Soils We cant live without it All land

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/earthsys tem/erosion/

Characteristics of Soil (how we can describe soils) • • Color Particle Size Texture Consistency • p. H • 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 p. H • p. H 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 p. H level do? • p. H of the soil affects how minerals dissolve. The best p. H for soils and plants is between 6 -7, slightly acidic. • At this p. H, 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 1930 s. 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 p. H • 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 • 1 st 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 • • 2 nd layer of soil Lighter in color (reddish brown) Fewer nutrients and water Limited plant growth

C Horizon: Parent Material • • 3 rd 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: Litter. N A Horizon: Topsoil B Horizon: Subsoil C Horizon: Parent Material R Horizon: Bedrock