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Do Earthworms Affect the Level of Nitrates and Phosphates Found in Fertilized Soil

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Purpose

To determine whether adding earthworms to fertilized soil will decrease levels of phosphates and nitrates found in fertilized soil.

Hypothesis

Fertilizer contains certain amounts of nitrates and phosphates that help lawns grow and look healthy. However, overuse of fertilizer can result in groundwater contamination. Earthworms may be effective in reducing the levels of nitrates and phosphates in soil.

Materials Needed

  • 24 cups of potting soil
  • measuring cups
  • 2 large clear plastic containers with small holes on bottom for aeration
  • soil fertilizer for potting soil
  • 1 cup of ground fruit or vegetables
  • distilled water
  • Rapitest® soil test kit
  • 20 earthworms

Experiment

Soil fertilizer, which raises the levels of phosphates and nitrates in soil, will be added to 2 containers of potting soil. The level of nitrates and phosphates present in the soil in each container will be tested and recorded. Then earthworms will be added to one container. The other container will not have any earthworms and will serve as a control. Both containers will be tested at the end of each week for a one-month period to find the level of nitrates and phosphates in each con-tainer's soil and to determine if the worms have decreased the level of phosphates and nitrates in the soil.

Procedure

  1. Add 12 cups of the potting soil to each of the 2 clear plastic containers.
  2. Add the recommended amount of soil fertilizer for 12 cups of soil to container 1 and mix well. Repeat for container 2.
  3. Container 1 will serve as the control. It will contain no earthworms and will be put aside.
  4. Mix ground fruit or vegetables into the soil of container 2.
  5. Add 1 cup of distilled water to each container and mix so that the soil in each container is damp.
  6. Use the Rapitest® soil test kit to test for the amount of phosphates and nitrates in container 1 and container 2 prior to beginning the experiment. Follow the directions that come with the kit.
  7. Once you have tested the level of phosphates and nitrates present in the soil samples, you are ready to test the effects of the worms. Add 20 earthworms to container 2 and leave them in the container for one month.
  8. Add 1 cup of distilled water each day to each container to keep the soil consistently damp.
  9. At the end of each week, repeat step 6 on both containers.
  10. Compare your recorded data results of the level of nitrates and phosphates present in the soil samples for each week to see if they changed when the worms were added to the soil in container 2.

Results

  1. What were the levels of nitrates and phosphates in the soil samples of each container prior to the start of the experiment?
  2. What were the level of nitrates and phosphates in the soil samples of each container at the end of each week?
  3. Did the level of nitrates and phosphates decrease in the soil samples from the container with the worms?
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