1. Introduction to Agriculture, Food, and Natural Resources
How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Introduction to Agriculture, Food, and Natural Resources
How Soils are Formed
Unit 4 – Lesson 4.1 Starting from the Ground Up
This presentation provides students a definition of soil and breaks down the five factors of soil formation. It also discusses the four processes that occur to physically develop soil and introduces erosion as a detrimental force to soil quality.

2. Five Formation Factors
How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Five Formation Factors
The basis of all soil will be derived by or aided in development by the following factors:
Climate
Organisms
Parent Material
Time
Topography

3. How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Climate
Climate includes several forces that act upon soils, which breakdown rock into smaller fragments and eventually down to small particles.
Rainfall
Temperature
Areas of high rainfall will have more plant material growing and more microorganisms living in the soil. More organic matter is developed that will decay, accumulate, and change the properties of the soil.
Low rainfall areas, such as deserts have very static soils because the lack of vegetation does not support many of the soil forming factors previously discussed.
Warmer climates speed up biological and chemical changes in the soil. You could expect to find very deep and well developed soils in areas with both high rainfall and warm temperatures.

4. How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Organisms
If conditions are appropriate to support plants and soil dwelling animals, organisms thrive and assist in creating optimal soils for plant production.
Temperature and rainfall levels have a major impact on organisms. Soil organisms add organic matter and physically breakdown larger particles.
Chemical reactions are also promoted by organisms.

5. How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Parent Material
Parent material is the substance from which soil is created.
In most cases, soil is formed from a type of rock that has been broken down by weathering or chemical processes.
The five factors are very interconnected. Parent material is the starting point of soil and can be transformed into soil over a long period of time.
The more climate forces, and thus, organism exposure will help speed up the process.
If the parent material is rock on top of a hill, the forces of gravity along with the other factors mentioned will eventually breakdown this parent material into soil. Time is the variable.

6. How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Time
Soils develop at varying rates depending upon the climate and other formation factors.
The forces that form a given soil indicate how long it took the soil to be formed.

7. How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Topography
What would soil be like on top of a hill compared to the bottom of the hill?
Top – larger particles and less organized
Bottom – smaller particles and deep
Why?
At the bottom of every hill there is a stream or at least a place for water to travel. Water is a major force in soil development.
Steep grades accelerate water that lands on the surface and water will accumulate energy as it flows downward.
Flat grades tend to collect water and allow it to soak in the ground rather than run off the slope.
These are important characteristics to remember as you investigate the classifications of soil formation.

8. Soil Development Classifications
How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Soil Development Classifications
There are four main ways that the process of soil formation occurs:
Addition – accumulation or deposition
Reduction – leaching and erosion
Translocation – movement within soil profile
Transformation – soil changes in place by weathering or microorganism conversion
The four processes form soil. These are not forces or variables, rather they are the result or cause of soil formation.
An addition occurs by a river bank where the stream deposits sediment and creates or moves the channel.
Reductions are usually viewed as detrimental effects on soil. Leaching occurs in areas with high rainfall. Nutrients and important minerals are washed through the soil profile and what is left is less desirable conditions for plants. Erosion is the physical removal of soil and will be explored more in upcoming slides.
Translocation happens within a soil profile. Leaching is a form of translocation.
Transformation is when soil changes in its place. Over time all material will decay and breakdown. If no forces are present to move parent material from one place to another, eventually over time the parent material will breakdown into smaller particles and become more soil-like in structure.

9. How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Erosion
The opposite of soil formation is erosion, which has a detrimental effect on soil.
Erosion comes in two forms:
Water
Wind

10. How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
Erosion Happens
In what circumstances is soil erosion more likely to happen?
Steep ground
Too much irrigation
Working soil in a rainy season
Not protecting soil with ground cover
Allowing wind to blow across worked soil
Have students brainstorm this question first before providing the listing.
The soil can be protected by making sure sound management practices are followed. For water related erosion it is best to maintain some kind of vegetation or thick layer of organic matter on the surface to absorb water and lessen its impact on soil particles.
Vegetation will provide protection against wind erosion as well, but in high wind areas wind breaks, such as tree lines are planted on the edge of fields to slow surface winds.

11. What happens when the soil is gone?
How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
What happens when the soil is gone?
Poor crop production
More inputs are required like water and fertilizers to grow crops
Soil could be unusable in some cases
Again, see if students can determine outcomes with this question.
Eroded soils become less efficient for growing crops and in some cases where the soil is shallow only bedrock could remain, which would be unusable.

12. How Soils are Formed
Introduction to Agriculture, Food, and Natural Resources
Unit 4 Lesson 4.1 Starting from the Ground Up
References
Huddleston, J. H., & Kling, G. F. (1996). Manual for judging Oregon soils. Corvallis, OR: Oregon State University.
Parker, R. (2010). Plant and soil science: Fundamentals and applications. Clifton Park, NY: Delmar.