Managed pastures are strong sources for the greenhouse gas nitrous oxide (N2O) through various nitrogen (N) inputs. So far, chamber measurements have been used to quantify N2O emissions and emissions factors of specific emissions sources like grazing cattle excreta. This study presents a three-year dataset of N2O emissions from a grazed and fertilized pasture measured by eddy covariance (EC) in eastern Switzerland. N2O fluxes were gap-filled and disaggregated into the emission sources (flux partitioning) by using random forest. The excreta N deposition in the pasture was estimated based on a cattle nitrogen budget approach using observed milk yield, body weight and feed intake of the cattle herd. Furthermore, a driver analysis was performed to quantify the relationship between N2O emissions and predictor variables. The observed annual N2O emissions amounted to 5.3 ± 0.8, 3.1 ± 0.5 and 4.4 ± 0.7 kg N2O-N ha-1 yr-1 and were disaggregated into background, fertilizer and excreta related N2O emissions with contributions of 27–46 %, 15–40 % and 30–51 %, respectively. Combining the excreta N2O fluxes with the excreta N inputs resulted in an average emission factor (EF) for cattle excreta of 1.1 ± 0.5 %, that tends to be higher than the IPCC default value of 0.6 % for wet climates. While maximum N2O emissions usually were observed after fertilizer application and under optimum soil moisture conditions as expected, distinct N2O emission peaks also occurred during a longer drought period in summer and could be parametrised as a function of precipitation and previous grazing activity. Moreover, peak N2O emissions occurred during the cold season at low temperatures and should be considered in future studies. Overall, we suggest that EC measurements under pasture conditions with subsequent flux partitioning by random forest are suitable for quantifying pasture N2O emissions of different sources.

中文翻译：

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放牧和施肥牧场的涡度相关因素 N2O 排放的分区和驱动因素分析


管理牧场通过各种氮 （N） 输入成为温室气体一氧化二氮 （N2O） 的重要来源。到目前为止，腔室测量已被用于量化 N2O 排放和特定排放源（如放牧牛排泄物）的排放因子。本研究提供了一个为期三年的瑞士东部放牧和施肥牧场的 N2O 排放数据集，该数据集通过涡度相关差 （EC） 测量。N2O 通量被间隙填充并使用随机森林分解到发射源（通量分配）中。牧场中的排泄物 N 沉积是根据牛氮预算方法估计的，该方法使用观察的牛群的产奶量、体重和采食量。此外，还进行了驱动因素分析以量化 N2O 排放与预测变量之间的关系。观察到的年一氧化二氮排放量为 5.3 ± 0.8、3.1 ± 0.5 和 4.4 ± 0.7 千克 N2O-N ha-1 yr-1，并分为背景、肥料和排泄物相关的一氧化二氮排放量，贡献分别为 27-46%、15-40% 和 30-51%。将排泄物 N2O 通量与排泄物 N 输入相结合，得出牛排泄物的平均排放因子 （EF） 为 1.1 ± 0.5 %，这往往高于 IPCC 在潮湿气候下的默认值 0.6 %。虽然通常在施肥后和预期的最佳土壤水分条件下观察到最大的 N2O 排放，但明显的 N2O 排放峰值也发生在夏季较长的干旱期，并且可以作为降水和先前放牧活动的函数进行参数化。此外，N2O 排放峰值发生在低温的寒冷季节，应在未来的研究中予以考虑。 总体而言，我们建议在牧场条件下进行 EC 测量，随后通过随机森林进行通量划分，适用于量化不同来源的牧场 N2O 排放。