SOIL PROFILE Soil genetic horizons HORIZON soil layer

SOIL PROFILE

Soil genetic horizons -HORIZON: soil layer parallel to surface with characteristics produced by soilforming processes

3 basic soil units (scale) Pedon: smallest volume called a soil Polypedon: soil body (2 or more pedons) in which soils are relatively uniform Soil Series: groups of like polypedons

profile: one side of pedon, showing all horizons; 2 -D

Master horizons O A E B C R Not every soil has all of these!!!

O horizon Organic material Same as litter layer or “duff”

Oi slightly decomposed (litter) : FIBRIC Oe intermediate decomposition: HEMIC Oa highly decomposed : SAPRIC Oi Oe Oa

A horizon (“TOPSOIL”) § topmost mineral horizon accumulation of well-decomposed O. M. § Often bioturbated § surface horizon disturbed by plowing (Ap)

A horizon in grassland

Buried A horizon Ab

E horizon § LOSS of § silicate clay, Fe & Al oxides, humus by eluviation § carbonates, gypsum by leaching

Leaching vs. eluviation LEACHING : removal of soluble minerals (Ca, Mg, Na) in solution ELUVIATION : loss (by water) of suspended materials (clay, humus, oxides) ”emigrating”

E horizon § lighter color than A § Because the colorful humus and Fe, Al oxides have eluviated away § coarser texture than B § Because the clay eluviated away

E horizon in forest soil

B horizon ACCUMULATED (illuviated ) ”immigration” silicate clay, Fe & Al oxides, carbonates, gypsum, humus § § distinguished from A or E: § stronger, redder, or darker color § OR different texture

Bh Has illuviated humus from E (dark, brown or black stain at top of B) Bs Has illuviated sesquioxides of Fe, Al from E (reddish color at top of B) Bhs Has both

E Bhs

O A E Bh Bs

E Bhs Bw

Bhs

E A Bhs

A E Bhs Bw

Bt An accumulation of silicate clay in B Can recognize it if you have clay in the B but not as much clay in the A ; can see clay skins Called an “argillic” horizon

Bk Has precipitated carbonates in it; White nodules or streaks Strongly effervescent

w : used if you see a change in B that is not accounted for by other subhorizon letters Bw If you see changes in color, texture, structure within a B

C horizon § Mineral horizon (not bedrock) underlying A, E, B horizons § not affected by soil-forming processes § may be parent material

R horizon Consolidated rock

Transitional horizons Zone of transition between master horizons AB A B; A dominates BA A B; B dominates AC A C; A dominates EB E B; E dominates etc….

Mixed horizons One horizon scattered within another horizon B/A mixed A&B; B is matrix for A E/B E is matrix etc….

Numbers after letters Changes within master horizon for which there is no subhorizon designation e. g. , A 1 A 2 for color change within A

g ss o n Additional subhorizons that you will need to know:

g : gleying Wet; grey; below water table Bg

ss : slickensides Shiny surfaces on clay peds that have Rubbed against one another, polishing the surfaces

o : all Fe, Al oxides Red, tropical Bo

Bss In Agassiz clay

n : accumulation of sodium (Na) Usually found in dry grassland or arid regions

Identifying horizons in the field

some terminology… Colloidal : submicroscopic humus and clay are colloidal Humus: ultimate stage of organic decay predominately protein, gums, lignin Sesquioxides: 1½ oxygens for each Fe, Al sesquioxides of Fe, Al: Fe 2 O 3 Al 2 O 3