Soils 205-90

Lecture 24- Soil Taxonomy

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Soil Taxonomy 

A. Orders

l 11 divisions

l use formative elements for classification

ü combine formative elements to make names at lower levels

B. Suborders

l subdivisions of order

l properties for genetic homogeneity (Table 3.8)

(wetness, climate, vegetation,…)

ΠAquents - entisols formed under wet conditions

L. "aqua" = water

 Borolls - mollisols formed in cool climates

G. "boreas" = northern

Ž Argids - aridisols with an argillic horizon

L. "argilla" = clay

 Udalfs - alfisols formed in humid climates

L. "udis" = humid

C. Great Groups

l subdivision of suborders

l largely based on diagnostic horizons (Table 3.9)

ΠFluvaquents - aquents on floodplains

fluv = floodplain

 Argiborolls - borolls with argillic horizons

argi = argillic

Ž Natrargids - argids with natric horizon

natr = natric

 Hapludalfs - udalfs with minimum of horizons

hapl = minimum horizons - no special features

like fragipans or wetness

D. Subgroups

l subdivision of great groups

l central concept vs gradation from central concept

1. Fully representative of central concept = Typic

ΠTypic Fluvaquents

2. Intergrades = features of other order, suborder,...

 Vitrandic Argiborolls

3. Extragrades = properties atypical of great group

Ž Lithic Natrargids

shallow to bedrock

 Vermic Hapludalfs

intense earthworm activity

E. Family

l based on soil properties important to management

1. particle size

- texture and rock fragments

ashy; fine-silty; clayey; skeletal

2. mineralogy

- major mineral species

kaolinitic; serpentinitic; mixed

3. soil temperature

- temperature regime at 50 cm

- correlated to air temperature

- relates to growing season

cryic; frigid; mesic

 fine loamy, mixed, mesic Vitrandic Argiborolls

F. Series

l most specific - common name of soil

l division of family based on profile properties

- number of horizons

- order of horizons

- thickness of horizons

l name of local significance (city, river,...)

Palouse, fine-silty, mixed, mesic, Pachic Ultic Haploxerolls

 

Santa, coarse silty, mixed, frigid Ochreptic Fragixeralfs

Santa, | coarse silty, mixed, frigid | Ochreptic | Fragi | xer | alfs

CATEGORY	CLASSIFICATION	FORMATIVE ELEMENT
order	alfisols	alf
suborder	xeralf	xer
great group	fragixeralf	fragi
subgroup	ochreptic fragixeralf	ochreptic
family	coarse silty, mixed, frigid
series	santa

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SOIL SURVEYS

Soil Mapping Units:

1. Phase

l subdivision of series or other category

l deviation that influences the use of the soil (texture, slope,...)

i.e. Palouse silt loam, 3-6 % slope

2. Consociations

l used with detailed soil surveys

l primarily, series and phase

- at least, dominates the area

3. Complexes

l pattern of 2 or more series

l intimately related (single unit)

i.e. Chilcott-Sebree complex

4. Soil Associations

l general grouping of soils

l commonly occur together in landscape

l large-scale soil maps - larger areas