Soil Profiles and Soil Classification

What processes result in the formation of soil horizons?

What are the typical characteristics of O, E, A, B, C and K horizons?

What is CEC? % base saturation? How do these vary among differentsoil types?

What is the role of clay minerals in nutrient retention?

How are soils classified? What are the characteristics of each of the followingsoil orders:

oxisol, alfisol, spodosol, mollisol, aridisol

Soil Horizons:

O – Organic(>50%) plus minerals (<50%)

A – Eluvial; resistate minerals plus organics

B – Illuvial; clays, oxides, active weaterhing

K – Cemented (carbonates, silica, gypsum)

C – Partially weathered parent material

Soil pH:

Organic decay – carbonic and organic acids

Mineral buffering capacity – carbonates – fastsilicates – medium to slow

Leaching –removal of buffer systems – wet climate soilsmore likely to be acidic; arid soils to be alkaline

Acid – 6.0 or lessNeutral – 6.0 to 7.5Alkaline (basic) – 7.5 or greater

Alfisols

Alfisol

Aridisols

Aridisol withsubsurface ‘calcrete’ (Bk)horizon

Inceptisols

Inceptisol

Mollisols

Mollisol

Mollisols

Mollisol

Spodosols

Spodosol

Spodosol