The Importance of Soil

Composition and Formation

1. What event has decreased the area of land available for farmland in the past few decades?

Urban Sprawls (growing cities)

2. Explain how the event mentioned in #1 has decreased the land available for farmland.

Increased amount of space used for housing, shopping malls, industrial

buildings, and highways.

3. Explain the difference between land and soil.

Land: part of the earth not covered by water

Soil: the layer of material that covers the land and supports the growth of plants. The place where seeds germinate and plants anchor their roots in.

4. What does soil contain?

A: Weathered rock particles, decomposing plant and animal matter, spaces for air and water

PHYSICAL PROPERTIES OF SOIL

Soil Texture

The particles that make up soil are categorized into three groups by size – sand, silt, and clay. Sand particles are the largest and clay particles the smallest.

Most soils are a combination of the three. The relative percentages of sand, silt, and clay are

what give soil its texture. A clay loam texture soil, for example, has nearly equal parts of

sand, slit, and clay.

These textural separates result from the weathering process.

What are soil horizons?

Horizons = a side profile of the layers of soil

O Organic A Topsoil B Subsoil C Parent Material R Bedrock

What are soil horizons?

Horizons = a side profile of the layers of soil

O Organic A Topsoil B Subsoil C Parent Material R Bedrock

What are soil horizons?

Horizons = a side profile of the layers of soil

O Organic A Topsoil B Subsoil C Parent Material R Bedrock

What are soil horizons?

Horizons = a side profile of the layers of soil

O Organic A Topsoil B Subsoil C Parent Material R Bedrock

What are soil horizons?

Horizons = a side profile of the layers of soil

O Organic A Topsoil B Subsoil C Parent Material R Bedrock

What are soil horizons?

Horizons = a side profile of the layers of soil

O Organic A Topsoil B Subsoil C Parent Material R Bedrock

5. Compare and contrast the three A horizons of the soil in grassland, forest and desert soils.

Grassland – “A” horizon topsoil is deep and supports most root growth,

Forest – “A” horizon is not as thick as grassland,

Desert – “A” horizon is very limited due to low precipitation and little decomposing matter

6. Describe how the plants and animals in the soil form a biological community.

Decomposers break down material to provide nutrients to the soil.

Some bacteria provide nitrogen to the plant.

Some organisms use the plants as food.

7.  What are the three most important factors that determine where populations of people will live?

Soil type Climate Vegetation

Regions with poor soils, which cannot be used for growing crops or grazing livestock, have the lowest densities of human population.

8. Explain why we can’t have domestic livestock grazing in the dry grasslands of the tropics.

Domestic animals get disease that the native herds are resistant to and they have a higher demand

for drinking water than wild herds.

What factors affect the ground’s ability to absorb water?

The type of soil Size of the spaces between eroded rock

and decomposing materials Size of the particles of the soil Shapes of the particles Kind of particles that make up the soil

The saturation state of the soil How much water is already in the soil

What factors affect the ground’s ability to absorb water?

Temperature If the ground is frozen then there is ice

filling the available spaces If the temperature is below freezing, the

precipitation will stay on the surface If the temperature is high, water will

evaporate before it has a chance to be absorbed

What factors affect the ground’s ability to absorb water?

The nature of water Water is a “sticky” particle There is a strong intermolecular force

between water particles This creates surface tension which holds

water molecules “together” This may prevent water from “falling”

into the spaces in the soil