Nitrate Leaching

[zabanda]

My daughter is doing a project on nitrate leaching. We were given a real scenario on a problem and now she is trying to make it a project. i am of no help. The problem....a person applied too much water to a field, which caused low oxygen. The nitrogen converted to ammonia and evaporated. but less nitrate leaching occured. She has her independent variable as oxygen in soil and the dependent variable as Nitrate leaching. She wants to set up four pots and change the irrigation rate of each pot and then test for nitrate leaching. She says she will graph Irrigation rate and Nitrate Leaching. Is she on the right path. Her teacher had her IV as nitrate concentration and the DV as the oxygen in the soil. She and I don't see how that relates to the problem and now are wondering if we have misunderstood the problem. She says overwatering should have caused more nitrate leaching, so she is a little confused on how to approach this problem but has a great understanding of nitrate leaching. Any help would be appreciated!

I thought I should add that the person who came up with this (we can't seem to contact) said we should look at irrigation rates and oxygen in the soil and how much nitrate leaching occurs. With the way her teacher has it, it has confused her as to what she would really be learning about.

[theborg]

zabanda,

Welcome to science buddies and thank you for your questions. I see you made your post several days ago, I hope this answer is still helpful to you. I normally monitor the physical science forums, and not the Earth Sciences, so I did some research into the nitrate cycle and how that relates to your proposed experiment.

From what I see, you are going to vary the irrigation rates across 4 samples (i.e. pots of soil). By definition, this is your IV. Irrigation rate is independent of the nitrate or oxygen or leaching effects. However, all 3 of those parameters, as well as soil pH can/may be affected by the irrigation rate...these are your dependent variables (remember, you should have only one IV that you change at a time, but you can have several DVs that are affected by a change in IV). As I understand, you want to relate the level of leaching with respect to irrigation rates. From what I understand of the nitrate cycle, the creation of nitrate is influenced by nitrogen and amonnia, oxygen, soil pH levels and the presence of 2 types of microorganisms: zabanda,

Welcome to science buddies and thank you for your questions. I see you made your post several days ago, I hope this answer is still helpful to you. I normally monitor the physical science forums, and not the Earth Sciences, so I did some research into the nitrate cycle and how that relates to your proposed experiment.

From what I see, you are going to vary the irrigation rates across 4 samples (i.e. pots of soil). By definition, this is your IV. Irrigation rate is independent of the nitrate or oxygen or leaching effects. However, all 3 of those parameters, as well as soil pH can/may be affected by the irrigation rate...these are your dependent variables (remember, you should have only one IV that you change at a time, but you can have several DVs that are affected by a change in IV). As I understand, you want to relate the level of leaching with respect to irrigation rates. From what I understand of the nitrate cycle, the creation of nitrate is influenced by nitrogen and amonnia, oxygen, soil pH levels and the presence of 2 types of microorganisms: (Nitrosomonas and Nitrobacter. Disrupting any one of these factors could lead to a reduction in nitrate production and therefore less leaching. If you have the means to measures these levels throughout the experiment, then you may be able to explain the reason over irrigation results in less leaching (if this is in fact your result...just providing an example).

For your experiment, I would ensure 4 or more identical potted sample (same initial nitrogen, oxygen, pH levels), then measure these parameters over time while watering each to different levels as well as the nitrate levels in the leached water/material. I would plot nitrate leaching over time, or irrigation cycle, for each sample (4 irrigation curves on one plot). If there is an interesting result, then plot the other variables with respect to nitrate leaching to see I'f there is a main mechanism causing the result. This could also be a follow on project.

[zabanda]

I really appreciate your reply. My daughter was going to use potted soil to keep the initial ph, nitrogen and oxygen levels the same. Then she would change the irrigation rate for each pot and then measure the oxygen level and nitrate leaching. Her teacher was going to lend her the instrument that would measure the oxygen, and then she would measure the nitrate leaching with test strips. In your response you mentioned if we could measure the parameters (I am assuming you were referring to nitrogen, ph, and oxygen) we could see what might be causing less leaching,( if that is the result) What if we can't measure all those parameters and we only measure the oxygen level and nitrate leaching? Is there any point to doing this project then? Will the results only show that overwatering may or may not cause nitrate leaching?

Also, what would the schedule be for monitoring/measuring and recording results? Daily? and for how long? Thank you again!

[donnahardy2]

Hi Zabanda.

Here is the reply that I accidentally posted in your son’s project. This advice applies to your daughter’s project. Theborg has given you some excellent advice for this project as well.

“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

[donnahardy2]

Hi Zabanda,

Here is a reply to your most recent post asking about the measurements.

It’s great that you will be able to measure both the nitrate and the oxygen levels. You can also include notes to record visual observations on the plants.

I recommend setting up the experiment to run for two to three weeks and making measurements every 2-3 days. That will give you between 5 and 7 data points that will make an excellent line graph to show the results. If you notice a significant change in results from one reading to the next, you can decide to start doing daily measurements.

You should also document the controlled parameters and make notes on the hours of light available daily and measure the temperature when you test the oxygen and nitrate levels.

Start writing up the project board now; you will be able to complete all of the sections except the results and conclusion section. Stop a few days before the project is due and focus on writing up the project board.

http://www.sciencebuddies.org/science-f ... oard.shtml

Good luck.


Donna Hardy

[theborg]

Ok, I figured oxygen would be the difficult measurement, but since you have access to a measurement device, that's easy. The nitrogen level is related to pH, so if you just got a pH kit, I believe that should be enough. A soil pH kit should be easy enough to find. I found an electronic soil moisture and pH tester at Lowes for < $10. From my research, high levels of nitrogen contributes to a low (acidic) pH, and I found that plants tend to like a neutral pH (a reading of around 7). The experiment proceedures you mentioned seem like they should be adequate (i.e. multiple pots where you measure leaching and oxygen levels). As for time between data points, that is hard to comment on without knowing your test Proceedures. However, a long test period (i.e. several days to weeks) then once per day is likely adequate. The idea is that you collect enough data to "see" the effect. For example, if you only take measurements at the start and end of the experiment and you see a change in nitrate leaching then you can conclude there is an effect, but you have no idea how or when it came about. Did it drop to that value right away or was it a gradual change.

To relate an experience I had conducting an experiment once: I was looking for the effect of some devices placed in a wind tunnel and I had my measurement instruments set up to take readings every 1 cm. Turns out the effect occured at a very specific spot right between two instrument readings with a margin of millimeters. After several trials of not seeing anything I just happend to change up my proceedures to include taking readings in the "sweet spot".

My point with the above example, is that some trial and error with data acquisition may be in order. If there is a huge change in the amount of leaching from initial conditions, you may need to take more samples closer together to get a finer read on the process, or if there is no change, the experiment may not have run long enough for the effect to be detected or may not be there at all. Dont be afraid to run the experiment again or even have more than the 4 samples, in fact, I might suggest duplicating the test at least 3 times. These can be run in parallel (i.e. at the same time)...that means 4 conditions x 3 trials = 12 pots. This will give you a good average to report on.