GEOG 1011
LANDSCAPES and WATER
-----SOILS INTERNET LAB-----
SPRING 2008
INSTRUCTOR:
|
Soil
formed in glacial outwash, Wisconsin |
HOMEWORK ASSIGNMENT:
Using the Worldwide Web to Find Information on Soils
OBJECTIVES:
- to look at characteristics of soils in the United
States;
- to utilize the internet to gather information.
BACKGROUND: The US Department of Agriculture Natural Resources Conservation Service (NRCS) publishes maps and reports describing soil characteristics in virtually all areas of the United States. The NRCS soil survey maps are very detailed, and often show many different soil types within a few square miles. The reports provide additional basic data on soil characteristics (porosity, available water capacity, rock fragments, etc.), and tables that rate each soil in terms of its potential for growing certain crops, drainage characteristics, suitability for building site development, ability to support wildlife, and so on. The soil survey maps and reports are thus very useful for agricultural and planning purposes.
Recently much of this map-based information has been converted from
hard-copy to digital format, making it easier to incorporate soils data into
climatological and hydrological models. These digital data bases are available
for every state in the US, hence the name State Soil Geographic (STATSGO) data
base. As before, various attributes of soils are included in the data bases,
thus they can be used for regional planning and land management purposes, as
well as forecasting the effects of changes in soil moisture and potential
evapotranspiration.
DATA: To obtain data for this lab, you will link to websites we have
identified in the text.
ASSIGNMENT:
You may print out this assignment and answer the questions in the spaces provided, OR to save paper, you may simply answer on a separate piece of paper, clearly identifying the question number, e.g. 1a) 1b) ..... 6a) 6b) and so on.
Be sure to include:
- your name
- your section & T.A.
HINT:
Open TWO WINDOWS in your web browser, and keep the assignment in
one. Use the other window to follow links to the soils websites. This
will allow you to have the questions available as you go to different sites.
Answer the following questions using this website:
http://www.soilinfo.psu.edu/index.cgi?soil_data&conus&data_cov
The
website should look like this:
1. Click on Soil Texture Class and then click on Image.You should see a map of soil texture for the US. Note the tremendous range in soil texture throughout the country. Looking at the map and the triangular diagram, what type of soil is most common in the Midwest? What type of soilis most common along the Atlantic Coastal Plain?
a) Midwest
b) Atlantic Coastal Plain
2. Click on Soil Texture Class (or use the Back command) and read
the explanation. At the bottom you'll see a table listing soil water
characteristics for different textures. The second column lists the volumetric
water content at saturation (also called porosity), the column labeled Ks
lists the saturated hydraulic conductivity (also called permeability
), and the last column lists the water content at the wilting point. Note that
porosity does not vary much with texture, but wilting point does. Explain the
trend in wilting point, i.e. why would a silty clay reach the wilting point at
a higher water content than a sandy loam?
3. If you scroll to the top, click on Porosity, then click on
Image, you'll see a rather bland map showing that, indeed, porosity does
not vary much from place to place. This suggests that most soils, when
saturated, hold about the same amount of water. However, the total volume of
water held in a soil is determined by other factors such as soil thickness or
depth to bedrock. Scroll to the top, click on Depth-to-Bedrock, and then
click on Image. List two general regions of the US where
depth-to-bedrock is less than 50 cm and two areas where it is greater than175
cm:
a) less than 50 cm:
b)
greater than 175 cm:
4. Recall that available water capacity (AWC) is defined as the difference
between field capacity and wilting point, and that AWC varies with soil texture
(see class notes or p. 239 of your text). Scroll to the top again,click on Available
Water Capacity, then click on Image. List the general region of the
US with the highest values of AWC:
5. Referring back to some of the previous images and your general knowledge
of soil moisture,
a) explain why the Rocky Mountain Region is characterized by low values of AWC:
b)
explain why the Southeast is characterized by intermediate values of AWC; this
is an area of abundant moisture, and very thick soils, so why isn't the AWC
higher here?
Now go to the following website:
http://soils.usda.gov/
Select
the link to Photo Galley, located in the middle of gray menu bar near
the top of the page, then select Dominant Soil Orders. This web page
provides photographs and brief descriptions of the 12 soil orders. The
descriptions for some soil orders are pretty detailed, but others are easily
understood if you know what a few words mean. Here's a short glossary of terms
used in soil descriptions:
argillic horizon a subsoil horizon characterized by an accumulation of illuvial clay.
natric horizon a subsoil horizon with 15% of more exchangeable sodium.
calcic horizon a subsoil horizon with 15% of more calcium carbonate (CaCO3).
base saturation percentage of base cations (Ca, Na, Mg, K) that make up the total cations; high values indicate nutrient rich soils.
available water capacity defined as the difference between the amount of soil water at field capacity and the amount at the wilting point.
6. Click on the link to Aridisols and click on map. Note the distribution of aridisols in
the US. These soils are located in areas of low precipitation and very high
evapotranspiration (90-95% of annual precipitation). Go back to
the previous page, and click on the photo with description. Notice that
many of the rocks in the middle of the photograph have a light-colored
coating. What is the coating, or what causes the light color?
7. Go back to the list of Dominant Soil Orders. Click on the
link to Mollisols, and compare the photo and description. These soils
are widespread and very important from an agricultural standpoint. Using
previous information on soil mositure and information contained in the
description, explain why these soils are productive agriculturally:
8. Go back to the list of Dominant Soil Orders. Click on
the link to Spodosols, and look at the photograph. The whiteish layer in
the upper part of the profile is an eluvial (E) horizon reflecting intense
leaching and removal of almost everything but quartz; this horizon is
diagnostic of spodosols. Now go to the following web site:
http://www.fs.fed.us/land/ecosysmgmt/ecoreg1_home.html
Click on the map labled Divisions, and click on the teal-colored area
encompassing all of eastern Maine. You should see a description with the
heading 210 Warm Continental Region. Note the comments on soil characteristics
in the last paragraph. Answer the following questions:
a) Why is an upper layer of humus present in this soil, when it is not
present in similarly leached tropical soils?
b) Spodosols are found in humid regions. Why are they poorly suited to crop
production?
c) What vegetation type thrives in these soils?