Soils

A look at this valuable resource & why we shouldn’t treat it like dirt.

Scott Poague, Holtville High School

Lesson Objectives

• We will determine what exactly soil is.

• We will determine what makes up the soil’s composition.

• Identify effective procedures for soil management.

What exactly is soil?

That’s a good question, I’m glad that you asked!

Soil is a general term that is used to describe the thin, variable layer of mineral and organic matter that covers the Earth’s

land surface. This layer is usually biologically active.

Soil Defined

• There are many definitions of soils, all depend on the user’s viewpoint.

– Some consider it a living & breathing substance at the Earth’s surface which

fosters life all scales.

Soil Defined

Soils sustain us on all levels.

Soil Defined

Others consider it to be an aggravating layer that must be moved out of the way for progress.

Soils Defined

• The study of soil is not the study of “dirt.”– Dirt does not have life sustaining properties.

– Greenhouse media is not considered soil either.

• In order to be considered a soil, it must have evolved as a function of place, time, & the environment.

Soils Defined

“Dirt” is simply defined as soil out of place.

Soils DefinedDon’t confuse greenhouse

potting mixes with soil. Potting mixes are usually

blends of organic materials and non-organic materials.

Soil Facts

• It can take up to 1,000 years to form 1inch of productive topsoil.

This pile of topsoil took more than 1,000 years

to form, but only 20 minutes to dig from the

ground.

•Soil formation is a never ending process.

How Do Soils Form?

• Soils form from parent material.

(a.k.a. rock)

How Do Soils Form?

Over a period of thousands of years rock has become disintegrated by a

process called weathering.

Example of ice breaking rock apart.

How Do Soils Form?

• Warming & cooling, freezing & thawing, wetting & drying, wind & water erosion, root penetration are examples of mechanical forces that aide in disintegration.

• Chemical forces such as oxidation aide the disintegration process as well.

Soil FormationWeathering has shaped these

rocks into interesting shapes.

Where’s Waldo?

Soil Formation

Soil Formation

• Productive soils develop on the Earth’s surface as the atmosphere, sunlight, water, & living things meet & interact with the mineral world.

• Soil is suitable for plant growth to a depth of 36” or more, that soil is regarded as “deep.”

• Most soils are shallower than this.

Soil Make Up

• Soil is made up of 4 key elements;– Air, water, organic matter, & minerals

• Air & water is found in pore spaces between solid particles.

• Organic matter is mainly composed of plant debris, & microorganisms such as bacteria & fungi.(typically most abundant at the surface of the soil)

Soil Make Up

• Soils form from 3 types of rock:– Igneous– Metamorphic– Sedimentary

Igneous Rock Types

Basalt

Pumice

Scoria

Granite

Metamorphic Rock Types

Slate

Schist

Marble

Quartzite

Sedimentary Rock TypesBreccia

Sandstone

Shale

Chert

Rock Salt

Rock Gypsum

Soil Texture

• Once soils are broken down into smaller particles they are considered to be either 1 of 3 particles or a mix of the 3.– Sand (largest)– Silt– Clay (smallest)

Soil Texture

Sand

Sand can vary in coarseness from very fine to very coarse like the sand pictured above. Notice the rock particles

present.

Rock particles

Soil Texture

Silt

Soil Texture

Clay

Soil Texture

• Information about soil types in a

particular area can be found in a Soil Survey Report.

• Every county in each state has one.

Soil Texture

Information about soil texture for soil survey reports is

often collected using drilling probes like

this one.

Soil Horizons

• Horizon O- layer dominated primarily by organic matter(leaves, grass, etc.)

• Horizon A- (topsoil) Layer formed below the organic matter. It is primarily soil, but contains organic matter.

• Horizon B- (subsoil) Layer dominated by pieces of the original parent material. Usually contains clay, silicate, gypsum

• Horizon C- (parent material) Contains parent material, but excludes hard bedrock.

Soil Horizons

Horizon O- Organic Material Layer

Horizon A- Topsoil Layer

Horizon B- Subsoil Layer

Horizon C- Parent Material/Bedrock

Soil Horizons

Soil Profile

Limrock Series Decatur Series

Examples of soil series profiles from soils in North Alabama

Soil Profile

Bama soil series profile. This is the Alabama state soil.

Soil series- a grouping of soils with similar characteristics.

Alabama has 370 soil series across the state that fall into 7 soil regions.

Limestone Valleys & Uplands

Appalachian Plateau

Piedmont Plateau

Blackland Praire

Coastal Plains

Major Flood Plains & Terraces

Coastal Marshes

Soil Water

Important terms associated with water movement in soils.

Soil Water

• Percolation- the downward movement of water in soil.

• Perc test- a test to evaluate the suitability of soils for on-site waste disposal by measuring the rate at which water enters the soil layers.

• Saturated- soil pores contain all of the water they can possibly hold. There is no air movement.

Soil Water

• Waterlogged- soil is saturated with water.

• Impermeable- soils are unable to transmit water. (horizontal water movement)

• Evaporation- vapor loss from soil directly into the atmosphere.

Soil Water

• Clogging- water pores are stopped up preventing water movement through the soil.

Corn field in Iowa that flooded, resulting in waterlogged & saturated soils.

Soil Water

• On level areas water soaks in and moves through the soil in a process called percolation.

• Soils that develop on level land at low elevations tends to be poorly drained, while soils on slight elevations tend to be better drained & more productive.

• Drainage (or lack of it) affects the water table in a particular field.

• The water table has a direct bearing on soil formation.

• When soil is saturated with water, little or no air can penetrate it.

• The lack of air reduces the action of fungi, bacteria, and other soil forming activities in the soil.

Soil Water

Soil Water

• A wet soil, is a slow-forming soil and usually is low in productivity.

• Due to the lack of air, organic matter turns black, thus causing the soil to be a blackish/gray color.

Land Classes

Look At This

The soil on the side of this hill has moved downward. This is called soil creeping. Notice the trees trying to correct their

posture.