Experiments to Try

Many interesting experiments suitable for science fairs and for school or 4-H projects can be performed with soilless culture. Two experiments, the first dealing with pH levels and the second with nutrient materials, are outlined here. You may want to work out variations of these experiments or try others of your own.

Experiment l: pH Levels

Use the nutrient solution given in the Nutrient Solutions section or a solution prepared from commercial premixed nutrients. Pour the solution into three containers. Adjust the pH of the solution in the first container to between 5.5 and 6.5. This solution is the "check" or "control" for the experiment. Lower the pH of the solution in the second container to less than 4.0 by adding small amounts of dilute sulfuric acid. Raise the pH of the solution in the third container to 8.0 or higher by adding a dilute sodium hydroxide (NaOH) solution. Test the pH of the solutions with an indicator.

The following plants do well at a pH range between 5.5 and 7.0: carrot, coleus, cucumber, geranium, orange, pepper, petunia, strawberry, turnip, and violet. Grow a plant from this list in each of the three solutions. Choose only one kind of plant (pepper, for example), and be sure the plants are about the same size. If you use seeds, plant them all at the same time.

Observe the difference in growth between the plants in the three solutions. Typical results are shown in Figure 9. You may want to set up various pl l ranges to find the best pH in which to grow a particular plant.

Figure 9. Effect of various pH levels on the growth of lettuce (from D. I. Arnon and C. M. Johnson).

Experiment 2: Nutrient Levels

You will need to prepare three nutrient solutions for this experiment. The first solution is a premixed nutrient solution or the "standard" solution listed in the nutrient solution tables. To prepare the second solution, use twice the recommended amount of each nutrient. For the third solution use one-half the recommended amounts of the nutrients. You will probably not want to prepare 25 gallons of each solution. The amounts of salts and water may be reduced by one-half, one-fourth, or even more as long as you mix the proper proportion of ingredients for each of the three solutions.

Be sure to grow the same kind of plant in each container so that you can compare results between the plants (Figure 10). If you transplant into these containers, choose plants that are uniform in size. By varying the nutrient and pH levels and observing the effects of these changes upon the plants, you can determine the proper pH and nutrient levels for a particular plant.

Figure 10. Effect of various nutrient levels on plant growth.

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