Soil Taxonomy:Orders

Suborders

Great groups

Subgroups

Families

Series

Geology and the Evolution of American Forests

Drummer – State soil of Illinois

Soil Orders

• All end in “sol” which is derived from “solum” meaning soil

• The twelve soil orders are: Alfisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Andisols, Spodosols, Ultisols, Vertisols and Oxisols

Geology and the Evolution of American Forests

Geology and the Evolution of American Forests

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Soil orders where natural forests occur

Maps and soil profiles NRCS

Geology and the Evolution of American Forests

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Soil orders where natural forests occur

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

High pHHigh OM accumulation in upper horizonsAreas of low rainfall

Grasslands with scattered trees

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Moderately high pHSome clay in B horizonsUsually rich in mineral nutrients

Areas of moderate rainfall with seasonal deficiencies

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Very recent deposits or exposures ofraw parent material

No soil development yetResult of a variety of events (volcanoes, landslides, etc)

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Organic soils on poorly aerated sites where water accumulates

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

AcidicResult of strongly leached soils with subsurface accumulations of aluminum and iron

Usually coarse-texturedRecently deposited by effects of

glaciation

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Moist, well-drained (adequate supply of water)

Effects of leaching have not yet led to subsurface accumulations of aluminum, iron, clay, or OM

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Geology and the Evolution of American Forests

Soil orders where natural forests occur

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

AcidicResult of strong leaching in temperate climates causing subsurface accumulation of clay

Moistaffected by brief seasonal dryness

Geology and the Evolution of American Forests

Mollisols

Alfisols

Entisols

Histosols

Spodosols

Inceptisols

Ultisols

Soil orders where natural forests occur

• Geologic definition: Loose surface of the earth as distinguished from solid bedrock (support of plant life not required).

• Traditional definition: Material which nourishes and supports growing plants (includes rocks, water, snow, air).

• Component definition: Mixture of mineral matter, organic matter, water, and air.

Soils

• Soil is the outer portion of the Earth’s crust that

supports plant growth ….• It is the natural medium on the Earth’s surface in which

plants grow ….• It is composed of organic and mineral materials ….

– 50% of soil volume is:

• decomposed rock

• plant and animal remains

– 50% of soil volume is:

• pore spaces (occupied by either air or water)

Soils

Major Components

• Minerals

• Organic matter

• Air

• Water

Air 25%

Mineral Matter 45%

Water 25%

Organic Matter 5%

Soils

GeologyChemistryPhysics

Soils

Engineering

Plant Sciences

Significance of soil science in natural resources:1) matching plant species to soil types2) evaluation of limitations to resource management

• Functions of soil– Offers mechanical support– Retains and transmits water and gases– Serves as a habitat for macro- and micro-organisms– Holds, exchanges, and fixes nutrients

Soils

Soil Formation

• Translocations

• Transformations

• Additions

• Losses

Soils

NRCS photo

• Soil formation is initiated by the process of weathering

• Weathering – the physical or chemical disintegration and/or decomposition of rocks and minerals under natural conditions

Soils

• Physical weathering – breaking down parent material by exposure to physical forces– Moving ice

– Moving water

– Wind

– Growing roots

• Chemical weathering – breaking down parent material by exposure to chemical forces– Rainwater

– Surface water

– Gases

– Secretions by organisms

Soils

• As a portion of the landscape: Collection of natural bodies occupying portions of the earth’s surface that support plants and that have properties due to the integrated effect of climate and living matter, acting upon parent material, as conditioned by relief, over periods of time.

Soils

• Factors influencing soil development– Parent material– Climate– Living organisms– Topography– Time

Soils

Parent Material

• The unconsolidated and more or less chemically weathered mineral or organic matter from which the solum of soils is developed

• Solum-The upper and most weathered part of the soil profile; the A and B horizons

Soils

Climate

• From an over-all standpoint, climate is perhaps the most influential factor affecting soil development

• Temperature and precipitation greatly influence the rates of chemical and physical weathering.

• Warm, wet, and flat areas have more rapid rates of soil formation than areas where the opposite conditions occur

Soils

Living Organisms

• Living organisms influence soil development by providing organic matter, profile mixing, nutrient cycling and structural stability

Soils

Topography

• Can speed up or slow down climatic forces

Soils

Time

• The actual length of time that materials have been subjected to weathering plays a significant role in soil formation

• Soils of the glaciated region are much younger and more fertile then soils that were not glaciated

Soils

• Residual soils – soils that are formed “in place”

• Transported soils – soils formed by the transfer of loose sediments from one area to another area by– Blowing wind

– Moving water

– Moving glacier

– landslides

Soils

• The detachment and movement of soil particles from one place to another

• Wind and water are the primary forces causing soil erosion

• Vegetative cover and roots help to keep the loss of soil in balance with topsoil replacement

Soils

Wind erosion

NRCS photo

Soil erosion by water is categorized into four types:

1. Splash

2. Sheet

3. Rill

4. Gully

Soils

Soil erosion by water is categorized into four types:

1. Splash

2. Sheet

3. Rill

4. Gully

Soils

The spattering of small soil particles caused by the impact of raindrops on very wet soils

The spattering of small soil particles caused by the impact of raindrops on very wet soils

Soil erosion by water is categorized into four types:

1. Splash

2. Sheet

3. Rill

4. Gully

Soils

Occurs when a wide flow of water moves across a sloping field

Recently tilled farmland with no vegetative cover

Occurs when a wide flow of water moves across a sloping field

Recently tilled farmland with no vegetative cover

Soil erosion by water is categorized into four types:

1. Splash

2. Sheet

3. Rill

4. Gully

Soils

Results from water moving through small channels in the soil surface

• Farmland that is partially tilled with some vegetative residue• Moderately overgrazed rangeland

Results from water moving through small channels in the soil surface

• Farmland that is partially tilled with some vegetative residue• Moderately overgrazed rangeland

Soil erosion by water is categorized into four types:

1. Splash

2. Sheet

3. Rill

4. Gully

Soils

Occurs where water is concentrated into a high velocity flow through a large channel that lacks vegetation

Occurs where water is concentrated into a high velocity flow through a large channel that lacks vegetation

NRCS photo

Controlling Erosion

• The key to controlling erosion is to maintain a good vegetative cover

• Farming practices used to control erosion include: conservation tillage, strip cropping, contour farming, terracing, gully reclamation, windbreak planting, and the retirement of highly erodible lands from cultivation

Soils

SoilsStrip Cropping

NRCS photo

Soils

Contour Farming

NRCS photo

Soils

Buffer Strip(gully reclamation)

NRCS photo

SoilsWindbreak Planting

NRCS photo

SoilsTree Planting

NRCS photo

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil Components

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil Components

Most abundant elements in the soil:

O

Si

Al

Fe

Ca

Na

K

Mg

SiO2, Al2O3, Fe2O3, CaCO3

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil Components

Macronutrients:

C

H from water and atmosphere

O

N

P depleted

K from inorganic

Ca minerals in

Mg the soil

S

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil Components

Micronutrients:

Fe

Mn

Mo

Zn from inorganic

Cu minerals in the soil

Cl

B

Co

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil Components

Plant litter

Animal and insect remains

Feces

OM serves as:

reservoir for moisture

temperature moderator

barrier to water vapor diffusion

home and food for microorganisms

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil Components

Partially decomposed organic matter is called Humus

Humus improves:

soil water holding capacity

soil ion-exchange capacity

soil structure

water infiltration

aeration

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil ComponentsWater holding capacity is the ability to retain water ….

precipitation

infiltration

dissolved minerals

plant uptake

Infiltration rates depend on soil porosity

Many spaces Few spaces

poor water good water

holding capacity holding capacity

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil Components

Air is necessary for root respiration and gaseous exchange

Pore spaces are either occupied by water or air

Soils with high water holding capacity usually have poor aeration.

• Soil Components– Inorganic minerals– Organic matter– Water– Air– Living organisms

Soil Components

Living organisms mix, churn, aerate, and decompose soil and organic matter.

bacteria earthworms

fungi insects

molds moles

protozoa gophers

mites ground squirrels

nematodes badgers

Soil textureThe individual mineral particles in a soil are classified into three

texture size classes:

Sand (.05-2.0 mm)

Silt (.002-.05 mm)

Clay (<.002 mm)

The texture of a soil is then described as:

The proportion in which particles of different size classes are found in the soil

Physical Properties of Soils

NRCS photo

Physical Properties of Soils

Soil structureThe way soil particles clump together in larger lumps and

clods are called

––– “Peds” –––

Peds are characterized on the basis of their

- size

- shape

- degree of distinction

Physical Properties of Soils

Factors that Affect Soil Structure

• Kind of clay

• Amount of organic matter

• Freezing and thawing

• Wetting and drying

• Action of burrowing organisms

• Growth of root systems of plants

All of these have a loosening effect on the soil, but they have no effect on aggregate stability

Physical Properties of Soils

Aspects of Soil Structure

Physical Properties of Soils

• The arrangement into aggregates of desirable shape and size

• The stability of the aggregate

• The configuration of the pores

Aspects of Soil Structure

• The arrangement into aggregates of desirable shape and size

• The stability of the aggregate

• The configuration of the pores

Physical Properties of Soils

Granular

Platy

Blocky

(Angular)(Subangular)

Wedge

ColumnarPrismatic

Granular

Platy

Blocky

(Angular)(Subangular)

Wedge

ColumnarPrismatic

NRCS photo

Aspects of Soil Structure

Physical Properties of Soils

• The arrangement into aggregates of desirable shape and size

• The stability of the aggregate

• The configuration of the pores

Factors that affect aggregate stability

- Kind of clay- Chemical elements associated with the clay- Nature of the products of decomposition or organic matter- Nature of the microbial population

Factors that affect aggregate stability

- Kind of clay- Chemical elements associated with the clay- Nature of the products of decomposition or organic matter- Nature of the microbial population

Aspects of Soil Structure

Physical Properties of Soils

• The arrangement into aggregates of desirable shape and size

• The stability of the aggregate

• The configuration of the pores

Bulk Density

- Determined by dividing the weight of oven-dry soil in grams by its volume in cubic centimeters

- The variation in bulk density is due largely to the difference in total pore space

Effects of Bulk Density

- Engineering properties- Water movement- Rooting depth of plants

Effects of Bulk Density

- Engineering properties- Water movement- Rooting depth of plants

The chemical properties of soils are determined by:

oxygen ( O2 )

water ( H2O )mineral and nutrient contentorganic matter contentpH

degree of alkalinity or acidity depends on the concentration of H+ and OH- ions acidic neutral alkaline

0 7 14

Chemical Properties of Soils

Water Holding Capacity

• The readily available soil water is considered to be the amount of moisture retained in the soil between field capacity (upper limit) and permanent wilting point (lower limit)

Chemical Properties of Soils

H2O H2O holding ion-exch

texture infiltration capacity capacity aeration

Sand good poor poor good

Silt medium medium medium medium

Clay poor good good poor

Loam medium medium medium medium

Relationship of Physical and Chemical Properties

As soils develop, they form layers or horizons

• Each horizon has a distinctive – thickness– color– texture– composition

• Soil profiles are used to determine the properties of a soil– to match species to the site– to facilitate management

Soil Horizons

Soil Color

• Indicator of different soil types

• Indicator of certain physical and chemical characteristics

• Due to humus content and chemical nature of the iron compounds present in the soil

Soil Horizons

Major Forms of Iron and Effect on Soil Color

Form Chemical Formula Color

Ferrous oxide FeO Gray

Ferric oxide (Hematite) Fe2O3 Red

Hydrated ferric oxide (Limonite) 2Fe2O3 3H2O Yellow

Soil Horizons

Soil Horizons

NRCS photoNRCS photo

Ideal Soil Profile

Soil Profile under aDeciduous Forest

Soil Profile under aConiferous Forest

Land Capability ClassificationLand Class

Characteristics Primary Uses Secondary Uses Conservation

IExcellent land

flat, well-drainedAgriculture

Recreation

Wildlife

Pasture

None

II

Good land

minor limitations such as slight slope, sandy soil, or poor drainage

Agriculture

Pasture

Recreation

Wildlife

Strip cropping

Contour farming

IIIModerately good land

important limitations of soil, slope, or drainage

Agriculture

Pasture

Watershed

Recreation

Wildlife

Urban Industry

Contour farming

Strip cropping

Waterways

Terraces

IVFair land

severe limitations of soil, slope, or drainage

Pasture

Orchards

Limited agriculture

Urban industry

Pasture

Wildlife

Limited contour

farming

Strip cropping

Waterways

Terraces

Land Capability ClassificationLand Class

Characteristics Primary Uses Secondary Uses Conservation

VFarming prevented by shallow soil, wetness, or slope.

Slightly limited by rockiness

Grazing

Forestry

Watershed

Recreation

Wildlife

No special pre-cautions if properly grazed or logged; must not be plowed

VIModerate limitations for grazing and forestry

Grazing

Forestry

Watershed

Urban industry

Recreation

WildlifeGrazing or logging limited at times

VIISevere limitations for grazing and forestry

Grazing

Forestry

Watershed

Recreation

Wildlife

Urban industry

Careful management required when used for grazing or forestry

VIII

Unsuitable for grazing or forestry due to steep slope, shallow soil, lack of water or too much water

Recreation

Watershed

Wildlife

Urban industry

Not to be used for grazing or forestry