In which form N will be lost from soil at pH < 6.5?

At pH < 6.5, NO form of Nitrogen is lost from the soil. Nitrous oxide arises from soils via the two biological pathways of nitrification and denitrification.
Nitrogen levels affect soil pH. It increases soil acidity unless the plant directly absorbs the ammonium ions. The greater the nitrogen fertilization rate, the greater the soil acidification.