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11) Each differing and distinct mineral and organic strata within a soil column is called a
horizon.
12) The O horizon is typically lacking in organic matter.
13) The A horizon is also commonly called topsoil.
14) In addition to designation of horizons, soil scientists also designate subhorizons, for instance,
indicating human activity or presence of organic matter.
15) A dark colored soil always indicates high organic content.
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16) Soil texture is probably the most permanent property of a soil.
17) Rounded peds have more pore space between them and greater permeability than do other
ped shapes.
18) Biological activity by plant roots or tunnelling animals tends to diminish porosity.
19) Soil oxygen concentrations are lower than atmospheric oxygen concentrations due to
ongoing respiration processes in the ground.
20) A high cation-exchange capacity (CEC) tends to indicate poor soil fertility.
21) Soils with a high concentration of hydrogen ions ( ) are considered alkaline.
22) A few centimeters' thickness of prime farmland soil may require 500 years to mature.
23) Practices such as no-till agriculture may help mitigate against soil erosion.
24) Between 1982 to 2007, there was actually a decrease in soil erosion on U.S. cropland.
25) Desertification is affecting over a billion people worldwide.
26) Over 15,000 soil series have been classified up to this time in the United States and Canada.
27) The U.S. soil classification system has not been updated since the mid-1970s.
28) A soil order is the lowest and most precise level of the Soil Taxonomy system.
29) The Soil Taxonomy is a hierarchical system consisting of six categories.
30) Prior to the U.S. Soil Taxonomy system, soils were classified based on pedogenic regimes.
31) Though Oxisols occur in the world's tropical rain forests, they tend to be poor in inorganic
nutrients.
32) Inceptisols are the largest single soil order, occupying approximately 22% of the Earth's land
surface.
33) Salinization is often associated with Aridisols.
34) Mollisols are widespread in the United States. occurring throughout the Great Plains region.
35) Alifols, Mollisols, and Aridisols form an east to west continuum in the north-central United
States and southern Canadian prairies.
36) Spodosols are solely associated with the northern coniferous forest and are never found
within mixed or deciduous forests.
37) Entisols are the least developed soils in the world.
38) Entisols have several very distinct horizons.
39) Oxisols are not very fertile.
40) Both Gelisols and Histosols have high organic matter content.
41) Histosols tend to be very dry soils found primarily in the world's arid regions.
42) Soils high in clay content may swell significantly when they absorb water.
43) Thawing of Gelisols caused by warming climates could result in the release of carbon
dioxide and methane to the atmosphere.
44) Soils are the foundation of basic ecosystem function and are a critical resource for
agriculture.
45) There is little evidence that human activity has an impact on soils.
18.3 Essay Questions
1) Soil science is an interdisciplinary study that incorporates aspects of physics, chemistry,
biology, mineralogy, hydrology, taxonomy, climatology, and cartography. Briefly describe how
these various fields may be beneficial to the study of soils.
2) What are the five primary soil forming factors? Describe each using examples.
3) What are the six main horizons found in soils? Briefly describe each.
4) List and briefly describe the various physical properties used to differentiate soils.
5) List and briefly describe the various chemical properties used to differentiate soils.
6) What are some of the concerns regarding the rate and amount of soil loss in the United States.
What does a cost benefit analysis of soil loss prevention show?
7) Describe the NRCS Soil Taxonomy.
8) What is the predominant soil order in the area in which you live? Describe the activities that
occur on these soils that reflect the characteristics thereof.
9) Describe and explain the distribution of soil orders across the United States.
10) What do you think are the biggest challenges related to soil conservation and management in
the coming decades?
