1. Understanding Soil Formation
Cover of N.C. Agric. Res. Bull. 467
Understanding Soil Formation

2. Mendocino Staircase Hans Jenny
( )

4. The Hans Jenny Pygmy Forest Reserve Extremely acid and infertile
In this complex “ecological staircase,” each terrace is
~ 100,000 years older than the one below it and supports a distinct association of soils, plants, animals and microbes.
Pygmy forest .
Giant trees
The highest and oldest of five wave-cut terraces that rise from the chilly waters of the Pacific Ocean.
Extremely acid and infertile
soil
Beach sand

5. How is it possible that soil can naturally become so unproductive?

6. Where is Macomb in this sequence?
Dr. Jenny also studied climosequences across the Great Plains.
Brady and Weil, 2002

7. 5 factors of soil formation
Soil = f (Cl, O, R, P, T…)
H Jenny refined the ideas of
Russian scientist VV Dokuchaev
into the following equation:
Relief
Time
Climate
5 factors of soil formation
Organisms
Parent material

8. Young Soils Older Soils Which factor is most important ??? Organisms
Climate
Which factor is most important ???
Young Soils
Older Soils
Parent material
Topography

9. Many of these deposits are hundreds of feet thick!
Understanding parent materials in Illinois
Glacial deposits cover most of Illinois
Many of these deposits are hundreds of feet thick!

10. Retreating Glacier

11. silt sized glacial flour, transported by wind,
Depth of loess cap
LOESS
silt sized glacial flour, transported by wind,
deposited near rivers

13. secondary clay minerals
Glaciation
Primary
minerals
chemical weathering
physical weathering
dissolution
chemical weathering
alteration
precipitation K+
HCO3-
Ca+2
Cl-
SO4-2
Na+
sand and silt
ions in solution
leaching
secondary clay minerals

15. Increasing temperature
Climatic variation
Increasing rainfall
Increasing temperature
RR Weil

16. NO ! Average annual precipitation in IL 1951-1990
Have precipitation levels remained constant during the last 10,000 years ?
NO !

17. Topographic variation
N.C. Agric. Res. Bull. 467
Topographic variation
Poorly drained
Interstream divide
Somewhat poorly drained
Moderately well drained
LANDSCAPE POSITIONS
Well drained
Poorly drained
Shoulder
Common in IL
Valley floor
SOIL DRAINAGE CLASSES
Backslope

18. Soil Associations in McDonough County, IL
Topography of McDonough County, IL
800 feet above sea level
A soil association is a group of soils that are found together in a landscape
470 feet above sea level

19. Vegetative variation Grassland Forest Organic- rich A horizon
From Brady and Weil, 2002

20. How much of Illinois was originally covered by tall grass prairie ?
How much of Illinois was originally covered by forest ?
13.8 million acres
22 million acres
Corn and soybean dominate IL landscapes today but we know where the prairie and forest use to be because of the soils
Illinois once was covered by a complex mix of prairie and forest
Prairie dominated the flat expanses
Forest dominated the hilly land
Old growth forest in

21. Temporal variation
Lake terrace chronosequence in northeastern Michigan

22. Young Soil in NC Old Soil in NC
Poorly Defined Horizons Low Degree of Weathering Slightly Leached Thin Solum
Well Defined Horizons High Degree of Weathering Highly Leached Thick Solum

23. Adapted from Stewart (1990)
Precipitation
plus solutes,
aerosols and
particulates
Additions
Additions
Sediment
Loss of gases
N2, N2O, CO2
Losses
Soil forming processes
Sediment
Losses
Capillary
rise of
dissolved
ions
E(i)lluviation of
clay
CaCO3
dissolved ions
dissolved OM
Organic residues  humus
Primary  Secondary
minerals minerals
TRANSLOCATIONS
TRANSFORMATIONS
TRANSLOCATIONS
Capillary
rise of
salts
Additions
Leaching of
dissolved
ions & OM
Losses
Adapted from Stewart (1990)

24. Water driven translocations
Illuviation
Eluviation
Illuviation
Illuviation

25. Typical Florida flatwoods soil
E uviation = depletion l
I uviation = accumulation ll

26. Conceptual chronosequence

27. Chronosequence in California
Foth, 8th ed.

28. Characteristics that differentiate soil horizons
Color
Texture
Density
Structure
Organic Matter content
Acidity
Mineral Accumulations
Biological activity
RR Weil

29. Soil horizons Master Soil Horizons Most Weathered Least weathered
RR Weil