What Is Soil?

The four components of

soil:

Decomposed rock

Humus

Air

Water

Soil is the layer of rock and mineral fragments along with organic matter, water and air that supports the growth of plants.

What is Dirt?

Dirt is what gets on your clothes and into your house

Controls on Soil Formation• Parent material – Bedrock vs.

Unconsolidated• Time – longer time, more soil• Climate – temperature and

precipitation• More plants and animals =

more organic matter• Poorly developed soils on

steep slopes

Soil Texture and StructurePoint A:

10% silt

40% clay

50% sand

Clay loam has no single

particle size percentage that

dominates!

Controls of Soil FormationIf the parent material is bedrock, then

we get residual soilsOn unconsolidated sediments, we get

transported soils

Soil composition

-Soil forms in layers-Larger materials are found on the bottom

How quickly is soil formed?

-It may take several hundred years for 1cm to form

Soil profile

A vertical column showing the

sequence of layers of particles in the

soil

Soil Horizons-A distinct layer or zone within a profile-There are four major zones (O, A, B, C)

O zone -Leaf litter, high decomposition

A Zone

-High organic matter

-Generally the darkest in color

-High humus content

B Zone

-Less developed

-Lighter in color

-Zone of accumulation (highly soluble mineral build-up)

-Red or brown in color

-Clay accumulated (Hard pan formation)

C Zone

-Contains weather parent material

Soil HorizonsO zone

-Leaf litter, high decomposition

A Zone-High organic matter-Generally the darkest in color-High humus content

B Zone-Less developed-Lighter in color-Zone of accumulation (highly

soluble mineral build-up) -Red or brown in color-Clay accumulated (Hard pan

formation)C Zone

-Contains weather parent material

Rill and Gully Erosion

Eroded channels ranging in size from rivulets to small gullies caused mainly by runoff waters rather than raindrop dislocation.

Gully erosion in Tanzania. What is the main factor for it’s cause?

Who cares about soil erosion?