SOILS What is soil Soil relatively thin surface

SOILS

What is soil? • Soil – relatively thin surface layer of the Earth’s crust consisting of mineral and organic matter

Soil Composition • Soil is composed of 4 distinct parts:

Importance of Soil • Organisms inhabit the soil & depend on it for shelter, food, & water. • Plants anchor themselves into the soil, and get their nutrients and water. • Humans need plants and, therefore, need soil.

Soil is a renewable resource • Soil is a slowly renewed resource • Soil formation begins when bedrock is broken down by________. • _______(soils that have developed over a long time) are arranged in a series of horizontal layers called ________

Soil Formation • Soils form from parent material • Parent material (rock) is slowly broken down into smaller particles by biological, chemical, and physical weathering. • It takes a long time to form soil. – Example: To form 2. 5 cm (1 in. ) it may take from 200 -1000 years.

Physical Weathering • Physical breakdown by wind, water, ice, etc.

Chemical Weathering • Chemicals interact with rock and break it down. • Example:

Biological Weathering • Parent material is broken down by tree roots or lichens. • Lichens play a big role in primary succession.

Soil Properties: Texture • The percentages (by weight) of different sized particles of sand, silt and clay that it contains.

Soil Properties: Texture, Cont. • Grain Size – 0. 05 to 2 mm = sand (the largest soil particles) – 0. 002 to 0. 05 mm = silt (about the size of flour) – <. 002 mm = clay (only seen under and electronic microscope)

Soil Properties: Texture, Cont. • To tell the difference in soil, take the soil, moisten it, and rub it between your fingers and thumb. – Gritty: – Sticky: – Smooth:

Soil Structure • How soil particles are organized and clumped together. – Sand – Silt – Clay

Porosity • A measure of the volume of soil and the average distances between the spaces.

Permeability • The rate at which water and air moves from upper to lower soil layers. • The Distances between those spaces.

Variability • Soils (Sand, Silt, & Clay) vary in – the size of the particles they contain – the amount of space between these particles – how rapidly water flows through them.

Big spaces, not a lot of them LESS surface area AL U EQ SITY O R PO Little spaces but lots of them GREATER surface area IMPORTANT TO REMEMBER The size of the rock particle DOES NOT change the porosity!

1 st trial: look at red yellow green only Demo #1 Which size held the most water?

Which one drains the fastest? Permeability! Which one is the fastest?

Slope • Steep slopes often have little or no soil on them because of gravity. • Runoff from precipitation tends to erode the slope also.

Depth • Some soils are very shallow. It can be only two inches of soil and then you hit rock. Other areas can have soil 36 inches deep or more.

Color • Dark soil is rich with lots of organic matter. • Light soil (like sand) is not so rich with very little organic matter.

Soil Horizons

Mosaic of closely packed pebbles, boulders Weak humusmineral mixture Desert Soil (hot, dry climate) Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts Alkaline, dark, and rich in humus Clay, calcium compounds Grassland Soil (semiarid climate) Fig. 3 -24 a, p. 69

Acidic light-colored humus Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Fig. 3 -24 b, p. 69

Forest litter leaf mold Humus-mineral mixture Light, grayishbrown, silt loam Dark brown firm clay Deciduous Forest Soil (humid, mild climate) Fig. 3 -24 b, p. 69

Acid litter and humus Light-colored and acidic Humus and iron and aluminum compounds Coniferous Forest Soil (humid, cold climate) Fig. 3 -24 b, p. 69