Download Soil Formation

Soil is a mixture of weathered rock
particles and other materials.
Soil Composition
Soil is a mixture of 4 materials
1. Weathered rock particles
2. Humus – decayed organic matter
3. Water
4. Air
Soil differs, depending on what
type of rock particles are present.
Soil Composition
• Humus – Is decayed organic matter found
in soil
Soil Composition
Different kinds of soil are made depending on a number
of factors…
• The kind of rock in the area
• The area’s climate, or overall weather pattern over time
• The landforms in the area, such as mountains and
valleys
• The plant cover in the area
• The animals and other organisms in the area
• Time
Soil Composition
Compare and Contrast: These three soils look different because they contain
different ingredients. How would you describe their differences?
Climate and Landforms Affect Soil
• Tropical Soils – form in warm, rainy regions. Heavy rains
wash away minerals, leaving only a thin surface layer of
humus. * Are not suitable for growing most crops.*
Climate and Landforms Affect Soil
Desert Soils –
Desert soils form
in dry regions.
These soils are
shallow and
contain little
organic matter.
Because of the
low rainfall,
chemical
weathering and
soil formation
occur very slowly
in desert regions.
Climate and Landforms Affect Soil
Temperate Soils
– Form in
regions with
moderate
rainfall and
temperatures.
Some
temperate soils
are darkcolored, rich in
organic matter
and minerals
and good for
growing crops.
Climate and Landforms Affect Soil
Artic Soils – Form in cold, dry regions where chemical
weathering is slow. They typically do not have well
developed horizons. * Contains a lot of rock fragments *
Organisms in Soil
Plants
 Ex. Trees, grasses, crops…
 Provide most of the organic matter that gets broken down to
form humus.
Microorganisms
 Ex. Decomposers, bacteria, fungi…
 “Very Small” organisms that can only be seen under a
microscope
 A spoonful of soil may contain more than a million
microorganisms
 They decompose dead plants and animals
Organisms in Soil
Animals
 Ex. Earthworms, ants, termites, mice, gophers, moles,
prairie dogs…
 These animals loosen and mix the soil as they tunnel
through it.
 Create spaces in the soil, adding to its air content and
improving its ability to absorb and drain water.
 Return nutrients to the soil when their bodies
decompose after death.
Properties of Soil
1. Texture – size of the weathered rock particles it contains.
Influences how easily air and water move through the soil.
1. Sand – largest particles; does not hold water well
2. Silt – smaller particles; hold more water than sand
3. Clay – Smallest particles; absorbs most water
2. Color – Red, brown, yellow, green, black, white.
• Reddish color soils have a high content of iron.
3. Pore Space – the spaces between soil particles.
4. Chemistry – plants absorb the nutrients they need from the
water in soil.
• Nutrients come from the minerals or the organic matter in
the soil.
Human Activity on Soil
Farming
• Over 10,000 years humans have been farming.
• Farming has a some harmful effects an can lead to soil loss
• Farmers add nutrients to the soil to make crops grow better. However,
some fertilizers can make it difficult for microorganisms in the soil to
produce nutrients naturally.
• Fertilizers also add too water pollution.
• Farmers are clearing tress and other plants and plow up the soil to plant
crops. Without trees and natural cover the soil is exposed.
• Overgrazing – occurs when farm animals eat large amounts of the land
cover. Desertification – the expansion of desert conditions in areas where
the natural plant cover has been destroyed.
Construction and Development
• Building houses, roads, shopping malls, and
other buildings soil is dug up
The soil at these construction sites washes way or blows
away and can end up in local streams or rivers. This can cause
a buildup of soil and can cause flooding, or effect the
contents of the water. This can harm the organisms that live
in the water.
Mining
• Mining causes soil loss.
• Digging of strip mines and open-pit mines involves the removal of
plants and soil.
• This exposes rocks and minerals to the air and to rainwater, these
forms of minding speed up the rate of chemical weathering.
• Can cause pollutants to enter the soil surrounding the areas.
Conserving Soil
Crop Rotation – planting different crops on the same field in different years or growing
seasons.
Conservation tillage – Reducing the # of times fields are plowed in a year. This keeps the
soil more nutrient.
Terraces – flat steplike areas built o a hillside to hold rainwater and prevent it from running
downhill.
Contour plowing – plowing along the curves of a slope. Channel rainwater so that it does
not run straight downhill, carrying away soil.
Windbreaks – are rows of trees planted between field to
“break” or reduce the force of wind that can carry of soil.