Soil Nutrient Lab
Our work in Michael’s 4th Grade Science class this year started with looking at the needs of living things. We came up with all kinds of things we thought we needed, but narrowed down to the basic needs of living things: food, water, air, habitat. We’ve been told that the plants bring the nutrients into the ecosystem by absorbing them from the soil. We wanted to see if we could find those nutrients ourselves. We learned that there are three main nutrients for life: nitrogen, potassium, and phosphorous. So we decided to test for these in the garden. Shouldn’t there be plenty of nutrients there since we were growing things to eat?
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| Collecting Soil Samples |
We collected soil samples from the garden beds, the pond, the area outside the garden beds under the woodchips, and in the runoff from the playground by the bridge. We tested each of these soils for the three nutrients and found that while there was sufficient phosphorous and potassium in the soil, there was very little nitrogen. When we went back to the garden, we could see the effect on the squash plants. Their leaves were yellow-green with yellow and brown spots and the edges of the leaves were dry brown. These were signs of not enough nitrogen.
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| These leaves don't look healthy. |
How can we grow healthy plants to eat in a garden without enough nitrogen? We wanted to find a way to improve the soil, so we brainstormed some solutions. We thought adding compost or fertilizer might help. We also remembered that there are some plants that help put nitrogen into the soil. We remembered from our “Three-Sisters” study last year (corn-beans-squash) that one of the things the beans did was help with nitrogen, we thought planting beans might help. We also wanted to try alfalfa. So we took some small pots and prepared the soil five different ways: control soil with no change, soil mixed with osmocote pellets, soil mixed with compost, soil planted with beans, soil planted with alfalfa. We put these under constant light and water and will test the soil nitrogen levels in a few weeks.
In the meantime, we learned that bacteria helped convert nitrogen from the air into nitrogen that plant roots could absorb. Maybe there wasn’t enough bacteria in the soil from the garden. Upperschool Science Teacher (and class parent) Howie Waldman came to class to help us grow some bacteria from the soil and compost. It only took a day for there to be a lot of growth. Howie is going to help us to try to make microscope slides of the bacteria next, so we can see individual cells.
We also noticed a lot of living things in the compost - macroinvertibrate decomposers. We found nematodes, earthworms, pseudoscorpions, weevils, isopods, and others we haven’t yet identified.
We’re learning a lot about soil, how it works and how it helps us to be healthy. Like the song says, dirt really did make our lunch. We can’t live without healthy soil.
DATA UPDATE 10/21/14
After one month, we tested our soil treatments for nitrogen levels with Rapitest kits:
Soil Treatment
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Nitrogen Level after 1 month
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Control
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Depleted (N0)
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Osmocote
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Surplus (N4+)
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Compost
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Surplus (N4+)
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Beans
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Deficient (N1)
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Alfalfa
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Deficient (N1)
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Conclusions
We can improve the nitrogen in the soil using compost and Osmocote. It only takes a little of these to raise the nitrogen in the soil. Planting beans and alfalfa changed the nitrogen a little bit, we need a lot more bean and alfalfa or more time to bring the nitrogen up enough. So, if we want healthy garden soil, we need to add a little compost to the soil.
