Hi Marianne,

it depends on what you want to do or measure. I´m working a lot with nitrifying activity in soils, sediments and water column. Next to that I did also enrichment cultures. If you want to measure potential rates you add some substrate, for ammonia oxidation like 0.5 or 1 mM ammonium. The same for nitrite oxidizers. If you use more there will be the problem of the toxidity of nitrite accumulation. I guess for denitrification also 1mM is a good option. But you have to keep in mind that the denitrifier also need a C source.

If you want to measure the more or less natural rates, the isotope dilution method can be used.

Cheers,

Tina

Thank you Tina, for your answer. I will be analyzing the potential rate of both, but the reference I am taking guidance of, uses approximately 0.7 mM ammonium and nitrate fertilizer. 

Is the range you are giving me in your answer the typical range for measuring rates in these processes? What considerations should I have on to whether my amount stays in the lower, neutral or upper limit within this range given? 

Under which circumstances do you apply a C source? The authors I have read don't add any source of C for measuring the potential rates, however, there may be a piece I am missing out of the big picture (?) 

Thanks for your kind help,

Marianne. 

In arid soils we find that 0.5mM concentration is the best for both the case4s

Thank you very much!

Since, this depends on the types and nature of the soils, it varies from place to place. So it is better to try by using several concentrations for proper standardization.