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The effect of soil components and organic matter on growth of plants.

The effect of soil components and organic matter on growth of plants.

Introduction: (Initial Observation)

Plants get the necessary nutrients for their growth from soil. The amount of nutrients in soil is limited, that’s why we add additional nutrients to the soil as needed. The type of nutrients and the amount of each type in the soil can affect the plant growth.

Not all organic mater is considered a nutrient for plants. In this project we will test different organic maters to see which one will affect the plant growth.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Information Gathering:

Plants need water, light and nutrients to grow. Nutrients for plants are almost like vitamins for human. (Notice that nutrients are not considered a food for plans. Plants make their own food trough the process of photosynthesis.) Some nutrients exists in the soil, but some times the soil does not have enough nutrients and we need to add some. The process of adding other material to the soil is called treating the soil. For example you may treat the soil with 5% crushed bone. That means adding 5% crushed bone to the soil. To do this you mix 95 scoop of soil with 5 scoop of crushed bone and mix them well.
(Nutrients for plants are material that contain Nitrogen, Phosphor and Potassium.)

Any soil that has enough nutrients for plants is fertile. That means that plants can grow on that soil. That is why nutrients for plants are also called fertilizers for soil. There are different types of fertilizers. Some are organic fertilizers that are made from other plants or animal parts. Some others are inorganic fertilizers that are made in chemical factories. In this project we will test different organic material to see which one is a good nutrient for the plant or a good fertilizer for the soil.

Organic material are any material originated from plants or animals. Some of the organic material that you can find at home are milk, cheese, meat, bone, egg, fruits, vegetables, leaves.


Question/ Purpose:

The purpose of this project is to see how organic material in soil can affect the plant growth. We will test and compare the effect of different organic material on plant growth.

Identify Variables:

We are going to test the effect of different organic material on plant growth. So the type of organic material is an independent variable and the growth of the plant is a dependent variable.

Some of the possibilities for organic mater that we may test are milk, cheese, meat, bone, egg, fruits, vegetables, leaves (compost).

Note: Compost is not just leaves. It is a mixture of decaying organic matter, as from leaves and manure, used to improve soil structure and provide nutrients.


My hypothesis is that we can get the best plant growth by creating a mix of many different organic maters. In this way plant will get every nutrients that it needs.

Experiment Design:

Material that you will need for this experiment are:


  • pots or planting trays
  • compost, milk, egg, crushed bone, grinded cooked meat, …
  • soil
  • seeds
  • light source (sunlight or artificial lighting)


1. Design your own experiment. There are many possibilities–a few ideas are listed here, but the variations are endless:

  • Test various combinations of soil and compost on plant growth. For example, you might wish to dig a soil sample from your school yard and mix it with various amounts of finished compost for planting experiments. (Natural soil is better than prepackaged potting soils for experiments such as this because the potting mixes are formulated for optimal plant growth and already contain significant amounts of compost or humus.). You may decide to test 10 different combination of soil with compost. Your first pot can be 100% soil. Second pot can be 90% soil and 10% compost. Keep increasing the compost and decrease the soil by 10% until the last pot that will be 100% compost.

Another possibility is using same percentage of different organic material. For example you may mix the soil with 20% crushed bone for pot number 1 and Mix the soil with 20% compost for pot number 2. Mix the soil with 20% cooked eggs for pot number 3, other pots can have 20% of dry milk, grinded fruits and etc.

2. Plant your seeds (about 4 in each pot, one inch deep in the soil), water them, and place them in a well-lit location. Many type of seeds will work, but radish or lettuce are often chosen because they grow quickly.

3. Keep all the pots in the same setting to minimize any variation in temperature, lighting, pests, and other environmental factors.

4. Record on a daily basis the number of seeds that have germinated, plant growth, and observations about plant health such as color, vigor, or damage due to pests and diseases. You can decide what measurements to use as indicators of plant growth; possibilities include plant height, number and size of leaves, and the weight of the entire plant at the end of the experiment.

Materials and Equipment:

  • pots or planting trays
  • compost, milk, egg, crushed bone, grinded cooked meat, …
  • soil
  • seeds
  • light source (sunlight or artificial lighting)

Results of Experiment (Observation):

Observe the growth of the seedlings in each pot as they germinate. Record your observation for 4 weeks in tables like this:

Table 1: Plant height for different rates for compost.

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%
Day 1
Day 2
Day 3
Day 30

You may want to have multiple tables for different observations. For example one for plant height, one for number of leaves and one for germination rate.

* Germination rate is the percentage of the seeds that germinated. If only one out of four seeds germinates, the germination rate is 25%.


Not needed.

Summary of Results:

Analysis and Interpretation

1. Graph germination rates and plant growth over time for your experiment.

2. You may not find any differences between the treatments. Or, you may discover that the plants grown without compost or any other organic mater did best. If this is the case, it may be difficult to determine whether the organic mater had no effect, or you did something wrong. However, the interpretation of results should not be biased by your predictions or preconceived ideas about the way experiments will turn out. Often unexpected results lead to important insights and questions.


The conclusions and recommendations that you are able to make based on your results will depend on how and where you carried out your experiments. For example, if you used potted plants in a room or greenhouse, it may be difficult to conclude from your results to what would happen if the same plants were grown outdoors in a garden. However, your results may give you some ideas about what would happen, allowing you to make predictions or hypotheses. You could then use these predictions to design a new experiment on plant growth in a garden setting.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Can human waste and garbage be used as nutrients for plants?

Can plants grow in sand?

Can some organic maters have negative affect on plant growth?

Possible Errors:

Some things may have gone wrong in your experiments. For example, you may have over-watered your plants, causing them all to die from fungal infection. Or you may have taken measurements only on plant height, and later decided that measuring the number of leaves and length of the main stem would have given better information. These types of problems are normal and can be used as a basis for redesigning the experiment. How might you change your experimental design if you were to carry out another set of growth experiments?