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 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 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 2 liters distilled water 1 liter each of walnut leaves, apple leaves, aspen leaves, maple leaves, poplar leaves, fir needles, and grass clippings 1 liter each of walnut leaves, apple leaves, aspen leaves, maple leaves, poplar leaves, fir needles, and grass clippings 8 gallon-size Ziploc bags 8 gallon-size Ziploc bags 24 clear plastic cups 24 clear plastic cups 24 plastic spoons 24 plastic spoons 20 liter bag of potting soil 20 liter bag of potting soil pH meter pH meter scissors scissors

Procedure 1. 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. 2. Place each type of leaves in a separate gallon-size Ziploc bag. 3. Let the leaves decompose inside the sealed bags for 4 weeks

Procedure Continued 4. 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. 5. 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. 6. Put no leaves into the three control cups.

Procedure Continued 7. Measure the pH of the soil/compost mixture in each cup, rinsing off the meter with distilled water in between each test. 8. Record the results and keep the cups for Phase 2 of testing.

Variables and Controls Independent Variable : type of compost Independent Variable : type of compost Dependent Variable: pH measurement 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 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 Control: cup with soil only and no compost

Data

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. 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.