Nitrification and denitrification as sources of atmospheric nitrous oxide – role of oxidizable carbon and applied nitrogen

Abstract.

Laboratory incubation experiments were conducted to study the influence of easily oxidizable C (glucose) and mineral N (NH₄ ⁺ and NO₃ ^–) on N₂O emission, evolution of CO₂ and consumption of O₂. A flush of N₂O was always observed during the first few hours after the start of soil incubation, which was significantly higher with NH₄ ⁺ compared to NO₃ ^– applications. The increase in N₂O emission was attributed mainly to enhanced soil respiration and subsequent O₂ limitation at the microsite level. Application of NH₄ ⁺ helped to develop denitrifying populations since subsequent additions of NO₃ ^– and a C source significantly enhanced N₂O emissions. In soils treated with NH₄ ⁺, N₂O emissions declined rapidly, which was related to decreasing concentrations of easily oxidizable C. Addition of glucose in different amounts and pre-incubation of soil for different lengths of time (to create variation in the amount of easily oxidizable C) changed the pattern of N₂O emissions, which was ascribed to changes in soil respiration.