Emissions of N2O following field incorporation of leguminous and non-leguminous cover crops

Cover crop (CC) cultivation can reduce N leaching from agricultural fields. It has also recently been proposed as a measure to mitigate climate change due to its potential for increasing soil carbon (C) stocks and reducing soil nitrous oxide (N 2 O) emissions during CC growth. However, the input of immature, low C/N ratio plant material to the soil can increase the risk of N 2 O emission upon CC termination. In a field trial under humid temperate conditions, N 2 O emissions from two leguminous CC species – hairy vetch ( Vicia villosa ) and crimson clover ( Trifolium incarnatum ) – and from two non-leguminous CC species – oilseed radish ( Raphanus sativus ) and winter rye ( Secale cereale ) – were measured in the spring from 24 days before to 54 days after incorporation. The vetch had a significantly higher shoot N concentration and consequently lower C/N ratio than the other three species, but this did not increase N 2 O emissions relative to the fallow control. Indeed, oilseed radish was the only cover crop to significantly increase N 2 O emissions by 290 g N 2 O-N ha −1 during the measurement period relative to the fallow control. These results suggest that factors other than the shoot C/N ratio, such as total biomass, N content or other biochemical parameters may be of greater importance for predicting N 2 O emissions from immature cover crop residues. • Leguminous cover crops did not produce higher N 2 O emissions than oilseed radish. • Oilseed radish generated significantly higher N 2 O emissions than the fallow control. • Total shoot biomass and N were better predictors of N 2 O emissions than C/N ratio.