Q: I am doing a Science Fair Project on, ‘How does the amount of nitrogen in a fertilizer affect the height of a bean plants stem under normal growing conditions’.

You could change the amount of water you mix in to make a different concentration of nitrogen.

A: One way to mix your own fertilizer to have differing amounts of nitrogen would be to get three basic fertilizer ingredients from the garden store: urea (46-0-0), triple super phosphate (0-46-0) and muriate of potash (0-0-60).

Mix 2 tablespoons of 0-46-0 with 1.5 tablespoons of 0-0-60. Dissolve the resulting mixture in one gallon of water. You’ll have a solution containing approximately 2000 parts per million of phosphorus and potassium.

Next, mix 2 tablespoons of 46-0-0 in a gallon of water. This will be your nitrogen source, also approximately 2000 ppm.

All three are pretty concentrated. Plants like their fertilizer concentrations to be around 100 ppm. That means you have to mix one part (of either of the two solutions) with twenty parts of water to make a 100 ppm solution that you can give your plants.

You could also change the amount of water you mix in to make different concentrations of nitrogen.