Science Buddies: "Ask an Expert"

One of my students is testing natural fertilizers againts a commercial one. She was wondering if she should have a synthetic fertelizer as a control or water group as a control and include natural and synthetic feterlizer in experimentation? Thank you.

I’m not sure what you mean by a water group as a control…

Is the student comparing several different natural fertilizers against a single, specific commercial one? If so, then the case with the commercial fertilizer is the control. If the student is comparing several fertilizers, natural and commercial, then the control would likely be a case without any fertilizer. And, of course, the student needs to ensure that as many other variables as possible (light, temperature, water, plants…) are kept constant across all the experimental cases.

One challenge I see with this experiment is “dosage”. For the commercial fertilizer, you would probably go with the manufacturer’s recommended dosage. But if, for example, you use a teaspoon of the commercial fertilizer, what is the appropriate amount of the natural fertilizer that should be used? Is the amount going to differ for each of the natural fertilizers? Perhaps that is another variable that comes into play.

Sounds like an interesting project that could have some very practical outcomes.
Mike