CHARACTERIZING SOILAg 1 Unit 1: Soil Science

Objectives

Outline the processes involved in soil formation

Describe a mature soil profile Discuss the eight land capability

classes Define soil series and explain

how those differ from land capability classes

What Is Soil?

Defining soil is not as simple as it seems.

How do you define soil? We will consider soil to be the

layer of organic material on earth’s surface containing both organic and inorganic matter that is capable of supporting plant life.

What Is Soil?

Supports our buildings, catches and stores our water and provides us with food, fiber and forest products.

So durable it can last as long as our species survives.

So fragile it can be destroyed over night

Complex. Once destroyed it can’t be replaced.

Soil Components

Inorganic material- 45-48%

Organic matter- 2-5%

Water- 25% Air-25%

Air

Water

InorganicMatter

Oraganic

Ideal Soil

½ air, ½ water ½ organic, ½ inorganic

Soil Formation

Slow Results from natural forces

acting on the mineral and rock portions of the earth’s surface

Parent Material

Materials that soil is formed from Five general categories

Minerals and rocks Glacial deposits Loess deposits Alluvial and marine deposits Organic deposits

Minerals

Solid InorganicChemically uniformCommon minerals that soils form from: Feldspars, micas, silica, iron oxides, calcium carbonates

Mica

Rocks

Not chemically uniform Made up of minerals Classified into three groups

Igneous Sedimentary

Almost ¾ of the earths surface Metamorphic

Glacial Deposits

During the Ice Ages, glaciers moved taking surface material with them.

Much of Midwestern US is covered by glacial deposits

Loess Deposits

Generally thought of as wind blown silt

Much of the soil in the eastern Mississippi Valley are loess soils

South Dakota- 1934

Alluvial & Marine Deposits

Alluvial deposits-left by fresh water Occur when water fans out after

traveling down hill and then slowing down on more level areas

Often in the form of floodplains and deltas

Marine deposits- formed on an ancient ocean floors

Organic Deposits

Occur in marshy or swampy areas where plant life is lush

When plants die they fall in the water and decay slowly

Eventually builds up and forms muck or peat soil

Peat & Muck Soils

Peat soils are made up of recognizable plant materials

Muck soils are more completely decayed so that plant parts are no longer recognizable

In the case of lakes the deposits may become thick

Weathering

Major types Temperature change Water action Plant roots Ice expansion Mechanical grinding

Soil Organic Matter

Two basic Original tissue: that portion of the

organic matter that remains recognizable

Humus: organic matter that is decomposed to the point that it is not longer recognizable

Soil Organic Matter Functions Acts as a cementing agent for soil

particles Returns plant nutrients to the soil,

most notably phosphorous, sulfur and nitrogen

Helps store soil moisture Makes soil more tillable Provides food for soil

microorganisms, which make the soil capable of plant production

SOIL PROFILE

Soil Profile

Horizons- visibly distinct layers in the soil A Horizon: Top and surface soil

B Horizon: Subsoil C Horizon: parent material

Soil Profile

C Horizon

Except for peat and muck soils consists of weathered rock and minerals

Looks like the rock it came from May be soft enough to dig in or to

crumble. Very few plant roots

B Horizon

More thoroughly weathered Often a different color Contains little organic matter May be much finer and harder packed Plant roots begin to appear

A Horizon

SurfaceHigh organic matter contentMay be grayish, brownish or blackish in color as a result of humus content

Most productiveMost plant nutrients are available here

PHYSICAL PROPERTIES

Slope

Single most important factor in determining the productive potential of the soil

Affects productive potential in many ways Runoff rates Relates to the danger of soil erosion Affects the use of farm machinery Size and shapes of fields

Texture

The proportions of sand, silt and clay

Course soils have more sand Fine soils have more clay.

Soil Drainage

How well water flows through the soil naturally

Well drained soils-excess water moves out quickly

Poorly drained soils- hold excess water

Flood Hazard

How likely a field will receive flood damage

Frequent flood plains do not have good productive potential

Example: James River Bottom

Erosion

Refers to the degree that the soil has already been damaged.

May range from none to severe

Top Soil & Subsoil Thickness

Refers to the depth of each layer that is available for plant root growth.

Very thin top and subsoil’s limit crop production

LAND CAPABILITY CLASSES

Land Capability Classes

Categorize the productive potential of the soil

System begins with class 1 (most useful) to class 8 (least useful)

Class 1

Very good, productive land Nearly level Well drained Medium textured Not subject to erosion or flooding Easily cultivated Very little land is class 1; even in the

most productive farming areas!

Class 2

Good for all types of farming Has some limitations

Gentle slope Suffers from the effects of past erosion Less than ideal soil depth May also have drainage problems that

can be corrected with the use of drainage systems

Requires careful soil management to prevent erosion damage

Class 3

Moderately good land May be cultivated and farmed regularly but it has

some important limitations Moderate slope; making it high susceptible to

erosion damage May already have severe erosion damage Drainage problems Shallow rooting zone

Some shallow wetlands are Class 3 if they can be improved with drainage systems

Should be farmed with care to prevent erosion damage

Class 4

Severe limitations Can be cultivated with careful soil

management practices May have strong slope and be subject to

severe erosion May be very shallow May be very dry or very wet

If wet even drainage systems may still allow occasional water logging

Class 5

Nearly level Little erosion hazard but may be in a

frequent floodplain May be very wet, very dry or very rocky Swampy areas are generally class 5 Quite suitable for pasture, wildlife habitat

or forest production

Class 6

Serious limitations May have very rocky or very shallow

unusable surface soil. Can be used for tree production,

permanent pasture or wildlife habitat

Class 7

Severely limiting properties May be very steep May be severely eroded with deep gullies Very strong slope with course soils may

cause land to be rated at a class 7 May be impractical for establishing

pasture but native grasses may be utilized with controlled grazing

Land may be used for forest production, wildlife and recreation

Class 8

Has one or more extreme limitations Examples of Class 8 land

Sand dunes River washes Stream beds Lake bottoms Other nearly barren areas

Soil Classification

NRCS and USDA use a soil taxonomy

They are broken down into:OrderSuborderGreat GroupSubgroupFamilySeries

SOUTH DAKOTA’S STATE SOIL

Houdek

Deep, well drained, loamy soil, Represents many soils formed in South Dakota

under the influence of prairie grass The dark color of the surface layer is a result of

decayedplants and other materials that have been

deposited overthousands of years. Of major economic importance to SD because

it is used as crop or rangeland.

South Dakotas State Soil

Designated as the State Soil in 1990 Has been mapped on about 600,000

acres. Total Land Area of SD is 75,885 sq mi. or

48,566,400 acres Average annual precipitation is 22 inches, Average annual air temperature is about

48 F.

South Dakota’s State Soil

Houdek Soil Profile

Houdek Soil ProfileSurface layer: dark grayish brown loamSubsoil - upper: dark grayish brown clay loamSubsoil - middle: grayish brown clay loamSubsoil - lower: light olive brown clay loamSubstratum: light yellowish brown clay loam