Soils are the Pits!
This material was originally developed as part of the Carleton College Teaching Activity Collection
through its collaboration with the SERC Pedagogic Service.
- Understand the relationships between observable and describable soil features and the factors of soil formation and soil forming processes
- Understand how soil characteristics co-vary
- (If lab extends to more than one soil pit) Understand the relationships among different soils in a series
- How to describe major soil characteristics
- How to recognize soil horizons
- How to complete a soil profile description
- How to read published soil profile descriptions
Context for Use
This lab will take between two and four hours, depending on whether the pit is dug beforehand or during the lab period, on how many soil properties per horizon you want students to describe and on how much advanced reading and lecture material students have absorbed.
This lab requires a site with a (relatively) undisturbed soil profile. See Teaching Notes for more details on pit sites.
A number of (on line and in print) are available for instructors and students to learn both how to describe soils and how to interpret their observations. A list of basic field equipment for soil description is also part of this site and includes information on teaching materials that should be laminated and provided to students (such as soil texture triangles, instructions on measuring consistence, etc.).
Teaching Notes and Tips
Find a good location to describe soils - Some natural exposures can be used, but it is useful and fun to dig a pit. If you know a backhoe operator, you can use a long trench that all students can work in simultaneously (but make it shallow and wide for safety reasons). Otherwise, you can have students dig several pits in the same area (so they all describe more or less the same soil) or in a variety of areas (so students can describe multiple soils, one pit at a time).
Essentials of pit digging - Pits should extend through the O, A, E and B horizons of the soil down into the C horizon (or into weathered rock, depending on the soil). Practically speaking, this means that the pit should be at least one meter to one and a half meters deep. The pit should have at least one face that extends through the entire profile cross-section. It is useful to build in a step on the side of the pit that faces this full exposure, so that a student can step into the pit and then sit on the step, if desired. Pit area and volume should be sufficient for one or two people to stand comfortably in the pit and for one person to work in it. It helps to have a variety of shovel types at your disposal to dig the pit. And keep a shovel handy; as students enter and exit the pit and pick at the exposed face, the bottom will slowly fill in so it will need emptying.
Fill in the pit when the lab is over - Unfilled pits, especially near highly traveled paths, are dangerous. After all the lab work is done, fill the pit back in with the excavated material. Piling the material on an inexpensive (but sturdy) plastic tarp or drop cloth as you excavate makes it easier to fill the pit in at the end.
Students' work on this lab can be assessed through an end-of-lab discussion and/or through grading of soil profile descriptions, sketches and other products. Quiz or exam questions can also test students' understanding of soil profile description techniques and their abilities to interpret the genetic significance of soil features. Finally, you may want to schedule a field exam, where students, individually or in groups, describe a soil profile that is new to them. In universities with soil science programs, intra and intercollegiate "Soil Judging (more info) Contests" occur each year.