SOIL

What is soil?

• The loose covering of broken rock particles and decaying organic matter (humus) covering bedrock.

Why is soil important?

• Grow food• Wood for building• Plants provide oxygen• Filter pollutants

How is soil created?• Rock is chemically and

physically weathered.• Bacteria, fungi, lichens, &

insects live in weathered rock.

• These organisms die and add nutrients to weathered rock.

• As soil builds, larger organisms can move in and colonize.

• Takes 100’s of years to create a few cm of soil.

What is a soil profile?• Vertical sequence of soil

layers (horizons).• O Horizon- vegetation/ leaf

litter on top of soil• A Horizon- dark-colored thin

layer; rich in organic matter; humus

• B Horizon- thick layer of subsoil; may be red or brown; clay based soil

• C Horizon- contains weathered parent rock; larger particles of rock; no organic matter

• R Horizon- unaltered parent bedrock

O horizon

R horizon

TYPES OF SOIL

• Polar soil– Form at high

elevations & high altitudes

– No distinct horizons- soil too thin

– Under top few inches of soil, ground is permanently frozen- PERMAFROST.

• Temperate soils– Vary depending on

rainfall & type of vegetation

– Tropical Grasslands- very thick, rich, humus

– Forests- thinner, less fertile clay soil

– Prairies- less rain, so soil not as thick, but still fertile.

• Desert soils– Very thin A horizon– Very little organic

matter– High in minerals– Soil is usually light

colored and coarse textured.

• Tropical soils– Intensely weathered

due to high precipitation and temp.

– Very little humus & very few nutrients

– High concentrations of iron- when oxidizes causes characteristic red color.

SOIL TEXTURES• Size of particles determines

– Water holding capacity– How compacted soil is– Ability to support plant

• Sand- larger particles• Silt- smaller particles• Clay- smallest particles• Loam- equal mix of sand, silt,

and clay

SOIL CONSERVATION

• Soil is easily eroded.• Methods to prevent

erosion include:

Contour Farming- plowing along slope instead of up and down it. Furrows btwn rows of crops collect water.

•Terracing- series of platforms are built into slopes. Effective with steep slopes, slows water flow.

•Shelter Belts- rows of trees planted along outer edges of s creating a windbreak to prevent wind erosion.

Strip-Cropping- Farmers plow so that plowed strips are separated by planted strips. Roots of planted strips hold soil in place.

• Reduce Grazing Permits

• Put up fencing– Animals cannot

compact and destroy plants