Soil Formation

What is the first step in soil formation?

The weathering of rocks

Mosses and lichens are called pioneer organisms because they are the first organisms to grow on rocks

What is the second step in soil formation?

the addition of humus (decaying organic matter)

Soil Profile- Draw this!(SS)

A soil profile is a cross section of soil.

There are three major soil horizons – A, B, and C.

Horizon A

top & darkest layer (high concentration of organic matter - humus)

Top soil

Horizon B

subsoil enriched with clay minerals leached from the topsoil.

Horizon C

bottom layer (weathered rock)

Parent Rock

Factors Affecting Soil Profiles

Topography (slope) of the land – Soils on slopes tend to be thinner soils in flat areas like valleys or plains are thicker

Age – older soils are thicker because they have had more time to develop.

Climate

Distribution of Soil Types

Soil Textures

Particles of soil are classified by size.

The particles of soil are clay, silt, & sand.

What determines a soil’s texture?

The relative proportions of these particles.

The texture of a soil affects its capacity to absorb and retain water & support plant growth.

Soil Texture Triangle