- 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.
- Humus is a dark, crumbly material resulting from the
decomposition of organisms and parts of organisms, and becomes part of
- 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 for Exercise
- 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
This exercise requires the following:
- several 2-liter soda bottles
- scissors and razor blade/knife
- sharp needles and a candle or a small, fine-tipped soldering
- plant & animal matter for composting along with the
dead Fast Plants
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?
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
- 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
- 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.
If you start the compost column/s in the fall, by
spring you can use the "humus" to fertilize the plants in your
- 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 the Teacher
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
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.
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.
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