Unit 1 Lesson 3 Soil Review

  1. Soil composition is broken into 4 groups in the graph in your notes. What are those 4 groups?

45% Inorganic mineral matter, 5% Organic matter (microorganisms and macro organisms), 25% Water, 25% Air

  1. What are the 6 soil components? Define each. Sand and Gravel-mineral particles from bedrock, either in place or moved from elsewhere, as in wind-blown sand.

- Silts and Clays: extremely small mineral particles; many clays are sticky and hold water because of their flat surfaces and ionic charges; others give red color to soil.

- Dead Organic Material: decaying plant matter stores nutrients and gives soils a black or brown color.

- Soil Fauna and Flora: living organisms, including soil bacteria, worms, fungi, roots of plants, and insects, which recycle organic compounds and nutrients.

- Water: moisture from rainfall or groundwater, essential for soil fauna and plants.

- Air: tiny pockets of air help soil bacteria and other organisms survive.

  1. Which two soil components fit into the inorganic mineral matter from the graph?
  1. Which two soil components fit into the organic matter category from the graph?

Dead organic matter, soil flora and fauna

  1. How are clays different from silts?
  1. What function do the soil fauna and flora serve?

recycle organic compounds and nutrients.

  1. A Soil profile has up to 5 layers or Horizons.
  2. List each of the horizons, along with any additional names of that layer. Define each layer by its characteristics.

The O horizon is comprised of organic materials, typically of prior living plants and animals.

The A horizon is considered the Top Soil. This is also considered the zone of leaching. Water moves through and takes nutrients and minerals with it.

The B horizon is the sub soil, also called the zone of accumulation. What does accumulation mean? Note that the plant zones reach into this zone.

The C horizon is labelled as the substratum which has weathered portions of bedrock.

R is the bedrock.

  1. What is erosion? What are possible causes of erosion?

the natural process of the movement or removal of the surface or top soil layer.

  1. What are the effects of erosion?

Loss of topsoil- The topsoil layer has the greatest volume of nutrients needed for plant growth. The loss of this horizon is also the loss of nutrients, which will reduce the ability to grow crops.

Soil compaction- the hardening of the remaining soil, which reduces the ability of soil to absorb water. The result would be an additional increase in water run off.

Desertification- the creation of less usable soil, which is considered to have the traits of the desert biome. This issue is growing, as we lose once productive land to desertification.

  1. What are fertilizers?

Fertilizers are important to allow plant growth in agricultural areas to continue. Too much fertilizer however, can be harmful.

Nitrogen cycle

Use the video in the course notes, or the diagram to assist in answering the following questions.

  1. The main source of nitrogen, N2, is from the atmosphere (air).
  2. Nitrogen fixing bacteria in plant roots converts N2 directly into nitrates for plant use.
  3. Plants require nitrogen in the form of Nitrates.
  4. Nitrogen fixing soil bacteria must make Ammonium first, then nitrifying bacteria make nitrites, and lastly nitrates is available for plant usage.
  5. Decomposers assist in the return of nitrogen to the soil. What form do they release back into the soil?


  1. How do animals get their nitrogen?

Eating plants and other animals that contain nitrogen

  1. List the options to using processed fertilizer.

Limit watering or adapt better water control practices.
Allow the decomposition of natural materials to return nutrients to the soil.
Alternate crops that require different nutrient loads in the same soil.

  1. What practices assist in the reduction of soil erosion?

Contour plowing- plowing across the hill rather than up and down.
Terracing- is shaping the land to create level shelves of earth to hold water and soil.
Crop rotation- alternate crop types for best use of land and its nutrients.
No till agriculture- leave plants or debris between rows.

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