Teaching Objectives

Beginning concepts

• Living organisms produce organic matter.
• Compost consists of decayed organic matter.
• Just as there is a cycle of life, there is a cycle of decomposition in which once living materials break down and release their nutrients to again support life.
• Many synthetic materials created by humans do not decompose.

Advanced concepts

• Humus is a dark, crumbly material resulting from the decomposition of organisms and parts of organisms, and becomes part of the soil.
• As decomposition occurs in a compost pile, heat is generated.
• Composting is the management of the biodecay of organic matter into a humus like material by other organisms.

Time Required

Stage 1: Construct the bottle columns - 2 to 3 hours
Stage 2: Fill the compost columns - 1 hour
Stage 3: Composting - Observation over several months

Materials Needed

This exercise requires the following:

40 day-old Fast Plants
marking pen
several 2-liter soda bottles
thermometer (optional)
scissors and razor blade/knife
pH paper (optional)
sharp needles and a candle or a small, fine-tipped soldering iron
plant & animal matter for composting along with the dead Fast Plants
water

Exploratory Questions

Ask your students questions and discuss ideas they might have such as:

What would happen if plants and animals (organisms) that die did not decay?
How are organisms broken down?
How long does it take for plant and animal matter to decay into humus?

Exploration

1. Construct a compost column from 2-liter soda bottles.

Fill a two-liter bottle with hot water and replace the cap.The heat will melt the glue and allow you to peel off the label and twist off the bottom easily.
Study Figures 2 through 5 to determine where to cut the bottles for a two or three bottle compost column. Options for cutting the bottles
Pour out the water and place the bottle on its side against a solid object, such as the sides of a drawer.Mark a ring on the bottle (Figure 6) where you want to make the cut.
Use a razor blade or knife to start a cut after marking the bottles, and then finish the cut with scissors (Figure7). Note in Figure 5 above that the shoulder of bottle #3 is cut at so that it fits into bottle #2.
Provide air and testing holes by poking holes in the sides of the bottle with a hot needle (heated in a candle flame, or a Bunsen burner) or the soldering iron.
Put a piece of netting or nylon stocking over the spout of bottle #2, securing it with a rubber band.
Put the pieces of column together, Figure 8.

2. Fill the compost column.

Place the dried Fast Plants and potting mix in the compost column along with grass clippings, newspaper, food waste, etc. Ask students to bring in whatever they can think of.
Add just enough water to lightly moisten the materials in the column.No additional water should drain from the column at the onset.

3. Observe periodically and record observations.

Observe the odor of the column.

Recycle water which drains into the bottom of the bottle column. Check the pH of the water as composting proceeds.
Look for evidence of the chain of decay organisms which will cycle through the composting proceeds.

The temperature in the column can be checked by punching a small hole in the sides of the column with a large, hot nail and putting a meat thermometer into the decaying matter.

Tips

If you start the compost column/s in the fall, by spring you can use the "humus" to fertilize the plants in your school.

Accompanying Activities

Mix some pieces of plastics along with organic matter (sticks, leaves, etc.) in the compost column. After several months, students can observe that the synthetic material did not decay. What is the position of the synthetic materials within the column now?
Make a second column, identical to the first. Add earthworms or something you want to test and observe the difference between the two.

Measure the total mass (amount) of material added to the column, including liquid. How does the amount of the mass change over a period of time? Does the amount of liquid change?

Background Information for teachers

In nature, the recycling of matter produced by living organisms is accomplished by decay organisms, largely bacteria and fungi. A succession of organisms, each group breaking down biodegradable materials into simpler and more usable material, is at the heart of the process. The end product is humus, a dark, crumbly material that then becomes part of the soil.

When people manage the recycling of organic matter, the process is called composting. Often this activity involves putting organic refuse (such as leaves, lawn clippings and garbage) into a compost pile, where the materials decompose. The resulting compost (humus) can be used as a soil conditioner, and as a source of plant nutrients. Almost any plant or animal material or animal material (leaves, grass clippings, straw, newspapers, food scraps or sawdust, for example) can be composted.

Decay organisms use some of the nutrients left in these materials as their food source. As these organisms decompose plant and animal material, energy is released. The organisms use some of this energy, but some is lost as heat. Decay organisms also require a moist environment to grow, so water (or rain) must be added to the compost. Decomposition occurs faster in the presence of oxygen (aerobic) than in its absence (anaerobic conditions). Therefore, good aeration must be provided. This is why gardeners will "turn" a compost file. Composting will occur most rapidly when organic matter is lightly moistened, loosely packed and maintained at temperatures favorable for decay organisms to grow and reproduce.

Different organic materials decompose at different rates. Succulent materials containing water and nutrients, such as fruits and vegetables, decompose more rapidly than fibrous and woody cellulose-containing items. Lignin, the structural material coating cellulose fibers in wood, is very resistant to decay. Only a few microorganisms are capable of decomposing lignin.

As municipal landfill sites become filled with refuse from our throw-away society, composting of all organic wastes becomes increasingly important. Composting is a method of returning organic wastes to the earth in an easily reusable form.

References

Cochrane, J., Plant Ecology, Bookwright Press, NY, 1987. Chapters 5 & 6.

Schuman, D.N., Living with Plants, A Guide to Practical Botany, Mad River Press, Inc., Eureka, CA, 1980. Excellent introductory chapter for background information entitled, "Introduction to a Plant," as well as other topics such as nutrients, soils and plant hormones.

Spurgeon, R., Ecology (Usborne Science and Experiments), EDC Publishing, Tulsa, OK, 1988. "Building a Compost Heap," p.38.