Post-harvest N₂O emissions can be mitigated with organic amendments

After the harvest of winter oilseed rape and faba bean crops, considerable high soil nitrate values may be built up before winter in central to north European regions. High precipitation and a low N uptake by the subsequent crop in fall cause a high risk of N₂O emissions and nitrate leaching. Microbial decomposition of crop residues or high carbon amendments may immobilize mineral N temporarily and may prevent losses by direct N₂O emissions. Five treatments, including crop residue removal and application of different organic amendments after harvest, were tested in a field trial in Northern Germany to elucidate the potential of this mechanism as a mitigation option. N₂O emissions and the soil mineral nitrogen status were monitored from August to March for three consecutive years. Observed emissions ranged from 0.1 to 3.4 kg N ha⁻¹ in 180 days. An empirical model approach was applied to separate the impact of spatially and temporally heterogeneous environmental conditions between the plots of the field experiment from treatment effects in the subsequent statistical analysis of N₂O emissions. Results show that the exchange of the initial crop residues with organic amendments with high C:N ratios (i.e., winter wheat straw and sawdust) after the harvest of faba bean or oilseed rape can reduce N₂O emission during fall and winter by up to 45%.