Observing leaves in a compost pile

A 5th to 8th Grade Science Experiment Project Lesson Plan

Description:

This is a small group activity to investigate whether clumping affects leaf decomposition in a compost pile.

Skills:

• Follow a set of written instructions for a scientific investigation.
• Distinguish between variable and controlled parameters in a test.
• Collect data in an investigation and analyze those data to develop a logical conclusion.
• Communicate the steps and results from an investigation in written reports and oral presentations.

Preparation:

If the school does not have a compost heap, directions for building one are readily available.

The project may be done with home composters. Students without composters can play a team role such as photographer or recorder.

Make copies of the two-page Experiment Description Worksheet.

Caution:

Students with allergies or aversions to compost or leaves should wear rubber gloves or play a team role which does not require them to touch the materials.

Procedure:

Read through the Experiment Description with the students. Discuss:

• Which experimental conditions are the same for both bags (type and size of leaf, being buried for the same length of time in the same compost heap, etc.)?
• What's different about the two bags (single leaf vs. clump of leaves)? Why is it important for all of the experimental conditions or variables, except for the contents of the bags, to be the same?

List possible results in a columns (both decompose at the same rate, contents of Bag #1 break down faster than those of Bag #2, and vice versa).

Start a second column headed "Suggests that:" and give an example: "both decompose at same rate" suggests that "clumping does not affect the rate of decomposition." Ask students to complete the column.

Students conduct the experiment, prepare a report, and discuss their results with the rest of the class, referring to the pre-experiment discussion above.

If more than one team conducted the experiment, were the results the same? If not, why not (which experimental conditions were different)?

Examine the observation records made by each group. Are they easy to read? Is it easy to compare them to another group's observations?

Extension:

Students choose a question of their own and then plan and conduct an experiment to investigate. For example: Which decomposes faster, eggshells or potato skins? Leaves or fruit and vegetable leftovers and parings? The contents of a compost pile that is turned daily with a pitchfork or one that is turned once a month or never?

Students should hold a pre-experiment discussion of their experiment plan similar to the one above.

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