Weathering: Plant Roots

 

Plants, specifically plant roots, are one source of weathering.  Cracks in driveways and sidewalks often provide evidence of this, but it's simple to watch it take place within your classroom. 

You'll need some Plaster of Paris*, seeds** and a small disposable cup or cupcake paper.

Mix the plaster according to the package instructions (usually 2 parts plaster to 1 part water).  Pour the plaster into your vessel. 

Poke two or three seeds into the plaster.  Place in a spot where it won't be disturbed while the plaster sets and the seeds germinate (there's enough moisture in the plaster for the seeds to begin germinating, no need to add anything). 

Within a day my seeds had swollen and begun to germinate.  The force the seed exerted was enough to crack the plaster. 

Now think about what happens in a driveway or sidewalk... a crack forms in the surface, seeds blow or fall into the crack, a bit of rain falls and the seeds begin to germinate.  The force of the seed germinating and the roots taking hold forces the more cracking.  Now there's a larger crack into which more seeds can gather and cause further cracking.  If nothing is done to curb the problem, eventually the sidewalk or driveway will be dessimated. 

*FYI Plaster of Paris does have a limited shelf life.  If it gets too old, it won't set up properly and you'll have a crumbly mess.

**I've mentioned it before, but dried beans (like you'd use to make soup or baked beans) will germinate.  They're cheaper to buy in a large quantity than garden seeds and they can be found easily year-round.

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Erosion & Run-Off: What affect does vegetation have?

 This is a really simple demonstration, but it does require some planning ahead (not always my strong suit... )

You'll need two shallow pans or boxes.  Fill each pan with dirt.  Sprinkle grass seed on one of the pans of dirt.  Keep the soil moist as the grass seed germinates and grows.  (You don't need to do anything with the other pan of dirt right now).

Once you have a nice crop of grass in the one pan, take both pans outside.  Prop up one end of each pan using bricks (or something else that will raise it a few inches).

Begin to spray both pans with a hose or spray bottles of water.  You can spray in any manner you'd like, just try to get both pans equally.

While you're spraying, observe what happens to both the soil and the water in each situation. 

When you've finished, discuss the impact of vegetation on soil erosion and/or water run-off. 

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