Peatlands lose their valuable carbon (C) sink function under intensive land use and turn into greenhouse gas (GHG) emission hotspots. Despite scarce empirical evidence, paludiculture is expected to have significant GHG mitigation potential for organic soils. This study provides the first comprehensive dataset on full GHG balances for newly established fen paludicultures over a water table (WT) gradient spanning an annual mean WT of -0.29 to +0.04 m, stratified into moderately rewetted conditions (-0.30 < WT < -0.10 m) and rewetted conditions (WT ≥ -0.10 m). We used manual and novel automated chambers to measure annual carbon dioxide (CO2), methane, and nitrous oxide emissions from five typical fen plant species (Carex acutiformis, Phalaris arundinacea, Phragmites australis, Typha angustifolia, and Typha latifolia) newly established as peatland biomass crops in three temperate fen peatlands in southern Germany. Our study confirms a significant GHG mitigation potential for the tested plant species and found a C sink function of paludiculture. The results yield preliminary emission factors of -0.1 and -12.0 t CO2-equivalents ha-1 year-1 under moderately rewetted conditions (n = 39) and under rewetted conditions (n = 43), respectively. We further identify an optimal annual mean WT of -0.07 m for maximizing GHG reduction across all plant species and sites with a net C sink achieved at a mean annual WT of ≥ -0.12 m. Presuming the conversion of arable land into paludiculture, a mitigation potential of up to -51.9 t CO2-equivalents is attainable per hectare and year. These findings highlight that well-managed paludiculture could make a considerable contribution toward achieving the politically targeted CO2 sink function in the LULUCF sector.

In Germany, emissions from drained organic soils contributed approximately 53.7 Mio. t of carbon dioxide equivalents (CO2-eq) to the total national greenhouse gas (GHG) emissions in 2021. In addition to restoration measures, shifting management practices, rewetting, or using peatlands for paludiculture is expected to significantly reduce GHG emissions. The effects of climate change on these mitigation measures remains to be tested. In a 2017 experimental field study on agriculturally used grassland on organic soil, we assessed the effects of rewetting and of predicted climate warming on intensive grassland and on extensively managed sedge grassland (transplanted Carex acutiformis monoliths). The testing conditions of the two grassland types included drained versus rewetted conditions (annual mean water table of − 0.13 m below soil surface), ambient versus warming conditions (annual mean air temperature increase of + 0.8 to 1.3 °C; use of open top chambers), and the combination of rewetting and warming. We measured net ecosystem exchange of CO2, methane and nitrous oxide using the closed dynamic and static chamber method. Here, we report the results on the initial year of GHG measurements after transplanting adult Carex soil monoliths, including the controlled increase in water level and temperature. We observed higher N2O emissions than anticipated in all treatments. This was especially unexpected for the rewetted intensive grasslands and the Carex treatments, but largely attributable to the onset of rewetting coinciding with freeze–thaw cycles. However, this does not affect the overall outcomes on mitigation and adaptation trends. We found that warmer conditions increased total GHG emissions of the drained intensive grassland system from 48.4 to 66.9 t CO2-eq ha−1 year−1. The shift in grassland management towards Carex paludiculture resulted in the largest GHG reduction, producing a net cooling effect with an uptake of 11.1 t CO2-eq ha−1 year−1. Surprisingly, we found that this strong sink could be maintained under the simulated warming conditions ensuing an emission reduction potential of − 80 t CO2-eq ha−1 year−1. We emphasize that the results reflect a single initial measurement year and do not imply the permanence of the observed GHG sink function over time. Our findings affirm that rewetted peatlands with adapted plant species could sustain GHG mitigation and potentially promote ecosystem resilience, even under climate warming. In a warmer world, adaptation measures for organic soils should therefore include a change in management towards paludiculture. Multi-year studies are needed to support the findings of our one-year experiment. In general, the timing of rewetting should be considered carefully in mitigation measures.

Rewetting of peatland is commonly accepted as a useful measure for counteracting climate change. To increase the acceptance, an agricultural use of fen plants is needed. In this study, the optimal harvest date of Typha latifolia, Typha angustifolia and Phalaris arundinacea regarding their biogas potential and biogas yield per hectare was identified. Furthermore, the influence of the chemical composition of Typha spp. and P. arundinacea on the biogas and biochemical methane potential was determined. Finally, the predictability of the biochemical methane potential (BMP) of Typha spp. and P. arundinacea by their composition with published regression models was examined. The three fen plant species were harvested on five different dates in 2018 and/or 2020. For each harvest, the biomass yield, biogas potential and BMP were determined, the chemical composition of the biomass was analyzed, and the biogas yield per hectare was calculated. The biogas potential of T. latifolia, T. angustifolia and P. arundinacea decreased with increasing plant maturity and ranged between 315 and 647 LN kg−1 VS, 405 and 596 LN kg−1 VS and 361 and 597 LN kg−1 VS, respectively. The biogas and BMP of all three plant species investigated were negatively correlated with the lignin content and could be predicted with published regression models, which included the lignin content as main regressor. The derived optimal harvest dates, which were a compromise between biomass yield and biogas potential, for all three fen plants ranged between the development stages of full flowering and shortly after the seed heads turned brown.

In the face of climate warming the accurate determination of greenhouse gas (GHG) fluxes from ecosystems is of crucial importance for the assessment and development of successful mitigation measures. Several different GHG measurement systems are already on the market. Micro metrological approaches (e.g. eddy covariance) operate with high frequency measurements to achieve a high temporal resolution without influencing the ecosystem. Manual chambers are well suited for capturing spatial heterogeneity or for conducting small-scale experiments. To overcome the low temporal resolution when using manual chambers, several commercial or self-made automatic chamber systems exist. As far as we know, up to date there are only two robotic chamber systems that are suitable for virtually undisturbed measurements of GHG on ecosystem scale: one at the Leibniz Center for Agricultural Landscape Research (ZALF) and one at the Karlsruhe Institute of Technology (IMK-IFU). However, to meet the challenge for accurate measurements in ecosystems with tall growing vegetation (up to 2 m height), we developed a new modular robotic chamber system. Opaque and transparent chambers on rails allow for alternating measurements of net ecosystem CO2 exchange (NEE), ecosystem respiration (RECO), CH4 and N2O measurements on up to 36 experimental plots (each 1 m²) distributed over an area of 16 x 30 m. The system is equipped with four infrared gas analyzers (LI-840, LICOR Biosciences, USA) for the detection of CO2 and H2O concentrations and one cavity ring-down spectroscopy (CRDS) instrument to measure N2O, CH4 and H2O concentrations (G2308, Picarro, USA). We installed the system in a small-scale paludiculture experiment with three different water levels and four different plant species. Depending on the time of year and magnitude of the flux rate, a maximum of 920 CO2 or 108 CH4/N2O measurements are achievable per measuring day at our test site. Ancillary measurements of chamber temperature and photosynthetic active radiation (PAR) as well as outside air pressure, PAR and wind speed are additionally recorded in 1-second intervals. All data are transferred to a database on a network server via a cellular communication system. We will give insights into the new automatic chamber system, discuss advantages and challenges. We will further share our experiences from a two-year measurement period and give an overview of some first results from GHG fluxes. The development of the system was funded within the MOORuse-project by the European Union (European Regional Development Fund) and the Bavarian State Ministry of the Environment and Consumer Protection [funding code: 64b-U8639.1-2015/8-14].

Pure, blended and additivated biomass pellets from four fen paludicultures were produced at TFZ and combusted in two small-scale biomass boilers (15 kW, 30 kW). Feedstocks derived from straw of Typha ssp., Phragmites australis, Phalaris arundinacea and Carex ssp. that were harvested during winter 2018, 2019 (used for pelletization) and 2020. Additivation of fuels with kaolin before pelletization or blending of fuels with ENplus wood pellets (A1 quality) after pelletization were applied. Straw and pellets were analyzed for physical and chemical fuel properties according to international standards for solid biofuels. Physical properties of pellets met the requirements of ISO 17225-6. Chemical properties of Typha indicated high TPM emissions due to high contents of K and Na in fuels while severe slagging was predicted for the other species by a high molar (Si + K + Al)/(Ca + Mg + P) ratio. During combustion in both boilers, CO and total particulate matter (TPM) emissions were high for Typha but slightly reduced by additivation with 2.3% kaolin. Blending of fuels significantly reduced NOX, SOX and HCl emissions due to lower N, S and Cl concentrations. Slagging was high for pure and additivated pellets of Phragmites, Phalaris and Carex with > 50% of total ash consisting of particles > 2 mm. No steady-state boiler operation could be achieved with either pure or additivated fuels. In conclusion, paludiculture pellets are challenging fuels for small-scale combustion plants. Their use cannot be recommended for the tested boilers. Technical solutions may be easier applied in medium sized combustions plants above 100 kW.

The concept of paludicultures is growing in importance as a promising sustainable alternative to current agricultural use of organic soils. Besides agricultural and economic viability, quantifying the climatic effects of paludicultures is essential to give reliable policy advice and facilitate sustainable management decisions with regard to climate change. Emission factors (EFs) of the relevant greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) for a variety of potential paludiculture plants are still rare, especially from comparable treatment and site conditions. In 2016, different temperate fen plant species (Carex acutiformis, Phragmites australis, Phalaris arundinacea, Typha latifolia) were established as paludicultures at a former grassland on fen peatland in the Freisinger Moos within the scope of the MOORuse-project. Three years after plant establishment, we measured fluxes of CO2, CH4 and N2O to obtain a one-year budget (2019) using manual closed chambers. Besides gas flux measurements we observed vegetation parameters and biomass development including a winter harvest. In 2019, the annual mean water level in these four plant treatments were between 5 to 10 cm below surface. We are currently analysing the data and will give an overview of the complete GHG balances and resulting global warming potentials of the four paludiculture plants. With these values we start to fill an important gap of knowledge for assessing the climate protection potential of paludicultures. The MOORuse-project is funded by the European Union (European Regional Development Fund) and the Bavarian State Ministry of the Environment and Consumer Protection [funding code: 64b-U8639.1-2015/8-14].

Fen plants cultivated on wet peatlands might be an environmentally friendly alternative biogas substrate to maize and grass grown on drained peatlands. This study demonstrates that if Typha latifolia, Phragmites australis, and Phalaris arundinacea were harvested in mid-June, then their specific biogas yields (SBY) reached values of up to 581 L-N kg(-1) volatile solids (VS), which is similar to the SBY of grass, but lower than the SBY, of 670 L-N kg(-1) VS, for maize. Mixtures with equal or more than 10% T. latifolia or 40% P. arundinacea (VS-base) exhibited a reduced SBY compared to 100% maize silage in a batch-test. From the composition of the substrates, it remains unclear why fen plants degraded that poorly. However, during the semi-continuous long-term experiment, this effect led to an accumulation of non-degraded material, which destabilized the degradation process at loading rates above 3 kg VS m(-3) d(-1). Destabilization became apparent with substantial increases in the viscosity of the fermenter content, enrichment of acids and a worsened methane formation. Our findings suggest that only small proportions of maize could be replaced by fen plants as substrate for biogas plants. (C) 2020 Elsevier Ltd. All rights reserved.

Drained organic soils are large sources of anthropogenic greenhouse gases (GHG) in many European and Asian countries. Therefore, these soils urgently need to be considered and adequately accounted for when attempting to decrease emissions from the Agriculture and Land Use, Land Use Change and Forestry (LULUCF) sectors. Here, we describe the methodology, data and results of the German approach for measurement, reporting and verification (MRV) of anthropogenic GHG emissions from drained organic soils and outline ways forward towards tracking drainage and rewetting. The methodology was developed for and is currently applied in the German GHG inventory under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol. Spatial activity data comprise high resolution maps of land-use, type of organic soil and mean annual water table (WT). The WT map was derived by a boosted regression trees model from data of more than 1000 dipwells. Emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) were synthesized from a unique national data set comprising more than 250 annual GHG balances from 118 sites in most land-use categories and types of organic soils. Measurements were performed with harmonized protocols using manual chambers. Non-linear response functions describe the dependency of CO2 and CH4 fluxes on mean annual WT, stratified by land-use where appropriate. Modelling results were aggregated into “implied emission factors” for each land-use category, taking into account the uncertainty of the response functions, the frequency distribution of the WT within each land-use category and further GHG sources such as dissolved organic carbon or CH4 emissions from ditches. IPCC default emission factors were used for these minor GHG sources. In future, response functions could be applied directly when appropriate WT data is available. As no functional relationship was found for N2O emissions, emission factors were calculated as the mean observed flux per land-use category. In Germany, drained organic soils emit more than 55 million tons of GHGs per year, of which 91% are CO2. This is equivalent to around 6.6% of the national GHG emissions in 2014. Thus, they are the largest GHG source from agriculture and LULUCF. The described methodology is applicable on the project scale as well as in other countries where similar data are collected.

Vegetation indices are widely used as model inputs and for non-destructive estimation of biomass and photosynthesis, but there have been few validation studies of the underlying relationships. To test their applicability on temperate fens and the impact of management intensity, we investigated the relationships between normalized difference vegetation index (NDVI), leaf area index (LAI), brown and green above-ground biomass and photosynthesis potential (PP). Only the linear relationship between NDVI and PP was management independent (R-2=053). LAI to PP was described by a site-specific and negative logarithmic function (R-2=007-068). The hyperbolic relationship of LAI versus NDVI showed a high residual standard error (s.e.) of 171-184 and differed between extensive and intensive meadows. Biomass and LAI correlated poorly (R-2=030), with high species-specific variability. Intensive meadows had a higher ratio of LAI to biomass than extensive grasslands. The fraction of green to total biomass versus NDVI showed considerable noise (s.e.=013). These relationships were relatively weak compared with results from other ecosystems. A likely explanation could be the high amount of standing litter, which was unevenly distributed within the vegetation canopy depending on the season and on the timing of cutting events. Our results show there is high uncertainty in the application of the relationships on temperate fen meadows. For reliable estimations, management intensity needs to be taken into account and several direct measurements throughout the year are required for site-specific correction of the relationships, especially under extensive management. Using NDVI instead of LAI could reduce uncertainty in photosynthesis models.

Entwasserte organische Boden sind in vielen Landern, darunter auch in Deutschland, eine starke Quelle anthropogener Treibhausgase (THG). Daher mussen sie bei der Berichterstattung gemas UNFCCC und Kyoto-Protokoll angemessen berucksichtigt werden. Hier beschreiben wir die Methodik, Daten und Ergebnisse der deutschen detaillierten Tier-3-Methodik zur Berichterstattung anthropogener Treibhausgasemissionen aus entwasserten organischen Boden, die fur das deutsche Treibhausgasinventar entwickelt und angewandt wurden. Der Ansatz basiert auf nationalen Daten und bietet das Potenzial, Anderungen der Landnutzung und des Wassermanagements zu verfolgen, falls Zeitreihen zu relevanten Aktivitatsdaten vorliegen. Die Aktivitatsdaten umfassen hochauflosende Karten zu Klima, Landnutzung, organischen Boden und vom mittleren jahrlichen Grundwasserflurabstand. Die Grundwasserkarte wurde durch ein statistisches Modell aus Daten von > 1000 Standorten abgeleitet. Die THG-Emissionen beruhen auf einem einzigartigen Datensatz mit mehr als 200 THG-Bilanzen fur fast alle Kombinationen von Landnutzungskategorien und Typen organischer Boden. Die Messungen wurden mit vollstandig harmonisierten Protokollen durchgefuhrt. Nicht-lineare Funktionen beschreiben die Abhangigkeit der Kohlendioxid- und Methan-Flusse vom mittleren jahrlichen Grundwasserstand und, wenn erforderlich, von der Landnutzung. Die daraus resultierenden angewandten fur jede Landnutzungskategorie berucksichtigen sowohl die Unsicherheit der nicht-linearen Funktionen als auch die Verteilung der Grundwasserstande in jeder Landnutzungskategorie. Da keine einfachen funktionellen Zusammenhange fur die Lachgasemissionen gefunden wurden, wurden die entsprechenden Emissionsfaktoren daher als Mittelwerte der Messwerte jeder Landnutzungskategorie berechnet. Fur kleinere THG-Quellen wie Methanemissionen aus Graben und Austrage von gelostem organischem Kohlenstoff wurden IPCC-Standard-Emissionsfaktoren verwendet.

A change in the European Union energy policy has markedly promoted the expansion of biogas production. Consequently, large amounts of nutrient-rich residues are being used as organic fertilizers. In this study, a pot experiment was conducted to simulate the high-risk situation of enhanced greenhouse gas (GHG) emissions following organic fertilizer application in energy maize cultivation. We hypothesized that cattle slurry application enhanced CO2 and N2O fluxes compared to biogas digestate because of the overall higher carbon (C) and nitrogen (N) input, and that higher levels of CO2 and N2O emissions could be expected by increasing soil organic C (SOC) and N contents. Biogas digestate and cattle slurry, at a rate of 150 kg NH4+ ha(-1), were incorporated into 3 soil types with low, medium, and high SOC contents (Cambisol, Mollie Gleysol, and Sapric Histosol, termed C-low, C-medium, and C-high, respectively). The GHG exchange (CO2, CH4, and N2O) was measured on 5 replicates over a period of 22 d using the closed chamber technique. The application of cattle slurry resulted in significantly higher CO2 and N2O fluxes compared to the application of biogas digestate. No differences were observed in CH4 exchange, which was close to zero for all treatments. Significantly higher CO2 emissions were observed in C-high compared to the other two soil types, whereas the highest N2O emissions were observed in C-medium. Thus, the results demonstrate the importance of soil type-adapted fertilization with respect to changing soil physical and environmental conditions.

Drainage has turned peatlands from a carbon sink into one of the world's largest greenhouse gas (GHG) sources from cultivated soils. We analyzed a unique data set (12 peatlands, 48 sites and 122 annual budgets) of mainly unpublished GHG emissions from grasslands on bog and fen peat as well as other soils rich in soil organic carbon (SOC) in Germany. Emissions and environmental variables were measured with identical methods. Site-averaged GHG budgets were surprisingly variable (29.2 ± 17.4 t CO2 -eq. ha-1  yr-1 ) and partially higher than all published data and the IPCC default emission factors for GHG inventories. Generally, CO2 (27.7 ± 17.3 t CO2  ha-1  yr-1 ) dominated the GHG budget. Nitrous oxide (2.3 ± 2.4 kg N2 O-N ha-1  yr-1 ) and methane emissions (30.8 ± 69.8 kg CH4 -C ha-1  yr-1 ) were lower than expected except for CH4 emissions from nutrient-poor acidic sites. At single peatlands, CO2 emissions clearly increased with deeper mean water table depth (WTD), but there was no general dependency of CO2 on WTD for the complete data set. Thus, regionalization of CO2 emissions by WTD only will remain uncertain. WTD dynamics explained some of the differences between peatlands as sites which became very dry during summer showed lower emissions. We introduced the aerated nitrogen stock (Nair ) as a variable combining soil nitrogen stocks with WTD. CO2 increased with Nair across peatlands. Soils with comparatively low SOC concentrations showed as high CO2 emissions as true peat soils because Nair was similar. N2 O emissions were controlled by the WTD dynamics and the nitrogen content of the topsoil. CH4 emissions can be well described by WTD and ponding duration during summer. Our results can help both to improve GHG emission reporting and to prioritize and plan emission reduction measures for peat and similar soils at different scales.

Drained organic soils are considered to be hotspots for greenhouse gas (GHG) emissions. Arable lands and intensively used grasslands, in particular, have been regarded as the main producers of carbon dioxide (CO2) and nitrous oxide (N2O). However, GHG balances of former peatlands and associated organic soils not considered to be peatland according to the definition of the Intergovernmental Panel on Climate Change (IPCC) have not been investigated so far. Therefore, our study addressed the question to what extent the soil organic carbon (SOC) content affects the GHG release of drained organic soils under two different land-use types (arable land and intensively used grassland). Both land-use types were established on a Mollic Gleysol (labeled Cmedium) as well as on a Sapric Histosol (labeled Chigh). The two soil types differed significantly in their SOC contents in the topsoil (Cmedium: 9.4–10.9 % SOC; Chigh: 16.1–17.2 % SOC). We determined GHG fluxes over a period of 1 or 2 years in case of N2O or methane (CH4) and CO2, respectively. The daily and annual net ecosystem exchange (NEE) of CO2 was determined by measuring NEE and the ecosystem respiration (RECO) with the closed dynamic chamber technique and by modeling the RECO and the gross primary production (GPP). N2O and CH4 were measured with the static closed chamber technique. Estimated NEE of CO2 differed significantly between the two land-use types, with lower NEE values (−6 to 1707 g CO2-C m−2 yr−1) at the arable sites and higher values (1354 to 1823 g CO2-C m−2 yr−1) at the grassland sites. No effect on NEE was found regarding the SOC content. Significantly higher annual N2O exchange rates were observed at the arable sites (0.23–0.86 g N m−2 yr−1) than at the grassland sites (0.12–0.31 g N m−2 yr−1). Furthermore, N2O fluxes from the Chigh sites significantly exceeded those of the Cmedium sites. CH4 fluxes were found to be close to zero at all plots. Estimated global warming potential, calculated for a time horizon of 100 years (GWP100) revealed a very high release of GHGs from all plots ranging from 1837 to 7095 g CO2 eq. m−2 yr−1. Calculated global warming potential (GWP) values did not differ between soil types and partly exceeded the IPCC default emission factors of the Tier 1 approach by far. However, despite being subject to high uncertainties, the results clearly highlight the importance of adjusting the IPCC guidelines for organic soils not falling under the definition in order to avoid a significant underestimation of GHG emissions in the corresponding sectors of the national climate reporting. Furthermore, the present results revealed that mainly the type of land-use, including the management type, and not the SOC content is responsible for the height of GHG exchange from intensive farming on drained organic soils.

Abstract. The carbon dioxide (CO2) exchange of five different peatland systems across Europe with a wide gradient in land use intensity, water table depth, soil fertility and climate was simulated with the process oriented CoupModel. The aim of the study was to find out whether CO2 fluxes, measured at different sites, can be explained by common processes and parameters or to what extend a site specific configuration is needed. The model was calibrated to fit measured CO2 fluxes, soil temperature, snow depth and leaf area index (LAI) and resulting differences in model parameters were analyzed. Finding site independent model parameters would mean that differences in the measured fluxes could be explained solely by model input data: water table, meteorological data, management and soil inventory data. Seasonal variability in the major fluxes was well captured, when a site independent configuration was utilized for most of the parameters. Parameters that differed between sites included the rate of soil organic decomposition, photosynthetic efficiency, and regulation of the mobile carbon (C) pool from senescence to shooting in the next year. The largest difference between sites was the rate coefficient for heterotrophic respiration. Setting it to a common value would lead to underestimation of mean total respiration by a factor of 2.8 up to an overestimation by a factor of 4. Despite testing a wide range of different responses to soil water and temperature, rate coefficients for heterotrophic respiration were consistently the lowest on formerly drained sites and the highest on the managed sites. Substrate decomposability, pH and vegetation characteristics are possible explanations for the differences in decomposition rates. Specific parameter values for the timing of plant shooting and senescence, the photosynthesis response to temperature, litter fall and plant respiration rates, leaf morphology and allocation fractions of new assimilates, were not needed, even though the gradient in site latitude ranged from 48° N (southern Germany) to 68° N (northern Finland) differed largely in their vegetation. This was also true for common parameters defining the moisture and temperature response for decomposition, leading to the conclusion that a site specific interpretation of these processes is not necessary. In contrast, the rate of soil organic decomposition, photosynthetic efficiency, and the regulation of the mobile carbon pool need to be estimated from available information on specific soil conditions, vegetation and management of the ecosystems, to be able to describe CO2 fluxes under different conditions.

Black alder (Alnus glutinosa (L.) Gaertn.) forests on peat soils have been reported to be hotspots for high nitrous oxide (N2O) losses. High emissions may be attributed to alternating water tables of peatlands and to the incorporation of high amounts of easily decomposable nitrogen (N) into the ecosystem by symbiotic dinitrogen (N2)-fixation of alder trees. Our study addressed the question to what extent drainage enhances the emissions of N2O from black alder forests and how N turnover processes and physical factors influence the production of N2O and total denitrification. The study was conducted in a drained black alder forest with variable groundwater tables at a southern German fen peatland. Fluxes of N2O were measured using the closed chamber method at two drained sites (D-1 and D-2) and one undrained site (U). Inorganic N contents and net N mineralization rates (NNM) were determined. Additionally a laboratory incubation experiment was carried out to investigate greenhouse gas and N2 fluxes at different temperature and soil moisture conditions. Significantly different inorganic N contents and NNM rates were observed, which however did not result in significantly different N2O fluxes in the field but did in the laboratory experiment. N2O fluxes measured were low for all sites, with total annual emissions of 0.51 ± 0.07 (U), 0.97 ± 0.13 (D-1) and 0.93 ± 0.08 kg N2O–N ha−1 yr−1 (D-2). Only 37% of the spatiotemporal variation in field N2O fluxes could be explained by peat temperature and groundwater level, demonstrating the complex interlinking of the controlling factors for N2O emissions. However, temperature was one of the key variables of N2O fluxes in the incubation experiment conducted. Increasing soil moisture content was found to enhance total denitrification losses during the incubation experiment, whereas N2O fluxes remained constant. At the undrained site, permanently high groundwater level was found to prevent net nitrification, resulting in a limitation of available nitrate (NO3−) and negligible gaseous N losses. N2O flux rates that were up to four times higher were measured in the incubation experiment. They reveal the potential of high N2O losses under changing soil physical conditions at the drained alder sites. The high net nitrification rates observed and high NO3− contents bear the risk of considerable NO3− leaching at the drained sites.

18 The change in the German energy policy has resulted in a strong increase in the 19 number of biogas plants in Germany. As a consequence, huge amounts of nutrient 20 rich residues, the by-products of the fermentative process, are used as organic 21 fertilizers. Drained peatlands are increasingly used to satisfy the huge demand for 22 fermentative substrates (e.g. energy-crops, grass silage) and the digestate is 23 returned to the peatlands. However, drained organic soils are considered as hot 24 spots for nitrous oxide (N2O) emissions and organic fertilization is additionally known 25 to increase N2O emissions from managed grasslands. Our study addressed the 26 questions a) to what extent biogas digestate and cattle slurry application increase 27 N2O and methane (CH4) fluxes as well as the mineral nitrogen use efficiency (NUEmin) 28 and grass yield, and b) how different soil organic matter contents (SOM) and nitrogen 29 (N) contents promote the production of N2O. In addition NH3 volatilization was 30 determined at one application event to obtain first clues with respect to the effects of 31 soil and fertilizer types. The study was conducted at two sites within a grassland 32 parcel, which differed in their soil organic carbon (SOC) and N contents. At each site 33 (named Corg-medium and Corg-high) three plots were established, one was fertilized 34 five times with biogas digestate, one with cattle slurry and the third served as control 35 plot. On each plot, fluxes of N2O and CH4 were measured on three replicates over 36 two years using the closed chamber method. For NH3 measurements we used the 37 calibrated dynamic chamber method. On an annual basis, the application of biogas 38 digestate significantly enhanced the N2O fluxes compared to the application of cattle 39 slurry and additionally increased the plant N-uptake and NUEmin. Furthermore, N2O 40 fluxes from the Corg-high site significantly exceeded N2O fluxes from the Corg-medium 41 sites. Annual cumulative emissions ranged from 0.91 ± 0.49 kg N ha yr to 3.14 ± 42 0.91 kg N ha yr. Significantly different CH4 fluxes between the investigated 43 treatments or the different soil types were not observed. Cumulative annual CH4 44 exchange rates varied between −0.21 ± 0.19 kg C ha yr and −1.06 ± 0.46 kg C 45 ha yr. Significantly higher NH3 losses, NUEmin and grass yields from treatments 46 fertilized with biogas digestate compared to those fertilized with cattle slurry were 47 observed. The total NH3 losses following the splash plate application were 18.17 kg 48 N ha for the digestate treatments and 3.48 kg N ha for the slurry treatments (36% 49 and 15% of applied NH4 -N). The observed linear increase of 16 days cumulative 50 N2O-N exchange or rather annual N2O emissions, with mean groundwater level and 51 ammonium application rate, reveal the importance of site adapted N fertilization and 52 the avoidance of N surpluses in Corg rich grasslands. 53