200_INTRO SOIL SCIENCE_2017_40

EPSc 413: Introduction to Soil Science
Spring 2017
Prof. Jeff Catalano

#1 Rule of this course:

Soil is not Dirt!!!!

Soils Dominate the Terrestrial
Landscape

Soil is a Complex
Dynamic System

Rates of Soil Production (Gain) and
Erosion (Loss)

• Average rate of natural soil production:
0.02 mm/yr

• Average rate of soil erosion from land used for
agriculture:
2 mm/yr

Soil as a Natural Resource

Soil Erosion in Central US

1000s yrs

Entisol Mollisol

• Soil formation on fresh material takes 1000s of years

• Soils may be eroded or degraded through poor
agricultural practices

• Many of our current practices amount to “mining” soil

• Once gone, some locations will not produce new soils
under current climate conditions

Question: What 1973 science
fiction movie is about soil
degradation?

Hint: The movie stars Charlton
Heston, and is NOT Planet of the

Apes



Soils were Critical to Human History

• Early civilizations developed in river
valleys with rich, fertile soil

• Collapse of many civilizations is often
connected to soil degradation

– Salinization of soils from irrigation in Severe soil salinization in Central
Mesopotamia California

– Erosion of hillside soils in ancient Greece

– Soil degradation across Roman empire

• Darks ages may represent periods of
time needed to regenerate soil

• Lifetime of our current civilization may

depend on our ability to manage and

sustain our soil*

*Read: Dirt: The Erosion of Civilizations by David Montgomery Severe soil erosion in the
for more thoughts on this topic. piedmont region of South Carolina

Population Growth Requires
Improved Soil Management

• Population is growing faster that the amount of
arable land

• Requires increased crop yields (food produced
per unit area of land) to sustain the population

Images from FAO

EPSc 413: Introduction to Soil Science
MW 10-11:30, Rudolph Hall 203

Instructor: Prof. Jeff Catalano
TA: Xandi Barrett

Textbook: The Nature and Properties of
Soils, 15th ed., by Brady and Weil, 2017

Website: http://epsc413.wustl.edu/

Grading Policy: 30%
Homework: 60% (20% each)
Exams : 10%
Field Trip Report:

Exam Policy: see syllabus
Late Work Policy: see syllabus
Grades: see syllabus

Field Trips: One 1-day trip:
Tyson Research Center on April 1





Introduction to Soils

What are the important roles of
soils on Earth?

Major Roles of Soils

“Soil” vs. “A Soil” vs. “The Soil”

• “Soil” is material composed of minerals, water,
gases, organic substances, and microorganisms

• “A Soil” is a specific, 3-dimension natural body

– Harvest silt loam dominates the Danforth campus
– Menfro silt loam dominates Forest Park
– A collection of silt loams dominate Tyson

• “The Soil” is the collection of individual bodies
that cover the Earth’s surface



Components of Soils

Soils are a Mixture of Minerals, Water,
Air, and Organic Matter

50% Holes 50% Solids

Mineral Constituents of Soil

• Soil minerals show a range of sizes and compositions
• Soil structure depends on proportions and

arrangements of soil particles

Soil Organic Matter (OM)

High OM = Good Structure

Mollisol: Grassland soil Histosol: Wetland soil Low OM = Poor Structure
high in OM at surface composed of OM

Soil Water

• Soil water coats the surfaces of minerals and OM

• Soil water contains many solutes, including many of
the elements need for plant growth: The Soil Solution

• Soil solution pH can vary widely

Soil Water

Soil Gases

Rhizosphere: Root-Soil
Interface

Soil is a Complex
Dynamic System

Soil Horizons and Profiles

Soil Horizons

• Soils display distinct layering
• O Horizon: Partially

decomposed organic matter
(OM)
• A Horizon: Near surface,
mineral soil rich in OM
• E Horizon: Leached layer below
A horizon (sometimes absent)
• B Horizon: Accumulation of
minerals, low in OM
• C Horizon: Weathered parent
material

Formation of Soil
Horizons

• Soil horizons form from the
downward transport of
minerals, solutes, and OM

– Downward movement of OM
forms A horizons

– Downward movement of minerals
forms A, E, and B horizons

• A & E lose minerals
• B accumulates minerals

– Downward movement of salts
forms B horizon

Forest Soils

Plains/Grassland Soils

Volcanic Soils

Young or Disturbed Soils

Old Soils

Dry Soils

Frozen Soils

Organic Soils

Man-Made Soils

Key Points

• Soils are diverse!
• Soils play key roles in supporting ecosystems and

food production
• Soils can be made of mostly mineral matter or

organic matter

– 50% Solids, 50% Holes (Pores) filled with air and water

• A soil is composed of horizons, layers formed by
the downward movement of water and solids