Indirect nitrous oxide emissions from oilseed rape cropping systems by NH3 volatilization and nitrate leaching as affected by nitrogen source, N rate and site conditions

•NH3 volatilization was measured with the Dräger Tube Method at five sites in Germany.•An adapted Plant-Soil-Atmosphere-Model (PSAM) was used to calculate site-specific N leaching.•NH3 volatilization amounts were lower than IPCC default emission factor.•N leaching levels were site-specific depending on fertilizer amount, fertilizer type and site conditions.•Calculated indirect N2O emissions were 61–89% lower than default values.