© 2007 Donald G. McGahan (aka soilman) All Rights Reserved
- Soil Taxonomy
- a systematic hierarchy of soil classification in which the selection of properties is based on concepts of soil genesis and soil management.
- based primarily on soil properties
- has a bias for agricultural soils and management practices
Soil Taxonomy Categories
- Order (12)
- Suborder (47)
- Great Groups (231)
- Subgroups (1250)
- Soil Series (18,000)
- major influence or properties influencing soil-forming processes (e.g., most important property).
- additional properties resulting from the major control of the current soil-forming processes (e.g., moisture regime, drainage)
- Great group
- properties resulting from additional, or subordinate controls of the current soil-forming processes (e.g., hardpans, presence of sodium, calcium carbonate).
- properties which represent two different kinds of genesis (thick vs. thin A horizons)
- additional properties which reflect the potential for change of the soil materials (e.g., broad textural classes, mineralogy, temperature).
- groupings of soils which have experienced a similar genesis and which will behave in similar ways to use and management.
Soil Taxonomy: Orders
- >30% clay in all horizons and cracks to 50 cm
- no significant soil development - young soils
- minimal soil development - young soils but more highly developed than Entisols
- occur in arid regions (desert soils)
- translocation of organic matter, Fe, & Al - forest soils in cold climates
- clay-rich subsurface horizon; Base Saturation < 35%
- clay-rich subsurface horizon; Base Saturation > 35%
- dark, organic-rich A horizon; Base Saturation > 50%
- highly weathered soils; only Fe/Al oxides/hydroxide minerals remain - tropical soils
- organic soil materials to a depth of 40 cm
- formed in volcanic materials, low bulk density and an abundance of noncrystalline minerals
- soils with permafrost
Soil Taxonomy Construction of Names
Soil Taxonomic names are constructed of formative units. This is accomplished by starting the most inclusive –highest category– Order and adding succesively more exclusive –lower categories– to the left.
The following is an example of a soil with a Soil Taxonomy classification:
very-fine, montmorillonitic, thermic Vertic Haplaquoll
|Category||Categorical Name||Formative Unit|
|Great group||no special feature||hapl|
|Family||temperature class||thermic (59–72° F)|
|texture||very-fine||very-fine (>60% clay)|
With each of the Categorical Name are definitions and limitations that exclude other soils.
- Storie Index
- A land rating system for evaluating the suitability of a particular soil for agricultural production. Developed for use in California agricultural soils.
- based on soil properties
- developed for irrigated agriculture
- calculates a numerical value (0–100); ratings of 60–100 indicate good agricultural soils
Storie Index: Important Soil Factors
Storie Index is a parametric indices.
Factor A × Factor B × Factor C × Factor X
|Factor A||Depth of rooting zone|
|Factor B||Surface texture|
|Factor X||drainage × salt affected × nutrient level × erosion × microrelief|
USDA Land Capability Classification (LCC)
- USDA Land Capability Classification
- Uses soil and climate data to group soils with similar management options or problems. Thirteen criteria are considered: effective soil depth, surface texture, permeability, drainage class, available water-holding capacity, slope, erosion, flooding hazard, salinity, sodium affected, toxic substance, frost-free days, and climate indices.
Seven Classes: I, II, III, IV, V, VI, VII
I - IV = suitable for cultivation (Class I & II generally considered Prime Farmland)
V - VII = not suited for cultivation
- c - climate
- s - soil condition (e.g., salts, low H2O holding capacity, etc.)
- e - erosion
- w - wetness