The Effect of Ammonical N Fertilizer Concentration on Nitrification and N2O Production in Different Soils.

The development of mitigation strategies to reduce nitrous oxide (N₂O) emission from soils is dependent on explicating the biophysical factors affecting different N₂O production pathways. Ammonia oxidation and heterotrophic denitrification are the main pathways of N₂O production, depending on soil conditions such as soil moisture content, oxygen (O₂) content and N substrate. Many researchers have reported that N₂O production increased as substrate concentration and soil moisture content increased. However, a mechanistic understanding of how concentration of different N fertilizers and moisture content interact to affect N₂O production pathways is lacking. We investigated the relationship between O₂ consumption, ammonical N fertilizer concentration, and water content in incubations of three agricultural soils (clay, sandy loam, and peat) amended with different concentrations of (NH₄)₂SO₄ (0-1000 µg N g^-1) under 50 %, 75%, and 100% of water holding capacity. All treatments additionally received ¹⁵N -KNO₃ to bring the concentrations of NO₃^--N in soils to 50 mg kg⁻¹ soil and the NO₃^- pool to an enrichment of 10 atom% ¹⁵N. In all soils, the total amount of O₂ consumption and N₂O production increased as soil ammonical N concentration increased. The increase in soil moisture significantly promoted N₂O production in sandy loam and clay soils, but not in peat soil. These results indicate that the increase in N₂O production may have been due to soil O₂ limitation caused by O₂ demand of ammonia oxidation.