1. Introduction to Soils
Instructor: Kitty O’Neil

2. AGPS 1103 – Intro Soils
• 3 credits, lecture & lab each week
• Syllabus
– Contact info
– Textbook, lab manual
– Course outline
– Exams, quizzes, lab reports, grading, project
– Policies
• Extensive use of Blackboard

3. Lecture 1 - overview
• Importance of soil
– Soil functions
• Definition of soil
• Components of soil
– Mineral, organic, air, water
• Soil formation, weathering
– Parent materials
– Soil formation processes
– Soil differs from parent material
• Soils vary in space and in time

4. Why do we care about soil?
?

5. Why do we care about soil?
• Soil resources were and are a central
factor in shaping human history and
development.
• Survival of humans and animals is
dependent on light, water, air and soil.
• Good, productive soil is a basic human
need.
– Grow our food, clean our water, clean our air

6. Why do we care about soil?
“All civilization is basically dependent upon
natural resources. All natural resources …are
soil or derivatives of soil. Farms, ranges,
crops and livestock, forests, irrigation water,
and even water power resolve themselves
into questions of soil. Soil is therefore the
basic natural resource.”
- Aldo Leopold, Erosion and Prosperity, 1921

7. Why do we care about soil?
• “Man—despite his artistic pretensions,
his sophistication, and his many
accomplishments—owes his existence to
a six-inch layer of topsoil and the fact
that it rains.”
- Author unknown

8. What does soil DO?
OK, so soil is important.
Why? What does soil actually DO?
?

9. What does soil DO?
1. Soil serves as a natural medium for the
growth of plants,
2. regulates and purifies water,
3. recycles organic wastes and nutrients,
4. provides habitat for soil organisms, and
5. serves as physical support for building and
construction.
= Soil functions

10. What is ‘soil?’
?

11. What is ‘soil?’
Soil = the unconsolidated
mineral and organic
material on the immediate
surface of the earth.

12. Soil = solids + pore space
Composition of typical soil, by volume
From Univ. of Massachusetts Extension Vegetable Program, Soil Basics, part I

13. Mineral particles
> 2.0mm = Gravel
0.05 – 2.0mm, don’t
stick together, gritty
0.002 - 0.05mm,
smooth when wet
<0.002mm, sticky when
wet, hard clods when dry
from Hillel, 1998, Environmental Soil Physics, Academic Press

14. Organic matter
• Wide range of organic
materials
– Living organisms
• Plants, roots
• Insects, nematodes
• Fungi, bacteria
– Non-living OM, products of
decomposition of living things
• Continuously decomposed,
new compounds
synthesized by other
microorganisms
• Holds mineral particles
together to form aggregates
• Over time, OM is lost from
soil as CO2

15. Pore space = air + water
• Air space provides gas
exchange to organisms and
plant roots
• Water is needed by plants
and organisms
• Soil water also contains
dissolved mineral
compounds & nutrients
needed by plants and
organisms

16. Where did soil come from?
?

17. Where did soil come from?
Soil has been formed by 5 major factors:
1.Parent material (original form)
2.Climate (precipitation and temperature
effects)
3.Macro- and microorganisms
4.Topography (elevation, slope, position)
5.Time

18. Where did soil come from?
Parent
material
Climate
x Organisms
Topography
Time

19. Where did soil come from?
Parent
material
Climate
x Organisms
Topography
Time

20. Soil Formation or ‘weathering’
from Brady & Weil, The
Nature and Properties of
Soils, Prentice-Hall publ.

21. Soil Formation or ‘weathering’
From T.H. Cooper, Soil 2125, U. Minnesota,
http://www.soils.umn.edu/academics/classes/soil2125/index.html

22. Weathering varies with climate,
organisms
From T.B. Walther, Introduction to Geography,
http://www.geography.hunter.cuny.edu/~tbw/ncc/

23. Weathering varies with
topography
From Smith, et al, Soil, in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI
10.1036/1097-8542.631500; after Simonson et al., Understanding Iowa Soils, Brown, 1952

24. Soil originated from ‘parent
material’
As a result of weathering, soil differs from the
parent material :
a)physically,
b)chemically,
c)biologically, and
d)structurally.
…this is an ongoing process…

25. Soils vary widely
Parent  Variable
material
Climate
x Organisms
Topography  Variable
Time
 Really Variable

26. Soils vary widely

27. Soils vary widely

28. Soils vary widely

29. Lecture 1 - overview
• Importance of soil
– 5 Soil functions
• Definition of soil
• 4 Components of soil
– Mineral, organic, air, water
• Soil formation, weathering
– Parent materials
– Soil formation processes
– Soil differs from parent material
• Soils vary in space and in time

30. Questions?

31. Questions?