Agricultural Science 1:

Soil ScienceAt the completion of this unit, students will be able to:A. Explain the components of soil

B. Investigate soil texture and structure

C. Explain soil profile

D. Explain what soil color indicates

E. Examine moisture-holding capacity and the characteristics of soil water

F. Explain soil pH

G. Describe the meaning and importance of soil fertility

H. Investigate soil degradation

I. Describe soil erosion and management practices

J. Identify careers in soil science and determine educational requirements, working

conditions, and earning potential for those careers

What is soil??

• Is it dirt?

• Is it mud?

Objective A: Explain the components of soil

What is soil?

• Soil is the top few

inches of the earth’s

crust and the

medium that plant

roots grow in.

Objective A: Explain the components of soil

Soil Components• There are four major soil ingredients:

– Minerals

– Water

– Air

– Organic Matter

Objective A: Explain the components of soil

Soil Components• Minerals and

organic matter are the solid particles in the soil.

• Water and air fill the spaces between the particles

• Soil also contains living organisms—some small, some large.

Objective A: Explain the components of soil

Mineral Materials• Inorganic elements are compounds that

naturally occur.

• Minerals in soil comes from rocks and other

materials that have weathered

Mineral Materials• Sand

• Silt

• Clay

• (and other trace minerals)

Mineral Materials: Sand

• Sand is the largest-size mineral particle in soil

Mineral Materials: Sand

• Sand does not hold water well

• Soils that are high in sand are not fertile

because water moves through it quickly and

washes the nutrients away

Mineral Materials: Silt

• Silt particles are smaller than sand—

midsize particle

Mineral Materials: Silt

• Silt particles fill spaces between sand

particles

• Sometimes deposited by water when

land is flooded or washed into the

oceans where streams empty

Mineral Materials: Silt• The Mississippi River Delta is an example of a

land mass that was developed by silt

settling from the flood water of the

Mississippi River.

Can you think of another

Famous river delta?

Mineral Materials: Clay

• Clay is the smallest particle in soil

Mineral Materials: Clay

• Clay fills the spaces

between sand and

silt particles

• It gives soil the ability

to hold water

• Soils that are high in

clay are slow to dry

out after a rainfall

• Clay holds minerals

that plants need for

growth

Mineral Materials: Clay

• The soil texture

triangle is a great

visual way to

examine what soil is

made of. To

determine what

your soil is, follow

these instructions:

Soil Texture Triangle How To:• To find the type of soil, follow these steps:

• 1. Find the Clay % on the left side of the triangle, and at that level, draw a straight line going left to right.

• 2. Find the Silt % on the right side of the triangle and at that % level, draw a line from the top right to the bottom left.

• 3. Find the Sand % at the bottom and draw a line from the bottom right to the top left.

• 4. Look for where the lines cross, and that will tell you your soil type!

Other Mineral Materials

• There are 4 Major Minerals:

– Calcium (Ca)

– Phosphorus (P)

– Nitrogen (N)

– Potassium (K)

Other Mineral Materials• When reading the label

on a bag of fertilizer,

the 3 numbers on the

bottom stand for

Nitrogen

Phosphorus

Potassium

Organic Matter• Organic matter is plant and animal

remains in various stages of decay.

• The decaying organic matter releases

nutrients

• These soils are dark brown or black,

are high in nutrients, and hold a lot of

water

Organic Matter

• Soils with high

organic matter are

more productive

• The soil is more

easily tilled and

made into a

seedbed for

planting

Air

• Air fills some of the space between soil

particles.

• Plant roots need air to live and grow

• Some plants need to adapt to

different environments in order to get

the air they need.

Air• For Example:

Cypress trees grow in wet places. For these trees to have hair,

the roots grow structures known as “knees”. The knees rise a few

feet above the water level.

Air

• Let’s test the amount of air in a soil sample!

• 1. Collect a clod of soil

• 2. Spray with polyurethane and let sit for 1-2

minutes.

• 3. Place the soil clod in a jar of water and

watch the bubbles form!

• The more bubbles, the more air!

Water

• Water is an important nutrient for plant

growth.

• It is held between soil particles and

sticks to their surfaces

• Soil that is too wet or too dry will not

support the growth of most crops and

ornamental plants

Soil Profile• A way of looking at

a cross section of soil

• Soil has layers known as horizons

• O Layer: Organic Material

• A Layer: Topsoil

• B Layer: Subsoil

• C Layer: Bedrock

Soil Profile

• O Horizon: “O”

Stands for Organic

Matter. Dead plant

and animal residues

in various stages of

decomposition are

here.

Soil Profile

• A Horizon: The

topmost mineral

horizon, or topsoil.

Many soil organisms

live here and it is

typically fertile. Most

plant roots grow

here.

Soil Profile

• B Horizon: This layer

is called subsoil and

is less weathered

and more compact

than the A Horizon.

Few plant roots

penetrate this layer.

Soil Profile

• C Horizon/Bedrock: This is un-weathered

geologic material

where soil is formed.

It is very dense and

typically requires

large machinery or

blasting to dig

through.

Soil Color

• Soil comes from

minerals and

organic matter.

• Color often tells us

what quality the soil

is. Usually, the

darker the soil, the

more fertile it is.

Soil Color

• Bright Colored Soils:

• Brown, Red, or

Yellow

• These colors mean:

– Good Drainage

– Oxidized Iron

Soil Color

• Dull Colored Soil:

• Gray or Olive Gray

• These colors mean:

– Poor Drainage

Soil Color

• Dark Colored Soil:

• Dark Brown, Black

• These colors mean:

– High levels of

organic matter

– Very fertile

Soil Color

• Mottled Soil:

• Clumps of various

colors.

• These colors mean:

– Variability of

moisture in the soil

– Spotted

appearance

Soil Chemistry-pH Levels• pH=Acidity or Alkalinity

• pH is based on a scale from 1 to 14

• 1=Most acidic

• 14=Most alkaline

• 7=Neutral

• Most soils are between 4-9

• Most plants do well in an acidic soil-6.6 being the best

Soil Fertility

• The ability of soil to support plant

growth and the many beneficial

processes that occur in soil.

Soil Degradation

• Soil Degradation: The decline in soil

quality caused by its improper use.

• Examples:

– Loss of organic matter

– Decline in soil fertility an structural

condition

– Effects of toxic chemicals, pollutants,

excessive flooding

Soil Erosion• What is soil erosion?

– The removal of soil by water and wind

• What causes soil erosion?

– Slope

– Water splash, runoff

– Wind drying and blowing soil

– Accelerated erosion caused by farming

and construction

Types of Soil Erosion• Sheet Erosion: The gradual and fairly uniform

removal of surface soil.

• Caused by splash erosion and slow runoff.

Types of Soil Erosion

• Rill Erosion: Small streamlets that are cut into

the soil surface by running water.

• Caused by runoff

Types of Erosion• Gully erosion is rills that have become

extremely large.

• Caused by uncontrolled runoff for an

extended period of time.

Types of Erosion

• Sandblows: The result

of wind picking up

soil particles and

carrying them away.

• Caused by the

removal of

vegetative cover,

which allows the soil

to become dry and

loose.

Soil Conservation

• Plant Trees

• Terraces

• No/Minimal Till

Farming

• Contour Plowing

• Crop rotation

• Soil pH

• Water in the Soil

• Salinity

Management

• Soil Organisms

• Indigenous Crops