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