Soil chemistry with household organic matter

I am mixing various types of household organic matter (ex. cabbage) with soil, letting the mixture sit for a few days, and testing the soil pH, nitrogen, phosphorus, and potassium.
Minel Aukerman
Grade 5


I think that the various substances will vary in their pH and chemical content. See logbook pages below for exact hypotheses.


- Soil testing is used both in small-scale gardening and in agriculture.
- The three primary plant nutrients (nitrogen, phosphorus, and potassium) are the ones we are testing in this project, but many larger --farms also test for other elements.
- Nitrogen and phosphorus may have negative effects on the environment when too much is applied.
- It is important to test pH because pH controls how plants use the nutrients available.

All plants need the correct pH (acidity/alkalinity) to survive. Every plant has its own pH preference, meaning that certain plants are difficult to grow together because they have different pH preferences. 

Nitrogen is what makes leaves grow. Too little nitrogen makes for small, yellow leaves and stunted growth. Too much causes too many leaves and less flowers and fruit.

Phosphorus aids plant growth and seed quality. A plant with too little phosphorus will have less fruit and may also have sterile seeds. Phosphorus also increases a plant’s resistance to disease.

Potassium makes plants strong and fruit tasty. Too little potassium causes stunted growth and weak root systems. Potassium also aids the plant in making carbohydrates and protein. It is also sometimes called potash.


If you want to see my citations, see citations section.



- Amount of soil

- Amount of distilled water

- Amount of organic matter (measured by volume)


- Types of organic matter used


- pH of mixture

- Nitrogen content of mixture

- Phosphorus content of mixture

- Potassium content of mixture


Pre-test procedure:

1. Fill each jar with 2 oz (by volume) of soil, 1 oz of distilled water, and 1 oz of organic matter (the control receives 3 oz of soil and no other organic matter). Mix thoroughly.
2. Let sit for at least 5 days.

     pH test:

1. Fill each test container to the soil fill line with soil mixture.
2. Fill test container to the water fill line with distilled water.
3. Empty one pH test capsule into the container. Cap container.
4. Shake thoroughly.
5. Let results develop for about 1 minute, then hold the container up to the light to find results.

 N, P, and K tests:

1. Fill a glass yogurt jar with 1 ½ tbsp. of soil mixture and 7 ½ tbsp. of distilled water. Cap jar and shake.
2. Let sit overnight to settle.
3. Fill each test container to the fill  line  with solution (only the liquid).
4. Empty one test capsule into the container. Cap container.
5. Shake thoroughly.
6. Let results develop for about 10 minutes, then hold the container up to the light to find results.




Best organic matter for various pH levels with a balance of nutrients

Low pH

Balanced pH

High pH

Sphagnum moss



Note that bread+tomato and kiwi+tomato are combinations of materials, not individual materials. See presentation for more info.


In the future, I could test various types/mixtures of organic matter as fertilizer and see which plants grow fastest. I could also test other types of organic matter or even inorganic matter. I hope that this work helps the world create better fertilizer and compost and make healthier and more sustainable gardens everywhere.


It is important to know about this because people could use this data to create better fertilizers and compost, like the ones I suggested in my analysis. Knowing what makes up your soil could spell the difference between life and death for your plants, so knowing what’s in your compost might save your garden. The data could also be used to create fertilizers from waste.

Sources Of Error

- The tests may not have been accurate.
- The organic matter may not have sat long enough to properly decompose.
- Several substances may have contained pigments which may have affected the results.
- The tests were taken over a span of a few days, so some organic matter had longer to decompose.


- No author. (No date). Rapitest Soil Test Kit Pamphlet.  Woodstock, Illinois: Luster Leaf.
- Mallarino, A. P. (2005). Testing of soils. In Encyclopedia of Soils in the Environment.  Retrieved from:


- Maren Aukerman (mother) provided assistance with photography, performing the tests, and my presentation. All ideas, however, are my own.