Feigenwinter Iris, Hörtnagl Lukas, Buchmann Nina
Department of Environmental Systems Science, Institute of Agricultural Sciences, ETH Zurich, Universitätstrasse 2, 8092 Zurich, Switzerland.
Department of Environmental Systems Science, Institute of Agricultural Sciences, ETH Zurich, Universitätstrasse 2, 8092 Zurich, Switzerland.
Sci Total Environ. 2023 Dec 10;903:166389. doi: 10.1016/j.scitotenv.2023.166389. Epub 2023 Aug 23.
Agriculture is the main contributor to anthropogenic nitrous oxide (NO) and methane (CH) emissions. Therefore, mitigation options are urgently needed. In contrast to carbon dioxide, eddy covariance measurements of NO and CH fluxes are still scarce, and thus little is known how environmental and biotic drivers as well as management affect the net NO and CH exchange in grasslands. Thus, we investigated the most important drivers of net ecosystem NO and CH fluxes in a temperate grassland, and continued a NO mitigation experiment (increased clover proportion vs. fertilization with slurry). Random forest gap-filling models were able to capture intermittent emission peaks, performing better for half-hourly NO than for CH fluxes. The unfertilized clover parcel (parcel B) continued to show lower NO emissions (4.4 and 2.7 kg NO-N ha yr) compared to the fertilized parcel (parcel A; 6.9 and 5.9 kg NO-N ha yr) for 2019 and 2020, respectively. Tier 1 nitrogen (N) emission factors of 2.6 % and 1.9 % were observed at the fertilized parcel during the study period. Lower soil N concentrations indicated a lower N leaching risk at the clover than at the fertilized parcel. Annual CH emissions (including periods with sheep grazing) were similar from both parcels, and ranged from 25 to 38.5 kg CH-C ha. The most important drivers of both NO and CH fluxes were lagged precipitation and water filled pore space, but also management (for NO from parcel B; CH from parcel A). Biotic variables such as vegetation height and leaf area index were important predictors for the NO exchange, while grazing temporarily increased CH emissions. Overall, reducing N fertilization and increasing the legume proportion were effective NO reduction measures. In particular, adjusting N fertilization to plant N demands can help to avoid high NO emissions from grasslands.
农业是人为一氧化二氮（N₂O）和甲烷（CH₄）排放的主要来源。因此，迫切需要采取减排措施。与二氧化碳不同，N₂O和CH₄通量的涡度协方差测量仍然很少，因此对于环境和生物驱动因素以及管理如何影响草地中N₂O和CH₄的净交换知之甚少。因此，我们研究了温带草地生态系统N₂O和CH₄通量的最重要驱动因素，并继续进行了一项N₂O减排实验（增加三叶草比例与施用粪肥）。随机森林填补模型能够捕捉间歇性排放峰值，对半小时N₂O通量的表现比对CH₄通量更好。与施肥地块（地块A）相比，未施肥的三叶草地块（地块B）在2019年和2020年的N₂O排放量持续较低，分别为4.4和2.7千克N₂O-N/公顷·年，而施肥地块（地块A）分别为6.9和5.9千克N₂O-N/公顷·年。在研究期间，施肥地块的一级氮（N）排放因子为2.6%和1.9%。较低的土壤N浓度表明三叶草地块的N淋溶风险低于施肥地块。两个地块的年度CH₄排放量（包括绵羊放牧期）相似，范围为25至38.5千克CH₄-C/公顷。N₂O和CH₄通量的最重要驱动因素是滞后降水和土壤孔隙含水量，但管理措施（地块B的N₂O；地块A的CH₄）也有影响。植被高度和叶面积指数等生物变量是N₂O交换的重要预测因子，而放牧会暂时增加CH₄排放量。总体而言，减少氮肥施用和增加豆科植物比例是有效的N₂O减排措施。特别是，根据植物的N需求调整氮肥施用有助于避免草地的高N₂O排放。
