Soil Formation Factors

Soil Formation Factors

  1. What are the soil forming factors specific to this site that contribute to the soils and ecosystem found in the saline ecosystem?

First, use the satellite photo below to get an idea of the location. What are some striking features of the piece of land? Match each feature with a number on the map. You should only match one feature with one number. 

Satellite photo of north 27th street area, Lincoln, Nebraska. Image courtesy of USGS, edited by UNL

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Question 1: Which number represents a local road?

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Question 2: Which number represents a 4-lane highway?

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Question 3: Which number represents a stream?

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Question 4: Which number represents a constructed terrace?

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Question 5: Which number represents growing vegetation?

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It’s okay if you couldn’t pick out many features on the satellite photo – the CIA employs specialists to do that full-time. But you might have spotted roads by their light color and straight-line layout, growing vegetation by its dark color, and Little Salt Creek which is a dark line mostly parallel to 27thStreet, running north and south in the center of the red square. This is not the natural channel of the stream – it was re-routed but you can see Little Salt Creek in its more natural state on the northern and southern edges of the photo. There is also an abandoned oxbow of the stream visible to the west (left) of the intersection. Another way of looking at this site is to use what is called a “block diagram” which is kind of a cartoon idealizing the relationships among the soils found on the site. A block diagram similar to what might be found on the photo is shown below. Data which describes the three soils follows the block diagram.

Block Diagram of soil and parent material distribution. Image Courtesy of USDA-NRCS, Editing Courtesy of UNL

 

Soil Series Depth to water table(M below soil surface, spring) Soil Salinity (ds/M) Plant stand compostion (% halophytic plants) Occurrence of Salt Creek tiger beetle (Y/N)
soil 1 2 2 5 N
soil 2 0.3 3 10 N
soil 3 0.0 8 50 Y

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Question 6a: The block diagram shows some of the soil forming factors which act independently to form unique soils. Is parent material a commonly accepted soil forming factor?

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Question 6b: The block diagram shows some of the soil forming factors which act independently to form unique soils. Is human activity a commonly accepted soil forming factor?

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Question 6c: The block diagram shows some of the soil forming factors which act independently to form unique soils. Is biological activity a commonly accepted soil forming factor?

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Question 6d: The block diagram shows some of the soil forming factors which act independently to form unique soils. Is drainage a commonly accepted soil forming factor?

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Question 6e: The block diagram shows some of the soil forming factors which act independently to form unique soils. Is time a commonly accepted soil forming factor?

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Question 6f: The block diagram shows some of the soil forming factors which act independently to form unique soils. Is climate a commonly accepted soil forming factor?

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Question 6g: The block diagram shows some of the soil forming factors which act independently to form unique soils. Is topography a commonly accepted soil forming factor?

Looks Good!

To review the soil formation factors, see Principles Lesson 3.2 - 3.6

We will focus our attention on three specific locations on the landscape that have very distinct soils formed. These are labeled as “soil 1”, “soil 2”, and “soil 3” on the block diagram above.

Toposequence and Drainage Sequence. Image courtesy of UNL, 2006

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Question 7a: From the block diagram and the simplified cross-section of the location shown above, is parent material a soil formation factor for any of the three soils?

Looks Good! Soil 1 is formed on loess, soils 2 and 3 on alluvium.
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Question 7b: From the block diagram and the simplified cross-section of the location shown above, is biological activity a soil formation factor for any of the three soils?

Looks Good! While there may be a difference in biological activity, mainly type or amount of vegetation, among the locations, the block diagram does not give definite evidence of any difference.
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Question 7c: From the block diagram and the simplified cross-section of the location shown above, is time a soil formation factor for any of the three soils?

Looks Good! The alluvium must have been deposited on top of the loess, so the soils forming on the alluvium are younger in years. However, other soil forming factors may develop these soils more deeply.
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Question 7d: From the block diagram and the simplified cross-section of the location shown above, is climate a soil formation factor for any of the three soils?

Looks Good! The macro (big scale) climate, such as rainfall or mean annual temperature, is very similar among the sites because they are located very close to each other.
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Question 7e: From the block diagram and the simplified cross-section of the location shown above, is topography a soil formation factor for any of the three soils?

Looks Good! The soils are formed on different topographic positions which mainly affect their slope.

To review the soil formation factors, see Principles Lesson 3.2 - 3.6

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