Calculations of gaseous and particulate emissions from German agriculture 1990–2020 : report on methods and data (RMD) submission 2022

The report at hand (including a comprehensive annex of data) serves as additional document to the National In-ventory Report (NIR) on the German green house gas emissions and the Informative Inventory Report (IIR) on the German emissions of air pollutants (especially ammo-nia). The report documents the calculation methods used in the German agricultural inventory model Py-GAS-EM as well as input data, emission results and uncertainties of the emission reporting submission 2022 for the years 1990 - 2020. In this context the sector Agriculture comprises the emissions from animal husbandry, the use of agricultural soils and anaerobic digestion of energy crops. As required by the guidelines, emissions from activities preceding ag-riculture, from the use of energy and from land use change are reported elsewhere in the national invento-ries. The calculation methods are based in principle on the international guidelines for emission reporting and have been continuingly improved during the past years by the Thünen Institute working group on agricultural emission inventories, partly in cooperation with KTBL. In particular, these improvements concern the calculation of energy requirements, feeding and the N balance of the most im-portant animal categories. In addition, technical measures such as air scrubbing (mitigation of ammonia emissions) and digestion of animal manures (mitigation of emissions of methane and laughing gas) have been taken into account. For the calculation of emissions from anaerobic digestion of animal manures and energy crops (including spreading of the digestate), the aforemen-tioned working group developed, in cooperation with KTBL, a national methodology. Total GHG emissions from German agriculture de-creased from 70.6 Tg CO2eq in 1990 to 56.1 Tg CO2eq in 2020 (-20.5 %). This reduction is a consequence of the fol-lowing emission changes of partial sources (rounded fig-ures): • decrease of 9.3 Tg CO2eq (-28.0 %) as CH4 from enteric fermentation, • decrease of 2.1 Tg CO2eq (-18.1 %) as CH4 and N2O from manure management, • increase of 1.6 Tg CO2eq as CH4 and N2O from anaer-obic digestion of energy crops (digester + storage of digestate; 1990: 0 Tg), • decrease of 4.1 Tg CO2eq (18.0 %) as N2O from agri-cultural soils, • decrease of 0.56 Tg CO2eq (-20.6 %) as CO2 from lim-ing (agriculture and forest), • increase of 0.02 Tg CO2eq (+5.1 %) as CO2 from appli-cation of urea. These changes are largely the result of the decline in animal numbers following reunification (reduction of oversized livestock numbers in Eastern Germany) and from the mid-2000s due to the limiting effect of the milk quota system (albeit with a renewed increase due to abolition of the milk quota system as of 31 May 2015). Increased nitrogen fertilization (mainly due to the appli-cation of increasingly larger amounts of digestate) led to an increase in greenhouse gas emissions from the mid-2000s. By contrast, the increasing use of manure in biogas plants has contributed to a reduction in methane emis-sions from manure storage. The NH3 time series as well is a result of counteracting processes. Here too, one of the important governing quantities is the animal number the decrease of which after the German reunification is the main reason for the considerable decrease of the emissions from 1991 to 1992. Mitigation measures like emission-reduced stor-age and application of manure led to a reduction of emis-sions in subsequent years. However, opposite trends are caused by increase of animal performance and, for some years, animal numbers. In addition, emissions from appli-cation of synthetic fertilizer were higher than in 1990 in the years between 1998 and 2017, even though the amount of synthetic fertilizer applied decreased (in units of nitrogen). The observed increase of emissions was due to the increasing share of urea, as urea has a considerably higher emission factor than other synthetic fertilizers. Since 2020, urea fertilizers must either be incorporated within four hours or be stabilized with a urease inhibitor, which is why the emission factor has been greatly re-duced from this year onwards. A major contributor to the increase in NH3 emissions in recent years has been the increase in anaerobic diges-tion of energy crops. Including anaerobic digestion of en-ergy crops (including spreading of digestates) leads 2020 to total NH3 emissions from agriculture of 512.3 Gg, which is 25.5 % less than 1990 and 8.6% less than 2005.