Grade 7 Science Unit 4: The Earths Crust

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Grade 7 ScienceUnit 4 The Earths Crust

• Soil

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Soil

• Can take thousands of years to form.
• Many processes are involved in the formation of
  soil.
• Weathered and eroded rocks form the parent
  material of soils.

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• Organic material from the decomposition of plants
  and animals provide the nutrient base for a
  variety of soil ecosystems.
• Soil develops faster in warm climates.

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3 Basic Types of Soil

• Clay
• Sand
• Gravel

The above are listed from the smallest to the
largest particle size.
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Factors that Determine how Soil Develops

• Refer to page 426

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Porosity vs. Permeability

• Porosity

• Permeability

• The amount of empty space in a soil or rock.

• A measure of the ease with which liquids and
  gases pass through a soil or rock.

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Soil Classification...

• Soil is classified according to their
  characteristics. These are usually based on
  texture or how they feel.

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Coarse Texture

• These soils have a sandy/ gravelly texture.
• They feel gritty and can roll between your
  fingers.
• Grains can be seen with the naked eye.

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Coarse Soil
Sand/ Gravel
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Medium Texture

• Also called loam. Farmers preference.
• Composed of sand, silt and clay in nearly equal
  proportions.
• May feel gritty and sticky at the same time.

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Medium Grain Soil

• Loam

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Fine Textured

• Made up of clay.
• Feel greasy or sticky.
• Have little texture when wet.

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Fine Grain Soil

• Clay

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Fine
Medium
Coarse
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Complete Core Lab Activity 12-2B

• Be a Soil Sleuth

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Fertilizers

• Substances that provide nutrients for plants.
• May contain decomposed plants and animals and
  other minerals.
• Can have natural or human-made fertilizers.

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Enriching Soils

• Compost
• Manure
• Chemical fertilizers

Refer to page 435
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Composting

• The breakdown of plant materials. (decomposition)
• Organic materials are piled together and under
  the right conditions will form humus.

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Good Things to Compost
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Enriching Soils... Positive effects

• Enhanced plant growth.
• This will decrease erosion, more food and better
  looking plants and crops.

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Negative effects

• Pollution in the form of run-off.
• Phosphate pollution in lakes and ponds may
  increase algal blooms. This removes oxygen and
  kills aquatic creatures.

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• Nitrogen compounds can also pollute water in the
  form of run-off.

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Solutions Refer in pages 437(8)

• Reduced reliance on chemical fertilizers.
• Limiting run-off
• Planting wind breaks
• No-till farming

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Desertification

• The process in which nutrient depleted soils are
  formed through erosion of fertile soil.
• Solutions?