I study the effect of transported soil nutrients into water bodies (creeks, lakes, etc.), and the potential negative effect of eutrophication.
I have 300 soil samples from crop fields. The lab charges three separate fees for Nitrogen testing and my budget is limited so I cannot pay for all N tests.
Which form of N could be more helpful for my research?
1) Nitrate Nitrogen; 2) Total Nitrogen; 3) Ammonium Nitrogen.
Any scientific reference and/or recommendation is greatly appreciated.
Jhony
Total nitrogen includes ammonium, nitrite and nitrate + any organically bound N. In terms of pollution, total nitrogen is the most important. Bound nitrogen in the environment changes form depending on the environment. Under oxidizing conditions it will often act as NO3. See nitrogen cycle https://en.wikipedia.org/wiki/Nitrogen_cycle
You have 300 soil samples, e.g., from a micro-catchment? How do you propose to relate whatever tests you have done on the soil to the N in the nearest water body? Are you considering surface flow or subsurface flow? If you answer these questions you can then make decisions about the tests you need done and how they should be done. The extraction process itself may be very important, i.e., you may not want a standard extraction at all.
For eutrophication, ISECA recommends several indicators to assess eutrophication (vliz.be/projects/iseca/en/science-for-all/how-do-we-measure-eutrophication.html), which you can choose depending on your experimental budget. As Paul mentioned, water samples are very important, and then you may not need as many soil samples.
Dear Jhony,
Because of your limited budget, you could try with laboratories which have equipment such as photometers or Kjeldahl method machine.
See link attached:
https://www.buchi.com/en/products/instruments/kjel-line
Regards,
Total nitrogen can be measured after oxidation with potassium persulphate. The method uses heating in an autoclave, but a pressure cooker for kitchen use is sufficient. An electrode that can measure nitrate, and is used together with a pH meter, is expensive, but if many analyzes are to be carried out, it can perhaps be defended? https://www.coleparmer.com/i/cole-parmer-ise-electrode-nitrate/2707710 With this electrode, you can measure NO3 directly, or Tot.N as nitrate. There are also kits that measure different forms of N colorimetrically. The reagents come in tablet form and are easy to dose. Used spectrophotometers may be found on Ebay
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