Field Description of Soil Profiles


The background for this lab is found in your study guide. You should read this prior to the lab.

Important terms for this lab

Web sites of interest

This is a field lab!
Unless the weather is severe we will be outside for most of the period, AND we will be in and out of the soil pit in Mitchell Field. We may have some rain between now and then, so the pit could definitely be wet and muddy. Wear old shoes or boots, expect to get muddy, and dress to keep warm if it is chilly (or to protect from sunburn if it is sunny!).

Before the lab, you should review Plaster (2003), chapter 2, (especially pages 27-31) and chapter 4 (especially texture and structure). Also, read the backgroud information in the study guide and be familiar with the terms listed above!

Lab Study Questions

Exam Questions from Labs 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Lab Study Questions

1. From the definitions of master horizons, identify the one most likely to be an illuvial horizon and explain why.

2. A soil profile includes the following horizons: Ap, Bt, Cr and R. Briefly define and describe the properties of these four horizons.

3. What is the difference between bedrock and parent material? Give an example of each.

4. What is the Munsell Color System? give an example of a color notation including the comon name. What do the terms hue, value and chroma mean?

5. What causes the gray color in gleyed or mottled soils?


Study Questions Answers

1. B horizons are illuvial. Material from any O, A, and E horizons above will move down into the B over time.

2.
Ap: Mineral horizon, formed at surface, eluvial, plowed or disturbed.
Bt: Mineral horizon, formed below A, E, or O, illuvial accumulation of clay.
Cr: Little weathered, weathered, or soft bedrock, excludes hard rock.
R: Hard bedrock

3. Bedrock is the solid or consolidated rock underlying the soil such as sandstone, limestone, and shale. Parent material is the unconsolidated somewhat weathered mineral or organic matter from which soil is developed, for instance, sandstone and shale colluvium and limestone residuum.

4. The Munsell Color System is a color designation system that specifies the relative degrees of hue, value and chroma. An example is 10YR 5/4, yellowish brown.
Hue is the dominant spectral color ("actual color" in Plaster) and is represented by page in the Munsell System. Value is the relative lightness or darkness (intensity) of the color and varies up and down each page (lightens from bottom to top). Chroma is the saturation (purity or strength) of color and varies across each page.

5. Waterlogged conditions reduce the amount of oxygen available in the soil atmosphere. As the oxygen is used by soil organisms, anaerobic conditions occur. Anaerobic bacteria (chemoautotrophs) get energy by removing an electron from Fe3+, reducing it to Fe2+. This ion (Fe2+) is more soluble in water and will gradually be carried through the profile by water movement. The red iron hydroxide, Fe(OH3), is what gives soil its color. As it is removed from the soil particle surfaces the gray color of the particles becomes visible.

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Exam Questions from Labs

Example Exam questions from Lab

1. A soil has a dark brown silt loam layer at the soil surface. The third layer (horizon) is reddish in color and fits in the clay textural class. Which of the following horizon symbols would you use for this underlying layer?

a. Ap
b. R
c. AB
d. O
e. Bt

2. Which horizon sequence best describes the pit that you observed in lab?

a. Ap1 Ap2 Bt1 Bt2 Cr R
b. Oe A E Bhir Bir C
c. A C C2 R
d. Oi Ap Bt Btg Bx R
e. Ap1 Ap2 Bca Bcam C

Click here for the Answers to these questions.

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This page last modified on April 18, 2005

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