Effect of Oxygen Content on Pathway of Nitrous Oxide Production from Different Nitrogen Fertilizers.

When aiming to develop adequate mitigation strategies for emission of nitrous oxide (N₂O) from soils, an accurate understanding of biochemical N₂O production pathways in soil is advantageous.  Nitrification, nitrifier denitrification, denitrification are considered as the main pathways of N₂O production, depending on soil conditions such as soil pH and oxygen (O₂) content. Most nitrogen fertilizers supply ammonium to the soil-plant system, some of which give an acidic reaction while others can temporarily raise soil pH. The primary pathway of N₂O production will therefore change based on the fertilizer type applied. At the same time, O₂ content is also a very important factor determining N₂O emission. However, there is still only limited understanding of how the mechanism of N₂O production from different fertilizers changes as O₂ becomes limiting. We used two agricultural soils to investigate the effect of urea, ammonium sulfate, monoammonium phosphate, and aqueous ammonia on the pathways of N₂O production under an oxygen atmosphere of 21, 3, 0% O₂. In both soils, N₂O emission from urea was significantly higher than the other fertilizer types under 21 and 3% O₂. Based on the relative amount of N₂O produced among treatments, nitrifier denitrification is likely the main source of N₂O from all fertilizer types under 3% O₂.