The Murder Plot That Failed: A Hydroponic Radish Story

Objective:

How does the concentration of magnesium in a radish plant's nutrient supply affect its growth?

Our hypothesis:

Radish plants require magnesium to grow, but they will not grow as well if they have too much magnesium.

Our prediction:

If radish plants require magnesium to grow, then the leaves of the plants with no magnesium in their nutrient supply will undergo chlorosis and the plants will die. If radish plants do not grow as well with too much magnesium, then the plants with double the magnesium in their nutrient supply will not grow to be as large as the plants with a normal amount of magnesium in their nutrient supply.

The Experiment

Bomb Boy and the Chemicals We mixed nutrient solutions according to Dr. Alan Cooper's formula in the manner outlined in S.H.A.R.P. Lesson Three. We made one nutrient solution with the amount of magnesium in the recipe, one with double the amount of magnesium in the recipe, and one with no magnesium at all. We were not able to find all the chemicals in the nutrient solution recipe, so we had to make calcium nitrate by doing an acid-base titration with nitric acid and calcium hydroxide. We also were not able to find any EDTA iron, so after much experimentation and frustration Josh was able to invent a procedure for making EDTA iron from EDTA acid and several other chemicals. This earned him the nickname "Bomb Boy."

We built three hydroponic apparatuses: one for the radishes with normal magnesium, one for the radishes with double magnesium, and one for the radishes with no magnesium. We built them according to the instructions in S.H.A.R.P. Lesson Four, Step One. We had built the hydroponic apparatuses a different way, but Ms. V said it wasn't going to work, so we changed the setup around and it worked fine.

Petri plate with germinating radishes Then we germinated our Cherry Belle Radish seeds according to the instructions in S.H.A.R.P. Lesson Four, Step Three. We put paper towels in four petri plates and put several seeds in each petri plate. We soaked the seeds and paper towels thoroughly with water, closed the lid of the petri plate, and rubber-banded it shut so the little plants would not grow up, push the lid off, and dry themselves out.

When the seeds had germinated and the little plants were about 1 ½ inch tall, we planted them in a big tray with Perlite and kept them watered. The plants grew some more, and we finally transplanted them into the hydroponic apparatuses. We gave all the plants a "starter solution" with normal concentration of magnesium so that they would start growing normally.

Watch our plants grow! Watch the whole experiment grow!

(caution: animations are large and may take some time to load)

We refilled the nutrient solution many times during the lab. Almost every day we added more water to replace what had evaporated. We put extra shrink-wrapped boards over the ends of the nutrient solution containers to reduce evaporation, but the water still evaporated. Unfortunately, we used tap water; this was what messed up our experiment. We also turned off the fan in the greenhouse to reduce evaporation, but then the greenhouse got so hot that we had to turn it back on.

We changed the nutrient solution about three times during the experiment. The second time we switched the plants from the starter solution to the test solutions. The "Nothing" plants had the solution with no magnesium, the "Double" plants had the solution with double the normal amount of magnesium, and the "Normal" plants stayed on the starter solution with the normal amount of magnesium.

Algae growing in our nutrient solution We ran into a few problems during the experiment. One of these problems was the algae. We weren't sure if it was harmful to the plants, but we thought it might use up nutrients from the system, and it looked pretty disgusting too. We tried to clean it out of the system every time we changed the nutrient solution, but it just kept coming back!

Another problem was the humidity. The greenhouse we had the plants in was very dry. Miss L decided to solve the problem one day by spraying the whole place with the hose. This not only solved the humidity problem but also soaked the entire greenhouse, which was not a good thing. We found a better solution to the humidity problem in the form of a hoochie-coochie machine. This is Miss L's silly way to say vaporizer. The hoochie-coochie machine required somebody to constantly fill it with water, but it did a good job of keeping the humidity up in the greenhouse.

Hydroponic setup with sun shade The temperature in the greenhouse also gave us trouble. There was one bad week where the temperature outside was in the 80's or 90's and the greenhouse was pushing 100°. That's why these plants are covered by a sun shade. This is not a great picture, but if you look closely you may notice that these plants don't look too good. We also added ice to the nutrient solution because it was getting hot too. Things cooled down the next week, and we removed the sun shade and the experiment went back to normal.

Oops! We predicted that the plants with no magnesium in their nutrient solution would die. The experiment did not turn out as we predicted; our murder plot failed miserably. We finally realized that this happened because we were mixing our nutrient solution with tap water instead of deionized water. The water we used came out of the sink in the biology lab, and we were told after the experiment that it was known to be very hard water. Ms. V won't even drink it; perhaps she thinks it's poisonous. But it certainly didn't poison the radish plants; on the contrary, we believe that the magnesium from the tap water was what kept our Nothing plants alive.

Did you say people ate these radishes?

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