( Unc ompres sed) dec ompr ess or
are needed to s ee this pic tur e.
Other Horizons
O Horizon ORGANIC MATTER
Plant or animal life
Organic plant residues
Decomposers
R Horizon BEDROCK
1’ to 1,000’+
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Land Capability Class
Land capability class is productive
potential of soil based on:
texture, structure, slope and depth
Class I best for agricultural production
Class VIII least useful for agriculture
Land Capability Class
Class 1 = Few limitations that restrict their use. Best for agriculture.
Class 2 = Moderate limitations that reduce the choice of plants or that require
moderate conservation practices.
Class 3 = Severe limitations reducing choice of plants or requiring very careful
management or both.
Class 4 = Very severe limitations reducing the choice of plants or requiring very
careful management or both.
Class 5 = Not likely to erode but have other limitations, impractical to remove,
that limit their use.
Class 6 = Severe limitations that making them generally unsuitable for cultivation.
Class 7 = Very severe limitations making them unavailable for cultivation.
Class 8 = Suitable only for wildlife, forests, and recreation.
Subclasses indicate major limitations within a class. Class I has no subclasses.
Subclass E = Risk of erosion unless close-growing plant cover is maintained.
Subclass W = Water in or on the soil interferes with plant growth or cultivation
Subclass S = Shallow, droughty, or stone.
Soil Classification System (SCS)
Developed by USDA to categorize the
different types of soils that exist
All soils broken into 12 orders, then
broken down further ending with series
About 10,500 known in the United States
alone
Similar to binomial nomenclature used
with plants, animals, etc.
Soil Classification System (SCS)
Living
Soils
Organisms
Kingdom
Order
Phylum
Suborder
Class
Great Group
Order
Subgroup
Family
Family
Genus
Series
Species
Phase
What did we learn today?
How do we classify soils?
What is a soil profile?
What is a land capability class?
What is the Soil Classification System?