Long-Term Simulated Direct N2O Emissions from German Oilseed Rape Cultivation below the IPCC Emission Factor

Abstract

The low nitrogen (N)-use efficiency of intensive winter oilseed rape (WOSR) cropping systems may cause negative environmental impacts, especially due to N leaching and gaseous losses. The aim of this study was to use data from field experiments (five sites across Germany representing typical WOSR regions) for parametrization of a nitrous oxide (N2O) emission component for implementation into a process-based dynamic plant-soil-atmosphere model (PSAM). After calibration and evaluation with three years of field data from five different N fertilizer treatments, a long-term simulation with 25-year historical weather data was conducted to derive functional relations and emission factors (EFs). The model performed best at higher aggregation levels (cumulative emissions over the entire cropping period, R2 of 0.48/0.77 for calibration/evaluation), but also reasonably simulated short-term dynamics (e.g., fertilizer applications, extreme weather events). Site-specific and year-specific N2O emissions varied within the range of medians from 0.56–4.93 kg N2O-N ha−1. Mineral fertilizer-induced EFs at economic optimal N inputs ranged from 0.16–0.65%, which was markedly below the aggregated IPCC standard value of 1% for direct N2O emissions. Generally, the simulated emissions were consistently higher with finer soil textures and increasing N inputs. The process-based approach, moreover, allowed the identification of the major source of N2O, which mainly originated from nitrification processes.