The hypothesis is what you think will happen during the experiment, based on what you already know. The written hypothesis should be included in your science fair presentation. If the results of the experiment did not support your hypothesis, state that fact in the presentation. Even experienced scientists find unexpected results.
The materials needed for this science fair project include 14 matching medium-size plastic pots, 14 large bowls or other containers to catch water, a 1-liter measuring cup, a triple balance beam scale, 2,000 grams sand, 2,000 grams garden soil, 1,500 grams manure and 1,500 grams sphagnum peat moss.
Constants are conditions or numbers that remain the same (without variation) through the entire experiment. For this experiment, the constants are the identical pots, the amount of garden soil, the amount of sand, the amount of manure, the amount of sphagnum peat moss, the room temperature, the amount of water, the amount of time and the amount of material in each pot. Variables are things that change during the course of the experiment. The variables you can manipulate are the type of organic material used and its proportion to the sand. The result, called the responding variable, is the amount of water absorbed by the various soil combinations.
Place a bowl under each pot. Label the first pot "Sand," and add 500 grams of sand. Label the second pot "1/4 sphagnum peat moss," and add 375 grams of sand plus 125 grams of sphagnum peat moss. Label the third pot "1/2 sphagnum peat moss," and add 250 grams sand plus 250 grams sphagnum peat moss. Label the fourth pot "3/4 sphagnum peat moss," and add 125 grams sand plus 375 grams sphagnum peat moss. Label the fifth pot "1/4 manure," and add 375 grams sand plus 125 grams manure. Label the sixth pot "1/2 manure," and add 250 grams sand plus 250 grams manure. Label the seventh pot "3/4 manure," and add 125 grams sand plus 375 grams manure. Repeat the process used for pots one through seven using garden soil in place of sand for the remaining seven pots.
Gradually add 1 liter of water to each pot, stirring to help the water mix with the soil. Wait 12 hours. One at a time, pour the drainage from each pot into the measuring cup, and record the amount. Subtract this amount from the initial 1 liter amount to determine how much water was retained in the soil of each pot. For the most accurate results, repeat the entire experiment four or more times.
Based on your data, did the results support your hypothesis? Which of the soil mixtures retained the most, and least, water? Were you surprised by any of the results? Can you come to any conclusions about plant health and productivity based on your experiment?