Notes 13-23 Soil Formation and Erosion & Soil Composition and Properties

APES 2024

Physical weathering

Physical weathering

The mechanical breakdown of rocks and minerals

Chemical weathering

The breakdown of rocks and minerals by chemical reactions, the dissolving of chemical elements from rocks or both

Erosion

The physical removal of rock fragments from a landscape or ecosystem

Erosion is usually the result of

• Wind, water and ice move materials downslope

• Living organisms burrowing in the soil

Soil

The mix of geologic rock and organic components

Components of soil

• Sand

• Silt

• Clay

• Humus

• Nutrients

• Water

• Air

• Living organisms

Humus

Main organic part of soil - biomass that is broken down ex. leaves, dead organisms, and waste

Nutrients of soil

• Ammonium

• Phosphates

• Nitrates

Factors that determine the properties of soil

• Parent material

• Climate

• Topography

• Organisms

• Time

Parent material

The underlying rock materialfrom which the inorganic components of a soil are derived

Climate

Warmer soil will form faster, more precipitation means more weathering, erosion, and deposition

Topography

Steep slopes will cause too much erosion, more level ground will have more deposition

Organisms

Bacteria, fungi, and worms will break down organic matter

Functions of soil

• Medium for plant growth

• Filter & purify water

• Habitat for living organisms

• Filters pollutants

Horizon

A horizontal layer in a soil defined by distinctive physical feature such as texture and color; there are 5 types

Types of horizons

• O

• A

• E

• B

• C

O horizon

The organic horizon at the surface of many soils, composed of organic detritus in various stages of decomposition

O Horizon includes

Plant roots, dead leaves and animal waste

What does the o horizon do

Provides nutrients and limits water loss to evaporation

The most fully decomposed organic matter of the lowest section of the o horizon

Humus

A horizon

Frequently the top layer of soil, a zone of organic material and minerals that have been mixed together

Has the most biological activity

A horizon

The a horizon is known as

Topsoil

E horizon

A zone of leaching or eluviation; found in some acidic soils under the o horizon, or less often, the a horizon

B horizon

A soil horizon composed primarily of mineral material with very little organic matter

The least weathered soil horizon

C horizon

C horizon always occurs beneath

B horizon

C horizon

Very similar to parent material, also called bedrock

The relative proportions of sand, silt, and caly determine

The physical properties of soil

The physical properties of soil

Size and weight

The order of horizons

O, A, E, B, C

Sizes of sand, silt, and clay

Clay<silt<sand