Transcript Caustic Compost

Caustic Compost
by Me
Science fair 2010
Introduction
My family just moved into a new house, and the
soil around the house is very bad. It has lots of
clay and rocks, so my dad is adding grass
clippings and leaves to the soil to help it grow
grass in the future.
I’ve also noticed that nothing grows
under my grandma’s walnut trees
and her pine trees.
Background Research
Internet research showed that plants need nutrients in
the soil to grow, as well as water and carbon dioxide.
Plants also need a neutral pH in the soil to grow best.
pH is a measurement of how
much acid is in something
pH of the soil can be changed
by chemicals or by plants.
(See citations section for details)
Question
What are the effects of leaf type on compost pH?
This could also be written as…
Does the type of leaves added to a compost pile
change the pH of the compost?
Hypothesis
If walnut leaves are added to potting soil, then
the pH of the mixture will be lower than plain
potting soil because walnut trees seem to
prevent growth of other plants.
Materials List
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2 liters distilled water
1 liter each of walnut leaves, apple leaves, aspen
leaves, maple leaves, poplar leaves, fir needles, and
grass clippings
8 gallon-size Ziploc bags
24 clear plastic cups
24 plastic spoons
20 liter bag of potting soil
pH meter
scissors
Procedure
1.
2.
3.
Gather 1 liter (approx) of each leaf type.
This includes aspen, poplar, maple, walnut,
apple, fir needles, and grass clippings.
Place each type of leaves in a separate
gallon-size Ziploc bag.
Let the leaves decompose inside the sealed
bags for 4 weeks
Procedure Continued
4.
5.
6.
Prepare the cups by mixing 150 ml of potting
soil with 100 ml of distilled water in each
cup. Mix with a clean plastic spoon.
Use scissors to cut up each type of leaves
into pieces no larger than 1 cm. Mix 100 ml
of each type of leaves into three soil cups.
Mix with a clean plastic spoon each time.
Put no leaves into the three control cups.
Procedure Continued
7.
8.
Measure the pH of the soil/compost mixture
in each cup, rinsing off the meter with
distilled water in between each test.
Record the results and keep the cups for
Phase 2 of testing.
Variables and Controls
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Independent Variable : type of compost
Dependent Variable:
pH measurement
Constants: amount of soil, amount of compost,
amount of water, type of cup, length of time to
decompose, stored at same temperature,
measured in the same way
Control: cup with soil only and no compost
Data
Ph OF VARIOUS TYPES OF LEAVES
MIXED WITH POTTING SOIL
7
pH measurement
6.8
6.6
6.4
6.2
6
5.8
Control
Apple
Aspen
Maple
Poplar Walnut
LEAF TYPE
Fir
Grass
Results
The data shows that the pH of the walnut leaves
and soil mixture was the lowest, which means
that walnut leaves have the most acid.
It was surprising to see that almost all of the soil
samples had very close to the same pH.
Conclusion
This experiment predicted that if walnut leaves
were added to potting soil, then the pH of the
mixture would be lower than plain potting soil
because walnut trees seemed to prevent growth
of other plants.
The data showed that walnut leaves lowered the
pH the most - from neutral to just slightly
acidic.
Conclusion Continued
The hypothesis was partially supported because
although the pH was lowest with the addition
of walnut leaves, the change in pH was not
significant.
Future Research
The acid in the walnut leaves was not enough to
cause plants not to grow under the trees. There
must be something else in the leaves besides
acid that prevents seeds from growing. Phase
2 of the project will be to actually plant seeds
in the soil cups and see which type of compost
produces the most plant growth.