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My professor wanted us to each conduct an experiment for class on something we thought would interesting. My experiment was very simple, but I'm not sure how to interpret my results. (Please note that this is not for homework – I'm just genuinely confused and trying to understand the data.)

Basic method:

Take soil samples, add varying concentrations of Roundup and water equalling a total of 50ml, seal in airtight jars, incubate for 7 days, run through a Gas Chromatograph, and record the rates of production for CO2, CH4, and N2O. Overall, there was the Control and then three treatments, for a total 8 jars because each had a duplicate:

  • Control (Roundup: 0, H2O: 50ml),
  • T1 (Roundup: 10ml, H2O: 40ml),
  • T2 (Roundup: 25ml, H2O: 25ml),
  • T3 (Roundup: 50ml, H2O: 0).

I expected the Control to have the highest levels of production, followed with a decrease in production for T1, followed by T2, and then T3, with T3 being the lowest because all microbial activity was inhibited by the massive dose of Roundup.

However, the results were a bit surprising.

In general:

  • The Control rates were the highest, as expected.
  • T1 showed a decrease in production, as expected
  • T2, again, showed a decrease in production, as expected.
  • And then T3 showed a significant increase in production.

Here are some graphs to illustrate this in more detail:

enter image description here

This is a new field of science for me, so forgive me if I'm missing something obvious, but my natural intuition is certainly not helping me out on this one. What are some possible causes for this increase – in particular for the N2O/denitrification? Or at the minimum, are there any particular resources I can take a look at to better understand why this happened?

Edit

This is my brain on paper, so forgive me again for any ridiculous things I say. But, could it have something to do with the denitrification process such that more gas is given off as N2O because the microbes responsible for processing the N2O into N2 have died. So in the previous Treatments 1 and 2, the N2O was lower because the N2O was being converted into N2 (but we never recorded the N2), but in the final treatment, no conversion occurred, so the N2O appears to go up, even through the microbes are functioning even less.

Thoughts?

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  • $\begingroup$ What was your process in collecting the soil samples? Prepackaged in any way, dug up by hand? $\endgroup$
    – CKM
    Nov 30, 2015 at 23:12
  • $\begingroup$ Dug up by hand, with gloves, placed in plastic bags temporarily for transportation, and then right into the jars. All were collected at the same time/day. $\endgroup$
    – Friendly King
    Nov 30, 2015 at 23:47
  • $\begingroup$ So, you have what could possibly be an outlier that's just due to that soil sample. It's a pain, but basically you would take more samples, have more replicates and data points, and you might see that the particular outlier point is just an artifact. The actual explanation why did that sample do that? would require a deeper investigation! $\endgroup$
    – CKM
    Dec 1, 2015 at 1:35
  • $\begingroup$ I am not a biologist so I have no idea. This said, the graphs do no show any error (actually incertainty) bars, which are needed to do any kind of interpretation. $\endgroup$
    – WoJ
    Dec 4, 2015 at 6:17

1 Answer 1

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This may have no correlation to your project but many insecticides, bacteriocides, and herbicides need a "solvent" or "transfer medium" such as water to be effective. Even when using ethanol in the laboratory against a variety of bacteria 100% ethanol becomes almost ineffective.

I would take a look at running round-up again by itself versus 95% roundup 5% water, and 90% roundup and 10% water and I am sure you may seem some results that will aid your experiment.

Good Luck!

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