Grass Decomposition Lab
Purpose: The purpose of this lab is to observe the relationship between moisture level
and plant (grass) decomposition. In addition, a comparison will be made between aerobic
and anaerobic decomposition.
Materials: 14 150 ml small, clear, plastic party cups, distilled water, plastic food wrap,
sharp probe or pin, #64 size rubber bands, and freshly cut lawn grass.
Procedure: Place 5 grams of grass in each of the 14 plastic cups. Make sure to
remove all small rocks, leaves, and twigs before massing the grass.
Measure the mass of the cup with grass and the cup with the grass and water.
Record your measurements.
Add each of the following amounts of water to two of the cups: 0ml, 2ml, 4ml,
8ml, 16ml, and 64 ml. Label the cups according to how much water they have.
After adding the water, cut up small squares of plastic wrap. Place plastic wrap
square on the top of each of the plastic cups securing it in place by placing a rubber band
around the rim.
Take a sharp probe or pin and punch four very small holes in just one of each of
the following containers 0ml, 2ml, 4ml, 8ml, 16ml, and 64 ml. Now you have two sets of
plastic decomposition cups, one with holes (aerobic) and one without (anaerobic).
Place all the cups together in the same area so as not to introduce extra variables
such as temperature and light.
Write a hypothesis for anaerobic and aerobic decomposition.
Data Collection: Mass the samples daily. Record measurements. Using the
measurements calculate the mg of grass decomposed daily. When the observation days
are finished construct a graph of total mg mass vs. time in days. Make this graph a part
of your lab write up.
H20 volume
0ml
2ml
4ml
8ml
16ml 32ml 64ml
Aerobic
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Anaerobic
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