Science Buddies: "Ask an Expert"

My science fair project is using 3 types of plants (10 of each) to see which plant can remove the most nitrates/nitrate nitrogen from water.
We set the project up. Waited 7 days and took the first test. We then waited 7 days and took a second reading. Our plan was to then wait 7 days and do a third reading.
After the second reading we found that 2 of the plant types removed most of the nitrates from the water. At this point should I be do a third reading? It almost seems pointless.
We also will be doing a calculation of of ppm of nitrates removed of biomass.
Not sure if it is important to know but we are growng the plants hydroponically and the plants used are grass, ivy and ferns. (normal plants found around lakes and rivers)

I am wondering if my original question was unclear. I appreciate all your help with this.
If we have done two sample testing of our plants is it nessessary to do a third testing?
10 water + 10 water = 20 water tests
10 fern + 10 fern = 20 fern tests
10 ivy + 10 ivy = 20 ivy tests
10 grass + 10 grass = 20 grass tests
We have conducted a total of 80 tests with this project. We plant to do 3 more using biomass. Example all ferns are dried and then weighted in grams. We will then add up the total amount of nitrates removed from the ferns. We will be able to see how much ppm of nitrate/gram of ferns was removed.
Thank you again for all your help. We appreciate it.

Since you have the experiment set up and the reagents available, I would recommend going ahead and getting the data for the third data point. Your graph of results will look more complete with one more data point, and maybe something will happen with the third plant type that has not utilized the nitrate yet. However, there would be nothing wrong with omitting the last data point since you have already seen a significant difference in results between the samples.

The standard sections for a science fair board are title, question, hypothesis, background, materials, method, results and discussion as described in the science buddies website:

https://www.sciencebuddies.org/science- ... oard.shtml

I don't know what the "recommended," section refers to, but your teacher may be requiring an additional section. For example, I have seen science fairs where the projects included a section on recommendations for changing the experiment if it were to be done again. I suggest that you go back and read the detailed instructions that were handed out when the science fair project was assigned and read through it and make sure you include every detail that is required. It sounds like you have a great project here, and you don't want to lose any points for omitting something that your teacher specifically requested.

Donna Hardy

Hi eriws,

I have just sent you a reply, but thanks for explaining more of the details. From your original inquiry, it sounded like you had just 3 data points (0,7, & 14 days) for each type of plant. But you have 10 data points for each time and plant type. With so much data, you really don't need to do the 21 day data point. You have lots of data to support your conclusions.

Donna Hardy