Assessing the Relative Potential of Organic Amendments to Emit Soil N2O : Towards a Standard Method.

Prediction of N₂O emissions following the application of organic amendments to soils is difficult because of their variable composition and of complex interactions with soil properties and conditions. In this study, we propose to determine the Relative Potential of Organic Amendments to produce soil N₂O emissions (RPOAN₂O). The potential was estimated based on N₂O dynamics during laboratory incubation of a clay loam soil at 22°C. Amendments included pig slurry (PS), poultry manure (PM), sheep manure compost (SMC), alfalfa residues (AR), wheat straw residues (WSR), mineral fertilizer (NH₄NO₃) and an unamended control (CTL). Four incubation methods were used.  In the Dry/Wet method, soil was allowed to dry for 45 d at ambient O₂ level, followed by a rewetting. The ISO method consisted of a 45-d incubation at constant soil water content at ambient O₂, followed by an anaerobic period under “N₂ + C₂H₂” atmosphere. For the other two methods, the glass jars were sealed and headspace was flushed with N₂ (OA^-) or “N₂ + C₂H₂” (OA⁺) when the O₂ level in headspace reached 5%. Estimates of RPOAN₂O obtained using each incubation method and the relationship between RPOAN₂O and chemical properties of amendments will be presented and discussed.