Transcript Caustic Compost

Caustic Compost
by Megan Harris
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
I checked on the Internet and found out 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.
I found out that pH is a
measurement of how much
acid is in the soil. I also
found out that the pH of the
soil can be changed by
chemicals or plants.
Question
Now I’m wondering…
Does the type of leaves used in compost change
the pH of the soil they are added to?
Hypothesis
I predict that walnut leaves and fir needles will
lower the pH the most because nothing grows
under those types of trees.
Materials List








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 every type of leaf
in my grandma’s yard. 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




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
7
6.8
6.6
6.4
6.2
6
5.8
Control
Apple
Aspen
Maple
Poplar Walnut
Fir
Grass
Results
My data shows that the pH of the walnut leaves
and soil mixture was the lowest, which means
that walnut leaves have the most acid.
I was surprised to see that almost all of the soil
samples had very close to the same pH. I
thought walnut and fir would be much more
acidic.
Conclusion
In this experiment, I tried to determine if
different types of composted leaves affected
the pH of the soil they were mixed into. My
data showed that walnut leaves lowered the pH
from neutral to just slightly acidic. My
hypothesis was partly supported, because I
predicted that both walnut leaves and pine
needles would make acidic soil. I was
surprised that the walnut leaves were not very
acidic.
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 my project will be to actually plant seeds
in the soil cups and see which type of compost
produces the most plant growth.