What happens when rain falls on bare soil with no plants? Water washes loose dirt away quickly. But roots hold the ground in place.
You set up two trays side by side. One tray has grass growing in soil. The other has bare soil with no plants. You tilt both trays at the same angle and pour the same amount of water onto each one. A paper towel filter at the bottom catches the displaced dirt.
The tray with bare soil loses far more dirt than the one with grass. This shows how removing trees from a rain forest speeds up erosion.
Hypothesis
The hypothesis is that the container with just soil will displace the greatest amount of soil when the same amount of water is poured on to each one.
Bare soil washes away fast when water hits it — wind and water strip the top layer of dirt right off the ground. Plant roots act like anchors. They hold that top layer in place so it cannot wash away. One test used two trays tilted at the same angle. The tray with bare soil lost far more dirt than the one with grass.
When trees are removed and no new ones are planted, roots no longer grip the ground — and rain washes loose dirt away. This experiment makes that difference visible. You set up two trays side by side: one with grass growing in soil, one with bare soil and no plants. Pouring the same amount of water onto each at the same angle, a paper towel filter at the bottom catches whatever soil gets displaced. The bare soil tray loses far more dirt than the one with grass, showing exactly how clearing a rain forest speeds up erosion.
Method & Materials
You will measure the amount of soil displaced when the same amount of water is poured onto two different containers - one with grass and soil, and one with just soil.
You will need bins containing soil, water, graduated cylinders, 5 trays (1 tray with grass growing in soil, 2 with just soil, 2 empty), a ruler, paper towels, rubber bands, a text book, rain forest journals, and an overhead projector.
The results showed that high amounts of soil were displaced in the container that just contained soil. This experiment demonstrates that soil erosion occurs when unprotected soil is washed away by rainfall, and that plants prevent soil erosion by stabilizing the soil with their root systems.
Why do this project?
This science project is interesting and unique because it allows students to observe the effects of soil erosion on the destruction of rain forests in a hands-on way.
Also Consider
Experiment variations to consider include tilting both trays with their science books so that one end is higher than the other, and stretching a paper towel around the tops of the empty containers to filter the water from the dirt as it is displaced.
Full project details
Additional information and source material for this project are available below.
