Science Buddies: "Ask an Expert"

I also have a son doing a project on whether "buffer zones" can decrease Nitrate leaching. Since it is common practice to plant buffer zones so that the nitrates are absorbed by the roots before entering our water systems, he wants to see how different shrubs will affect nitrate leaching. His IV would be different shrubs or trees and his dv would be nitrate leaching. Do you think this is an eighth grade project, and if not do you have any suggestions to make it an eighth grade project. Also how long should he water each pot and take nitrate readings? thanks for any help

Hi Zabanda,

I apologize for the long delay in responding to your inquiry.

This is a unique and really great science fair project idea. An example from real life is always a good topic and here are suggestions for developing the experimental protocol:

Your daughter should try to use plants that are well established in pots and have a quantitative method for measuring the amount of nitrate applied to each plot and leached from the pot. Since there is no procedure written for this, I recommend doing a small pilot scale experiment with one pot and see if it is possible to get reproducible results on measuring leached nitrates.

There are test kits for nitrate available at aquarium stores, but these might be expensive to use for the quantity of testing that needs to be done. Here is a description of two nitrate testing methods:

http://water.epa.gov/type/rsl/monitoring/vms57.cfm

And here is a power point that shows pictures of different methods.

http://www.usu.edu/cpl/Nitrate%20analys ... ometti.pdf

If your daughter can identify a suitable quantitative method, then she should be able to do this experiment.

What is your daughter thinking about doing for an experimental design? How is she going to reproduce the report of the nitrate being converted to ammonia under low oxygen conditions? It sounds like bacteria in the soil may have been responsible for the conversion, so she should try to think of a way to add a suitable source of microorganisms to one pot. What will be use for controls for the experiment?

Anaerobic conditions are not usually good for the plants, so she should include an evaluation of the health of the plants and make a note of any yellowing leaves or wilting

I recommend using just one type of plant, and include at least two pots of each plant, if possible.

Please post again in this topic if you have any other questions.


Donna Hardy

Thanks Donna for your reply. I think you may have read both of my posts...which were separate projects for both my kids. This project was for my son and was just testing different trees/shrubs and seeing "buffer" would reduce nitrate leaching. The part of the of the nitrate converting to ammonia is on the other project. On this one, we would use four different plants/shrubs and fertilize them with the same amount of fertilizer. Then we would water each one every day and test the amount of nitrate leaching. The control pot would just have soil with the same amount of fertilizers as the trees/shrubs. Was your answer for this project or could it be for the other? Thank you so much for all your help.

Hi Zabanda,

I apologize for the confusion. I read the question about your daughter’s project and wrote my reply and posted it in your son’s topic. You were correct to post the questions in two different topics, and I’m really sorry I did not notice my error. I see the theborg has also given you some excellent advice for your daughter’s project that should be helpful, so here are some suggestions for you son’s projects:

Your son would also need a method of measuring nitrate so he would have quantitative results to report. This is definitely a good eighth grade project.

Since your son wants to compare nitrate leaching in different plants, then all other parameters including fertilizer, potting soil, sunlight, size of the plants, size of the pots and temperature should remain controlled. Different plants might require different amounts of water, but this should be optimum for the plant.

It would be helpful also in the project to include some type of plant measurement so any effect of the nitrate can be noted. Here is information on this topic from the Science Buddies website:

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

It would be better to include at least two of each type of plant so you can evaluate the reproducibility of your experiment.

Watering plants every day might lead to overwatering. Plants in pots need to dry out a little in between watering. You can evaluate how often the plants need to be watered and since you do have a little time, plan to water every 3-4 days; this will give your son several data points to graph for his results. He can graph results with time on the x axis and nitrate levels on the y axis; there will be different colored lines representing the different plants and controls. The control pot with no plant is a good plan.

Please post again in this topic for your son’s project. I will move my reply for your daughter’s project to the right topic so I will be notified if you have more questions on that project.


Donna Hardy

Thanks again for your reply. Since it is winter, we had originally thought about some sort of shrubs instead of plants so that I can keep them out in my garage. Is that ok? If we were able to use plants, would keeping them in the house near a window be ok or could they also be left in garage. Also, we were going to use the nitrate leaching test strips that you find in a garden store.

Hi Zabanda,

Yes, temperature and light will be controlled parameters so keep all of the plants together. Hopefully you will be choosing plants that will stay alive in the garage. If you have a choice, place the plants where more light and a higher temperature are available; the plants will be able to utilize the nitrate more quickly. If it is dark and too cold, the plants will be growing very slowly.

Donna Hardy

Thanks again for all your help.

Just one last question that is something I have wondered about as we are beginning this project. If I have a pot with soil that is fertilized and one with a potted plant fertilized....would you think that the nitrate difference would be evident from the first watering? I happened to try a "test" case and they were the same or is it a decreasing over time.

Thanks

Zabanda,

For your last question, if you start with identical soil parameters, and irrigation cycle in both, you have a new scientific methodology where your independent variable is plant vs no plant and your dependent variable is still nitrate leaching. I would expect leaching to be less with the pot with a plant than the one without, but can't say for sure. Try the additional permutation and find out scientifically.

Hi Zabanda,

Good question. Nitrate is an extremely water soluble ion, so I would expect it to start leaching immediately after fertilization. The soil has ion exchange properties and will bind the nitrate, but with continued watering, it will leach out of the pot. It is likely that a normal fertilization would exceed the anion exchange capacity of the soil. So if you fertilized the pot at the beginning of the experiment, I would expect a lot of leaching at the beginning, and once all of the excess nitrate has been rinsed through, then the nitrate would leach very slowly. After the initial watering, there should be a difference between the pots with and without plants.

You should not get 100% recovery of the nitrate because the plant and perhaps microorganism will use the nitrate that exchanges onto the soil. I would recommend doing an initial test before you add the nitrate fertilizer to measure any residual nitrate remaining in the pot.

Donna Hardy