SOIL TAXONOMY
02/26/2005 11:16:28 AM
Clip Art: Soil Quality Institute
You need to know
- How the soil taxonomy is constructed with roots and formative elements
- The location, profile characteristics, and management concerns of the eleven major soil orders
Learning Objective One: How the soil taxonomy is constructed with roots and formative elements
The minimum area to classify a soil is the soil _____________ . It's a 1-10 m2 area and is deep as the roots of crops can grow. Combinations of pedons are called polypedons.
To classify soils a nested or hierarchical system exists containing six categories: order, suborder, great group, subgroup, family, and series.
 | The soil order is the highest and most in the classification system, with all the soils in the world fitting into eleven orders. The soil series is the lowest and most specific level. Soil series are identified by mapping unit numbers in the soil survey manual. Look in the soil survey manual and find a mapping unit and their corresponding soil series identification. |
| within soil orders are differentiated on the basis of soil moisture, temperature, texture, and chemical properties, climate, wetness, vegetation, and the presence of diagnostic horizons., |
| great groups: are subdivisions of the suborders and are
differentiated on the basis of soil horizons and soil features like clay
properties and soil temperatures. |
| subgroups: great groups are further classified on how well
the soil represents the central concept or major characteristic of the great
group. Look for the word
. |
| family: subgroups are divided on the basis of agricultural
or engineering properties. |
| series: families are differentiated on the basis of observable and mapable soil properties like soil texture, slope, stoniness, etc. Soil series are what's mapped in the soil survey manual. |
STEPS FOR CLASSIFYING A SOIL:
1. START WITH THE ROOT: To begin classifying soils start by identifying the root of each soil order:
| Root | Order | Root | Order | Root | Order |
| alf | alfisol | ent | entisol | ept | inceptisol |
| oll | mollisol | ult | ultisol | id | aridisol |
| ox | oxisol | ert | vertisol | od | spodosols |
| ist | histosols |
These roots are the LAST letters in any family or higher taxonomic classification. See p. 195 in the Saginaw Soil Survey Manual.
2. THEN ADD FORMATIVE ELEMENTS: add formative elements to classify soils to the suborder and great group levels. What are formative elements? Formative elements are used to suggest properties of soils used in the suborder and great group.
a) The formative element closest to the soil order root refers to suborder properties.
b) The next formative element refers to great group properties.
Example 1: a haplboralf is an alfisol developed in a cool region with minimum horizon development. hapl - great group formative element classification, bor - suborder formative element classification, alf root for alfisol;
Example 2: A udipsamment is an entisol that is quite sandy with a soil moisture regime that isn't dry for longer than 90 cumulative days. udi - great group formative element classification, psamm - suborder formative element classification, ent root for entisol.
See pp. 212-213 in the textbook for examples of how classifications are built in the soil taxonomy.
The list below is alphabetized from left to right.
| formative element | meaning | formative element | meaning |
| acr | Extreme weathering | alb | An albic horizon, Fe and clay have been removed |
| agr | An agric horizon in which clay, silt and humus are accumulate from an overlying cultivated and fertilized layer. | anthr | An anthropic horizon |
| al | High exchangeable aluminum | aqu | Evidence of wetness |
| arg | An argillic (clay) horizon | calc | A calcic horizon |
| aridic | A soil moisture regime that has no water available for plants for more than half the year | camb | A cambic horizon, slightly altered horizon but without an eluvial or illuvial layer |
| bor | Cool | cry | Cold |
| dur | A duripan, durable, hard | frag | Presence of fragipan |
| dystr, dys | Low base saturation | gel | Soil temperature <0ºc |
| endo | Wet from below | fragloss | See the formative elements frag and gloss |
| epi | Wet, perched | gloss | Tongued |
| eutr, eu | High base saturation | gyps | Presence of gypsic horizon |
| ferr | Presence of iron | hal | Salty |
| fluv | Floodplain | kandhapl | See kand and hapl |
| hapl | Minimum horizon development | luv | Illuvial |
| hum | Presence of humus | med | Normal, default Histosol class |
| hydr | Presence of water | melan | Black, high C, and short-range-order minerals |
| kand | Presence of low activity clay | nadur | See the formative elements natr and dur |
| natr | Presence of natric horizon, similar to an argillic horizon, with an accumulation of Na. | oxic | accumulation of Fe, Al, and kaolinite |
| ochr | light in color, high in chroma, low in OM. |
pale | Old development |
| petro | Hardened calcic or gypsic horizon | psamm | Sand textures |
| plac | Presence of a thin cemented layer of Fe or Mn | quartz | High quartz content |
| plag | Presence of plaggen horizon | rhod | Dark red color |
| plinth | Presence of plinthite | sal | Presence of salic horizon |
| sombr | A dark horizon | torr | hot and dry |
| sphagn | Presence of Sphagnum moss | trop | Continually warm and humid |
| spod | illuviated layer of Al, Fe, and humus | ud | A soil moisture regime that isn't dry for longer than 90 cumulative days |
| sulf | Sulfides or their oxidation products | umbr | Presence of umbric epipedon |
| ust | intermediate between the aridic and udic regimes and common in temperate subhumid or semiarid regions | vitr | Presence of glass |
| verm | Wormy, or mixed by animals | xer | a soil moisture regime common to Mediterranean climates that have moist cool winters and warm dry summers. |
Learning Objective Two :The location, profile characteristics, and management concerns of the eleven major soil orders
For an overview of the soil orders and an on-line quiz from San Diego State University, click here. (require Flash viewer)
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(ent) are
generally thought of as young soils. This
soil order lacks horizons
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Inceptisols (ept)
have horizons of alteration but none of the subsurface diagnostic horizons
of the other orders. These soils are
to show weathering characteristics and faintly derived horizons but have
insufficient translocated clay to have an argillic horizon. These soils
do not have an illuvial horizon.
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Spodosols
(od)
The _______ horizon is characterized by an eluvial horizon where
clay and free Fe oxides have been removed. This horizon is whitish in
color. The B horizon can have a diagnostic
consisting of a subsoil accumulation of illuvial (translocated) humus
combined with aluminum, or humus combined with iron. Sometimes the
spodic horizon becomes impenetrable to water and roots in which case this
layer will be called a placic horizon.
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Histosols:
(ist)
are
soils and are sometimes referred to as _____________ soils.
These soils are wet long enough to periodically produce anaerobic
conditions, thereby inhibiting organic decomposition.
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Mollisols (ol)
are soils with a high surface accumulation of organic matter. Mollisols have
a mollic epipedon which is characterized by
1. soft character
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(alf) have accumulations of
translocated (illuviated) clay in the subsoil. The argillic horizon is
diagnostic (required) for an
alfisol. The depth to which clays will be illuviated depends on the efficacy of evaporation.
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Aridisols (id) are
soils from arid regions. Precipitation is transient and either quickly runs
off or is evaporated. As a result, there is little leaching,
thus soluble minerals accumulate. A subsurface accumulate of salt is called
a
endopedon.
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Andisols are
soils formed on volcanic parent materials such as volcanic ash, pumice,
cinders, or lava. What is the
location of these soils? | ||
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Ultisols (ult) are
similar to alfisols except that _____________ fertility is lower.
Precipitation can be high, washing away essential nutrient.
Temperatures are also higher resulting in the rapid decomposition of
_____________________.
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Oxisols (ox) are
most common in hot humid climates where rates of
weathering are intense. Like ultisols, soil color tends to be _____or ____________ due to the presence of ____________
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Vertisols
(ert) form
in clay-textured parent materials and have clay textures that swell when
__________and shrink when dry so the large cracks, diagnostic of the order,
are obvious.
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