Exploring Soil Science
Characteristics of Soils
Introduction to Agriculture
Thursday, May 6, 2010
Importance of Soils
Medium for plant growth
Anchors plant roots
Stores and supplies water
Provides air for roots
Provides minerals for plants
Useful geologic substance
Roads, buildings, foundations, landfills
Filter in the hydrologic cycle
What is soil?
Mineral Matter (45%)
Weathered minerals
broken into smaller
particles
Organic Mater (5%)
Dead or decaying
organisms
Pore Space (50%)
Water (25%)
Air (25%)
How is soil formed?
Five factors contributing to soil
formation:
Parent Material
Climate
Living Organisms
Topography
Time
Parent Material
Materials from which the soil originated
Six categories of soil material
Mineral and rocks
Deposits of organic material
Deposits from glaciers
Deposits from wind (aeolian)
Deposits by water (alluvium)
Deposits by gravity (colluvium)
Climate
Precipitation, temperature and wind
Can determine organic matter and
organisms which inhabit the soil
Weathering – physical and chemical
changes produced in rocks by temperature
and precipitation
Temperature causes expansion and
contraction
Climate (continued)
Precipitation dissolves minerals, wears away
surfaces and can freeze into ice
Wind wears away surfaces when it picks up
particles
Glaciers break up and transport parent materials
as they move
Living Organisms
Roots can grow into cracks
and openings
Plant matter, animal wastes
and decaying animals add
organic matter (humus)
Humans change the
landscape though agriculture,
development and use of
natural resources
Topography
Slope affects soil
formation
Steeper slope equals
faster moving water
Landslides can also
attribute to soil
formation (colluvium)
Time
Parent material, climate, living organisms
and topography all depend on amount of
time these process have been occurring
Longer time means more impact
Not days, but years!
Review Questions
1. List the 5 factors responsible for soil
formation.
2. Draw a pie chart showing the volume
composition of soil. Label each piece
and include percentages.
3. How does soil support plant growth?
Give four reasons.
Review Questions
4. Climate includes what three things?
5. How does slope affect soil formation?
6. Which of the five soil forming factors
controls all the others?
7. Define colluvium, alluvium, loess and
humus.