Soil Monoliths and lab introduction
Background Information


Plaster, Chapters 1 & 2. Also see Study Guide

Important terms for this lab.

Lab Study Questions

Study Question Answers

Exam Questions from Labs

Soil Definitions

For soils observed in the Soil Monoliths and Samples lab, go to the Soils Data Sheets

Soil Definitions

  • Edaphological:
    • The unconsolidated mineral material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
    • The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects) and macro- and microorganisms conditioned by relief and acting on parent material over a period of time. The soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.
  • Pedological: The unconsolidated mineral material on the immediate surface of the earth that formed by the interaction of prent material, climate, organisms, and topography acting over a period of time.
  • Ecological: The unconsolidated mineral matter on the surface of the earth - a result of the interaction over time of the atmosphere, biosphere and hydrosphere with the lithosphere.
  • a geologists: Weathered, unconsolidated material underlain by bedrock - the upper part of the regolith (Plummer and McGeary, 1979).
  • a MicrobiologistsSolid inorganic material, such as rocks and minerals, in a complex mixture along with organic matter, water, air, and living organisms that together form a very thin surface layer (6 inches to 20 feet in depth) on the earth (Tortora et al., 1992; Waksman and Starkey, 1931).

Soil Formation

Soils are formed through a combination of five factors:
  • Parent material is the solid matter, usually weathered rocks and minerals but sometimes decomposed organic matter, that becomes soil after the other soil-forming factors have acted upon it. Parent material terminology includes not only the actual material (sandstone, limestone, shale, granite, etc.) but also the method by which it arrived at the location where it developed into soil (residuum, alluvium, colluvium, loess, etc.).
  • Relief (topography) affects soil formation greatly due to its effect on water and soil movement, vegetation, solar radiation, and water table. The topographic position of soils, (ridge-top, sideslope, upland, footslope, floodplain, etc.) can have a great effect on the soil properties.
  • Climate provides the environment in which the processes of soil formation act and also affect the rates of various physical, chemical, and biological activities.
  • The effect of biological activity (organisms) on soil formation comes through the physical mixing of materials, additions of biological materials and chemicals, recycling of minerals, etc.
  • The effect of time on soil development is evident in the differences between young, mature and old soils. These differences are apparent in both physical and chemical characteristics.

Soil Horizons and profiles

A hole dug into the soil, or a road cut exposing the soil, will reveal different layers, or horizons. Soil horizons are layers approximately parallel to the soil surface which differ from adjacent layers in properties such as texture, color, structure, and chemical composition. A vertical section of a soil, including all of its horizons is called a soil profile.

Soil Master Horizons

Under the current (United States) soil taxonomy system, established in 1982, there are six master soil horizons recognized. The previous system recognized five master horizons. Since many publications currently available were written prior to 1982, it is necessary to understand both.
Current SystemDescriptionFormer System
O HorizonOrganic material (decomposed leaves, etc.)O Horizon
A HorizonTopsoilA Horizon (A1)
E HorizonEluviated topsoilA Horizon (A2)
B HorizonSubsoilB Horizon
C HorizonParent materialC Horizon
R HorizonBedrockR Horizon

The only difference in the master horizons is in topsoil; what used to be considered one horizon (A1 & A2) is now considered as two horizons (A & E). Other differences occur at more detailed classification levels. These are not important for this exercise.

Soil Monoliths

Soil monoliths are thin, vertical sections of soil profiles that have been mounted on boards. They provide a convenient means of observing and comparing different soils without traveling long distances in the field. Soil monoliths provide a quick and easy method of observing some of the soil properties. They cannot substitute completely for field observation, however.

Lab Study Questions

Study Questions

1. For a given soil monolith, use any properties you can observe to discuss its potential for use in agriculture, forestry, and building construction.

2. Given two or more monoliths (or soil profile descriptions), compare their suitabilities for agriculture or building construction using their soil properties.

3. What is the difference between a soil profile and a soil monolith?

4. How do soil and land properties affect the potential for use in agriculture, forestry, and/or building construction?

5. Which of the soil forming factor(s) is/are dominant in the formation of the soils of Nittany Valley?

6. What are some important properties that characterize soil horizons? Name and describe four.

7. Explain the difference between bedrock and parent material and provide an example of each.

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Study Question Answers

Answers to Lab Study Question

1. Important factors to consider include soil depth, texture, rocks, limiting layers, fertility, drainage class. Other observable factors that provide information about the soil include color, OM, structure.

2. The properties above will help guide land use decisions for any soil. When you know the factors and properties of a soil, then its suitability for agriculture, building construction, recreation, forest, or any other use can be determined.

3. A soil profile is a vertical soil exposure in place that includes all horizons.
A soil monolith is a thin, mounted vertical section of a soil profile.

4. Properties such as depth, drainage class, texture, rocks, fertility, and limiting layers combined with land properties such as slope, topography, physiography, and underlying bedrock affect potentential for land use in a variety of ways. They determine effective rooting depth, water movement, nutrient availability, equipment limitations and more. These will in turn determine whether the soil and land is suitible for agriculture, or for residential, or for woodland, golf courses, natural areas, ski slopes, whatever.

5. The dominant soil forming factors for soils of the Nittany Valley are Parent Material and Topography. The limestone residual parent material found throughout the valley has provided the region with its rich agricultural soils. A transition to limy sandstone and sandstone resulted in residual soils around the area that are less fertile, droughty, and less well suited for most uses. Along the ridges colluvial materials produced soils with a fragipan (dense, impermeable layer) and potential drainage problems. The regions topography, the karst in the limestone valley as well as the ridges and valleys that define this area, have also impacted development of our soils.

6. Soil horizons may be differentiated and described based on a number of physical and chemical properties. Some properties, such as color, texture, structure, stoniness, mineral concentrations, depth, and horizon thickness are usually easy to identify in the field.

7. Bedrock is the consolidated (solid) rock that underlies soil or in places is found at the earth's surface. Examples of bedrock include: limestone; shale; sandstone; granite; and others.

Parent material is the unconsolidated and somewhat chemically weathered material from which soils are formed. Rocks that have undergone minimal pedogenesis will be parent material. Parent material may be mineral (from rock) or organic. For our definition, parent material includes the name of the source material (rock or organic) and, in the case of PM from rocks and minerals also will include the method of transport. Examples of parent material include: Limestone residuum (formed in place); sandstone and shale colluvium (moved by gravity); alluvium from limestone and shale (transported by moving water); glacial till (by glaciers, obviously); and others.

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Exam Questions from Labs

Example Exam questions from Lab

1. The A horizon is different than the B horizon because
a. A is always black and B is always red.
b. A is sandy and B is clayer.
c. A is a zone of eluviation and B is a zone of illuviation.
d. A typically contains prismatic structural units and B contains granular structural units.
e. A is a zone of illuviation and B is a zone of eluviation.

2. Which of the following is considered subsoil?
a. O
b. A
c. E
d. B
e. C

3. Which horizon is not considered part of the solum?
a. A
b. A2
c. E
d. B
e. C

4. Which of the following is a parent material that is not found in "Nittany Valley?"
a. shale
b. limestone residuum
c. alluvium
d. glacial till
e. sandstone residuum

Click here for the Answers to these questions.

References
Plummer, C.C. and D. McGeary. 1979. Physical geology (4th Ed.).
Wm. C. Brown Publishers. Dubuque, IA

Tortora, G.J., B.R. Funke, and C.L. Case. 1992. Microbiology - an introduction
(4th Ed.) The Benjamin/Cummings Publishing Co., Inc. Redwood City, CA.

Waksman, S.A. and R.L. Starkey. 1931. The soil and the microbe. John Wiley
and Sons, Inc. NY, NY.

This document last modified on January 17, 2006

For information about this page contact Kate Butler at: katebutler@psu.edu

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