Soils

What is soil?

Solid portion of Earth’s crust that has formed from rocks and minerals and is where plants grow

4 things that soil provides

1. Nutrients

2. Water

3. Air

4. Mechanical support

4 components of soil

1. Solid

2. Organic

3. Liquid

4. Gas

Solid fraction

Rock fragment, minerals

Organic fraction

Decayed/ing plants, microbes, + soil animals

Liquid fraction

A solute for minerals

Gas fraction

Air

Pore spaces

Voids between solid fraction, location of air + water

Accumulation

Parent material accumulates from the breakdown of parent rock; accumulates in masses that later form horizons

Differentiation

Parent materials differentiate by mechanical separation or dissolution into a soil profile

5 soil formation factors

1. Parent rock

2. Climate

3. Organisms

4. Topography

5. Time

Igneous rock

Formed from cooling + solidification of molten rock

Ex of igneous rock

Granite

Sedimentary rock

Formed from materials originally deposited as sediment by wind, water, or glaciers

3 ex of sedimentary rock

1. Limestone

2. Sandstone

3. Shale

Metamorphic rock

Where igneous or sedimentary rock has been subjected to intense heat + pressure

2 ex of metamorphic rock

1. Slate

2. Marble

2 origins of parent material

1. Residual

2. Transported

Residual

Formed in place w/out much disruption or transport; rate of soil formation is very slow

Transported

Moved to its location by various forces

3 types of transported

1. Glacial

2. Loess

3. Alluvial

Glacial

Transported + deposited by moving ice

Loess

Transported by wind

Alluvial

Soil or sediments deposited by a river, stream, or other running water

Weathering

Processes that act on parent material to break it into finer particles

2 processes of weathering

1. Chemical

2. Physical

Chemical weathering

Reactions that help to disintegrate parent material

Physical weathering

Freezing, thawing, scraping, grinding, tumbling, cracking due to enviro factors

Hydrosis

Reaction w/ water to dissolve minerals

Oxidation

Reaction w/ oxides of parent material w/ oxygen

Hydration

Addition of water to hydrate the mineral

Dissolution

Addition of weak acid to leach parent material

Exfoliation

Changes in temp cause expansion + contraction

Mechanical action

Scraping + grinding breaks parent material; glaciers

Physical

Water movement and wind break down parent material

Topography

Influences drainage + runoff

5 soil horizons

O, A, B, C, R

O

Organic (humus)

O: organic/humus

Mainly decomposed plant + animal materials

A

Topsoil

B

Accumulation

C

Parent material

R

Consolidated rock/bedrock

Alfosol

Moderately leached forest soils that have relatively high fertility

Cation Exchange Capacity

• The sum total exchangeable cations that soil can hold

• The ability of soil to hold nutrients that have a positive charge

CEC is influenced by…

The amount + type of clay present

CEC is important because…

1. Cations are held in a form available to plants

2. Minimization of the amount of leaching

3. Buffers soil pH

Strength of nutrient attraction to soil particles

Ca > Mg > K > NH4 > Na > H

pH

Hydrogen concentration in soil

Plants that grow in pH 5.5 to 6.5

Corn, oats, wheat

Plants that grow in pH 6.5 to 7.5

Alfalfa, soybeans, sweet clover

Plants that grow in pH 4.5 to 5.5

Blueberry, cranberry, potato

Availability of most nutrients is best betweeen pH of…

5.5 to 6.5

To raise soil pH, apply…

Lime

To lower soil pH, apply…

Sulfur

What 3 minerals form a majority of soils on Earth?

1. Sand

2. Silt

3. Clay

Soil textures by size (largest to smallest)

Sand > silt > clay