Anyone who did not attend
Lecture I, see me after class for materials and course basics

Soil Basics

knowledge known only to the initiated
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What is Soil?
It is not Dirt

…unconsolidated surficial material
Short-sighted Engineer, 1985

A dynamic natural body composed of mineral and organic materials and living forms in which plants grow . The collection of natural bodies occupying parts of the earth’s surface that support plants and have varying properties due to the integrated effects of climate and life acting upon geologic materials, mediated by relief (topography) and time
Brady and Weil, 2000

What is Soil?
Agronomist
Forester
Horticulturalist
Engineer
Environmentalist
Ecologist

Medium for plant growth
Regulator of water supplies
Recycler of raw materials
Habitat for soil organisms
Engineering medium

Fundamental Components of Soil

Idealized Surface Soil
Voids
Avenues
Storage
Distribution
Movement
Solids
Interactive Media
Minerals
Organic matter
Reactivity

Components of Soil
Gases ~ 25%
Oxygen:
Carbon Dioxide:
Atmosphere Soil Atmosphere
21% 5-10%
0.038% 0.3-3%
Microorganisms tend to reduce oxygen and enrich carbon dioxide

Components of Soil
Liquid ~ 25%
Dissolved and Suspended Constituents
Nutrients
Metals
Salts
Acids/Bases
Organic Compounds
Contaminants
Gases
Solid Phase

Components of Soil
Mineral + Organic ~ 50%
Solid soil particles and organic matter
Organic: decomposed plant and animal material
Mineral: Sands, silts, clays, oxides (Al and Fe)
• reactivity
• Water movement/retention

Organic Matter
Mineral Soil Organic Soil
< 20% O.M.
> 20% O.M.
5% >50%

Vegetative Influences
Deciduous
Forested
Coniferous Grasses

Organic Matter
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Generalizations
Soil color – the darker the color, the more OM .
Soil structure – cementing agents, fibers.
Soil nutrients – organically derived (P, S, N, Ca, Mg, K) .
Energy sources – energy for soil organisms.
Soil Water – increases water holding capacity
Soil reactivity – increases chemical reactivity of soils

Components of Soil Mineral ~ 45%
Rocks, stones, gravel, particles, aggregates
Particles: primary minerals (quartz, feldspars) secondary minerals (clays, oxides)
Rocks Primary Minerals Secondary Minerals
Can be highly reactive

Additions
Losses
Translocations
Transformations

Soil as a Natural Body
Differentiation
Additions
Losses
Translocations
Transformations
Parent Material
Bedrock Bedrock

The Essentials of Soils
Soil Profile – 2D representation of a vertical section of soil from the surface to its deepest layers.
Differentiation of layers
Is highly variable.
Soil Profile

Soil Horizons
Roughly parallel layers in the soil with varying composition and properties

Soil Master Horizons

A horizon

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• topsoil/plow layer.
Accumulates organic material
Often darker than soil below.
high in plant roots, biotic activity
Zone of gas and water exchange
A horizon
A horizon

A horizon
B horizon

Accumulates material transported from above, or forms in place.
(translocation, transformation)
Zone of Illuviation (translocation) .
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clays, O.M., Fe/Al oxides, salts good soil structure
Strong color development
Potentially high reactivity
B horizon

A horizon
B horizon
C horizon

-Weakly altered by soil forming processes.
-Closely resembles parent material
C horizon

A horizon
B horizon
C horizon
E horizon

Zone of Eluviation
Eluviation = exit
Illuviation = into
•Organic matter
•Clay
•Carbonates
•Fe, Al oxides
•color
A horizon
E horizon
(Elluvial)
B horizon
(Illuvial)

A horizon
B horizon
C horizon
R Horizon
Florida?
E horizon

limestone R horizon

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• Surface Horizon
Organic horizon
Non-mineral dark-colored
Often called peat, muck
Some are very fertile, valuable
In some countries, O horizon used as fuel.

O Horizon

O horizon
O horizon
A horizon
A horizon
C horizon
B horizon
R Horizon
Master Horizons
 O organic
E horizon  A topsoil
 E elluvial
 B developed
 C parent material
 R bedrock

Criteria for Characterizing
Soil Horizons
Color
Texture
Density
Structure
Organic matter
Mineralogy
Chemistry

Determinants
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Mineralogy of the soil/parent material
Relative amount of organic matter or iron
Hydrology of the soil
Oxygen status

Value related to total amount of light reflected.
Munsell Soil Color
Hue dominant spectral color; related to the wavelength of light. Related to the proportions of red to yellow.
Chroma measure of the strength of spectral color

Hue = 10 YR
Value = 6
Chroma = 3
Munsell Color
10 YR 6/3

Hue dictates dominant spectral color for a given page.
Low value indicates dark soil colors. (O.M.?)
High chroma indicates strong color expression
10YR 3/6

Communication
Water table depth
Oxygen status
Development decisions

Criteria for Characterizing
Horizons
Color
Texture
Density
Structure
Organic matter
Mineralogy
Chemistry