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Hydroponics

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Author: Marc Rosner

Hydroponics is the science of growing plants in nutrient solutions rather than in soil. The nutrients in these liquids are chemicals that provide energy and promote or stimulate growth and life. In this activity, you compare different growing conditions, such as the ingredients in your nutrient solution, or "broth," and the type of media that your plants are rooted in, such as gravel, sand, and so on, to find out what conditions work best to nurture plants.

Hydroponics may be the most efficient way to grow vegetables on the Moon or on other planets where there is no soil.

Materials

You can acquire the materials needed for this experiment from aquarium suppliers, garden shops, hardware stores, and hobby shops.

  • safety razor (requires adult help)
  • large plastic container (Rubbermaid dishpan size works well.)
  • approximately 2 m of plastic tubing (aquarium tubing or hose) to match pump
  • metric ruler
  • silicone aquarium or bathroom sealant
  • large piece of wire screen
  • utility scissors
  • lightweight water pump, or second container, tube, clamp, and tray (You can use a pump designed for outdoor fountains and pools, or modify an aquarium pump.)
  • wire (may be useful for securing and supporting tubes)
  • wire cutters
  • plant seeds (Beans and peas work well.)
  • assorted root media (e.g., perlite, vermiculite, pumice, gravel, sand, sawdust, peat moss)
  • assorted nutrient compounds (magnesium sulfate, calcium phosphate, potassium nitrate, calcium sulfate, potassium chloride)
  • meterstick or tape measure
  • notebook and pencil
  • metric scale
  • metric measuring cup
  • l-L (liter) pitcher
  • water

Procedure

Build Your Hydroponic Facility.

  1. Have an adult use a safety razor to cut a hole close to the bottom of one of the walls of a plastic container. The hole should be the same size as the outside diameter of your tubing so that the tube fits snugly in the hole. Pass the tube through the hole, from the outside, 1 cm into the container. Apply sealant to the area between the tube and the container on both sides, and allow it to harden overnight. Apply more sealant if necessary for a good seal and allow that to dry. Cut a 5-cmdiameter circular piece of wire screen with utility scissors, place it over the inside opening of the tube, and secure it in place with sealant. The screen prevents clogging. Save the rest of the screen for later.
  2. Connect the free end of the tube to the water pump intake. Connect a second tube, from the outflow of the pump, back to the top of the container. This is for the return flow. Have an adult make a hole at the top of the container for the return flow tube, and seal it in place as you did the other tube.
  3. Hydroponics

  4. After positioning and attaching the tubes, and waiting for the sealant to dry, check all connections to make sure they are secure. If you feel that the tubes might pull away from the apparatus or lose their seal, you can secure them with wire. Gently twist one end of the wire around itself into a loop on one end of the tube connection. Then wrap the wire around the object to which the tube is connected (e.g., the container). Then cut the wire, leaving enough wire free to fasten it to the tube again, near the wire loop. Do this for each tube as needed.

Design and Conduct Your Experiment

  1. You will place seeds in the medium in the hydroponic container, and circulate nutrient broth to allow them to grow. What you have to decide is:
    • What variables will you change?
    • How will you measure plant growth?
  2. The main variables you can control are the root media and the nutrient broth. You can measure plant growth with a simple meterstick or tape measure. Record the distance from the soil line to the top of the plant, gently extending the plant to its full length.

    If you can't get a water pump, you can create a drip apparatus with a second container, a tube, and a clamp. The tube runs out of one hydroponic tank (supported on a shelf, ladder, or table) and into the other, like an IV. You regulate the dripping with the clamp, collect the outflow in a tray, and return it to the drip container twice a day.

    Hydroponics

  3. To make nutrient broth, dissolve in water small quantities of different combinations of the nutrient compounds listed in the materials section: 250 to 750 mg/L of water. One idea would be to use four out of five of each of the compounds in five trials, each time leaving out one of the compounds to see which one is most essential. Be sure to use the same amount of each nutrient in each trial.
  4. To test different media, you can divide your container into square sections with extra wire screen and use a different media mixture in each section. What conditions work best? For instance, you can determine which two media work best together.
  5. You can also compare different concentrations of nutrient broth. Make several five-compound mixtures, one containing 250 mg/L of each compound, another containing 500 mg/L, and so on.

    Record the average plant height after a specific time (e.g., 2 weeks) for the gravel-sand mixture, the gravel-pumice mixture, and so on, adding as many combinations in additional columns and rows as you see fit.

References

Beginning Hydroponics: A Beginners Guide to Growing Vegetables, House Plants, Flowers, and Herbs without Soil by Richard E. Nicholls (philadelphia: Running Press, 1990).

Exploring Classroom Hydroponics (Growing Ideas series) by Eve Pranis and Joreen Hendry (Burlington, Vt.: National Gardening Association. 1995).

Bradley Hydroponics web site: www.hydrogarden.com/az.htm

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