Soil Review
Soil – Soil is a mixture of weathered rock, decayed organic matter, mineral fragments,
water, and air
Formation of Soil – can take thousands of years – is influenced by
1. Climate
2. Slope of the land
3. Type of Rock
4. Types of vegetation
5. Length of time that rock has been weathered
Composition of Soil – the ingredients that make up soil
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Clay (smallest particles), Silt (medium particles), and Sand (largest
particles) are all small particles of sediments
Decaying, dark-colored plant and animal material is called humus
Small spaces between soil particles may be filled with air or water
Good soil has an equal mix of sand, silt, and clay called loam
Soil Profile – Horizons are the different layers of soil
O Horizon: Organic material
A Horizon: the top soil layer of soil, usually covered with
litter, or leaves, twigs, and other organic material
B Horizon: the subsoil layer. Lighter in color due to less
humus and is less fertile.
C Horizon: the parent material. Mostly weathered rock and
is bottom of the soil profile. It is most like the bedrock.
Leaching – the removal of minerals (from the organic material-humus) that have been
dissolved in water
When it rains the water picks up minerals and nutrients and carries them to Horizon B
Soil Types
Parent rock affects soil formation
Climate affects soil development
Time affects soil development
Weathered Rock – broken up rock
in the form of sand, silt, and clay
Bacteria and Fungi – agents that help break down organic matter (decaying plants
and animals)