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Natural Recyclers- Decomposition Lab Activity

Decomposition: A Study of The Natural Recycling Process


By: Arpa Ghazarian



        1.     What factors affect the decomposition of various materials under different conditions?

        2.     What is the biodegradability and rates of decomposition of various materials under different conditions?




        ·      High School Ecology 6e (Students know a vital part of an ecosystem is the stability of its producers and decomposers).

        ·      7th-Grade Science Investigation and Experimentation 7a, b, c, e


Independent variable

The independent variables are the different conditions the materials are put into: Sand, Dry nutrient-rich top soil, and moist nutrient-rich top soil.

Dependent variables

The dependent variables are the rates at which each of the materials decomposes over an 8-week (or longer) period.


The controlled variables are the same materials used in each condition as well as the temperature each condition is kept at.



o   Plastic pots with trays (3)

o   Sand

o   Top Soil

o   Plastic pipets

o   Magnifying glass

o   Water

o   Materials to be studied:

§  Plastic strips

§  Biodegradable plastic strips

§  Natural fibers synthetic fibers

§  Dried plant material (leaves)

§  Newspaper strips

o   Gloves (plastic)  


o   Each team of 3 students will test the biodegradation of materials in sand, dry soil rich in organic matter and moist soil.

1.     Pre-label the pots (set of 3 per student team) and assign a pot to each student in the team as follows:

        a.     Pot #1-Sand- assign to student A

        b.     Pot #2-Dry top soil-assign to student B

        c.      Pot #3- Moist top soil-assign to student C

2. Student A should fill pot #1 with sand, up to 3 cm form the top, packing the sand lightly.

3. Students B and C should fill pots #2 and #3 with top soil, up to 3 cm form the top, packing the soil lightly.

4. Student C should water the top soil in pot #3 using the plastic pipet. Soil should not be excessively moist so that there is water at the bottom of the pot. Over watering can create soggy condition, which will suppress growth of fungi and aerobic bacteria. 

5. Make initial observations of the original condition of the materials to be tested and record your observations in Table 1

Decompostion Lab Table 1


6. Test the original strength of the fibers by stretching it and record fiber strength using the key in Table 2.

Decompostion Lab- Table 2 Fiber_Strength

7. Insert a piece of each of the materials to be tested into the soil of each pot, covering about half of its surface area.

8. Press the material lightly into the soil and cover each pot with a clear plastic top. Place each pot on the individual trays and store at room temperature.

9. Observe your set up once a week for 8-10 weeks. Graph your data from your tables.