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Abstract

Drainage of peatlands affects the fluxes of greenhouse gases (GHGs). Organic soils used for agriculture contribute a large proportion of anthropogenic GHG emissions, and on-farm mitigation options are important. This field study investigated whether choice of a cropping system can be used to mitigate emissions of N2O and influence CH4 fluxes from cultivated organic and carbon-rich soils during the growing season. Ten different sites in southern Sweden representing peat soils, peaty marl and gyttja clay, with a range of different soil properties, were used for on-site measurements of N2O and CH4 fluxes. The fluxes during the growing season from soils under two different crops grown in the same field and same environmental conditions were monitored. Crop intensities varied from grasslands to intensive potato cultivation. The results showed no difference in median seasonal N2O emissions between the two crops compared. Median seasonal emissions ranged from 0 to 919 µg N2O m−2 h−1, with peaks on individual sampling occasions of up to 3317 µg N2O m−2 h−1. Nitrous oxide emissions differed widely between sites, indicating that soil properties are a regulating factor. However, pH was the only soil factor that correlated with N2O emissions (negative exponential correlation). The type of crop grown on the soil did not influence CH4 fluxes. Median seasonal CH4 flux from the different sites ranged from uptake of 36 µg CH4 m−2 h−1 to release of 4.5 µg CH4 m−2 h−1. From our results, it was concluded that farmers cannot mitigate N2O emissions during the growing season or influence CH4 fluxes by changing the cropping system in the field.

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... However, based on current research it appears that crop choice has little consistent effect on the magnitude of GHG emissions. Differences between years and sites are in general much larger than differences between crops grown on the same field (Norberg et al., 2016). Some sites with barley emit less CO 2 than grassland (Lohila et al., 2003;Maljanen et al., 2001) while the opposite has been measured at other sites Lohila et al., 2004. ...
... Some sites with barley emit less CO 2 than grassland (Lohila et al., 2003;Maljanen et al., 2001) while the opposite has been measured at other sites Lohila et al., 2004. CO 2 emission rates are often lower from peat soil cropped with potato than from barley and grassland (Lohila et al., 2004;Elsgaard et al., 2012;Norberg et al., 2016). Additionally, when comparing N 2 O emission from sites under grass and sites under barley some studies show that grassland emissions are higher (Maljanen et al., 2003) while other studies show that grassland emissions are lower (Maljanen et al., 2004;Regina et al., 2004;Kasimir-Klemedtsson et al., 2009). ...
... Kasimir-Klemedtsson et al., 2009;Maljanen et al., 2010) and the impact of cultivation on the emission differences is not consistent. A recent study concludes that farmers cannot mitigate N 2 O emissions during the growing season or influence CH 4 fluxes by changing the cropping system in the field (Norberg et al., 2016). ...
Article
Management of peat soils is regionally important as they cover large land areas and have important but conflicting ecosystems services. A recent management trend for drained peatlands is the control of greenhouse gases (GHG) by changes in agricultural practices, peatland restoration or paludiculture. Due to complex antagonistic controls of moisture, water table management can be difficult to use as a method for controlling GHG emissions. Past studies show that there is no obvious relationship between GHG emission rates and crop type, tillage intensity or fertilization rates. For drained peat soils, the best use options can vary from rewetting with reduced emission to efficient short term use to maximize the profit per amount of greenhouse gas emitted. The GHG accounting should consider the entire life cycle of the peatland and the socio-economic benefits peatlands provide locally. Cultivating energy crops is a viable option especially for wet peat soils with poor drainage, but harvesting remains a challenge due to tractability of wet soils. Paludiculture in lowland floodplains can be a tool to mitigate regional flooding allowing water to be stored on these lands without much harm to crops. This can also increase regional biodiversity providing important habitats for birds and moisture tolerant plant species. However, on many peatlands rewetting is not possible due to their position in the landscape and the associated difficulty to maintain a high stable water table. While the goal of rewetting often is to encourage the return of peat forming plants and the ecosystem services they provide such as carbon sequestration, it is not well known if these plants will grow on peat soils that have been altered by the process of drainage and management. Therefore, it is important to consider peat quality and hydrology when choosing management options. Mapping of sites is recommended as a management tool to guide actions. The environmental status and socio-economic importance of the sites should be assessed both for continued cultivation but also for other ecosystem services such as restoration and hydrological functions (flood control). Farmers need advice, tools and training to find the best after-use option. Biofuels might provide a cost-efficient after use option for some sites. Peat extraction followed by rewetting might provide a sustainable option as rewetting is often easier if the peat is removed, starting the peat accumulation from scratch. Also this provides a way to finance the after-use. As impacts of land use are uncertain, new policies should consider multiple benefits and decisions should be based on scientific evidence and field scale observations. The need to further understand the key processes and long term effects of field scale land use manipulations is evident. The recommended actions for peatlands should be based on local condition and socio-economic needs to outline intermediate and long term plans.
... Observed average monthly CH 4 fluxes ranging from − 30 to 7 µg m − 2 h − 1 correspond closely to those reported in Swedish cultivated peatlands by Norberg et al. (2016) (seasonal CH 4 fluxes ranged from uptake of 36 µg m − 2 h − 1 to release of 4.5 µg m − 2 h − 1 ) and in Danish soils (Petersen et the classes were rather imbalanced, with the number of emissions measurements in most cases comprising less than 13% of the total number of measurements. Precision of the CTs in correctly predicting the occurrence of CH 4 emissions varied from 0.05 to 0.98, with an average of 0.48 (excluding one chamber and year combination with no occurrence of CH 4 emissions at all). ...
Article
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Optimizing the level of groundwater presents a viable strategy for mitigating the greenhouse gas (GHG) emissions associated with the cultivation of peatlands. This study investigated the impact of soil hydrological conditions on carbon dioxide (CO 2 ) and methane (CH 4 ) emissions. The CO 2 and CH 4 emissions from bare soil were continuously measured using an automated chamber system throughout the growing seasons from 2021 to 2023 at a boreal cultivated peat soil site. Annual CO 2 emissions from soil respiration averaged to 21,600 kg ha ⁻¹ (April-November) corresponding to carbon (C) loss of 5890 kg ha ⁻¹ . The CO 2 emissions were highly temperature dependent. Lowering the groundwater level (GWL) was found to increase the CO 2 emissions nearly linearly. The soil functioned as a CH 4 sink for the majority of the growing season, and the total sink corresponded to 27 and 20 kg ha ⁻¹ yr ⁻¹ CO 2 equivalent in 2022 and 2023, respectively. The CH 4 emissions occurred generally when soil water content (SWC) exceeded 0.6 m ³ m ⁻³ and when GWL was at the depth of less than 30 cm from soil surface. For optimal climate efficiency the mitigation measures must be implemented during the mid-growing season, and the water table should be brought close to the soil surface. Potentially, this can hamper the operation of machinery on the field and reduce the harvested yield. Thus, comprehensive cost-benefit analysis is necessary before adopting a raised water table level in large-scale crop production.
... The higher CH4 consumption from the unplanted cores indicates that even though soil water content was lower in the planted cores, the lettuce either increased CH4 production or reduced its consumption in soil. Methane emission rates from agricultural peatlands vary between different crops (Norberg et al., 2016), although bare soils are typically associated with lower CH4 uptake than soils where crops are grown (Maljanen et al., 2004), as root exudates stimulate microbial activity (Girkin et al., 2018;Laanbroek, 2010). In this experiment, lettuce root secretions likely enhanced CH4 production (Serrano-Silva et al., 2014; Girkin et al., 2018) given the higher DOC content in soil pore water of the planted cores. ...
Article
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40% of UK peatlands have been drained for agricultural use, which has caused serious peat wastage and associated greenhouse gas emissions (carbon dioxide ‐ CO2, methane ‐ CH4). In this study we evaluated potential trade‐offs between water table management practices for minimising peat wastage and greenhouse gas emissions, whilst seeking to sustain romaine lettuce production: one of the most economically relevant crop in the East Anglian Fenlands. In a controlled environment experiment we measured lettuce yield, CO2, CH4 fluxes and dissolved organic carbon (DOC) released from an agricultural fen soil at two temperatures (ambient and + 2°C) and three water table levels (‐30 cm, ‐40 cm and ‐50 cm below the surface). We showed that increasing the water table from the currently used field level of ‐50 cm to ‐40 cm and ‐30 cm reduced CO2 emissions, did not affect CH4 fluxes, but significantly reduced yield and increased DOC leaching. Warming of 2°C increased both lettuce yield (fresh leaf biomass) and peat decomposition through the loss of carbon as CO2 and DOC. However, there was no difference in the dry leaf biomass between the intermediate (‐40 cm) and the low (‐50 cm) water table, suggesting that romaine lettuce grown at this higher water level should have similar energetic value as the crop cultivated at ‐50 cm, representing a possible compromise to decrease peat oxidation and maintain agricultural production.
... There was a correlation between increasing N 2 O emissions and decreasing pH of the soil cores tested in this study, as also found in some previous studies (Weslien et al., 2009;Andert et al., 2012;Norberg et al., 2016). However, this is not always the case (Maljanen et al., 2010;Taft et al., 2017). ...
Article
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Greenhouse gas emissions from drained agricultural peatlands contribute significantly to global warming. In a laboratory study using intact cores of peat soil from eight different sites in Sweden, factors controlling the emission of the greenhouse gases nitrous oxide (N2O) and methane (CH4) were examined. Soil properties, and the abundance of the total microbial community (16S rRNA gene abundance), and genes encoding for functions controlling N2O emissions (bacterial and archaeal amoA, nirS, nirK, nosZI, and nosZII) were analyzed and compared against measured greenhouse gas emissions. Emissions were measured at different drainage levels, i.e., higher soil water suction values, since drainage is an important factor controlling greenhouse gas emissions from peat soils. The results showed that N2O and CH4 emissions were generally low, except for N2O emissions at near water-saturated conditions, for which three soils displayed high values and large variations in fluxes. Relationships between N2O emissions and soil properties were mainly linked to soil pH, with higher emissions at lower pH. However, specific assemblages of nitrogen cycling guilds that included nosZII, typically present in non-denitrifying N2O reducers, were detected in soils with low N2O emissions. Overall, these results indicate that both pH and biotic controls determine net N2O fluxes.
... For days when both methods were used, CO 2 fluxes are presented as the mean of both methods. For N 2 O and CH 4 , the headspace was sampled by circulating the air between the chamber and 22 ml vials for approximately 30 s (Norberg et al., 2016a). Gas samples were taken at 0, 10, 20, and 30 min after closure, and analyzed in the laboratory using gas chromatography (Perkin Elmer Clarus 500, USA). ...
Article
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Northern peatlands are important carbon (C) reservoirs, storing about one-third of the global terrestrial soil C pool. Anthropogenic influences, such as drainage for agriculture and forestry, lower the originally high groundwater level, leading to peat aeration and decomposition. This is particularly reflected in significant losses of CO2, while fluxes of N2O and CH4 are generally considered of minor importance for the overall greenhouse gas (GHG) balance of cultivated peatlands in Scandinavia. Setting land aside from agricultural production has been proposed as a strategy to reduce GHG emissions from drained peatland, restore natural habitats, and increase C sequestration. However, the evidence for this is rather scarce unless drainage is terminated. In this study, we measured respiration using dark automatic chambers, and CO2, N2O, and CH4 fluxes using manual static chambers, on: 1) cultivated peatland and 2) adjacent set-aside peatland in Central Sweden. The set-aside site was found to be a greater source of respiration than the cultivated site, while higher N2O fluxes and lower CH4 uptake rates were observed for the cultivated site. However, to compare the full GHG balance and assess the abandonment of drained cultivated peatland, additional measures, such as gross primary production (GPP) but also dissolved organic C losses would have to be taken into account.
... In 2017, mean N 2 O emissions were significantly lower in timothy and reed canary grass plots (71 and 75 μg m −2 h −1 , respectively) than in tall fescue plots (126 μg m −2 h −1 ). A previous study on peat soils comparing the effect of different crops on N 2 O and CH 4 fluxes during the growing season found no difference in median seasonal emissions, but emissions differed widely between sites (Norberg et al., 2016a). This indicates that soil properties are a regulating factor (Norberg et al., 2018). ...
Article
Loss of organic matter from cultivated peat soils is a threat to farmers, due to the surface subsidence associated with organic matter loss, and to the atmosphere, due to CO2 and N2O emissions from the soil. In a three-year field experiment (2015–2017) on a drained, cultivated fen peat in southern Sweden, we tested whether reed canary grass (Phalaris arundinacea L.) and tall fescue (Festuca arundinacea Schreb.) perform better on peat soils than the commonly grown timothy grass (Phleum pratense L.), without increasing greenhouse gas emissions. In the experiment, we compared yield, nutrient uptake, penetration resistance and loss of organic matter measured as greenhouse gas emissions (CO2, N2O and CH4). Yield of timothy was significantly lower than that of reed canary grass and tall fescue in 2016, and lower than that of reed canary grass in 2017. Yield level increased over time, with total dry matter yield in 2017 of 11.7 Mg ha⁻¹ yr⁻¹ for timothy, 13.5 Mg ha⁻¹ yr⁻¹ for tall fescue and 14.3 Mg ha⁻¹ yr⁻¹ for reed canary grass. Total removal of all macronutrients in 2016 was higher in reed canary grass and tall fescue than in timothy. For nitrogen (N), reed canary grass removed a total of 173 kg N ha⁻¹ yr⁻¹, tall fescue 169 kg ha⁻¹ yr⁻¹ and timothy 121 kg ha⁻¹ yr⁻¹, while the fertilisation rate was only 50 kg N ha⁻¹. There were no differences in trafficability, measured as penetration resistance. Measurements of greenhouse gas emissions in the snow-free season in 2016 and 2017 using manual dark chambers (CO2, N2O and CH4) and in 2016 automatic dark chambers (CO2) revealed only small differences in CO2 emissions between the treatments. The N2O emissions were also low and CH4 emissions were very low and in general negative. The estimated carbon capture efficiency (ratio of C in aboveground biomass plus roots to emitted CO2-C measured by the automatic chambers) for the growing season (May–October) in 2016 was lowest for timothy (0.61) and higher for reed canary grass and tall fescue (0.70 and 0.70, respectively). Reed canary grass and tall fescue are thus promising alternatives to timothy on peat soils regarding yield, nutrient removal and carbon capture efficiency.
... Hence, although the existing data were inconclusive on the role of deeper N losses, it appears that the rather short summer period of potato growth is surrounded by periods of increased N 2 O emission risk at drained organic peat soils Taghizadeh-Toosi et al., 2018) likely linked to availability of NO 3 outside the cropping season. These results may add to the interpretation of similar N 2 O emissions from potato and other cropping systems on organic soils in southern Sweden (Norberg et al., 2016b) as these data were based merely on monthly measurements during the growing season. The two neighboring oat sites with contrasting mean soil pH (4.0 and 4.8) were partly selected to assess potential differences in N 2 O fluxes as mediated by impediment of the denitrification enzyme N 2 O reductase at low pH (Liu et al., 2010;Bakken, 2014). ...
Article
Peatlands drained for agriculture are sources of atmospheric carbon dioxide (CO 2) and nitrous oxide (N 2 O). Resulting emissions may depend on land-use, often as grassland or cropland, but few studies have directly compared the effects of land-uses. Here, we measured annual emissions of CO 2 , N 2 O and methane (CH 4) from five sites in a temperate bog, representing an undrained natural bog (NB) site, and four drained sites used as permanent grassland (PG) and croplands with rotations of oat-potato, oat-spring barley and potato-spring barley (PO:SB) in the study year. Gas fluxes were measured at 1-2 week intervals using static chambers, and auxiliary data were obtained, such as temperature, depth of water table, ratio-vegetation index, pH and soil mineral N. Annual CO 2 emissions were derived from empirical modelling, whereas CH 4 and N 2 O emissions were linearly interpolated between measurement dates by bootstrapping. Soil respiration was lower at the NB site (1.8 Mg CO 2-C ha −1 yr −1) than at the drained sites where emissions were in the range of 5.0-8.8 Mg CO 2-C ha −1 yr −1. The N 2 O emission was negligible at NB (0.3 kg N 2 O ha −1 yr −1), low at three of the drained sites (1.5-3.7 kg N 2 O ha −1 yr-1), but high at PO:SB (37.7 kg N 2 O ha −1 yr −1). The CH 4 emission was high at NB (172 kg CH 4 ha −1 yr −1), but negligible at the drained sites (−1.5 to 1.5 kg CH 4 ha −1 yr −1). The soil respiration at the drained sites indicated that peat losses were rather similar among the different cropping systems and depended mostly on drainage status, although soil respiration and peat mineralization may not scale directly. The pattern of N 2 O emissions suggested an increased risk of N 2 O emission from potato cultivation before and after the period of potato growth, likely due to microbial availability of NO 3-outside the growing season. For initiatives aiming at reduction of greenhouse gas emissions from agricultural peat soils, this means that, e.g., conversion from cropland to permanent grassland should preferably be accompanied by measures of rewetting, whereas for potato cropping, N availability outside the growing season should be minimized.
... Studies by Norberg et al. (2016aNorberg et al. ( , 2016b found that greenhouse gas emissions varied between sites (i.e. soils), which indicates that soil properties are a regulating factor. ...
Article
Drained peatlands contribute to anthropic emissions of carbon dioxide (CO2), so a better understanding of the underlying processes and identification of mitigation options for agricultural peatlands are urgently required. Peatland soil properties vary greatly and, in combination with drainage, can affect emissions of CO2 both directly and indirectly. Drainage reduces soil water content but increases CO2 production, so it is important to find the optimum drainage level that minimises CO2 emissions without affecting agricultural use. Intact soil cores from nine different sites (topsoil, plus subsoil at four sites) were collected and brought into a controlled laboratory environment. Repeated measurements of CO2 fluxes were performed at increasing soil water suctions corresponding to different drainage levels. Physical and chemical properties of the soils were determined and compared with the CO2 emissions. The soil cores displayed different CO2 emission patterns with increasing soil water suction head. In some cores, emissions increased rapidly to a high level, while in others they remained at lower levels. At a soil water suction head of only 0.5 m of water, the average soil CO2 emissions had already reached a maximum. The soil cores represented peat soils with a wide range of soil properties, e.g. bulk density from 0.17 to 0.47 g cm-3 and total carbon from 26.3 to 43.5 %, but none of the properties measured was clearly correlated with CO2 emissions.
... As described by Le Mer and Roger (2001) CH 4 emissions from soil are again affected by many factors and a negative correlation between CH 4 emissions and C/N ratio was reported. An enrichment of available C stimulates the population soil microorganisms that use a great part of C for their metabolism with a reduction of available C for methane production (Bernet et al., 2000;Norberg et al., 2016). In this respect, the composition of manure used to obtain the two levels of OM, which represent the 25% of total organic C, partially explain the behavior of CH 4 emissions from organic fertilisers. ...
Article
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Greenhouse gas emissions (GHGs) into the atmosphere derived from the use of fertilisers is a serious issue for the sustainability of agricultural systems, also considering that the growing global demand for food requires an increasingly productive agriculture. Emissions dynamics are very variable and are determined by many factors and their reciprocal interactions. Among driving factors, soil type (mineral, organic and microbiological composition), fertilisation method, climate, and the cropping system. In the present experiment, the combined effect of soil organic matter (SOM) and fertilisation method on the emissions of GHGs and ammonia (NH3) was investigated. Liquid fraction of digestate from pig slurries, compost from organic fraction of municipal solid wastes, and urea were applied on bare soil with two levels of organic matter (OM1: 1.3% and OM2: 4.3%). Emissions were directly monitored by a static chamber system and a portable gas analyser. Results show that soil organic matter as well as the composition of the fertilisers affect greenhouse gasses emissions. Emissions of methane (CH4) produced by digestate and compost during experimental period were higher in correspondence of lower organic matter content (0.58 – 0.49 kg CH4 C/ha/ day and 0.37 – 0.32 kg CH4 C/ha/day for digestate and compost respectively), contrary to what was observed for urea. For all fertilisers, carbon dioxide (CO2) and nitrous oxide (N2O) emissions were higher in correspondence of higher organic matter level. In particular, CO2 emissions were 11.05%, 67.48% and 82.84% higher in OM2 than OM1 for digestate, urea and compost respectively. Likewise, N2O emissions were 87.45%, 68.97% and 92.11% higher in OM2 than OM1 for digestate, urea and compost respectively. The obtained results show that the content of organic matter in soils plays a key role on the emissions of GHGs, generally enhancing the levels of gas emissions.
Chapter
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Organic soils of intact peatlands store 1/4 of the global soil organic carbon (SOC). Despite being an important source of methane (CH4), they are climate coolers because they continuously accumulate new organic carbon. However, when these organic soils are drained for agriculture, the resulting aerobic conditions lead to fast decomposition of the peat and the release of carbon dioxide (CO2) and nitrous oxide (N2O), turning them into net greenhouse gas (GHG) sources. Reducing the environmental footprint of managing these soils requires a good understanding of the processes during drainage of formerly anoxic soil horizons and eventual subsequent rewetting. We describe changes in soil properties and carbon dynamics following drainage of peatlands and discuss management strategies to reduce carbon loss from drained peatlands by raising the water table to either restore the peatland ecosystem, or to cultivate water-tolerant crops. In addition to rewetting, engineering approaches with continuous management at deeper water tables are evaluated in terms of SOC loss.
Technical Report
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Undisturbed peatlands represent long-term net sinks of carbon; however, peat extraction converts these systems into large and persistent sources of greenhouse gases. Although rewetting and restoration following peat extraction have taken place over the last several decades, very few studies have investigated the longer term impact of this restoration on peatland carbon balance. We determined the annual carbon balance of a former horticulturally-extracted peatland restored 10 yr prior to the study and compared these values to the carbon balance measured at neighboring unrestored and natural sites. Carbon dioxide (CO2) and methane (CH4) fluxes were measured using the chamber technique biweekly during the growing season from May to October 2010 and three times over the winter period. Dissolved organic carbon (DOC) export was measured from remnant ditches in the unrestored and restored sites. During the growing season the restored site had greater uptake of CO2 than the natural site when photon flux density was greater than 1000 μmol m−2 s−1, while the unrestored site remained a source of CO2. Ecosystem respiration was similar between natural and restored sites, which were both significantly lower than the unrestored site. Methane flux remained low at the restored site except from open water pools, created as part of restoration, and remnant ditches. Export of DOC during the growing season was 5.0 and 28.8 g m−2 from the restored and unrestored sites, respectively. Due to dry conditions during the study year all sites acted as net carbon sources with annual balance of the natural, restored and unrestored sites of 250.7, 148.0 and 546.6 g C m−2, respectively. Although hydrological conditions and vegetation community at the restored site remained intermediate between natural and unrestored conditions, peatland restoration resulted in a large reduction in annual carbon loss from the system resulting in a carbon balance more similar to a natural peatland.
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Nitrous oxide emissions from a network of agricultural experiments in Europe and Zimbabwe were used to explore the relative importance of site and management controls of emissions. At each site, a selection of management interventions were compared within replicated experimental designs in plot based experiments. Arable experiments were conducted at Beano in Italy, El Encin in Spain, Foulum in Denmark, Logården in Sweden, Maulde in Belgium, Paulinenaue in Germany, Harare in Zimbabwe and Tulloch in the UK. Grassland experiments were conducted at Crichton, Nafferton and Peaknaze in the UK, Gödöllö in Hungary, Rzecin in Poland, Zarnekow in Germany and Theix in France. Nitrous oxide emissions were measured at each site over a period of at least two years using static chambers. Emissions varied widely between sites and as a result of manipulation treatments. Average site emissions (throughout the study period) varied between 0.04 and 21.21 kg N2O-N ha−1 yr−1, with the largest fluxes and variability associated with the grassland sites. Total nitrogen addition was found to be the single most important determinant of emissions, accounting for 15% of the variance (using linear regression) in the data from the arable sites ( p < 0.0001), and 77% in the grassland sites. The annual emissions from arable sites were significantly greater than those that would be predicted by IPCC default emission factors. Variability in N2O within sites that occurred as a result of manipulation treatments was greater than that resulting from site to site and year to year variation, highlighting the importance of management interventions in contributing to greenhouse gas mitigation.
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This article provides an overview of the effects of land-use on the fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and from peatlands in the Nordic countries based on the field data from about 100 studies. In addition, this review aims to identify the gaps in the present knowledge on the greenhouse gas (GHG) balances associated with the land-use of these northern ecosystems. Northern peatlands have accumulated, as peat, a vast amount of carbon from the atmosphere since the last glaciation. However, the past land-use and present climate have evidently changed their GHG balance. Unmanaged boreal peatlands may act as net sources or sinks for CO2 and CH4 depending on the weather conditions. Drainage for agriculture has turned peatlands to significant sources of GHGs (mainly N2O and CO2). Annual mean GHG balances including net CH4, N2O and CO2 emissions are 2260, 2280 and 3140 g CO2 eq. m−2 (calculated using 100 year time horizon) for areas drained for grass swards, cereals or those left fallow, respectively. Even after cessetion of the cultivation practices, N2O and CO2 emissions remain high. The mean net GHG emissions in abandoned and afforested agricultural peatlands have been 1580 and 500 g CO2 eq. m−2, respectively. Peat extraction sites are net sources of GHGs with an average emission rate of 770 g CO2 eq. m−2. Cultivation of a perennial grass (e.g., reed canary grass) on an abandoned peat extraction site has been shown to convert such a site into a net sink of GHGs (−330 g CO2 eq. m−2). In contrast, despite restoration, such sites are known to emit GHGs (mean source of 480 g CO2 eq. m−2, mostly from high CH4 emissions). Peatland forests, originally drained for forestry, may act as net sinks (mean −780 g CO2 eq. m−2). However, the studies where all three GHGs have been measured at an ecosystem level in the forested peatlands are lacking. The data for restored peatland forests (clear cut and rewetted) indicate that such sites are on average a net sink (190 g CO2 eq. m−2). The mean emissions from drained peatlands presented here do not include emissions from ditches which form a part of the drainage network and can contribute significantly to the total GHG budget. Peat soils submerged under water reservoirs have acted as sources of CO2, CH4 and N2O (mean annual emission 240 g CO2 eq. m−2). However, we cannot yet predict accurately the overall greenhouse gas fluxes of organic soils based on the site characteristics and land-use practices alone because the data on many land-use options and our understanding of the biogeochemical cycling associated with the gas fluxes are limited.
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Executive summary The European Commission has recently adopted the Thematic Strategy for soil protection (COM(2006)231 final), with the objective to ensure that Europe’s soils remain healthy and capable of supporting human activities and ecosystems. Climate change is identified as a common element in many soil threats. Therefore the Commission intends to assess the actual contribution of the protection of soil to climate change mitigation and the effects of climate change on soil productivity and the possible depletion of soil organic matter as result of climate change. The objective of this study is to provide a state of the art and more robust understanding of interactions between soil under different land uses and climate change than is available now, through a comprehensive literature review and expert judgment. 1 Carbon stock in EU soils The amount of carbon in European soils is estimated to be equal to 73 to 79 billion tonnes. These estimates are based on applying a common methodology across Europe, the larger estimate was based on a method developed by the Joint Research Centre of the European Commission and the smaller estimate on a soil organic carbon (SOC) map of the United States Department of Agriculture. These two methodologies gave similar estimates for most of the European countries. The estimates were of the same order of magnitude as national estimates based on national methodologies and are therefore deemed reliable. Carbon in EU27 soils is concentrated in specific regions: roughly 50% of the total carbon stock is located in Sweden, Finland and the United Kingdom (because of the vast area of peatlands in these countries) and approximately 20% of the carbon stock is in peatlands mainly in the northern parts of Europe. The rest of soil C is in mineral soils, again the higher amount being in northern Europe. 2 Soils sink or source for CO2 in the EU Uptake of carbon dioxide (CO2) through photosynthesis and plant growth and loss (decomposition) of organic matter from terrestrial ecosystems are both significant fluxes in Europe. Yet, the net terrestrial carbon fluxes (uptake of CO2 minus respiration by vegetation and soils) are typically smaller relative to the emissions from use of fossil fuel. The current changes in the carbon pool of the European soils were estimated from different studies using different methods, by land use category using models that simulate carbon cycling in soil. The results of the different studies deviated considerably from each other, and all results were accompanied with wide uncertainty ranges. Some studies on the basis of measurements in UK, Belgium and France on soil carbon over longer periods show losses of carbon especially from cropland; other studies from the UK and from the Netherlands show no change or increases in soil carbon stocks over time. Grassland soils were found in all studies to generally accumulate carbon. However, the studies differ on the amount of carbon accumulated. In one study, the sink estimate ranged from 1 to 45 million tonnes of carbon per year and, in another study, the mean estimate was 101 million tonnes per year, although with a high uncertainty. Cropland generally acts as a carbon source, although existing estimates vary highly. In one study, the carbon balance estimates of croplands ranged from a carbon sink equal to 10 million tonnes of carbon per year to a carbon source equal to 39 million tonnes per year. In another study, croplands in Europe were estimated to be losing carbon up to 300 million tonnes per year. The latter is now perceived as a gross overestimation. Forest soils generally accumulate carbon in each European country. Estimates range from 17 to 39 million tonnes of carbon per year with an average of 26 million tonnes per year in 1990 and to an average of 38 million tons of carbon per year in 2005. It would seem that on a net basis, soils in Europe are on average most likely accumulating carbon. However, given the very high uncertainties in the estimates for cropland and grassland, it would not seem accurate and sound to try to use them to aggregate the data and produce an estimate of the carbon accumulation and total carbon balance in European soils. 3 Peat and organic soils The current area of peat occurrence in the EU Member States and Candidate Countries is over 318 000 km2. More than 50% of this surface is in just a few northern European countries (Norway, Finland, Sweden, United Kingdom); the remainder in Ireland, Poland and Baltic states. Of that area, approximately 50% has already been drained, while most of the undrained areas are in Finland and Sweden. Although there are gaps in information on land use in peatlands, it can be estimated that water saturated organic rich soil (peatland) have been drained for: - agriculture – more than 65 000 km2 (20% of the total European peatland area); - forestry – almost 90 000 km2 (28%); - peat extraction – only 2 273 km2 (0.7%). This is important as the largest emissions of CO2 from soils are resulting from land use change and related drainage of organic soils and amount to 20-40 tonnes of CO2 per hectare per year. The emission from cultivated and drained organic soils in EU27 is approximately 100 Mt CO2 per year. Peat layer have been lost by oxidation during land use, but the estimate derivable from the published data, ca. 18 000 km2, is very probably an underestimate. 4 Land use and soil carbon Monitoring programs, long term experiments and modelling studies all show that land use significantly affects soil carbon stocks. Soil carbon losses occur when grasslands, managed forest lands or native ecosystems are converted to croplands. Vice versa soil carbon stocks are restored when croplands are either converted to grasslands, forest lands or natural ecosystems. Conversion of forest lands into grasslands does not affect soil carbon in all cases, but does reduce total ecosystem carbon due to the removal of aboveground biomass. The more carbon is present on the soil, the higher the potential for losing it. Therefore the potential losses of unfavourable land use changes on highly organic peat soils are a major risk. The most effective strategy to prevent global soil carbon loss would be to halt land conversion to cropland, but this may conflict with growing global food demand unless per-area productivity of the cropland continues to grow. 5 Soil management and soil carbon Soil management practices are an important tool to affect the soil carbon stocks. Suitable soil management strategies have been identified within all different land use categories and are available and feasible to implement. These are: - On cropland, soil carbon stocks can be increased by (i) agronomic measures that increase the return of biomass carbon to the soil, (ii) tillage and residue management, (iii) water management, (iv) agro-forestry. - On grassland, soil carbon stocks are affected by (i) grazing intensity (ii) grassland productivity, (iii) fire management and (iv) species management. - On forest lands, soil carbon stocks can be increased by (i) species selection, (ii) stand management, (iii) minimal site preparation, (iv) tending and weed control, (v) increased productivity, (vi) protection against disturbances and (vii) prevention of harvest residue removal. - On cultivated peat soils the loss of soil carbon can be reduced by (i) higher ground water tables. - On less intensively / un-managed heathlands and peatlands, soil carbon stocks are affected by (i) water table (drainage), (ii) pH (liming), fertilisation, (iii) burning (iv) grazing. - On degraded lands, carbon stocks can be increased after restoration to a productive situation. Given that land use change is often driven by demand and short term economic revenues, the most realistic option to improve soil carbon stocks is to a) protect the carbon stocks in highly organic soils such as peats mostly in northern Europe, and b) to improve the way in which the land is managed to maximise carbon returns to the soil and minimise carbon losses. Increased nitrogen fertilizer use has made a large contribution to the growth in productivity, but further increased use will lead to greater emissions of nitrous oxide (N2O). Hence future emphasis should be concentrated on the other main driver of productivity, i.e. improved crop varieties. 6 Carbon sequestration Soils contain about three times the amount of carbon globally as vegetation, and about twice that in the atmosphere. There is a significant and large uncertainty associated with the response of soil carbon (and other pools of biospheric carbon) to future climate changes. Most response are calculated with simulation models with some models predicting large releases of additional carbon from soils and vegetation under climate change, and others suggesting only small feedback. The maximum possible amount of carbon that soil sequestration could achieve is about one third of the current yearly increase in atmospheric carbon (as carbon dioxide) stocks. This is about one seventh of yearly anthropogenic carbon emissions of 7500 Mt C. In Europe emissions of greenhouse gases amount to approximately 4100 Mt CO2 (or 1000 Mt C) per year. Today, soils in Europe are most likely a sink and the best estimate is that they sequester up to 100 Mton C per year. Higher sequestration is possible with adequate soil management. Soil C-sequestration alone is surely no ‘golden bullet’ to fight climate change but is it realistic to link climate change with soil carbon conservation, as soil carbon sequestration is cost competitive, of immediate availability, does not require the development of new and unproven technologies, and provides comparable mitigation potential to that available in other sectors. Therefore, given that climate change needs to be tackled urgently if atmospheric carbon dioxide concentrations are to be stabilized below levels thought to be irreversible, soil carbon sequestration or the even more effective conservation of current carbon stocks in soils has a key role to play in any raft of measures used to tackle climate change. 7 Effects of climate change on soil carbon pools We have not found strong and clear evidence for either an overall combined positive or negative impact of climate change (raised atmospheric CO2 concentration, temperature, precipitation) on terrestrial carbon stocks. There are suggestions for enhancing soil C stocks at higher atmospheric CO2 concentration and reducing soil C stocks when temperatures are rising. Most studies have taken moderate changes in temperature increases and sudden and more severe changes in temperature of precipitation have not been considered, as the management of land and soils overrules any impact on soil carbon from climate change. All of the factors of climate change (raised atmospheric CO2 concentration, temperature, precipitation) affect soil C, with the effect on soils of CO2 being indirect (through photosynthesis) and the effects of weather factors being both direct and indirect. Climate change affects soil carbon pools by affecting each of the processes in the C-cycle: photosynthetic C-assimilation, litter fall, decomposition, surface erosion, hydrological transport. Due to the relatively large gross exchange of CO2 between atmosphere and soils and the significant stocks of carbon in soils, relatively small changes in these large but opposing fluxes of CO2 may have significant impact on our climate and on soil quality. Therefore, managing these fluxes (through proper soil management) can help mitigate climate change considerably. 8 Monitoring systems for changes in soil carbon Today, monitoring and knowledge on land use and land use change in EU27 is insufficient, yet land use and land use change are a key source of greenhouse gas emissions in many of the EU27 member states. Soil monitoring in EU27 seems like the Tower of Babel: countries tend to have their own systems, if any, sometimes even more than one system, and the results are not fully compatible across EU27. The few existing systems tend to have been set up for different purposes, often not including that of providing evidence concerning the impact of climate change on soil carbon pools. This 19 lack of systematic and comparable data gathering and analyses seriously hampers any attempt to provide reliable, EU-wide data on the soil carbon stock and changes therein. Moreover, the new goal of monitoring stock-changes rather than stock-magnitudes may necessitate significant changes to current soil sampling procedures. Given the lack of reliable national monitoring systems and without an EU wide harmonized system of monitoring of soil carbon in place, it would be a significant advance if the EU were to ask for a design or initiate implementation of a harmonized EU27 monitoring for land uses and for specific activities that affect soil carbon stocks and emissions of CO2. Such monitoring would also allow for adequate representation of changes in soil carbon in EU27 in reporting to the United Nations Framework Convention to Combat Climate Change (UNFCCC). 9 EU policies and soil carbon We have critically reviewed EU policies that are likely to have impacts on soil carbon (C) to assess whether any of those policies might have adverse impacts on soil C in the long term. Policies reviewed were the Common Agricultural Policy (CAP), the Nitrates Directive, the Renewable Energy Sources Directive, the Biofuels Directive, Waste policy and the EU Thematic Strategy for soil protection. Legislation to encourage the production of arable crops to provide feed stocks for renewable energy is perhaps the legislation most likely to lead to decreases in the overall carbon content of European soils. While studies may indicate much of the demand may be met by imports from outside the EU, and hence may have little impacts on soil C within the EU, there may be serious implications for soil C stocks in those countries which supply renewable energy or their substrates. We conclude that the need to comply with environmental requirements under the Cross Compliance requirement of CAP is an instrument that may be used to maintain SOC. The measures required under UNFCCC are not likely to adversely impact soil C. Nor are there any measures in the proposed Soil Framework Directive that would be expected to lead to decreases on soil C.
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Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N2O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N2O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N2O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 μg NO-N m–2 h–1, with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 μg N2O-N m–2 h–1. Seasonal shifts in soil aeration caused maximum N2O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N2O emission was best related to a combination of bulk density and clay content and the NO/N2O ratio decreased logarithmically with increasing water filled pore space.
Article
Fluxes of the greenhouse gases methane (CH4) and nitrous oxide (N2O) from histosolic soils (which account for approximately 10% of Swedish agricultural soils) supporting grassley and barley production in Sweden were measured over 3 years using static chambers. Emissions varied both over area and time. Methane was both produced and oxidized in the soil: fluxes were small, with an average emission of 0.12 g CH4 m−2 year−1 at the grassley site and net uptake of −0.01 g CH4 m−2 year−1 at the barley field. Methane emission was related to soil water, with more emission when wet. Nitrous oxide emissions varied, with peaks of emission after soil cultivation, ploughing and harrowing. On average, the grassley and barley field had emissions of 0.20 and 1.51 g N2O m−2 year−1, respectively. We found no correlation between N2O and soil factors, but the greatest N2O emission was associated with the driest areas, with < 60% average water-filled pore space. We suggest that the best management option to mitigate emissions is to keep the soil moderately wet with permanent grass production, which restricts N2O emissions whilst minimizing those of CH4.
Article
Grassland is a major source of nitrous oxide (N2O) and methane (CH4) emissions in the UK, resulting from high rates of fertilizer application. We studied the effects of substituting mineral fertilizer by organic manures and a slow-release fertilizer in silage grass production on greenhouse gas emissions and soil mineral N content in a three-year field experiment. The organic manures investigated were sewage sludge pellets and composted sewage sludge (dry materials), and digested sewage sludge and cattle slurry (liquid materials). The organic manures produced N2O and carbon dioxide (CO2) consistently from time of application up to harvest. However, they mitigated N2O emissions by around 90% when aggregate emissions of 15.7 kg N ha−1 from NPK fertilizer were caused by a flux of up to 4.9 kg N ha−1 d−1 during the first 4 days after heavy rainfall subsequent to the NPK fertilizer application. CH4 was emitted only for 2 or 3 days after application of the liquid manures. CH4 and CO2 fluxes were not significantly mitigated. Composting and dried pellets were useful methods of conserving nutrients in organic wastes, enabling slow and sustained release of nitrogen. NPK slow-release fertilizer also maintained grass yields and was the most effective substitute for the conventional NPK fertilizer for mitigation of N2O fluxes.
Article
Greenhouse gas (GHG) emissions from farmed organic soils can have a major impact on national emission budgets. This investigation was conducted to evaluate whether afforestation of such soils could mitigate this problem. Over the period 1994–1997, emissions of methane (CH4) and nitrous oxide (N2O) were recorded from an organic soil site in Sweden, forested with silver birch (Betula pendula Roth), using static field chambers. The site was used for grazing prior to forestation. Soil pH and soil carbon content varied greatly across the site. The soil pH ranged from 3.6 to 5.9 and soil carbon from 34 to 42%. The mean annual N2O emission was 19.4 (± 6.7) kg N2O-N ha−1 and was strongly correlated with soil pH (r = −0.93, P < 0.01) and soil carbon content (r = 0.97, P < 0.001). The N2O emissions showed large spatial and temporal variability with greatest emissions during the summer periods. The site was a sink for CH4 (i.e. −0.8 (± 0.5) kg CH4 ha−1 year−1) and the flux correlated well with the C/N ratio (r = 0.93, P < 0.01), N2O emission (r = 0.92, P < 0.01), soil pH (r = −0.95, P < 0.01) and soil carbon (r = 0.97, P < 0.001). CH4 flux followed a seasonal pattern, with uptake dominating during the summer, and emission during winter. This study indicates that, because of the large N2O emissions, afforestation may not mitigate the GHG emissions from fertile peat soils with acidic pH, although it can reduce the net GHG because of greater CO2 assimilation by the trees compared with agricultural crops.
Article
Forested histosols have been found in some cases to be major, and in other cases minor, sources of the greenhouse gas nitrous oxide (N2O). In order to estimate the total national or global emissions of N2O from histosols, scaling or mapping parameters that can separate low- and high-emitting sites are needed, and should be included in soil databases. Based on interannual measurements of N2O emissions from drained forested histosols in Sweden, we found a strong negative relationship between N2O emissions and soil CN ratios (r2adj=0.96, mean annual N2O emission=ae(−b CN ratio)). The same equation could be used to estimate the N2O emissions from Finnish and German sites based on CN ratios in published data. We envisage that the correlation between N2O emissions and CN ratios could be used to scale N2O emissions from histosols determined at sampled sites to national levels. However, at low CN ratios (i.e. below 15–20) other parameters such as climate, pH and groundwater tables increase in importance as regulating factors affecting N2O emissions.
Article
Trace gas fluxes of N2O and CH4 were measured weekly over 12 months on cultivated peaty soils in southern Germany using a closed chamber technique. The aim was to quantify the effects of management intensity and of soil and climatic factors on the seasonal variation and the total annual exchange rates of these gases between the soil and the atmosphere. The four experimental sites had been drained for many decades and used as meadows (fertilized and unfertilized) and arable land (fertilized and unfertilized), respectively. Total annual N2O-N losses amounted to 4.2, 15.6, 19.8 and 56.4 kg ha–1 year–1 for the fertilized meadow, the fertilized field, the unfertilized meadow and the unfertilized field, respectively. Emission of N2O occurred mainly in the winter when the groundwater level was high. At all sites maximum emission rates were induced by frost. The largest annual N2O emission by far occurred from the unfertilized field where the soil pH was low (4.0). At this site 71% of the seasonal variation of N2O emission rates could be explained by changes in the groundwater level and soil nitrate content. A significant relationship between N2O emission rates and these factors was also obtained for the other sites, which had a soil pH between 5.1 and 5.8, though the relation was weak (R2 = 15–27%). All sites were net sinks for atmospheric methane. Up to 78% of the seasonal variation in CH4 flux rates could be explained by changes in the groundwater level. The total annual CH4-C uptake was significantly affected by agricultural land use with greater CH4 consumption occurring on the meadows (1043 and 833 g ha–1) and less on the cultivated fields (209 and 213 g ha–1).
Article
N2O, NO, NO2, CO2 and CH4 fluxes were measured simultaneously from tilled and compacted soil in a factorial design to investigate the effect of management on trace gas emissions. Six treatments in combinations of with and without N application, tillage and compaction were investigated for a period of 3 weeks using the closed-chamber technique (for N2O, CO2 and CH4) and the open-chamber technique (for NO and NO2). Total NO emissions from the tilled plots were 2.4 times greater than from the non-tilled plots, whereas CO2 emissions were 1.8 times greater from the non-tilled plots. Compaction increased the emissions of N2O and CH4 3.5- and 4.4-fold, respectively, compared with emissions from uncompacted plots. The effects of tillage and compaction on the gaseous emissions are discussed in relation to their production, transport and lifetime within the soil. The results showed that the best option for reducing gaseous emission from fertilised soil, with regards to tillage or compaction, would be the least compacted system, regardless of the tillage status as reflected, at least in the short term, by minimal emissions of N2O and CH4 and to some extent those of NO, NO2 and CO2.
Article
Consideration of the environmental effects of the no-tillage practice should be made on the basis of its effects on both carbon and nitrogen cycles. There is a lack of data on the effects of the no-till management in the cool and humid climate and typical soil types of Northern Europe. We measured the fluxes of nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) on conventionally ploughed agricultural soils and on respective soils that had been under no-till practice for 5–7 years. Ten chamber measurement investigations were carried out during a 10-month period on six pairs of tilled and no-till fields on clayey (Vertic Cambisols, three pairs), coarse (Eutric Regosols, two pairs), and organic (Dystric Histosols, one pair) soils located between latitudes 60° and 62° N. The results suggest that there is a risk of increased N2O emissions in the first years of no-till practice under small grain spring cereal cultivation in Northern European boreal climate. Carbon dioxide emissions measured as total ecosystem respiration were either unchanged, increased or decreased under no-till. Fluxes of CH4 were negligible and not affected by no-till practice. Dry bulk density and soil moisture were higher in no-till soils compared to annually mouldboard ploughed soils. Variation in the greenhouse gas fluxes was best explained by the content of carbon and nitrogen in the topsoil of 0–20 cm.
Article
Methane (CH4) oxidation in soils is the only known biological sink of CH4. The sink strength of agricultural soils is known to be affected by soil properties and agricultural practices. We studied fluxes of CH4 in southern and northern Finland in arable soils with different texture and crops. The annual fluxes ranged from uptake of −1.2 kg CH4 ha−1 to emission of 40 kg CH4 ha−1. The CH4 oxidation decreased in the order loamy sand > well drained peat > clay > poorly drained peat. The more there were macropores or the less there were micropores in the soil, the higher was the mean annual CH4 oxidation rate. Calculated on the basis of the soil type specific CH4 flux rates from our study and the soil type distribution of Finnish agricultural soils, the total agricultural area in Finland would form an annual CH4 sink of −19 Gg CO2 equiv., which is 0.3% of the total reported greenhouse gas emissions from agriculture in 2004.
Article
As in other drained, intensively cultivated Histosols of the world, soil subsidence is a growing concern of vegetable farmers in the muck crops region of North Central, Ohio. Subsidence in organic soils is caused primarily by aerobic degradation of soil organic matter (SOM), which in turn makes available large quantities of once bound C and N. Upon drainage and cultivation, soil C and N dynamics shift drastically. Organic soils transition from CO2 and organic N sinks, to persistent sources, whereas CH4 uptake capacity increases. Therefore, this study was conducted to assess the short-term (within the first year) impact of conversion of intensively tilled organic soils to no-till management. The specific objectives of this study were to: (i) compare soil moisture content, soil temperature, and greenhouse gas (GHG) emission rates from moldboard/disking (MB), no-till (NT), and bare (B) treatments in cultivated organic soils, and (ii) estimate the rate of subsidence associated with these tillage practices. Over the year, soil moisture content (SMC) was significantly higher in MB (0.90 kg kg−1) than B (0.84 kg kg−1) treatments; however NT (0.87 kg kg−1) was not significantly different from either MB or B treatments. Mean annual temperatures at 5 cm depth were significantly higher in B (16.9 °C) compared to MB (16.2 °C) and NT (15.9 °C) treatments The CO2 emissions were not significantly different among treatments, while N2O emissions were significantly higher from MB (96.9 kg N2O-N ha−1 yr−1) than NT (35.8 kg N2O-N ha−1 yr−1) plots. Both CH4 uptake and CH4 emission exhibited low annual flux in all treatments.
Article
Short-term changes in fluxes of nitrous oxide and methane were measured with an automatic opaque chamber method in boreal organic soils growing barley, grass or birch and on bare agricultural organic soil. The diurnal variation in these gas fluxes were compared with that of CO2 production which is known to be highly temperature-dependent. Here, the mean daytime (10:00–16:00) CO2 production rates were 14–23% higher than the mean daily fluxes. The Q10 (air temperature range 15–25 °C) for the CO2 production was 1.5 in the agricultural soils and 1.3 in the forest. The N2O fluxes followed the changes in the temperature of the surface soil (depth of 3 cm) in the agricultural soils. The maximum emissions occurred in the afternoon, a few hours later than the maximum air temperature and CO2 production. There was a clear diurnal variation in the N2O fluxes in all sites. The mean daytime emissions of N2O were up to 1.3-fold higher than the daily average fluxes. At maximum, the daytime emissions were as much as 5-fold higher than those measured during night. All the sites were net sinks for CH4, and no clear diurnal fluctuation was seen. Higher net CH4 uptake during the measuring period was measured in the forest than in the agricultural soils. The results showed that the short-term variation in the N2O fluxes, especially during periods with wide variation in temperature or during periods of rainfall, can cause a 60% overestimation in the N2O emission for boreal organic soils if the daytime fluxes only are measured, a common practice with the manual chamber techniques.
Article
Nitrous oxide (N2O) in soils is produced through nitrification and denitrification. The N2O produced is considered as a nitrogen (N) loss because it will most likely escape from the soil to the atmosphere as N2O or N2. Aim of the study was to quantify N2O production in grassland on peat soils in relation to N input and to determine the relative contribution of nitrification and denitrification to N2O production. Measurements were carried out on a weekly basis in 2 grasslands on peat soil (Peat I and Peat II) for 2 years (1993 and 1994) using intact soil core incubations. In additional experiments distinction between N2O from nitrification and denitrification was made by use of the gaseous nitrification inhibitor methyl fluoride (CH3F). Nitrous oxide production over the 2 year period was on average 34 kg N ha-1 yr-1 for mown treatments that received no N fertiliser and 44 kg N ha-1 yr-1 for mown and N fertilised treatments. Grazing by dairy cattle on Peat I caused additional N2O production to reach 81 kg N ha-1 yr-1. The sub soil (20–40 cm) contributed 25 to 40␘f the total N2O production in the 0–40 cm layer. The N2O production:denitrification ratio was on average about 1 in the top soil and 2 in the sub soil indicating that N2O production through nitrification was important. Experiments showed that when ratios were larger than l, nitrification was the major source of N2O. In conclusion, N2O production is a significant N loss mechanism in grassland on peat soil with nitrification as an important N2O producing process.
Article
Intensively managed grasslands are potentially a large source of nitrous oxide (N2O) in the Netherlands because of the large nitrogen (N) input and the fairly wet soil conditions. To quantify the effects of soil type, N-fertilizer application and grazing on total N2O losses from grassland, fluxes of N2O were measured weekly from unfertilized and mown, N fertilized and mown, and N fertilized and predominantly grazed grassland on a sand soil, a clay soil, and two peat soils during the growing season of 1992. Total N2O losses from unfertilized grassland were 2.5–13.5 times more from the peat soils than from the sand and clay soils. Application of calcium ammonium nitrate fertilizer significantly increased N2O flux on all sites, especially when the soil was wet. The percentage of fertilizer N applied lost to the atmosphere as N2O during the season ranged from 0.5 on the sand soil to 3.9 on one of the peat soils. Total N2O losses were 1.5–2.5 times more from grazed grassland than from mown grassland, probably because of the extra N input from urine and dung. From 1.0 to 7.7% of the calculated total amount of N excreted in urine and dung was emitted as N2O on grazed grassland. The large N2O losses measured from the peat soils, combined with the large proportion of grassland on peat in the Netherlands, mean that these grasslands contribute significantly to the total emission from the country.
Degradation of cultivated peat soils in Northern Norway based on field scale CO 2 , N 2 O and CH 4 emission measurements
  • A Grönlund
  • T E Sveistrup
  • A K Søvik
  • D P Rasse
  • B Klöve
Grönlund A, Sveistrup TE, Søvik AK, Rasse DP, Klöve B. 2006. Degradation of cultivated peat soils in Northern Norway based on field scale CO 2, N 2 O and CH 4 emission measurements. Archives Agron Soil Sci. 52:149-159.
Kvävetillgång i odlade mulljordar i Kvismardalen i Närke [Nitrogen supply to crops in organic soils in the Kvismar Valley in central Sweden
  • B Lindén
Lindén B. 2015. Kvävetillgång i odlade mulljordar i Kvismardalen i Närke [Nitrogen supply to crops in organic soils in the Kvismar Valley in central Sweden]. Uppsala: Department of Soil and Environment (Rapport 16).
International conventions, agencies, agreements and programmes -implications for peat and peatland management
  • J O Rieley
  • S Lubinaite
Rieley JO, Lubinaite S. 2014. International conventions, agencies, agreements and programmes -implications for peat and peatland management. Jyväskylä: International Peat Society.
Swedish meteorological and hydrological institute
  • Smhi
SMHI. 2014. Swedish meteorological and hydrological institute, Norrköping. Available from: http://www.smhi.se/ klimatdata Soil Survey Staff. 2014. Keys to soil taxonomy. 12th ed. Washington, DC: USDA-Natural Resources Conservation Service.