What it shows
Organic manures add nutrients and improve the soil. Growing the same bean in plain soil, compost and vermicompost shows the effect of each on growth.
The science
Plants need nitrogen, phosphorus and potassium plus trace minerals. Compost and vermicompost release these slowly and hold water in the soil. Vermicompost often has more available nutrients because worms have already broken the waste down.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Bean seeds
- Three equal pots or cut bottles
- Garden soil
- Home compost and vermicompost
- Water
- A ruler and a kitchen scale
Safety
For this project: Wear gloves and wash hands after handling compost. Keep the pots in a shaded place away from food.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Fill pot A with plain soil only.
Fill pot B with three parts soil and one part compost.
Fill pot C with three parts soil and one part vermicompost.
Plant three bean seeds in each at the same depth.
Water all pots equally and keep them in the same light.
Measure the height of the tallest plant every three days.
Count the leaves and note their colour each week.
Weigh the fresh plants at the end and draw a bar chart.
What you should see
The plants in compost and vermicompost usually grow taller and greener than those in plain soil, and the bar chart makes the difference clear.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What is compost?
Rotted plant and kitchen waste used as manure.
02Why is vermicompost special?
Earthworms break the waste into fine, nutrient-rich castings.
03What did we change?
Only the type of manure.
04Why use manure instead of chemicals?
It improves soil life and structure.
Take it further
Try different proportions of vermicompost to find the best mix.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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