Adapted with permission by Ward's Natural Science.
Soil is often overlooked as a natural resource. Like fossil fuels, we depend on it for energy in the form of foods. And, like fossil fuels, it is nonrenewable. Soil is a delicate balance of inorganic minerals, organic matter, living organisms, soil water, and soil atmosphere. The natural development of soil is an exceedingly slow process. In a few hours, a heavy rain falling on exposed soil can remove inches of what took hundreds of years to form.
Here is a simple exercise that will allow you to compare the rates and amounts of erosion that result from various land uses.
- 6 plant trays (or shoe boxes cut to 5 cm deep)
- 6 sprinkling cans
- 6 beakers (600 ml)
- Local soil
- Sod (grass covered soil from a lawn)
- Supports to form inclines
- Cut a "V" notch in one end of each plant tray.
- Line each tray with plastic, leaving an overhang of a few centimeters at the notch. This will serve as a spout.
- Fill each of the six boxes differently, as follows:
- Moist soil packed firmly (bare soil)
- Sod (cover crop)
- Moist soil packed firmly; make packed furrows running across the tray's width (contouring).
- Moist soil packed firmly; make packed furrows running down the length of the tray (plowing up and down a hill).
- Moist soil packed firmly; form steps across the width of the tray with the trowel (terracing).
- Alternate three strips of moist packed soil with three strips of sod (strip cropping).
- Position the trays on supports so they all are tilted at an equal incline. Place beakers under the plastic overhangs at the "V" notches (spouts).
- Measure an equal amount of water into each sprinkling can.
- Hold sprinkling cans about 1 foot over the high point of each tray. Pour water steadily for 5 seconds onto each box simultaneously.
- Record the amount of time that water continues to flow from the spout of each box. After the water has finished draining, record the amount of runoff in each beaker. Let the runoff settle, and then measure the volume of sediment in each beaker.
- Finally, for an extra activity, arrange the boxes to increase the slope. Repeat steps 1-7 and compare results with your first observations.
Discuss: Which tray had the most runoff? Which tray lost the most soil? Which tray's contents were most resistant to erosion? Is there a relationship between the time it took for each tray to drain and how much soil washed off? How does the slope affect the amount of soil loss? How would you apply your observations to implement a program of soil conservation?