N2O emission from organic barley cultivation

Biogeosciences Discussions This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. Abstract Legumes are an important source of nitrogen in stockless organic cereal production. However, substantial amounts of N can be lost from legume-grass leys prior to or after incorporation as green manure (GM). Here we report N 2 O emissions from a field experiment in SE Norway exploring different green manure management strategies: 5 mulching versus removal of grass-clover herbage during a whole growing season and replacement as biogas residue to a subsequent barley crop. Grass-clover ley had small but significantly higher N 2 O emissions as compared with a non-fertilized cereal reference during the year of green manure (GM) production in 2009. Mulching of herbage induced significantly more N 2 O emission (+0.37 kg N 2 ON ha −1) throughout the grow-10 ing season than removing herbage. In spring 2010 all plots were ploughed (with and without GM) and sown with barley, resulting in generally higher N 2 O emissions than during the previous year. Application of biogas residue (110 kg N ha −1) before sowing did not increase emissions neither when applied to previous ley plots nor when applied to previously unfertilized cereal plots. Ley management (mulching vs. removing 15 biomass in 2009) had no effect on N 2 O emissions during barley production in 2010.