Science project

Dirty Composition

Research Questions:

How does the presence of organic material in soil affect water absorbency? Would using soil with more organic material conserve water?

As plants and animals decay, they produce organic materials, including soil particles called humus. Dark brown or black humus holds large amounts of water and contributes nutrients into the soil. In most mineral soils, only 6% to 12% of the volume of particles is organic. Peat or turf is an accumulation of decayed vegetation in dense structures. Peat is created in wetlands. Peat is important in agriculture, because it contains greater concentrations of organic particles than average soil.

The independent variable in this project is the composition of the soil, and the dependent variable is the amount of water absorbed by the soil. The constants include the pots, the conditions and the amount of water fed to each pot.


  • Eight small plastic pots with saucers.
  • Small amount of sand.
  • Small amount of dirt.
  • Small amount of peat moss
  • Tap water.
  • Measuring cup.

Experimental Procedure:

  1. Fill one pot with sand and label it “Sand.”

  2. Fill another pot with ¾ amount of sand and ¼ amount of peat moss. Mix thoroughly and label it “1/4 peat.”

  3. Fill the third pot with half of each, mix thoroughly and label it “1/2 peat.”

  4. Fill the fourth pot with ¼ sand and ¾ peat. Mix thoroughly and label it “3/4 peat.”

  5. Fill the fifth pot with common dirt and label “dirt.”

  6. Fill the sixth pot with ¾ sand and ¼ dirt. Mix thoroughly and label “1/4 dirt.”

  7. Fill seventh pot with half of each, mix thoroughly and label “1/2 dirt.”

  8. Fill eighth pot with ¼ sand and ¾ dirt. Mix thoroughly and label “3/4 dirt.”

  9. Place saucers beneath pots.

  10. Saturate the mixture in each pot with the same amount of water.

  11. Wait 12 hours and check each saucer for run off.

  12. Measure the water in the saucer and subtract from the original amount of water.

  13. Record run off for each pot.

  14. Repeat two times for a total of three trials (or more).


A simple graph will visually display the results:


Terms/Concepts: Decomposition; Organic material; Wetlands


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