Soil is a mixture of weathered rock particles and other materials.

Soil Formation

Soil is a mixture of 4 materials1.Weathered rock particles2.Humus – decayed organic matter3.Water4.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?

Soil Composition

• 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 dark-colored, 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 *

Climate and Landforms Affect Soil

PlantsEx. Trees, grasses, crops…Provide most of the organic matter that gets broken

down to form humus.

MicroorganismsEx. Decomposers, bacteria, fungi…“Very Small” organisms that can only be seen under

a microscopeA spoonful of soil may contain more than a million

microorganismsThey decompose dead plants and animalsProduce nutrients that plants need to grow.

Organisms in Soil

AnimalsEx. 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.

Organisms in 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 well2. Silt – smaller particles; hold more water than sand3. 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.

Properties of Soil

Human Activity on Soil

• 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.

Farming

• Building houses, roads, shopping malls, and other buildings soil is dug up

Construction and Development

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 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.

Mining

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.

Conserving Soil