1. Plant and Soil Science Standard 4 Objective 2
Properties of Soil
Plant and Soil Science Standard 4
Objective 2

2. Objectives Explain Soil Components
Describe the physical characteristics of soil and soilless media
Describe the biological activity within soil and soilless media
Describe the chemical properties of soil and soilless media
Explain the characteristics of water movement in the soil and soilless media

3. 4 Soil components
Average soils will contain 45% minerals and 5% organic matter.
The components air and water equal the other 50%.

4. 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. 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

6. 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.

7. Soil Profile
consists of 3 basic layers
topsoil
subsoil
soil bedrock

8. Topsoil
represents depth normally plowed

9. Subsoil
deep rooting plants send roots down into subsoil

10. 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

11. 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

12. Soil
classified according to percentage of sand, silt, and clay they contain.
We call this Soil texture!

13. 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)

14. Soil Structure
Soils have three different particle sizes The largest particles are sand. They range from mm in diameter

15. Soil Structure
Particles that are between mm in diameter are considered silt. The soil particles .002 mm in diameter and smaller are clay particles.

16. 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

17. 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

18. Soil Texture Sand What will sand do to the soil?
It will improve the soil by improving the water infiltration and aeration

19. 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.

20. Soil Texture must contain at least 30% 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

21. Loamy Soil
most desirable soil
equal parts sand, silt and clay

22. Soil Texture

23. Soil Texture
There are 12 textural classes which can be seen in the next slide.

25. Textural triangle

26. Soil Texture
Pass out picture of triangle and lets see if we can classify some soils.

27. Soil Texture 1. 40% sand 22% clay and 38% silt
What is the soil classified as?

28. Soil Texture 2.
90% sand 10 % clay and 25 % silt
What is it?

29. Soil Texture 3.
30% sand 50 % clay and 15% silt
What is it?

30. Soil Texture 4.
10 % sand 80% clay and 30% silt.
What is it?

31. Soil Texture Ribbon Method Soil Sedimentation 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

32. 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

34. Biological Properties
The Soil Ecosystem
Interaction of biotic and abiotic factors in a soil environment. The process of organisms growing and decomposing.

35. 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

36. 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

37. 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.
There are many different types of clays in soils. Many of these clays are known as layered clays and have a structure similar to what is shown in this diagram. They are built up of several sheets stacked together. Each sheet is slightly separated from the ones on either side of it. It is this structure that gives layer clays such a high surface area for just a little bit of clay. Every surface of these clay sheets will hold a film of water. Some of that water is available for plant roots to use. This structure of clays is what provides soils with much of their ability to store water for plant growth. Notice the size of the clay particle. We are talking about extremely small things here.
Each clay sheet is made up of crystals containing oxygen, silicon, and aluminum. When the clay sheets form, aluminum will often go into the crystal where silicon normally would be. This causes a negative electrical charge on the clay surface. This substitution of aluminum for silicon happens over and over in every clay sheet. Thus every clay sheet has many negative charges on every surface.
Nature cannot tolerate an unbalanced system, so these negative charges must be balanced by positive charges. Just as the negative pole of a magnet attracts the positive pole of another magnet, these negatively charged clays attract positive charges.
The amount of negative charge on the clay that can hold positive charges (cations) is called the “Cation Exchange Capacity” or CEC for short
Where do these positive charges (cations) come from?
1/20,000 in

38. Cation Retention on Organic Matter
Hydrogen
Nutrients
Increasing pH
increases cation
exchange capacity
of organic matter
Stable soil organic matter is made up of large complex organic molecules that are resistant to further attack from soil microbes. Pieces of soil organic matter appear like coiled, twisted strands. This material coats particles of silt and clay and helps to hold clay and silt together in soil aggregates. The coiled structure also gives organic matter a very large surface area.
Soil organic matter is also like a sponge. It can soak up large amounts of water and store it for plants to use.
Soil organic matter has a very high cation exchange capacity. Unlike many layer clays, the cation exchage capacity of organic matter changes as soil pH changes. As soil pH decreases (becomes more acid) more and more hydrogen cations stick to organic matter. At low pH this hydrogen is held very tightly and will not exchange with nutrients or other elements. As soil pH increases the hydrogen is held less strongly and readily exchanges with other nutrient and trace element cations like calcium, magnesium, potassium, and sodium. These cations will also exchange with each other at near neutral pH.
Low pH, 4 - 5
(acidic soil)
Neutral pH, 7
(“sweet” soil)

39. 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
Together, clays and organic matter account for most of the cation exchange capacity of the soil.
Cation exchange capacity refers to the total amount of cations that a soil can retain.
The higher the exchange capacity, the better the soil is able to retain plant nutrients and other elements. The exact cation exchange capacity of soil depends on:
what type and how much clay it has,
how much organic matter it has, and
what its pH is.

42. Transportation of Soils
Gravity-colluvial
water
stream-alluvial
ocean-marine
lake-lacustrine
ice -glacial
wind-aeolian

43. Erosion
One of the largest environmental problems stemming from agriculture is erosion.
Erosion lowers productivity because of the loss of topsoil.

44. Erosion Prevention/Reduction
1. Minimum or No till farming-Leaving stubble in the fields to hold soil and planting over it.
2. Terracing-Planting crops in a zig-zag formation.

45. 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.

46. Types of Water in Soil Free moving capillary water
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

47. 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