Properties of Properties of SoilSoil

Plant and Soil Science Standard 4 Plant and Soil Science Standard 4 Objective 2Objective 2

Objectivesa. 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

4 Soil components

Average soils will contain 45% minerals and 5% organic matter.

The components air and water equal the other 50%.

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 Factors3. 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 Profileconsists of 3 basic layers

topsoil

subsoil

soil bedrock

Topsoilrepresents depth

normally plowed

Subsoildeep 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

Soilclassified 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 StructureParticles 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 Soilmost 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.

Textural triangle

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.

90% sand 10 % clay and 25 % silt

What is it?

Soil Texture 3.

30% sand 50 % clay and 15% silt

What is it?

Soil Texture 4.

10 % sand 80% 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 onOrganic Matter

Low pH, 4 - 5(acidic soil)

Neutral pH, 7(“sweet” soil)

Hydrogen

Nutrients

Increasing pHincreases cation exchange capacity of organic matter

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. Terracing-Planting 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