Soils

We can’t live without it All land life depends on it There isn’t very much good soil available on Earth Required to grow plants All animal life on land depends on plants

What is soil?

Where does soil come from? All soil starts from rock. Rock that has never been worn down is called bedrock. Rock must weather (break down) into smaller and smaller pieces Rock can break down in two ways. Chemical weathering Physical weathering

Chemical and Mechanical Weathering http://www.brainpop.com/science/weather/weathering/

Weathered Rock Weathered rock doesn’t stay put, but is usually moved by erosion Erosion can happen from wind water ice

Erosion http://www.brainpop.com/science/earthsystem/erosion/

Characteristics of Soil (how we can describe soils) Color Particle Size Texture Consistency pH Moisture Temperature

Soil Color Two sources of color in soils Minerals in the soil: for example. red clay soils have a lot of iron; brown/black soils have manganese….different minerals have different colors Mica is dark Quartz is light Hematite is red

Soil Color, continued The more organic material, the darker the soil. Organic material comes from dead plants and animals. Organic material in soil is called humus. Humus is THE most important factor in soil color. The more humus, the darker the soil.

Soil Particle Sizes Sand—smaller than gravel, you can still see it, feels grainy, water flows through easily Silt—smaller than sand, can’t see individual particles, feels smooth like powder, water has a harder time flowing through Clay—smaller than silt, feels sticky, water usually doesn’t flow through

Consistency Soil consistency means how the soil likes to stick together. It depends on the kinds of minerals in the soil and how much water is in the soil Does it stick together when you squeeze a handful of it? Does it crumble apart? Is it sticky?

Soil pH pH is the way we measure how acid or basic something is It usually ranges from 0 to 14. 1 is very acidic while 14 is very basic, 7 is neutral like pure water Acids: lemon juice, orange juice, sodas Bases: Clorox, ammonia, baking soda

Some plants like acidic soils

Other plants like basic soils But if soil is too acid or basic, no plants can grow

What does the pH level do? pH of the soil affects how minerals dissolve. The best pH for soils and plants is between 6-7, slightly acidic. At this pH, the nutrients from minerals become available to plants. The water in the soil will dissolve the nutrients from the minerals in the soil! Happy plants!

Nutrients Nutrients are the chemicals that an organism needs to grow or maintain its life.

Soil moisture Plants need moisture. If soil is too dry, plants won’t grow. If soil is too wet, plants won’t grow. Moisture must fall in a range for plants to grow. too wet too dry

When soil becomes too dry, it can more easily erode in the wind. An important example of this is the Dust Bowl from the 1930s. A drought in the plains states, along with poor farming practices, caused heavy erosion of topsoil.

Dust Bowl, cont. Dust bowl lasted 10 years! It took place in the southern Plains States

Soil temperature If soil temperatures are too high or low, plants can’t grow

Review of Good Soil Dark in color means high nutrients, both organic (humus) and inorganic (mineral) Not too dry or wet Slightly acidic pH Not too much sand or clay Deep layer of topsoil

Soil Horizons

Horizon Horizon: a side profile of the layers of soil Soil is usually divided into 3 main layers, but will also include the layers above and below for a total of 5 layers.

O Horizon: Litter Not really a layer of soil It’s on top of the first layer of soil Contains grass, plants, and animals

A Horizon: Topsoil 1st layer of soil Darkest layer of soil (dark brown or black) Contains humus, plant roots, small animals, water, and nutrients for plant growth The darker the soil, the more nutrients it contains

B Horizon: Subsoil 2nd layer of soil Lighter in color (reddish brown) Fewer nutrients and water Limited plant growth

C Horizon: Parent Material 3rd layer of soil Lightest in color (gray) No nutrients, animals, or plant growth Contains weathered rock and sediment

R Horizon: Bedrock Below the last layer of soil Solid Rock Has not been weathered or broken down yet No soil in this layer

Soil Horizons Diagram Copy this into your notes O Horizon: LitterN A Horizon: Topsoil B Horizon: Subsoil C Horizon: Parent Material R Horizon: Bedrock