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

Abstract The aim of this study was to quantify site-specific levels of indirect nitrous oxide (N2O) emissions from oilseed rape (OSR) cropping in Germany, resulting from ammonia (NH3) volatilization after organic fertilizer application and nitrate (NO3−) leaching based on measurement in field experiments and additional simulation modelling. In field experiments in three years (2012/13–2014/15) at five sites representing the main OSR growing areas N fertilizer amount and type of fertilizer (mineral N or digestate (DIG)) were varied. NH3 emissions were measured after application of DIG with the Drager Tube Method and dynamics of soil water and soil mineral nitrogen (SMN) were monitored for three years, besides other parameters influencing the N balance like plant growth. A Plant-Soil-Atmosphere-Model (PSAM) was developed from existing components to calculate site-specific N leaching. Furthermore, long term scenario analyses allowed to simulate site-specific N leaching and to analyze the impact of total N input and fertilizer N form on N uptake of OSR and the subsequent N leaching. Results showed site-specific differences in measured NH3 emissions after DIG application ranging from 7.6 to 18.3 % of total applied N representing a lower volatilization level than the IPCC default emission factor of 20 % for organic fertilizers. PSAM was able to reproduce observed dynamics of soil water and SMN, but with site-specific accuracy. N leaching levels varied site-specifically and were dependent on fertilizer amount, fertilizer type and site conditions (weather, soil), but ranged with 5.0–17.6% also considerably below the default value of 30 % N input used by IPCC. Finally, calculated N2O emissions resulting from measured NH3 volatilization was up to 61 % lower than the default value and N2O emissions from determined N leaching levels were 64–89% lower.