Plant Growth in Different Soils

We planted radish seeds (because they sprout quickly) in gravel, topsoil, sand, and clay and then we observed them every day for five days. Gravel, sand, and topsoil all sprouted, while clay had no growth at all. We noticed the topsoil sprouted faster than gravel and sand. We also observed the topsoil had the healthier-looking sprouts. Gravel's sprouts were a bit brown in color, and sand's sprouts were more withered. The kids were surprised the seeds grew in gravel and sand! We discussed that gravel and sand were not providing as much nutrients as the topsoil, hence the pitiful sprouts. Also, clay didn't produce plant growth because it is too packed together to allow roots to grow. We concluded topsoil was the best soil with regards to plant growth.

Water Retention

Gravel Water Retention

Water retention in different types of soils is one of those concepts where figuring out the process for the experiment is every bit as important as the actual results. I want the kids to come up with a way to test this on their own and be able to measure their results. They generally come up with lots of great ways to allow soil to absorb water, but they can struggle a bit when trying to make the amount of water absorbed measurable. The discussion of our plan oftentimes takes longer than our actual experiment. It's worth it, though, because it really makes them use their noggins! Eventually they come up with this...

To test water retention of different types of soils, we use a graduated cylinder, panty hose (which the kids think is hilarious!) and different types of soil. We put each individual type of soil (200ml) into the panty hose, SLOWLY add 200 ml of water, and figure our how much water was retained by the soil by looking at the amount of water than fell into the beaker. The kids are always surprised by how much water the sand retains!

Sand Water Retention

Top Soil Water Retention

Soil Texture

The students are responsible for knowing the properties of soil in 4th grade - color, texture, water retention, and plant growth. We began by looking at color and texture. The students observed top soil, clay, sand, silt and gravel. They added a bit of water to each soil type to help them really feel the texture. They had to determine if the soils make a ball, and if they are grainy, silky, or sticky. Then they predicted what the texture would be like when different soils were mixed together, such as clay and sand, before actually mixing them together. We had a bit of a water spill on one of the plates, so we used that opportunity to revisit erosion. They were able to see the soil being carried away by the water, while the rocks stayed in their place. We discussed the fact that rocks take much longer to erode than soil.

Adding water to our soil

Water eroding the soil