Plant and Soil Science Standard 4
Objective 2
Objectives
Explain Soil Components
b. Describe the physical characteristics of
soil and soilless media
c. Describe the biological activity within soil
and soilless media
d. Describe the chemical properties of soil
and soilless media
e. Explain the characteristics of water
movement in the soil and soilless media
a.
SOIL
Mixture of mineral
matter, organic
matter, water, and
air.
 Properties of soil

4 Soil components
Average soils will contain 45%
minerals and 5% organic matter.

The components air and water
equal the other 50%.

Air
25%
Mineral
Matter
45%
Water
25%
Organic
Matter 5%
Soil components


The two components Water and Air
change depending on the amount of
water or rain fall a soil receives.
The four parts of a soil:
 mineral
 organic matter (HUMUS)
 water
 air
5 Soil Formation Factors
1. Parent material-The material that
soils will be formed from.
2. Climatic factors* Most influential of
the four factors.
a. Temperature
b. Rain
c. Wind
*Active factors
Soil Formation Factors
3. Relief (topography)The elevation or
slope of the land.Soil Formation
Factors
4. Biota* (biosphere) All Living organisms
in an environment
5. Time-The amount of time that materials
have been weathered, determine the
type of soil and it’s properties.
Soil Profile
consists
of 3 basic layers
topsoil
subsoil
soil
bedrock
Topsoil
represents
plowed
depth normally
Subsoil
deep
rooting plants send
roots down into subsoil
Master Horizons

O-(organic) forms above
the mineral soil. This horizon
is usually found in forested
areas.

A-This is the top soil. It is a
dark humus layer where
most plant rooting occurs
Master Horizons

B-zone of illuviation or
accumulation from zones
above it.
 C-parent material composed
of wind-blown
silt(loess),river deposits or
glacial till,
 R-Bedrock
Soil
classified
according to
percentage of sand, silt, and
clay they contain.
We call this Soil texture!
Soil Physical Characteristics

What is Soil Texture?
 It is the proportion of three sizes of soil
particles.
○ Which are:
 Sand (Large)
 Silt (Medium)
 Clay (Small)
Soil Structure
Soils have three different particle sizes
The largest particles are sand. They range
from 2.0-.005 mm in diameter
Soil Structure
Particles that are between .005-.002
mm in diameter are considered silt.
The soil particles .002 mm in diameter
and smaller are clay particles.
Soil Texture

What is Sand?
 It is the largest and is further divided into
four subcategories.
 They are:
○ Very coarse sand
○ Coarse sand
○ Medium sand
○ Fine Sand
Soil Texture

Sand
 it is the largest soil separate and is





composed mainly of weathered grains of
quartz.
Sand is also gritty to the touch.
Sand grains will not stick to each other.
silt and clay make up less than 20% by
weight
drain well
little water holding capacity
Soil Texture

Sand
 What will sand do to the soil?
○ It will improve the soil by improving the water
infiltration and aeration
Soil Texture

Silt
 is the medium sized soil separated.
 Silt particles are silky or powdery to the touch
 Silt grains will not stick to one another just like
sand grains.
 Silt is the best soil as it has the ability to hold
large amounts of water in a form plants can
use.
Soil Texture

Clay
 is the smallest size soil separate.
 It is composed of tiny crystals
 Clay is formed by chemical reactions between
weathered minerals to form tiny particle of new
minerals.
 Clay will hold more plant nutrients than any other
separate.
 Clay grains will stick to one another.
must contain at least 30% clay
 holds more moisture than is good for plants
 poor drainage

Loamy Soil
most
desirable soil
equal parts sand, silt and
clay
Soil Texture
Soil Texture

There are 12 textural classes which can
be seen in the next slide.
Soil Texture

Pass out picture of triangle and lets see
if we can classify some soils.
Soil Texture

1.
 40% sand 22% clay and 38% silt
 What is the soil classified as?
Soil Texture

2.
 30% sand 30 % clay and 40 % silt
 What is it?
Soil Texture

3.
 40% sand 10 % clay and 50% silt
 What is it?
Soil Texture

4.
 40 % sand 30% clay and 30% silt.
 What is it?
Soil Texture

Ribbon Method
 See if you can make a ribbon and with which
one?
 Which one feels grittiest?
 Which one feel powdery?

Soil Sedimentation Method
 Place soil in a jar
 Mix soil and water
 Let it settle
Time for a lab

Before we begin put everything away (this
could get a little dirty)

Pick up lab sheets
 Soil Texture by Feel Answer Sheet
 Soil Texture Flow Chart
You will need to texture each of the four
samples of soil
 Keep your area as clean as possible

Biological Properties

The Soil Ecosystem
 Interaction of biotic and abiotic factors in a soil
environment. The process of organisms
growing and decomposing.
Chemical Properties
Important for plant growth and
availability of nutrients
 Dissolved mineral salts determine soils

 Acidity: pH of less than 7.0
 Alkalinity: pH of more than 7.0
 Neutrality: pH of 7.0
Cation Exchange Capacity (CEC)
Total number of exchangeable cations
soil can hold (amount of its negative
charge)
 Depends on amounts and kinds of clay
and organic matter present
 Increases as organic matter increases

Properties of Soil Clays
Clay particles are stacked in layers like
sheets of paper.
Each clay sheet is slightly separated
from those on either side.
Each sheet has negative charges on it.
Negative charges have to be balanced
by positive charges called cations.
1/20,000 in
Cation Retention on
Organic Matter
Hydrogen
Nutrients
Increasing pH
increases cation
exchange capacity
of organic matter
Low pH, 4 - 5
(acidic soil)
Neutral pH, 7
(“sweet” soil)
Cation Exchange Capacity
 Cation
exchange capacity (CEC) is
the total amount of cations that a
soil can retain
 The
higher the soil CEC the
greater ability it has to store
plant nutrients
 Soil CEC increases as
 The amount of clay increases
 The amount of organic matter
increases
 The soil pH increases
Transportation of Soils


Gravity-colluvial
water

stream-alluvial
 ocean-marine
 lake-lacustrine


ice -glacial
wind-aeolian
Erosion
One of the largest environmental
problems stemming from agriculture is
erosion.
 Erosion lowers productivity because of
the loss of topsoil.

Erosion Prevention/Reduction
1. Minimum or No
till farming-Leaving
stubble in the
fields to hold soil
and planting over
it.
 2. TerracingPlanting crops in a
zig-zag formation.

Erosion Prevention/Reduction
3. Leave crop residue to cover the soil! Utilize
mulches!
4. Use cover crops! Use windbreaks. Use
contour farming and strip cropping.
Types of Water in Soil
Gravitational water is water that soil is
unable to hold
 Capillary water is held against the force of
gravity

 Free moving capillary water
○ Moves in all directions
Types of Water in Soil
• Capillary water is held against the force
of gravity
– Available capillary water (field capacity)
• Water left after capillary movement stops
– Unavailable capillary water
• Water not available to plants