Elaborate: Use Keys to Identify Soils
Part A. Identify Soil Orders as a Degree of Development
Source: NRCS
Students use several keys and descriptors to identify soil orders. The first exercise challenges student understanding of soil orders definitions as a factor of degree of development and ClORPT and is a follow-up to the activities in the previous sections of this module.
Soil Identification Exercise 1. Use Clues to Identify Soil Orders (Word Doc (Microsoft Word 2007 (.docx) 14kB Mar11 21)) (PDF)
Key to Soil Exercise 1. -- educator-only file
HidePart B. Use Dichotomous Keys to Classify Soil
In this exercise students use a series of keys and descriptors to identify epipedonsEpipedon (Gr. epi, over, upon, and pedon, soil) is a horizon that forms at or near the surface and in which most of the rock structure has been destroyed. It is darkened by organic matter or shows evidence of eluviation or both. They are characterized by their physical properties: (e.g., color, texture, structure, and content of organic matter) chemical properties including certain plant nutrients (e.g., calcium, phosphate). and soil orders. In this activity, students apply their knowledge and understanding of physical, chemical, and biological soil properties to identify soils.
This activity is more advanced than the first and may require more guidance. By completing this exercise students will apply the knowledge they gained in earlier modules.
Soil Identification Exercise 2. Identify a Soil Order with a Dichotomous Key (Word Doc (Microsoft Word 2007 (.docx) 18kB Mar11 21)) (PDF)
PowerPoint with Keys to use with Exercise 2 (PPT (PowerPoint 2007 (.pptx) 68kB Mar11 21)) (PDF (Acrobat (PDF) 100kB Mar11 21))
Begin Soil Exercise 2 by reviewing the following 11-minute video.
Soil Classification Basics and Dichotomous Keys for Selected Surface Horizons and Soil Orders
In this video, soil scientist Dr. Clay Robinson explains why we describe soil profiles, and the basics of classification with dichotomous keys. Teachers may choose to share this video directly with students or use it to learn the material before class.
- Diagnostic HorizonDiagnostic horizons are soil horizons used in classifying soil; they differ from horizon designations in a soil description, such as Ap-Bt1-Bt2, as they may contain multiple horizons from a profile, for example, a mollic horizon may contain a group of horizons in the profile: Ap-A, and the top portion of a B horizon. They are also referred to as epipedons.
- EpipedonEpipedon (Gr. epi, over, upon, and pedon, soil) is a horizon that forms at or near the surface and in which most of the rock structure has been destroyed. It is darkened by organic matter or shows evidence of eluviation or both. They are characterized by their physical properties: (e.g., color, texture, structure, and content of organic matter) chemical properties including certain plant nutrients (e.g., calcium, phosphate).
- IlluvialA soil layer or horizon in which material carried from an overlying layer has been precipitated from solution or deposited from suspension. The layer of accumulation.
- EluviationThe removal of soil material in suspension (or in solution) from a layer or layers of a soil. Usually, the loss of material in solution is described by the term "leaching."
- Soil ProcessesThe 4 basic soil processes are Additions, Losses, Transformations, and Translocations.
Part C. Relate Soil Classification to State Soils
Once students understand how soils are classified, and the importance of classification to determining suitable uses and limitations of soils, return to state soil booklets and read about the soil in a state of interest or the soil from their soil postcard. – how'd they do? Did they identify the correct soil from the images and uses?
State Soils