Cultivated organic soils can be a major source of GHG emissions in countries with high coverage of peat soils. Targeting mitigation measures based on mapping of cultivated organic soils would reduce these emissions and increase sustainability of agriculture. Different georeferenced datasets were combined to study the area trend and describe current agricultural use of organic soils. The area was also mapped regionally into classes based on intensity of cultivation and organic layer depth, and an example allocation of potential mitigation measures was made at the country scale. The area and proportion of cultivated organic soils have increased in Finland since 1990 but the clearance rate has decreased in recent years. More than half of the area retains a peat layer deeper than 0.6 m indicating long-lasting mitigation potential with measures capable of slowing peat decomposition. Sixty-five percent of the cultivated organic soil area was not considered a priority area for radical management changes, for various reasons, but there are 85,000 ha of field with more realistic potential for GHG mitigation. The mapping method was found to be a practical tool for depicting the GHG mitigation potential of cultivated organic soils. Significant reductions in agricultural GHG emissions can be expected with implementation of the suggested mitigation measures.
Climate policies encourage the search for greenhouse gas (GHG) mitigation options in all economic sectors and peatland rewetting is one of the most efficient mitigation measures in agriculture and land use. The benefits shown in the national GHG inventories, however, depend not only on the actual mitigation actions on the ground but also how well the effects can be reported. Currently there are no specific emission factors for reporting GHG emissions from rewetted agricultural soils as the current emission factors are aggregated for several pre-rewetting land use types. Also, rewetting can aim at either restoration or different forms of paludiculture which may differ in their GHG profile and thus demand disaggregated emission factors. We compiled the current knowledge on GHG emissions on sites where rewetting has occurred on former agricultural peatland in temperate or boreal climate zones. The recent data suggest that on average the current emission factors for rewetting nutrient-rich sites published by the Intergovernmental Panel for Climate Change (IPCC) provide a good estimate for reporting emissions from rewetting in the temperate zone. However, the total GHG balances differed widely in restoration, Sphagnum farming and production of emergent plants in paludiculture and it is evident that disaggregated emission factors will be needed to improve the accuracy of reporting the effects of mitigation measures in the GHG inventories.
<p>Greenhouse gas emissions of a spring cereal monoculture under conventional tillage and no-till treatments were measured in a peatland in Southwestern Finland for three years in 2018-2021. Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes were measured with an opaque chamber technique approximately biweekly throughout the years. During the growing season, canopy net ecosystem exchange (NEE) was measured with a transparent chamber technique and hourly ecosystem respiration (ER) and gross photosynthesis (GP) were modelled with empiric models. On average, the annual emissions were 6.4&#177;2.4 Mg CO2-C ha <sup>-1</sup> yr<sup>-1</sup>, 7.6&#177;3.5 kg N2O-N ha<sup>-1</sup> yr<sup>-1</sup>, and -0.35&#177;0.42 kg CH4-C ha<sup>-1</sup> yr<sup>-1</sup> for NEE, N2O and CH4, respectively. The effect of no-till management on the GHG balance was non-consistent through years and thus generally of minor significance. No-till reduced annual CO2 emissions by 24% in 2019 and N2O emissions by 33% in 2020 compared to conventional tillage while there were no differences in other years. Measured differences in ER occurred mostly during the winter periods, especially after ploughing. The results indicated that no-till may reduce CO2 and N2O emissions from cultivated peat soil, but it does not lead to large consistent reductions during the first years of NT management.</p>
Greenhouse gas emissions of a spring cereal monoculture under conventional tillage and no-till treatments were measured in a peatland in Southwestern Finland for three years in 2018–2021. Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes were measured with an opaque chamber technique approximately biweekly throughout the years. During the growing season, canopy net ecosystem exchange (NEE) was measured with a transparent chamber technique and hourly ecosystem respiration (ER) and gross photosynthesis (GP) were modelled with empiric models. On average, the annual emissions were 6.4 ± 2.4 Mg CO2-C ha − 1 yr− 1, 7.6 ± 3.5 kg N2O -N ha− 1 yr− 1, and − 0.35 ± 0.42 kg CH4-C ha− 1 yr− 1 for NEE, N2O and CH4, respectively. The effect of no-till management on the GHG balance was non-consistent through years and thus generally of minor significance. No-till reduced the annual CO2 emissions by 24% in 2019 and N2O emissions by 33% in 2020 compared to conventional tillage while there were no differences between the treatments in other years. Measured differences in ER occurred mostly during the winter periods, especially after ploughing. The results indicated that no-till may reduce CO2 and N2O emissions from cultivated peat soil, but it does not lead to large consistent reductions during the first years of NT management.
<div> <p><span data-contrast="auto">Cultivated peatlands are a major source of greenhouse gas (GHG) emissions and water pollution in northern Europe, and their future management is a key issue on the path to carbon neutral societies. Conventional cultivation requires drainage, and above the drainage depth all peat is prone to decomposition with the implication that these soils have the highest emission rates per area compared to any other land use. Paludiculture is a management option in which wet-tolerant crops are produced with raised ground water levels. It is thus a GHG mitigation method that allows for slowing down peat decomposition in drained peatlands while still maintaining agricultural income for the landowner. There are tradeoffs to consider when implementing paludiculture: 1) methane emissions rise with the switch of aerobic to anaerobic decomposition, 2) slowing down decomposition reduces nutrient mineralisation from the peat and compromises productivity and 3) harvesting reduces the potential to sequester carbon to the ecosystem compared to natural wetlands.</span><span data-ccp-props="{&quot;201341983&quot;:0,&quot;335559739&quot;:160,&quot;335559740&quot;:259}">&#160;</span></p> </div> <div> <p><span data-contrast="auto">We experimented paludiculture at a highly degraded peat site in southern Finland with plots of willow, forage, and mixed vegetation (set-aside). We recorded the yields, emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and auxiliary environmental data for four years, as well as nutrient content of the soil water for two years. We will present the results of these measurements, including estimates on the net ecosystem carbon balance of each crop based on empiric models.&#160;</span><span data-ccp-props="{&quot;201341983&quot;:0,&quot;335559739&quot;:160,&quot;335559740&quot;:259}">&#160;</span></p> </div> <div> <p><span data-contrast="auto">Raising the ground water level to the desired depth (-20 cm) turned out to be challenging. The mean annual ground water table levels during the four study years were about 80, 40, 40 and 30 cm (the measurements of the last year are still ongoing). The preliminary results suggest that even a slight raise of the ground water level was able to slow down CO2 emissions from soil respiration, while an increase in CH4 emission partly counteracted this benefit especially when the ground water level was above 30 cm. Nitrous oxide emissions were extremely high after the initial disturbance of the site but remained at a relatively low level after that. The results will be compared to an adjacent site with an annual crop, and paludiculture as a mitigation measure discussed.&#160;</span><span data-ccp-props="{&quot;201341983&quot;:0,&quot;335559739&quot;:160,&quot;335559740&quot;:259}">&#160;</span></p> </div>
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