Nitrification inhibitors have been proposed as a tool to mitigate nitrous oxide (N2O) emissions from agriculture, which are caused mainly by fertilization. The nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) was tested in a winter rapeseed field after dairy slurry application in Central Estonia. N2O emissions were monitored using the closed chamber method. Soil and leachate chemical parameters were also analyzed. N2O emissions increased from pre-slurry application values of 316 and 264 µg m−2 h−1 for the control and treatment plot, respectively, to maximum values of 3130.71 and 4834 µg m−2 h−1, with cumulative emissions during the study period of 12.30 kg ha−1 for the control plot and 17.70 kg ha−1 for the treatment plot. The intense precipitation period that began with the application of the slurry resulted in changes in soil moisture and water-filled pore space (WFPS), modifying the nitrification/denitrification balance. Positive significant correlations (p = 0.016 and p = 0.037, for the control and treatment plot, respectively) were found between N2O fluxes and WFPS. Future studies should consider the role of nitrifier and denitrifier communities in order to better assess in-field nitrification inhibitor effectiveness.

<p>In the terrestrial biosphere, peatlands represent the most important long-term soil carbon storage. They cover only 3% of the land surface but are responsible for about one-third of the total. Ecosystem degradation and changes made in hydrology may affect the biogeochemistry of peatlands and, together with projected global warming, may lead to significant changes in greenhouse gas fluxes. Aeration of peatlands increases organic matter's aerobic decomposition and enhances wetlands’ change from a net carbon sink to a carbon dioxide source and low soil water content in drained histosols results in lower CH<sub>4</sub> emissions. In contrast, N<sub>2</sub>O emissions may increase due to increased mineralization and more favorable conditions for nitrification.</p><p>However, soil CH<sub>4</sub> and N<sub>2</sub>O fluxes in peatlands are spatially and temporally (interannual, seasonal) variable, and there is little detailed information on drained nutrient-rich organic soils in the hemiboreal zone. We conducted a two-year study in drained peatland forests with different tree species Scots pine<em> </em>(<em>Pinus sylvestris</em>), Norway spruce (<em>Picea abies</em><em>), </em>birch<em> </em>(<em>Betula sp</em><em>.</em>), and black alder (<em>Alnus glutinosa</em>) and with various water levels and a natural wetland (fen) as a reference site in Estonia and Latvia from January 2021 to December 2022.</p><p>CH<sub>4</sub> and N<sub>2</sub>O fluxes were measured twice per month using the manual static chamber method. Environmental parameters in soil, such as groundwater level, temperature, and moisture were monitored and stored hourly by a data logger. Detailed studies of soil physio-chemical parameters and microbial community were conducted to relate greenhouse gas fluxes with environmental conditions.</p><p>Our preliminary results for the first year showed that all drained forest soils with low groundwater levels were annual methane sinks (−48.9 ± 12.9 μg m<sup>−‍2</sup> h<sup>−‍1</sup>), whereas the reference fen studied had a higher emission potential of 396 ± 214 μg m<sup>−‍2</sup> h<sup>−‍1</sup>. In contrast, birch and alder forests with poorly drained soils consumed less CH<sub>4</sub> and were annual emitters than artificially drained sites. Methane flux had a statistically significant correlation with water level and soil temperature. Most of the sites were annual emitters of N<sub>2</sub>O; wetter forest sites were higher emitters (21.0 ± 10.49 μg m<sup>−‍2</sup> h<sup>−‍1</sup>) than drier sites (17.97 ± 4.8 μg m<sup>−‍2</sup> h<sup>−‍1</sup>). Higher N<sub>2</sub>O emissions and temporal variability were associated with sites where water levels exhibited large seasonal fluctuations. N<sub>2</sub>O flux was controlled by soil temperature and moisture content, and emission peaks occurred in spring (freeze-thaw period).</p><p>This research was supported by the LIFE programme project "Demonstration of climate change mitigation potential of nutrients rich organic soils in the Baltic States and Finland", (2019-2023, LIFE OrgBalt, LIFE18 274CCM/LV/001158).</p>

<p>Organic soils are one of the largest natural terrestrial carbon stores, especially in boreal, temperate, and tropical wet climates. In these environments, scarcity of oxygen due to soil wetness has enabled the accumulation of organic carbon deposits over the past millennia. In Europe, organic soils account for only 3% of total agricultural land. Yet, they play a significant role in meeting Europe's 2030 and 2050 climate change mitigation targets. However, drainage of these soils, as a common management practice aiming for higher agricultural productivity, transforms these carbon-rich soils into a significant GHG source.</p> <p>Water-level management practices are critical in agriculture to minimize soil degradation and nutrient leaching. Fluctuations in water levels may alter soil physical and chemical conditions and potentially cause GHG emissions. Deep draining leads to an increase in carbon dioxide (CO<sub>2</sub>) and nitrous oxide (N<sub>2</sub>O) emissions due to increased soil mineralization. On the other hand, methane (CH<sub>4</sub>) emissions are lower compared to natural wetlands where soil drainage and tillage do not occur. Land use, climate zone, soil nutrient status, fertilization, and drainage status are closely related to estimating GHG budgets from managed sites on organic soils.</p> <p>Available data on actual GHG emissions from drained and nutrient-rich organic soils under different management practices show considerable variation. Therefore our study's main objectives are: (I) to update GHG emission factors for organic soils in drained croplands and grasslands and (ii) to calculate soil carbon and nitrogen budgets applicable to the Baltic countries. A two-year study was conducted from January 2021 to December 2022 to assess the impact of drainage and land use on GHG fluxes in the Baltic countries.</p> <p>Fluxes in croplands and perennial grassland on nutrient-rich organic soils with different drainage conditions were determined by groups: (I) excessively drained croplands, (II) excessively drained grasslands, (III) moderately drained grasslands, (IV) rewetted grasslands, and (V) non-managed fens as reference sites. Measurements were done monthly (Latvia and Lithuania) or twice per month (Estonia) using the manual static dark chamber method (N<sub>2</sub>O, CH<sub>4</sub>), the dynamic transparent chamber method for net ecosystem exchange, and the dynamic dark chamber for soil heterotrophic respiration (CO<sub>2</sub>). In addition, we measured associated environmental parameters (water table level, soil moisture and temperature, and solar radiation). For biomass analyses, we took samples once in the measurement period.</p> <p>Our preliminary results show that all grasslands were annual CH<sub>4</sub> sinks, while fens soils in natural status were a source of CH<sub>4</sub>. All studied sites were N<sub>2</sub>O sources on an annual basis, and croplands were the strongest emitters, as was expected. Higher N<sub>2</sub>O emissions and temporal variability were associated with sites characterized by high groundwater levels with high seasonal fluctuations. Soil heterotrophic respiration fluxes peaked over all the study sites during the summer. As the last field campaign shortly ended, more detailed data analyses will be presented at the conference.</p> <p><em>This research was supported by the LIFE programme project "Demonstration of climate change mitigation potential of nutrients rich organic soils in Baltic States and Finland", (2019-2023, LIFE OrgBalt, LIFE18 274CCM/LV/001158).</em></p>

<p>Nutrient-rich organic soils are one of the largest key sources of greenhouse gas (GHG) emissions in cool moist climate regions in Europe, and around 15 Mha of wetlands are drained for forestry across the world's temperate and boreal areas. Drainage promotes the decomposition of the organic material stored in these naturally water-saturated organic soils, turning the wetland from a carbon sink into an emitter of CO<span xml:lang="EN-US"><span><sub>2</sub></span></span>. Lower soil water content in drained histosols leads to reduced CH<sub>4</sub> emission, while N<span xml:lang="EN-US"><span><sub>2</sub></span></span>O emission can increase due to increased mineralization and more favorable conditions for nitrification. However, detailed information of GHG emissions from drained organic soils under different land use and management in the hemiboreal zone is still scarce.  </p><p xml:lang="EN-US"><span xml:lang="EN-US">We conducted a full-year study at drained peatland sites with different land uses to assess the impact of drainage and land-use on GHG fluxes in Estonia. We investigated ten sites: (I) five forests with different tree species, (II) three grasslands with different water regimes, (III) cropland and (IV) natural wetland (fen). The GHG fluxes were measured twice per month using the manual static (CH</span><sub>4</sub> and N<sub>2</sub>O) and dynamic (heterotrophic respiration (CO<span xml:lang="EN-US"><span><sub>2</sub></span></span>)) closed chamber method from Jan 2020 to Dec 2021. Additionally, groundwater level, soil temperature and moisture were measured hourly with automatic loggers to determine soil conditions.   </p><p xml:lang="EN-US"><span xml:lang="EN-US">Our preliminary results show that all drained forest soils were annual CH<sub>4</sub> sinks (−59.4 ± 2.5 µg m</span><span xml:lang="EN-US"><span><sup>-2</sup></span></span> h<sup>-1</sup>, mean ± SE). However, CH<span xml:lang="EN-US"><span><sub>4</sub></span></span> uptake from the studied fen, crop and grasslands were lower, –13.2 ± 4.4, -12.2 ± 2.0 and -8.2 ± 3.3 µg m<span xml:lang="EN-US"><span><sup>-2</sup></span></span> h<sup>-1</sup>, respectively, while grassland with poor drainage soil was a less source of CH<sub>4 </sub><span xml:lang="EN-US">emission. Most of the sites were annual emitters of N</span><sub>2</sub>O; forest sites were higher emitters (15.9 ± 2.3 µg m<sup>-2</sup> h<sup>-1</sup>) than cropland (12.7 ± 4.1 µg m<span xml:lang="EN-US"><span><sup>-2</sup></span></span> h<sup>-1</sup>) and fen soils (6.3 ± 1.1 µg m<span xml:lang="EN-US"><span><sup>-2</sup></span></span> h<sup>-1</sup>). N<sub>2</sub>O fluxes from grasslands depend on drainage intensity and the site with poor drainage emitted less. Higher N<span xml:lang="EN-US"><span><sub>2</sub></span></span>O emissions and temporal variability were associated with sites where the water level had high seasonal fluctuations. Soil CO<sub>2</sub> fluxes (heterotrophic respiration) were highest from grasslands and peaked over all the study sites during the summer. Methane flux had a statistically significant correlation with water level and soil moisture, while N<sub>2</sub>O flux was controlled by soil temperature, having higher emissions in a warmer season. <span xml:lang="EN-US">The results provide insights into GHG fluxes over temporal and spatial scales and indicate the need for mitigation measures and further enhancement of modeling tools for climate-friendly land management practices in nutrient-rich organic soils.  </span> </p><p xml:lang="EN-US"><span xml:lang="EN-US">This research was supported by the LIFE programme project “Demonstration of climate change mitigation potential of nutrients rich organic soils in Baltic States and Finland”, (2019-2023, LIFE OrgBalt</span>, LIFE18 274CCM/LV/001158)<span> </span></p>

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