Mrs. Kuhl’s fourth grade class has begun a composting project in conjuction with their math unit in graphing. They began the project by learning about, and recording, the process of decomposition. After examining a fossilized shell encased in sandstone from a local canyon, the students considered the question: With all of the billions of living things on earth over millions and billions of years, why don’t we find more fossils? The answer, of course, is that most living things decompose.
Decomposition, they learned is caused by three elements: the F.B.I., Fungus, Bacteria and Invertebrates.
For their first activity, students put small pieces of food in Petri dishes, covered with a small amount of dirt and some water. On a worksheet, they recorded what they observed in the dish. Over the next three weeks, the students continued to observe and draw the process of decomposition, as the food in the Petri dish began to decompose.
For their second activity, students made a “compost bag,” a hefty bag filled with soil, air, some water, and a variety of objects. Students predicted which objects would decompose, and which objects would remain the same after a month. Objects included: wet toilet tissue, a nail, a piece of aluminum foil, a styrofoam cup, some lettuce leaves, a corn chip, bread, and some grass clippings. Every week or so, students add some air to the bag to make sure it stays aerated. In a month, they will check to see which of their predictions were accurate — which objects decomposed, and which stayed in tact.
For their third activity, students created a large compost heap for the school garden. They learned that compost can be created from two main elements:
Green Waste, rich with nitrogen: grass clippings, coffee grounds, bread, veggies, fruits
Brown Waste, rich in Carbon: dry brown leaves, shredded paper, cardboard, wood chips and shavings
And they learned what NOT to put in a compost pile (Dairy products, meat, plastic, oils)
- Students first dug a hole about four inches deep in a square as big as our plastic composter.
- They placed the plastic composter on top of the hole.
- They filled it with a 4 – 6 inch layer of brown waste — dried leaves and shredded paper.
- They piled on a 4 inch layer of greens — grass clippings and old food.
- Then a layer of brown.
- Then a layer of green.
- In between layers they tossed in a bit of old compost from last year, so that the old bacteria could get to work making new compost in the pile;
- They added layers until they ran out of materials.
- Then they measured the size of the pile — how tall it was (about 20 inches)
- Then they took the temperature of the pile with a long compost thermometer. (About 85 degrees)
In the coming weeks, the students will continue to measure and graph the size of the compost pile, and the temperature of the pile as the process of decomposition takes place.