What is background nitrous oixde emissions?

Background N₂O emissions are defined as N₂O emission from soils that received no nitrogen (N) fertilizer and soil management (e.g., Bouwan, 1996; Lu et al., 2006; Neftel et al., 2007; Gu et al. 2009; van Beek et al., 2011). Gu et al. (2009) noted that BNE in agricultural lands originates from residual N that has remained in the soil from N addition in previous years or seasons, and other N sources, such as biological N fixation, that are present in the soil. Crop residues can provide substrate for microbial activities such as nitrification and denitrification which produce N₂O (Aulakh et al., 1991; Huang et al., 2004; Miller et al., 2008). Also soil disturbance for agricultural activities can enhance N₂O emission through changing soil microclimate (i.e., soil temperature and moisture) and soil properties (i.e., bulk density, porosity and diffusivity) (Dobbie and Smith, 2001; Saggar et al., 2011). Kim et al. (2009) observed that soil temperature and soil moisture in crop fields were significantly different from adjacent grass lands and soils in crop fields had severe soil drought and frozen which caused peak N₂O emissions following rewetting and thawing events (Kim et al., 2012).  In animal grazing grassland, treading and trampling by the animals cause soil compaction, making the soil more anaerobic and stimulating denitrification activity, thus facilitating N₂O production (van Groenigen et al., 2005; Bhandral et al., 2007; Uchida et al., 2008). In agricultural land, magnitude of BNE may be influenced by the fertilization and soil management during previous years (Bouwan, 1996).