SOIL - Fundamental ConceptsSOIL - Fundamental Concepts

ABIOTICABIOTICPrepared by Prepared by

Earl D. LockridgeEarl D. Lockridge

National Soil Survey CenterNational Soil Survey Center

Lincoln, NELincoln, NE

SOIL (Know this one)

A mixture of mineral matter, organic matter, water, and air that originated from weathered bedrock and has become differentiated with depth into horizons

Composite definition added Geomorphology book

SOIL

Mature soil- clearly defined horizons produced by the weathering process. Each layer encroaches on the layer below it

Paleosols - ancient soils removed from the zone of soil formation, usually by burial from younger sediments.

Major Components

Mineral matter

Organic matter

Air

Water

Air 25%

Mineral Matter 45%

Water 25%

Organic Matter 5%

SOIL

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

Example:

CLIMATE and TIME –are the most important factors in soil formation

bedrock- The igneous, metamorphic, and sedimentary components of the Lithosphere that may exist as mountains, cliffs, or low lying plains

Types of Bed Rock

Igneous- rock from volcanic sources or locations…can be very old

Examples- Granite & Quartz

Types of Bed Rock

Sedimentary- rock formed by long term deposition by wind and water. Frequently found in layers.

Examples- Sandstone & Shale

Types of Bed Rock

Metamorphic- rock which has been altered by high heat or pressure

Examples- slate (altered shale), gneiss (altered granite), diamond (carbon, coal)

parent rock- an area of bed rock that is the source of an area of soil

How do we get soils?

Over time the weathered material from the bed rock is covered by both living and dead organic material and a soil horizon develops in a dynamic way.

These layer become characteristically differentiated over time due to climatic factors in their environment

Weathering

Disintegration and decomposition of rocks by surface processes.

Geomorphology book

Weathering

Mechanical- the physical process of breaking apart rocks (frost/salt wedging, root growth)

Chemical- breakdown through chemical alteration (oxidation, hydrolysis, acid inorganic or organic derived from Lichen, fungi, bacteria, mosses and all vascular plant roots)

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

Important Note

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

Soil Forming Processes

Translocations

Transformations

Additions

Losses

Only one millimeter of topsoil is created on 2.5 acres every year (The Way the World Works, 1996 )

Differentiated layer of developed soils are known as HORIZONS

The Horizons O- organic layer of

decomposing plant material little mineral content

A- Organic acid design decomposing the parent material giving it a dark color. This is the zone of leaching. Dissolved chemical carried down from the surface. Accessible by plant roots. Most soil organisms found here

O

A

The Horizons B- Zone of

accumulation. More weathering then C. Parent material is hard to identify. Can be full of clay (more so then the above layers) and impermeable (red brown color common because of oxidation). Nutrients collect in this region-mineral leach up form the parent rock below

B

C

The Horizons C- Slightly weathered

parent material (bed rock). Has not undergone leaching and accumulation to the same extent of above layers less oxidation then the B layer

D or R- Bed Rock

Bed Rock(Exposed)

B

A

O

C

Hint!!

Not all layers of soil may be present, but if they are they will always be in the following order O-A-(E)-B-C-R (or D)

Three Fractions of Mineral Matter

Sand 2-.5mm (diameter)

Silt .49-.002mm

Clay smaller than .002mm

USDA Textural Triangle

Granular

Platy

Blocky

(Angular)(Subangular)

Wedge

ColumnarPrismatic

Examples of Soil Structure

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

loams – most fertile soil (silt, sand and clay in equal parts with partials of intermediate size)

Why is loamy soil best?

Porosity

Porosity- the measure of how much water a rock can hold

finer (silt, clay) the grain greater overall surface area so more porosity, more poorly connected however

Permeability

permeability- how easily the water can be transmitted

larger pores allow water to pass through easily (sand size and larger)

http://www.earthnet-geonet.ca/glossary/display_term_e.php?term=permeability&showLetters=true

There are 20,000 different types of soil in the United States! (The Way the World Works, 1996 )

Local Soil Types

PedogenicPedogenic means pertaining to processes that add, transfer, transform, or remove soil constituents.

http://earthquake.usgs.gov/image_glossary/pedogenic.html

Physical Properties of Soil

Soil texture

Soil structure

Soil color

Bulk density

Aspects of Soil Structure

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 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

Important Note

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

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

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

Abiotic soil lab interpretation questions:

1. What soil layers were present at HWWP? 2. Which layer was thickest, which was thinnest? 3. How does the climate present in this area lead

to the development of this type of soil? 4. How do you think this type of soil affect the life

forms present in the HWWP (plants, animals, bacteria, and fungi)?