Denitrification in a cultivated soil: Optimal glucose and nitrate concentrations

An experiment was conducted in the laboratory on a cultivated soil incubated in serum bottles with a range of C-to-nitrate concentrations. C was added in form of glucose and nitrate in form of Ca(NO₃)₂. It was shown that an C-N concentration of respectively 500 μg C (glucose-equivalent, Glc-Eq.) and 36 μg N g⁻ dry soil was optimal for denitrification. Results obtained either in the laboratory, in soil columns or in the field were in good agreement with one another. In particular, the root zone was shown to be favorable for denitrifying activity because the water-soluble C (Glc-Eq.) and N concentrations were more favorable than in bare soil. Furthermore, the water-soluble extractable Glc-Eq. appeared to be closely related to the denitrification rate and is thus likely to represent the energetic C pool supporting denitrification.

This was related to an inhibiting effect of increasing NO₃⁻ and NO₂⁻ concentrations on NO₃⁻ loss and N₂O production. Such inhibition can affect short-term measurements of denitrification in the field.