Soil Profile

Horizons, Sub-horizons, subordinate distinctions, epipedons

O Horizon

O Horizon

organic matter, in forests usually, absent in cultivated soils

A Horizon

First mineral horizon, dark, humus, granular, finer materials lost to eluviation and erosion

E Horizon

light colored, eluviation of clay, Fe, Al, and/or organic matter, coarse, forests usually

B Horizon

illuvial: clay, Fe, Al, (humid), CaCO3/CaSO4 (arid), blocky/prismatic

C Horizon

unconsolidated under solum, may or may not be the parent material

R Horizon

bedrock, no weathering

b

buried

g

mottling/gleying (in B horizon): Fe reduction and oxidation from fluctuating water table

k

accumulation of carbonates (in B horizon): arid regions

n

accumulation of sodium (in B horizon): destroys soil structure

p

plowing (in A horizon): low structural stability

t

accumulation of clay (in B horizon)

w

weakly developed

x

fragipan (below B horizon): loamy, low water flow

Factors that drive soil formation

Vegetation, rainfall, climate, topography, animals

Distinguishing features of horizons

color, organic matter content, texture, structure

Illuviation

Accumulation of materials

Eluviation

Leaching of materials

Albic (sub horizon)

Light colored eluvial (E) horizon, depleted clay,, Fe, and Al oxides, low fertility

Argilic (subhorizon)

Illuvial (Bt) horizon, clay accumulation, 2-30% higher clay content than A or E

Natric

Illuvial (Btn), accumulation of clay and Na, columnar or prismatic structure, High pH, poor physical properties due to soil dispersion, arid and semi arid regions

Cambic

Illuvial (Bw or Bg), limited clay accumulation, may show carbonate depletion

Kandic

Illuvial, accumulation of low activity clay, Fe, and Al oxides, occurs below abrupt boundary, Southeast USA

Oxic

Illuvial, extensive accumulation of low activity clay, Fe, and Al oxides, not sticky, humid tropical and sub tropical regions

Spodic

Illuvial, accumulation of organic matter and Fe/Al oxides, coarse textured, highly leached forest soils in cool humid climates

Calcic

Illuvial (Bk) accumulation of CaCO3, arid and semiarid regions

Epipedon

Surface part of the pedon: organic matter, texture, color, structure, cation comp

Mollic

under grass, dark, thick, high organic matter (1-30%)

Umbric

like mollic but more acidic, in areas with higher rainfall

Ochric

mineral horizon that is not mollic or umbric: too thin, too light, too low in organic matter

Melanic

Developed from volcanic ash, thick dark, high organic matter content, light and fluffy

Histic

formed in wet areas, thick organic horizon under mineral soil, light and fluffy