SOILS - Lecture 3

master horizons

• O – Organic matter on the surface of a mineral soil.

• A – the topmost horizon (TOPSOIL). Often darker.

• E – this is the horizon of maximum eluviation (washing – movement out of) and leaching; often lighter.

• B – SUBSOIL. this is the horizon of maximum illuviation (accumulation). often darker or heavier in texture (such as more clay).

• C – weathered rock; unconsolidated material, may be parent material

• R – consolidated rock beneath the soil, no weathering

illuvial master horizon

B – often darker or heavier in texture (such as more clay).

elluvial master horizon

E – often lighter.

subordinate distinctions

p, g, w, t, r and x

subordinate distinction p

plow depth

subordinate distinction g

gleying or mottling (the grey color of wet soils)

subordinate distinction w

distinctive color or structure

subordinate distinction t

accumulation of silicate clays

subordinate distinction r

weathered or soft bedrock

subordinate distinction x

fragic or fragipan characteristics that result in genetically developed firmness, brittleness, or high bulk density

diagnostic epipedons

1. Mollic

2. Umbric

3. Ochric

4. Melanic

5. Histic

6. Fostic

7. Antrophic

8. Plaggen

Mollic

mineral horizon that is deep and dark, and is high in bases (Ca, Mg, K etc.)

Umbric

mineral horizon that is deep and dark, but LOW in bases.

Ochric

the surface horizon is too thin, too light in color or too low in bases to be mollic or umbric.

Melanic

very dark, volcanic ash.

Histic

organic

Fostic

organic, but not as wet as histic.

Antrophic

human modified mollic-like, high in phosphorus.

Plaggen

human-made from years of manuring.

diagnostic subsurface horizons

• Argillic

• Natric

• Spodic

• Kandic

• Albic

• Oxic

• Placic

• Cambric

Argillic

accumulation of clay

Natric

accumulation of salts (think Na = sodium)

Spodic

accumulation of Al oxides and OM, illuvial horizon

Kandic

accumulation of low acidity clays, very highly weathered soils

Albic

eluvial horizon from which Fe oxides and clay have been removed, light colored (albino = white, light)

Oxic

highly weathered subsurface horizon, humid tropics/subtropics (ALABAMA)

Placic

thin black to dark reddish Fe, Mn, or Fe humus-cemented pan.

Cambric

little development, some color or structure

hierarchy from least descriptive to most specific of the 6 categories of classification for soil

• Order (12 of these)

• Sub Order (28)

• Great group (240)

• Subgroup (1300)

• Family (8000)

• Series (lots)

the 12 soil orders

1. Alfisol (alf)

2. Andisol (and)

3. Aridisol (id)

4. Entisol (ent)

5. Gelisol (el)

6. Histosol (ist)

7. Inceptisol (ept)

8. Mollisol (oll)

9. Oxisol (ox)

10. Spodosol (od)

11. Ultisol (ult)

12. Vertisol (ert)

Alfisol (alf)

argillic, natric or kandic horizon, high-med base saturation

Andisol (and)

volcanic

Aridisol (id)

dry soil, ochric epipedon

Entisol (ent)

little profile development, ochric epipedon

Gelisol (el)

permafrost (frozen)

Histosol (ist)

peat or bog soil (organic)

Inceptisol (ept)

embryonic soil with few features, ochric or umbric epipedon, cambric horizon

Mollisol (oll)

Mollic epipedon, dark, high in bases

Oxisol (ox)

oxic horizon, no argillic, highly weathered

Spodosol (od)

spodic horizon with iron/Al oxides

Ultisol (ult)

argillic or kandic horizon, low base saturation

Vertisol (ert)

high in swelling clays, deep cracks when wet

aquasols

a new soil order; wet, water-saturated soils