Soils in the Landscape and Slope
Background Information
Important terms for this lab:
- fragipan
- Redoximorphic features (mottles)
- topographic position
- parent material
- drainage class
- soil horizons
- land use
- catena
A generalized drawing of the geology of the area discussed for this lab is illustrated below. (This is also found in your study guide in the Soils, geology and land use lab).
Figure 1. Geologic cross-section, State College, PA
In this illustration the "bench" formed as a result of the differential weathering of the sandstone and shale formations, and the high ridge formed
by the resistant Tuscarora sandstone is shown to the southeast of the map (below Tussey Mountain).
This map will be helpful as you write your report for the Soils in the Landscape - if only to enhance your understanding of what is happening
and what has happened geologically and pedologically throughout this region.
You will need to check out the soil descriptions for Buchanan, and Andover soil series for your lab report. These are found in the Soil Survey of Centre County, and on the WWW. Follow the link to the Official Soil Series Description home page. Click on "view OSD by Series Name", type the name of the soil in the space provided, and hit "process".
Another important link for this lab. Check out the SSSA glossary of terms . Particularly, check out the definition for fragipan.
Lab Study Questions
1. Define soil catena
2. Explain how the soil series Nolin, Chagrin, Lindside and Melvin are similar and how they are different. (Check desceiptions in Soil Survey of Centre County, PA (Braker, 1981) and on the NRCS web site)
3. Rate each of the soils you inspected for field crop production. State reasons for low yielding soils.
4. Rate each of the soils you inspected for septic tank absorption fields (slight, moderate, or severe limitations). For any moderate or severe ratings, state the reason(s).
5. Rate each of the soil you inspected for buildings with basements (slight, moderate, or severe limitations). For any moderate or severe ratings, state the reason(s).
6. What is a fragipan? How does slope affect the depth to the fragipan and the soil's drainage?
7. Define slope and list three reasons why knowledge of slope is important
8. Write the formula to calculate percent slope.
9. Explain the relationship between slope and depth to fragipan.
10. Explain the cause for the gray and red splotches that you may have seen in the Andover and Buchanan soils (and that are noted on the link to the virtual tour site
Study Questions Answers
1. A soil catena is a table that groups soils according to their parent material, depth and drainage.
2. Nolin, Chagrin, Lindside, and Melvin are all deep soils, formed in alluvium and underlain by limestone and shale. Chagrin is additionally underlain by sandstone. Nolin is nearly level to gently sloping in areas of local alluvium on uplands, while Chagrin, Lindside, and Melvin are nearly level and on flood plains. Chagrin and Nolin are well drained, Lindside is moderately well drained, and Melvin is poorly drained.
3, 4, & 5. NOTE: The soils observed in pits for the Spring 2003 semester are different than in other years. You should have this information in your worksheet pages from the LUP assignment #2.
Your instructor advised you as to the soils that you visited.
You may also check the Virtual landscape tour to see the soils you observed this year on your trip.
| Use | Andover | Buchanan | Laidig | Murrill |
| 3. Agriculture | severe (high water table, rocks) | moderate (seasonal high water table, rocks) | severe (slope, rocks) | slight |
| 4. Septic | severe (high water table, slow permeability, rocks) | severe (seasonal high water table, slow permeability, rocks) | severe (slope, moderately slow permeability) | slight |
| 5. Buildings with basements | severe (high water table) | moderate (seasonal high water table) | severe (slope) | moderate (shrink-swell potential; sinkhole hazard) |
6. According to the Glossary of Soil Science Terms (SSSA, 1996):
[A fragipan is] a natural subsurface horizon with very low organic matter, high bulk density and/or high mechanical strength relative to overlying and underlying horizons; has hard or very hard consistence (seemingly cemented) when dry, but showing a moderate to weak brittleness when moist. The layer typically has redoximorphic features, is slowly or very slowly permeable to water, is considered to be root restricting, and usually has few to many bleached, roughly vertical planes which are faces of coarse or very coarse polyhedrons or prisms.
7. Slope can be defined aritmatically as rise/run (Y/X). It may be expressed in degrees, as a percent, or as a slope class. Percent Slope can be determined by measuring the verticle change over a horizontal distance, and multiplying the result by 100. Field instruments, such as the clinometer used in this lab, measure this ratio and provide the user with either % slope, or degree of slope, or both. We report slope as a percent.
Slope is very important for land use decisions and for soil erosion, to name a couple of reasons.
8. % slope = rise/run * 100
9. The diagram on page 90 of your study guide is helpful for explaining this. On steeper slopes, the depth to the fragipan is greater allowing for better drainage. On less steep slopes, the depth to the fragipan is shallower, water remains closer to the surface and drainage is poorer.
10. These are redoxomorphic features - "mottles" - that are caused by the reduction and oxidation of iron in soils. They occur when the soil is wet for prolonged periods of time due to seasonal high water tables, fragipans, and other wetness problems.
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Exam Questions from Labs
1. On your field trip to Penn Statešs Agronomy Research Farm you observed and/or read about the following soils: Andover, Buchanan, Hagerstown, Laidig, Murrill, and Opequon. Which would be the best soil for agricultural (corn) production?
a. Buchanan
b. Laidig
c. Andover
d. Murrill
e. Opequon
2. A soil is observed to be mottled due to poor drainage, this means that
a. gray limestone rock fragments occur in the soil
b. clay coatings occur on soil structural units
c. patches of rust and patches of gray colored soil were observed side by side in the soil
d. strong, angular blocky structure was observed in the soil
e. the soil has a clay subsoil
Which soil properties are used to distinguish one soil of a catena from another soil of the same catena such as that observed on the Agronomy Farm?
a. parent material and stoniness
b. sinkhole formation and drainage class
c. texture, structure, and stoniness
d. parent material, depth, and drainage class
e. sinkhole formation, texture, and depth
Click here for the Answers to these questions.
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This page last modified on April 14, 2003
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