Managed agricultural ecosystems (grassland and cropland) are an important source and/or sink for greenhouse gases (GHG) as well as for reactive trace gases. Due to the simultaneous influence of various environmental drivers and management activities (e.g. fertilizer application, harvest, grazing) the flux patterns are often complex and difficult to attribute to individual drivers. Management related mitigation options may often result in trade-offs between different GHG or between emission of GHG and reactive gases like NH3, NO, or VOCs.
The session addresses experimentalists and modelers working on carbon and nitrogen cycling processes and related fluxes on plot, field, landscape, and regional scale. It is open to a wide range of studies including the development and application of new devices, methods, and model approaches as well as field observations and process studies.
Particularly welcome are studies on the full carbon, nitrogen or GHG budgets, as well as studies comparing GHG and reactive gas exchange. We also encourage contributions about emission factors for relevant gases.
vPICO presentations: Thu, 29 Apr
Emissions of ammonia (NH3) from agriculture have a significant impact on the environment. Its atmospheric transport and subsequent deposition has been shown to alter nutrient-poor ecosystems thereby reducing biodiversity. As the most abundant base in the atmosphere, NH3 plays a key role in secondary aerosol formation impacting air quality and climate. Due to the lack of long term observations and challenges in performing NH3 flux measurements, large uncertainties exist in both emission quantification from fertilized crop fields and in the bi-directional exchange of NH3 with agroecosystems. We measured NH3 fluxes above a corn field using the eddy covariance technique together with a quantum cascade laser spectroscopy analyzer over two consecutive growing seasons in 2017 and 2018. We found that after initial NH3 emissions following fertilizer application, periods of both NH3 emission and deposition with similar flux magnitudes prevailed throughout the growing seasons (ranging approximately between ±300 ng m-2 s-1), highlighting the importance of the corn crop canopy for regulating the net NH3 exchange. To evaluate the underlying processes of the NH3 bi-directional exchange, a two-layer compensation point model was used. Based on the large range of environmental conditions encountered during the extensive flux measurements periods, the validity of different parameterizations could be assessed. In particular, processes regulating stomatal and non-stomatal flux pathways will be discussed.
How to cite: Moravek, A., Singh, S., Pattey, E., Hdrina, A., Li, T., Pelletier, L., Admiral, S., and Murphy, J.: Bi-directional exchange of ammonia above a corn crop canopy: from flux measurements to model parameterizations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15229, https://doi.org/10.5194/egusphere-egu21-15229, 2021.
We designed a fast-response two-channel converter called NOy-TRANC for eddy covariance measurements of reduced and oxidized reactive nitrogen compounds (Nr). It is a combination of the Total Reactive Atmospheric Nitrogen Converter (TRANC), which converts all reactive forms of nitrogen (ΣNr), except for nitrous oxide (N2O) and molecular nitrogen (N2), to nitrogen monoxide (NO), and a heated gold catalyst, which converts NOy to NO. NOx, which is the sum of NO and nitrogen dioxide (NO2), and higher oxidized nitrogen compounds are described by the term NOy. The NOy-TRANC is coupled to a two-channel chemiluminescence detector (CLD) for measuring NO. Due to a high sampling frequency and a fast response time, the system meets the requirements for flux calculation based on the eddy-covariance method. With this setup, a separation of ΣNr fluxes in reduced and oxidized nitrogen can be done.
We conducted flux measurements at a typically deeply drained, intensively managed grassland site on peat in an intensive dairy region in Northwest Germany for one year. ΣNr concentration was 12.4 ppb and NOy concentration was 6.3 ppb on average. We observed mostly emission fluxes at the site after the first fertilization in early spring. The winter month were characterized by slight nitrogen dry deposition. Monthly median of ΣNr fluxes ranged from -8 to 57 ng N m-2s-1 with the exchange being enhanced during summer. We found that ΣNr and NOy dry emission were comparatively higher under dry conditions, i.e., low air humidity and soil moisture. The emission factors of applied nitrogen after the respective fertilization released as NHx can reach up to 2.0%.
Site management included five fertilization events and five grass cuts. The first fertilization event was at the end of March starting with mineral fertilizer followed by organic fertilizer a week later. The fertilization scheme was the same for second and third event, but approximately two days were between the application of the fertilizer types. The second fertilization was at the end of May, subsequent fertilizations were done in intervals of 4-5 weeks. Only for the fourth and fifth event, organic fertilizer was used. Organic fertilizer was injected in slits made by v-shaped discs, mineral fertilizer was spread on the soil surface. The emission factor was lower after the first fertilization event compared to events in summer probably indicating a beginning nitrogen saturation after the first fertilization.
Our study demonstrates the application of a novel measurement technique for the determination reactive nitrogen compounds and gives insight into the exchange characteristics of reactive nitrogen under a common agricultural management.
How to cite: Wintjen, P., Rüffer, J., Sokolowsky, L., Ammann, C., and Brümmer, C.: Flux measurements of NHx and NOy with a dual-channel converter above an intensively managed grassland on peat, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12347, https://doi.org/10.5194/egusphere-egu21-12347, 2021.
The recycling of organic waste in biogas plants is proposed as a measure to close nutrient cycles and possibly reduce nitrogen losses such as nitrous oxide emissions and nitrate leaching. Ammonia volatilization after fertilizer spreading is yet another nitrogen loss pathway which is often understudied and not yet fully understood but the knowledge is needed in order to optimize fertilizer management. We therefore aimed to quantify the volatilization of ammonia after the trail-hose application of digestates compared to cattle slurry. We hypothesize that digestates have larger and longer lasting nitrogen losses via ammonia volatilization due to higher NH4+ contents and pH values compared to fresh manure. In this project, digested and un-digested organic fertilizers were applied twice per year in a 2.5-years field experiment with three consecutive arable crops (maize, winter wheat and winter barley) under organic farming. We used Automated Low Cost Impinger Systems to measure ammonia emissions after fertilizer application. The emissions were then modeled using the backwards Langrangian stochastic dispersal model with respect to wind conditions. A preliminary presentation of the data indicates that ammonia emissions from the cattle slurry, slurry-based digestate, and industrial digestate are alternately higher or lower. In 2018, emissions from cattle slurry tended to be lower than those from slurry-based digestate and industrial digestate, while in 2019 and 2020 all three liquid organic fertilizers had similar emissions. In the measurement period after the second fertilizer application in 2018, which took place at the end of May, conspicuously high emissions were measured. This can be explained by the high temperatures during this period. Adaptive strategies in fertilizer management should thus consider reduced inputs of organic fertilizers during warm periods.
How to cite: Efosa, N., Krause, H.-M., Häni, C., Six, J., and Bünemann, E.: Ammonia emissions from cattle slurry and digestates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15587, https://doi.org/10.5194/egusphere-egu21-15587, 2021.
In recent years there has been growing scientific interest in agricultural emissions of volatile organic compounds (VOCs) and their potential effects on air quality and the biogeochemical cycling of carbon and nitrogen. Among the many VOCs emitted, amines are particularly challenging to measure with currently available instruments.
In light of these analytical challenges, the Atmospheric Chemistry Group at the Department of Chemistry of the University of Oslo has developed a novel analytical instrument for the detection of atmospheric amines. The instrument is a modified version of a commercial Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS). After modification, this instrument has proven able to detect atmospheric amines down to single-digit-ppt levels. This instrument also benefits from a very short response time, which makes it possible to monitor rapid dynamic changes of amine concentrations in the atmosphere.
The novel instrument was deployed at the Livestock Production Research Centre (SHF) of the Norwegian University of Life Sciences (NMBU) in Ås (Norway) for characterizing agricultural emissions of VOCs in general, and of amines in particular.
Data analysis has so far revealed a very complex VOC emission pattern. Methylamine, trimethylamine and skatole were among the atmospheric amines detected in the ambient air in proximity of the facility. In addition to the field measurements, we also carried out laboratory experiments for analyzing VOCs in the dynamic headspace of different source materials (manure, animal feed, straw litter, etc.).
We will present the new instrument and preliminary data collected from this measurement campaign.
How to cite: Håland, A., Mikoviny, T., Syse, E. E., Oskam, I. C., and Wisthaler, A.: Amine Emissions from Agricultural Sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13245, https://doi.org/10.5194/egusphere-egu21-13245, 2021.
The presence of cows on a pasture considerably modifies exchanges of biogenic volatile organic compounds (BVOCs). By regulating the biomass present, they can have an impact on the constitutive flux (exchanges from soil and grass that are not induced by leaf wounding or trampling by cows) but they can also cause direct emissions from exhalation and indirect emissions by leaf injury (grazing), trampling and wastes. In this study conducted on the ICOS pasture site of Dorinne (Belgium), we disentangled these different sources/sinks for three oxygenated BVOCs commonly exchanged on grasslands (methanol, acetaldehyde and acetone), using a combination of turbulent flux measurements, enclosure flux measurements, tools to detect the presence and activity of cows in the footprint of the turbulent flux measurements and a flux footprint model. Direct exhalation emissions were low, representing only 2.3% and 10% of the spring total flux of methanol and acetone respectively. Comparison of grazed and non-grazed enclosures pointed out that emissions following leaf wounding were significant for all studied BVOCs, decreased exponentially with time to become negligible after maximum five days. Cow indirect emissions at the pasture scale (turbulent flux measurements) where likely dominated by grazing and were shown to be a major component of the total diurnal flux for each of the three studied BVOCs. Comparison with a hay meadow also showed that the temporal dynamics of those BVOC emissions were very different according to the grass management type, calling for specific parametrization in up-scaling emission models.
How to cite: Heinesch, B., Michel, C., Amelynck, C., Schoon, N., Mozaffar, A., Aubinet, M., Bachy, A., and Dumortier, P.: The role of cows on OVOC exchanges of a pasture, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13117, https://doi.org/10.5194/egusphere-egu21-13117, 2021.
The annual global leaf litter production has been estimated between 75 and 135 Pg DM yr-1 contributing to the 10% of the global annual emission of acetone and methanol. Besides their impact on atmospheric chemistry, little attention has been drawn to leaves litter and their contribution to the bVOC emissions and their SOA formation potential.
The purpose of this study is to analyze the bVOC (biogenic volatile organic compounds) emissions from rapeseed leaves litter and their contribution to SOA (secondary organic aerosol) formation under three different conditions: (I) the presence of a UV light irradiation (II) the presence of ozone, and (III) a combination of the previous two. To reach this goal, bVOC and aerosol numbers have been measured for 6 days in a controlled atmospheric chamber containing leaf litter samples.
Results showed that VOC emission profiles were affected by the UV light irradiation, which increased the summed VOC emissions compared to the experiment with O3. Furthermore, the diversity of the VOC emitted from the rapeseed litter increased with the UV light irradiation. The highlight of this study is that the SOA formation rate observed when leaf litter was exposed to both UV light and O3 indicates a potentially large source of atmospheric pollution at the local scale. To our knowledge, this study investigates for the first time the effect of UV irradiation and O3 exposure on both VOC emissions and SOA formation for leaf litter samples. A detailed discussion about the processes behind the biological production of the most important VOC is proposed.
How to cite: Abis, L., Kalalian, C., Wang, T., Lunardelli, B., Perrier, S., Loubet, B., Ciuraru, R., and George, C.: Biogenic VOC profiles emissions of Rapeseed leaf litter and their SOA formation potential, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14981, https://doi.org/10.5194/egusphere-egu21-14981, 2021.
The ecosystem-atmosphere flux of biogenic volatile organic compounds (BVOCs) has important impacts on tropospheric oxidative capacity and the formation of secondary organic aerosols, influencing air quality and climate. In particular, this is true in managed boreal forests in the Northern Hemisphere, where BVOC emissions often dominate over anthropogenic sources of VOC.
Here we present measurements of BVOCs in a managed boreal forest located at the ICOS station Norunda in Sweden, collected using proton transfer reaction mass spectrometry (PTR-MS). This managed forest consists of a mix of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). These long-term PTR-MS measurements were collected at six heights (4m, 8.5m, 13.5m, 19m, 24.5m, and 33.5m) in the forest canopy over several periods during 2014 to 2016. Ozone concentrations were simultaneously measured in conjunction with these PTR-MS measurements. The main BVOCs investigated with the PTR-MS were isoprene, monoterpenes, methanol, acetaldehyde, and acetone. The distribution of BVOC sources and sinks in the forest canopy was explored using several Lagrangian dispersion matrix methods, including localized and continuous near-field theory. The canopy resistance and deposition velocities for ozone and the BVOCs were investigated, and the results for isoprene and monoterpene emissions were found to agree well with several standard BVOC emission algorithms. These results will have importance for constraining BVOC emission estimates from managed boreal forests in the future.
How to cite: Petersen, R. C., Rinne, J., Holst, T., and Mölder, M.: Sources and Sinks of BVOCs in a Managed Boreal Forest, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15430, https://doi.org/10.5194/egusphere-egu21-15430, 2021.
Semiarid oak savannas (grasslands with scattered trees), partially covered, subject to regular droughts, grazing, and high levels of solar radiation, are nonetheless, typically carbon sinks regarding CO2. However, dehesas are a productive system, a trait shared with other savannas, and they are shaped by their uses for economic production. One of its multiple uses, livestock extensive farming, key to its economic profitability and to the preservation of the agrosilvopastoral system structure, modifies the Greenhouse gas (GHG) balance by adding a significant amount of CH4 and N2O into the cycle. Recent reports and publications have evaluated and compared different types of livestock management within the context of climate change. GHG emissions, extensive use of the soil resource, or the introduction of nitrogen into the system, are some of the generated effects that cause a negative evaluation of extensive farming. Nevertheless, the importance of this sector, given its extension and impact on production and rural development, demands a more rigorous evaluation. It is necessary to precisely account for the fluxes in their totality (including the CO2 sink effect) and the relationships between them. Currently, there are few studies that determine the GHG balance of dehesas, and they are mainly centred on CO2 fluxes without integrating the influence of livestock, or in meadows without a tree layer (which changes the CO2 balance). The net global warming potential of dehesas is unknown, given that very few direct and long-term flux measurements have been taken on them. In this work, CO2 and H2O fluxes from an eddy covariance tower located in an Andalusian dehesa were processed (standard corrections), filtered and homogenized, including filling gaps using artificial neural networks. We calculated the annual CO2 budget since 2015, to assess the sink/source nature of the area. In a modeling exercise to be able to close the carbon cycle, we estimated CH4 and N2O depending on the number of livestock present in the area by season/year, evaluating the tipping point.
How to cite: Andreu, A., Carpintero, E., Gómez-Giraldez, P., and González-Dugo, M. P.: Accounting for carbon exchanges in a semiarid oak savanna (dehesa)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14189, https://doi.org/10.5194/egusphere-egu21-14189, 2021.
The Philippines' agriculture sector continues contributing to country-wide soil trace gas emissions; however, field-based estimation of emissions from this sector remains inadequate. While there’s a need to increase crop production to provide for a fast-increasing population, it is equally essential to reduce greenhouse gases (GHG) from agricultural production to protect the environment. A reliable assessment of soil GHG is a requisite to attain these, thus the present study. We conducted spatially replicated quantification of soil greenhouse gas fluxes, i. e. N2O, CH4, and CO2, with monthly measurements from May 2018 to May 2019, as well astheirsoil controlling factors in nine plots of secondary forest and ten farms, all on comparable Andosol soil in Leyte Island, the Philippines. The management practices of these vegetable farms were those implemented by the farmers, and our measurements were carried out on these actual farm practices, reflecting their commonly varied fertilization rates (200 – 610 kg N ha-1 cropping period-1 with 2 – 3 cropping periods each year). Soil N2O emissions from vegetable farms were larger than the forest (P ≤0.01) and were stimulated during the dry than the wet season (P ≤0.01). Its temporal variation was mainly driven by soil NO3– (r = 0.52, P ≤0.01). Large stocks of soil extractable NO3– in the top 50 cm (9250 ± 2830 mg N m–2, mean ± SE) and 50 – 100 cm soil depth (11255 ± 5980 mg N m–2) supported the substantial soil N2O emissions from these vegetable farms, which were larger than those from other agricultural areas in South East Asia on similar soil and climate. These small-scale vegetable farms had annual fluxes of 12.7 ± 2.6 kg N2O–N, –1.1 ± 0.1 kg CH4–C and 11.6 ± 0.7 Mg CO2–C ha-1 yr-1, whereas the secondary forest as reference land use had 0.10 ± 0.02 kg N2O–N, –2.0 ± 0.2 kg CH4–C, and 8.2 ± 0.7 Mg CO2–C ha-1 yr-1. The forest had larger soil CH4 uptake than the vegetable farms (P ≤0.01). For the forest, CH4 uptake was positively correlated with soil moisture (r = 0.60, P ≤0.01), suggesting diffusion limitation of atmospheric CH4 into the soil and/or soil CH4 production during high rainfall months. For the vegetable farms, CH4 uptake was negatively correlated with both soil NO3– and NH4+ (r = –0.46, P ≤0.01), suggesting CH4 consumption enhanced by mineral N. Soil CO2 emissions were higher in vegetable farms relative to the forest (P ≤0.01), reflecting the former’s reduced soil organic carbon stocks in the top 1 m (P ≤0.01) but compensated with regular application of chicken manure (460 – 1940 kg C ha-1 cropping period-1) as organic fertilizer. Our study expounded understanding on the extent of changes in soil GHG from an Andosol soil that underwent land-use conversion. Such data will be beneficial in developing sound management and policy strategies for reducing soil GHG fluxes from this economically vulnerable agricultural sector.
How to cite: Quiñones, C. M. O., Veldkamp, E., Lina, S. B., Bande, M. J. M., Arribado, A. O., and Corre, M. D.: Soil trace gas fluxes from secondary forest converted to small-scale vegetable farms on an Andosol soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2433, https://doi.org/10.5194/egusphere-egu21-2433, 2021.
Tillage practices influence soil CO2 emissions, hence many research investigate the long-term effects of conservation and conventional tillage methods e.g. ploughing and no-tillage on soil greenhouse gas emission.
The experiment site is an 18-years-old long-term tillage trial established on chernozem soil. During 2020, we took weekly CO2 emission measurements in the mouldboard ploughing (MP), no-tillage (NT), and shallow cultivation (SC) treatments Tillage depth was 26-30 cm, 12-16 cm and 0 cm in the cases of MP, SC and NT respectively. The experiment was under wither oat cultivation.
We investigated the similarity in the CO2 emission trends of SC to MP or NT treatments. Besides CO2 emission measurements, we also monitored environmental parameters such as soil temperature (Ts) and soil water content (SWC) in each treatment.
During the investigated year (2020 January - December) SC had higher annual mean CO2 emission (0.115±0.083 mg m-2 s-1) compared to MP (0.099±0.089 mg m-2 s-1) and lower compared to NT (0.119±0.100 mg m-2 s-1). The difference of the CO2 emissions was significant between SC and MP (p<0.05); however, it was not significant between SC and NT (p>0.05) treatments. The Ts dependency of CO2 emission was moderate in all treatments. CO2 emissions were moderately depended on SWC in MP and SC, and there was no correlation between these parameters in NT.
The annual mean CO2 emission of the SC treatment was more similar to the NT, than to the MP treatment.
How to cite: Dencső, M., Horel, Á., Bakacsi, Z., and Tóth, E.: Comparison of soil CO2 emissions from three different tillage methods on chernozem soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14675, https://doi.org/10.5194/egusphere-egu21-14675, 2021.
The agriculture sector is one of the largest users of water and a significant source of greenhouse gas (GHG) emissions. The development of low-GHG-emission and water-conserving agriculture will inevitably be the trend in the future. Because of the physiological differences among crops and their response efficiency to external changes, changes in planting structure, climate and input of production factors will have an impact on regional agricultural water use and GHG emissions. This paper systematically analyzed the spatial-temporal evolution characteristics of crop planting structure, climate, and production factor inputs in Heilongjiang Province, the main grain-producing region of China, from 2000 to 2015, and quantified the regional agricultural water use and GHG emissions characteristics under different scenarios by using the Penman-Monteith formula and the Denitrification-Decomposition (DNDC) model. The results showed that the global warming potential (GWP) increased by 15% due to the change in planting structure. A large increase in the proportion of rice and corn sown was the main reason. During the study period, regional climate change had a positive impact on the water- saving and emission reduction of the agricultural industry. The annual water demand per unit area decreased by 19%, and the GWP decreased by 12% compared with that in 2000. The input of fertilizer and other means of production will have a significant impact on GHG emissions from farmlands. The increase in N fertilizer input significantly increased N2O emissions, with a 5% increase in GWP. Agricultural water consumption and carbon emissions are affected by changes in climate, input of means of production, and planting structure. Therefore, multiple regulatory measures should be taken in combination with regional characteristics to realize a new layout of planting structure with low emissions, water conservation, and sustainability.
How to cite: Sun, S. and Tang, Y.: Impact assessment of climate change and human activities on GHG emissions and agricultural water use, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-57, https://doi.org/10.5194/egusphere-egu21-57, 2021.
Agricultural greenhouse gas (GHG) emissions account for almost half of New Zealand’s total emissions, and therefore considerable attention has been given to identifying and testing mitigation options. At plot scale, plantain (Plantago lanceolate L.) in the pasture sward has been demonstrated to reduce nitrous oxide (N2O) emissions but has not been tested at paddock scale on an operating farm. Our aim was to test the efficacy of a pasture sward containing >30% plantain as a GHG mitigation option at paddock scale (2.5-3 ha) on a year-round rotationally grazed commercial dairy farm in the Waikato region of New Zealand. Utilising eddy covariance measurements of CO2, N2O and CH4 coupled to farm management records, N2O, carbon (C) and GHG balances (sign convention: positive value = emission to the atmosphere) were calculated for two adjacent paddocks – a control paddock containing an existing ryegrass/clover sward (RC), and a paddock that underwent renovation with the establishment of a ryegrass/clover/plantain sward (RCP). Establishment of RCP was via spraying and direct drilling and occurred in March 2018 (autumn). For the establishment period between initial herbicide application and the first grazing of the new RCP sward 66 days later, N2O emissions were 2.58 kg N ha-1 compared with 1.69 kg N ha-1 for the RC paddock. During the same period, C losses from the RCP paddock were greater than from the RC paddock (2.40 t C ha-1 for RCP and 1.29 t C ha-1 for RC) primarily due to reduced photosynthetic inputs associated with the herbicide application. The GHG budget (including enteric methane emissions from feed grown and eaten in the paddock) during the 66 day establishment period was an emission of 6.56 t CO2-eq ha-1 for RC and 9.85 t CO2-eq ha-1 for RCP. Unfortunately, the RCP sward establishment was poor, and after one year, total pasture production was unexpectedly lower than RC. Additionally, plantain accounted for <7% of the total RCP dry matter production. N2O, C and GHG balances for RCP in the first year following (and including) establishment were 6.61 kg N ha-1 y-1, 3.25 t C ha-1 y-1 and 21.40 t CO2-eq ha-1 y-1 respectively, while for RC they were 7.21 kg N ha-1 y-1, 0.95 t C ha-1 y-1 and 13.29 t CO2-eq ha-1 y-1. Due to the poor establishment of plantain, any N2O and GHG benefits of this species were unable to be initially concluded, but additional plantain was sown and measurements are ongoing. However, we did identify several relevant findings: any N2O/GHG benefits of plantain must firstly offset emissions (including C losses) associated with the establishment of the sward (>3 t CO2-eq ha-1 in this study), and furthermore, there is a risk that should the establishment be poor, GHG emissions can be considerably greater (and pasture production lower) than an existing pasture.
How to cite: Wall, A., Goodrich, J., Wecking, A., Pronger, J., Campbell, D., and Schipper, L.: Plantain as a GHG mitigation option: N2O, C and GHG balances from an intensively grazed New Zealand dairy pasture, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13415, https://doi.org/10.5194/egusphere-egu21-13415, 2021.
Agricultural activities can have several adverse impacts on the environment; such as important greenhouse gas (GHG) emissions. To implement effective mitigation measures and create effective policies, it is necessary to know the full carbon and nitrogen budgets of agro-ecosystems. However, very often, information regarding the pools or fluxes involved in the carbon and nitrogen cycles is limited, and essential complementary data needed for a proper interpretation is lacking.
This study aimed to quantify all the relevant pools and fluxes of a winter rapeseed, a widely spread crop in the Europe and Baltic regions. The N2O and CH4 fluxes were measured weekly using the closed static chamber method from August 2016 to August 2017 in a winter rapeseed field in Central Estonia. Additionally, nutrient leaching and soil chemical parameters, as well as environmental parameters like soil moisture, electrical conductivity and temperature were monitored. At the end of the season, the rapeseed and weed biomasses were collected, weighed and analyzed. The remaining relevant fluxes in the N cycle were calculated using various non-empirical methods: NH3 volatilization was estimated from slurry and environmental parameters, N deposition and NOx emissions were obtained from national reports, and N2 emissions were calculated with the mass balance method. Regarding the C cycle, gross primary production (GPP) of the rapeseed field was also calculated by the mass balance method. Simultaneously, for comparison and validation purposes, GPP was estimated from the data provided by MOD17A2H v006 series from NASA, and N2 was estimated from the measured emissions of N2O using the N2:N2O ratio calculated from the DAYCENT model equations.
N2 emissions and GPP were the biggest fluxes in the N and C cycles, respectively. N2 emissions were followed by N extracted with plant biomass in the N cycle, while in the carbon cycle soil and plant respiration and NPP were the highest fluxes after GPP. The carbon balance was positive at the soil level, with a net increase in soil carbon during the period, mainly due to GPP carbon capture. Contrarily, the nitrogen balance resulted in a net loss of N due to the losses related to gaseous emissions (N2 and N2O) and leaching.
To conclude, it was possible to close the C and N budgets, despite the inherent difficulties of estimating the different C and N environmental pools and fluxes, and the uncertainties deriving from some of the fluxes estimations.
How to cite: Escuer-Gatius, J., Lõhmus, K., Shanskiy, M., Kauer, K., Vahter, H., Mander, Ü., Astover, A., and Soosaar, K.: Carbon and nitrogen budgets of a winter rapeseed field in Estonia: a methodology for the quantification of all relevant pools and fluxes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15668, https://doi.org/10.5194/egusphere-egu21-15668, 2021.
The need to sustain global food demand while mitigating greenhouse gases (GHG) emissions is a challenge for agricultural production systems. Since the reduction of GHGs has never been a breeding target, it is still unclear to which extend different crop varieties will affect GHG emissions. The objective of this study was to evaluate the impact of N-fertilization and of the use of growth regulators applied to three historical and three modern varieties of winter wheat on the emissions of the three most important anthropogenic GHGs, i.e. carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Furthermore, we aimed at identifying which combination of cultivars and management practises could mitigate GHG emissions in agricultural systems without compromising the yield. GHG measurements were performed using the closed chamber method in a field experiment located in Göttingen (Germany) evaluating three historical and three modern winter wheat varieties, with or without growth regulators under two fertilization levels (120 and 240 kg nitrogen ha-1). GHG measurements were carried out for 2 weeks following the third nitrogen fertilizer application (where one third of the total nitrogen was applied), together with studies on the evolution of mineral nitrogen and dissolved organic carbon in the soil. Modern varieties showed significantly higher CO2 emissions (i.e. soil and plant respiration; +23 %) than historical varieties. The soils were found to be a sink for CH4, but CH4 fluxes were not affected by the different treatments. N2O emissions were not significantly influenced by the variety age or by the growth regulators, and emissions increased with increasing fertilization level. The global warming potential (GWP) for the modern varieties was 7284.0 ± 266.9 kg CO2-eq ha-1. Even though the GWP was lower for the historic varieties (5939.5 ± 238.2 kg CO2-eq ha-1), their greenhouse gas intensity (GHGI), which relates GHG and crop yield, was larger (1.5 ± 0.3 g CO2-eq g-1 grain), compared to the GHGI of modern varieties (0.9 ± 0.0 g CO2-eq g-1 grain), due to the much lower grain yield in the historic varieties. Our results suggest that in order to mitigate GHG emissions without compromising the grain yield, the best management practise is to use modern high yielding varieties with growth regulators and a fertilization scheme according to the demand of the crop.
How to cite: von der Lancken, E., Nasser, V., Hey, K., Siebert, S., and Meijide, A.: Effect of wheat varieties and growth regulators on soil greenhouse gas emissions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8605, https://doi.org/10.5194/egusphere-egu21-8605, 2021.
The agricultural emissions are the dominant sources of N2O and CH4 in the Netherlands. In this study, we have estimated nocturnal surface fluxes of both N2O and CH4 using atmospheric measurements at the Cabauw tall tower (4.927◦ E, 51.971◦ N, - 0.7 m a.s.l.). The nocturnal N2O and CH4 surface fluxes were derived using two different methods, the vertical gradient method (VGM), i.e. the sum of the storage flux and the turbulent flux, and the radon-tracer method (RTM), for the period of March 2017-December 2018 and 2016-2018, respectively. For N2O, we show that a few events occurring between May 30 and June 4 in 2018 dominated the monthly means. Using the VGM, we have estimated the annual mean nocturnal surface flux to be 0.59 ± 0.38 g/m2/yr (1 σ, the same as below) and 0.53 ± 0.19 g/m2/yr with and without events, respectively. The fluxes are high in the summer and low in the winter, with a seasonal amplitude of around 1.0 g/m2/yr and 0.5 g/m2/yr, with and without events, respectively, which is likely caused by the seasonality of agricultural activities. For CH4, the annual mean nocturnal surface flux is 12.1 ± 3.3 g/m2/yr and the amplitude is around 9.9 g/m2/yr. Using the RTM, the mean fluxes of the whole period for N2O and CH4 are estimated to be 1.18 ± 2.25 (1.08 ± 1.29, without the events) g/m2/yr and 26.9 ± 24.8 g/m2/yr, respectively; in contrast to the VGM, no apparent seasonal pattern has been found. However, there is a good linear correlation between the estimated N2O fluxes from the two methods and the monthly means show a similar pattern when the same nights are considered; the R-squared value is around 0.9 with events and 0.6 without events, and the slope varies from 1.9 to 0.8 when different estimates of radon fluxes are used. Furthermore, we found that large N2O fluxes are related to the amount of rainfall occurring days before, with the correlation coefficient of around 0.6 (p value<0.01). For CH4, there is no correlation between the estimated CH4 fluxes from the two methods. Our findings demonstrate that nocturnal N2O and CH4 fluxes in the Cabauw area are highly variable and vary over different seasons, and that both VGM and RTM are useful to quantify regional N2O and CH4 fluxes.
How to cite: Tong, X., Bosveld, F., Hensen, A., Scheeren, B., Frumau, A., and Chen, H.: Nocturnal surface fluxes of N2O and CH4 determined from atmospheric measurements at the Cabauw tall tower, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14400, https://doi.org/10.5194/egusphere-egu21-14400, 2021.
Greenhouse gas (GHG) emissions contribute to climate change. Agricultural production contributes 10 – 14 % of the global anthropogenic GHG emission, including 37 % from soils (Paustian et al., 2016). Monitoring and analysis of emissions from agriculture is the basis for reducing GHG emissions and applying mitigation options. Measuring and estimating emissions from the agricultural sector are challenging and modelling is a useful tool to capture the heterogeneity of the dynamics. Agricultural management is the main driver for the carbon and nitrogen dynamics in croplands, which makes model approaches difficult, as potentially there is great heterogeneity in the influencing factors, but also a lack of robust data for management data for larger scales. Additionally, measurements of GHG emissions are scarce, on small (spatial and temporal) scales, or do not reflect the entire range of system variable combinations. This hinders the evaluation of large scale simulation results. The objective of the study was to simulate the GHG emissions (CO2 and N2O) for European croplands and use national inventory data for the evaluation of the results. We used the model ECOSSE which is based on the carbon model RothC and the nitrogen model SUNDIAL. For yield production, the primary production model MIAMI is coupled with ECOSSE. The model structure allows small scale differences (resolution for simulation is 0.1°) to be captured, while simulating monthly time steps. This balances the uncertainty of the available input data with the accuracy of the simulated results. The model shows reasonable results for the CO2 emissions, but underestimates heterotrophic respiration, which leads to an overestimation of carbon fluxes to the soil. Nitrogen emissions are underestimated due to underestimation of fertilizer applications in some hot spots. The comparison with national inventories that depend mainly on statistics using simpler approaches shows differences to the simulation approach, which indicates the strong dependency of the emissions on the management data. The model approach provides the spatial distribution of the emissions as well as inter-annual dynamics. The changes on the model showed already the improved performances by the model and the extension to include more target variables. More sub-national and sub-annual data sets for evaluation will allow a further improvement of the model performance.
How to cite: Kuhnert, M., Martin, M., Mcgrath, M., and Smith, P.: Modelling of greenhouse gas emissions from European croplands with the biogeochemical model ECOSSE, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12249, https://doi.org/10.5194/egusphere-egu21-12249, 2021.
Agricultural soils are a significant source of greenhouse gas (GHG) emissions. To study these emissions, we are currently building three research platforms that consist of full eddy covariance instrumentation for determination of net ecosystem carbon dioxide exchange and fluxes of methane and nitrous oxide. These platforms will be completed with supporting weather, plant and soil data collection. Two of our platforms are sites on organic soils with a thick peat layer (>60 cm) and the third one is on a mineral soil (silt loam). To study the role of the grassland management practises at these sites, we have initiated ORMINURMI-project. Here, we will characterise the effects of ground water table (high vs. low), crop renewal methods (autumn vs. summer) and plant species (tall fescue vs. red glover grass) on greenhouse gas budgets of grass production. Also effect on yield amount and nutrient quality will be determined. In this presentation, we will present the preliminary data collected at these research platforms and our plans for the use of these data in the coming years.
How to cite: Lind, S., Maljanen, M., Myllys, M., Räty, M., Kykkänen, S., Korhonen, P., Termonen, M., Shurpali, N., and Virkajärvi, P.: GHG mitigation potential of agricultural management practises on mineral and organic soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5567, https://doi.org/10.5194/egusphere-egu21-5567, 2021.
Monoculture croplands are considered as major sources of the greenhouse gas, nitrous oxide (N2O). The conversion of monoculture croplands to agroforestry systems, e.g., integrating trees within croplands, is an essential climate-smart management system through extra C sequestration and can potentially mitigate N2O emissions. So far, no study has systematically compared gross rates of N2O emission and uptake between cropland agroforestry and monoculture. In this study, we used an in-situ 15N2O pool dilution technique to simultaneously measure gross N2O emission and uptake over two consecutive growing seasons (2018 - 2019) at three sites in Germany: two sites were on Phaeozem and Cambisol soils with each site having a pair of cropland agroforestry and monoculture systems, and an additional site with only monoculture on an Arenosol soil prone to high nitrate leaching. Our results showed that cropland agroforestry had lower gross N2O emissions and higher gross N2O uptake than in monoculture at the site with Phaeozem soil (P ≤ 0.018 – 0.025) and did not differ in gross N2O emissions and uptake with cropland monoculture at the site with Cambisol soil (P ≥ 0.36). Gross N2O emissions were positively correlated with soil mineral N and heterotrophic respiration which, in turn, were correlated with soil temperature, and with water-filled pore space (WFPS) (r = 0.24 ‒ 0.54, P < 0.01). Gross N2O emissions were also negatively correlated with nosZ clade I gene abundance (involved in N2O-to-N2 reduction, r = -0.20, P < 0.05). These findings showed that across sites and management systems changes in gross N2O emissions were driven by changes in substrate availability and aeration condition (i.e., soil mineral N, C availability, and WFPS), which also influenced denitrification gene abundance. The strong regression values between gross N2O emissions and net N2O emissions (R2 ≥ 0.96, P < 0.001) indicated that gross N2O emissions largely drove net soil N2O emissions. Across sites and management systems, annual soil gross N2O emissions and uptake were controlled by clay contents which, in turn, correlated with indices of soil fertility (i.e., effective cation exchange capacity, total N, and C/N ratio) (Spearman rank’s rho = -0.76 – 0.86, P ≤ 0.05). The lower gross N2O emissions from the agroforestry tree rows at two sites indicated the potential of agroforestry in reducing soil N2O emissions, supporting the need for temperate cropland agroforestry to be considered in greenhouse gas mitigation policies.
How to cite: Luo, J., Beule, L., Shao, G., Veldkamp, E., and Corre, M. D.: Gross rates of soil N2O emission and uptake and denitrification gene abundance in temperate cropland agroforestry and monoculture systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-886, https://doi.org/10.5194/egusphere-egu21-886, 2021.
Agricultural soils are an important source of nitrous oxide (N2O) emission and are mainly affected by the application of N fertilization. In addition to the effect of fertilizer form (mineral/organic), N2O production and consumption processes in agricultural systems are influenced by the soil characteristics. However, knowledge of this is still very limited for erosion-affected arable soils. Therefore, the aim of our investigations was to find the impact of soil erosion state associated with the landscape position and N fertilization form have on N2O emission. This information is needed to evaluate the effects/benefits of new agricultural practices in future mitigation strategies aiming towards lower N2O emissions.
We present 3 years of N2O flux measurements in a two-factorial experiment by using a non-flow-through non-steady-state (NFT-NSS) manual chambers. Three sites were established on the summit position having similar soil type (Albic Luvisols; non-eroded soil) and were treated with organic fertilizer (100% organic biogas fermented residues (BFR)), mineral fertilizer (100% mineral calcium ammonium nitrate (CAN)), and a mixture of both fertilizers (50% CAN + 50% BFR). Two additional sites were established on the extremely eroded soil (Calcaric Regosols; on a steep slope with very dense parent material) and at a colluvial site in a depression (Endogleyic Colluvic Regosols) and treated with 100% CAN. The crop rotation was identical for all sites during the study period which includes: Maize (Zea mays L.) – Maize (Zea mays L.) – Winter rye (Secale cereale L.) – Sorghum (Sorghum bicolor) – Triticale (Triticosecale).
Our results show that the N2O emission exhibited temporal and spatial variability and is mainly influenced by fertilization form and soil type. Among the three fertilization treatments within the same soil type (non-eroded soil), the site with the application of organic fertilization shows the highest cumulated N2O emission which is accumulated to 13.5 kg N2O-N ha-1 compared to the site with mixed fertilization (11.4 kg N2O-N ha-1) and mineral fertilization (4.5 kg N2O-N ha-1). Among the three distinct soil types with an identical application of mineral fertilizer, the cumulated N2O emission is higher at the depression (7.3 kg N2O-N ha-1) compared to the non-eroded (4.5 kg N2O-N ha-1) and extremely eroded soil (1.6 kg N2O-N ha-1). In general, our results suggest a stronger influence of N fertilization form than erosion affected soil on N2O emission.
Keywords: NFT-NSS manual chamber; soil erosion; N fertilization form, nitrous oxide, soil type
How to cite: Vaidya, S., Macagga, R., Thalmann, M., Jurisch, N., Pehle, N., Verch, G., Sommer, M., Augustin, J., and Hoffmann, M.: Agricultural N2O emission is influenced by N-fertilization form rather than landscape position, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1063, https://doi.org/10.5194/egusphere-egu21-1063, 2021.
Monoculture cropland is a major contributor to agriculture-related sources of N2O emission, a potent greenhouse gas and an agent of ozone depletion. Cropland agroforestry has the potential to minimize deleterious environmental impacts. Presently, there is no systematic comparison of soil N2O emission between cropland agroforestry (CAF) and monoculture systems (MC) in Western Europe. Our study aimed to (1) quantify the spatial-temporal dynamics of soil N2O fluxes, and (2) determine their soil controlling factors in CAF and MC. We selected three sites with different soil types (Phaeozem, Cambisol, and Arenosol) in Germany. Each site has paired CAF and MC (agroforestry sites consisted of 12-m wide tree row and 48-m wide crop row and were established in 2007, 2008 and 2019 in these soil types, respectively). In each management system at each site, we had four replicate plots. In the CAF, we conducted measurements in the tree row and within the crop row at 1 m, 7 m, and 24 m from the tree row. We measured soil N2O fluxes monthly over 2 years (March 2018‒February 2020) using static vented chambers method. Following gas sampling, we also measured soil temperature, water-filled pore space (WFPS), and mineral N (NH4+ and NO3-) within the same day. Across all sites, soil moisture and N availability were major drivers of soil N2O fluxes. Both CAF and MC were net sources of soil N2O at all sites. At the site with Phaeozem soil, annual soil N2O emissions from CAF in both years (1.84 ± 0.35 and 1.17 ± 0.30 kg N ha−1 yr−1) were greater than MC (0.89 ± 0.09 and 0.34 ± 0.05 kg N ha−1 yr−1) (P = 0.03). At the site with Cambisol soil, annual soil N2O emission did not differ between MC (0.49 ± 0.07 kg N ha−1 yr−1) and CAF (0.73 ± 0.13 kg N ha−1 yr−1) in 2018/2019 (P = 0.20) whereas in 2019/2020 MC was 134% greater than CAF (2.92 ± 0.45 and 1.25 ± 0.08 kg N ha−1 yr−1, respectively; P = 0.03). The inter-annual differences were largely related to crop types and to climate conditions. At the site with Arenosol soil, there was no difference between CAF and MC. Our results indicated that CAF may decrease, maintain and/or increase soil N2O emissions compared to MC depending on tree age, soil characteristics, management and precipitation.
How to cite: Shao, G., Martinson, G., Luo, J., Bischel, X., Niu, D., D. Corre, M., and Veldkamp, E.: Soil N2O emissions from temperate cropland agroforestry and monoculture systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2553, https://doi.org/10.5194/egusphere-egu21-2553, 2021.
Pristine boreal peatlands are often considered neutral or even small sinks for nitrous oxide (N2O). However, drained peatlands are a significant source of N2O. In these managed sites, oxygen becomes more available, increasing denitrification and therefore N2O release into the atmosphere. N2O emissions do not typically follow a strong seasonal pattern like carbon dioxide but instead, have high spatial and temporal variability. Short-term N2O peak emissions can be observed after various meteorological or soil management events throughout the year, for example after soil freezing or thawing, or fertilization. However, it is not well known how exactly those events trigger the N2O emission peaks. Therefore, N2O annual budget based on punctual chamber measurement can introduce large uncertainties. That is why it is important to measure N2O emissions with a continuous method to better understand the controlling factors and to estimate the annual budgets more accurately.
For the first time in the boreal region of Europe, N2O emissions were continuously observed during a full year in a drained agricultural peatland with the eddy covariance (EC) technique. The study site is a managed peatland in northern Finland, in Ruukki (Latitude: 64.684010; Longitude: 25.106473), with a peat depth between 10 and 90 cm. It is currently managed as a grass field, composed of a mixture of timothy and meadow fescue. We will show a first overview of the N2O fluxes measured since November 2019 with the EC technique. We will present how various meteorological and management events can explain some short-term variations. Then, we will compare the N2O annual budget estimated from the EC measurements to the IPCC emission factor and to different estimates achieved using several sets of non-continuous data points, representing manual chamber measurements with varying frequency.
How to cite: Gerin, S., Laurila, T., Kulmala, L., Tuovinen, J.-P., Vekuri, H., and Lohila, A.: Full year of continuous N2O flux measurements in a drained agricultural peatland in northern Finland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5632, https://doi.org/10.5194/egusphere-egu21-5632, 2021.
Nitrogen (N) fertilization in agricultural soils significantly contributes to the atmospheric increase of nitrous oxide (N2O). Application of nitrification inhibitors (NIs) is a promising strategy to mitigate N2O emissions and improve N use efficiency in agricultural systems. We studied the effect of 3,4-dimethylpyrazol phosphate (DMPP) as an NI on N2O mitigation from soils with spring barley and spring rape. We used both manual and automatic chamber technologies to capture the spatial and temporal dynamics of N2O emissions. Intensive manual chamber measurements were conducted two months after fertilization and fortnightly afterwards. A mini-plot experiment with different levels (0 %, 50 %, 100 %, 150 %, and 200 %) of standard N fertilizer application and 100% N with NI was also conducted for two months in soil planted with spring barley. N2O emissions were affected by the N amount and by the use of NI. Higher emissions were observed in treatments with high N levels and without NI. The effect of NI in reducing N2O emissions from spring barley plots was significant in the small chamber experiments, where NI reduced N2O emissions by 47 % in the first two months after fertilization. However, the effect of NI on N2O reduction was non-significant in the full-plot chamber experiment for the whole season. In contrast, NI significantly reduced (56 %) the seasonal N2O emissions from the soils planted with spring rape. After the initial peaks following the fertilizer application, high N2O fluxes were observed following substantial rain events. The continuous flux measurements in automated chambers showed the dynamic of N2O changes during the whole season, including some peaks that were unobservable with manual chambers because of the low temporal resolution. The concentration of nitrate was higher in the soils treated with mineral N without NI compared to soils treated with NI, which clearly showed the inhibition of the nitrification process with the application of NI. The grain and biomass yield were not affected by the use of NI. In conclusion, application of NI is an efficient mitigation technology for N2O emissions in the period following the fertilizer application, but had little effect on subsequent emissions following rain events.
Keywords: nitrification inhibitors, DMPP, nitrous oxide, mitigation, agricultural soils
How to cite: Tariq, A., Larsen, K. S., Hansen, L. V., Jensen, L. S., and Bruun, S.: Nitrous oxide emission from agricultural soils in response to nitrification inhibitor and N-fertilizer amount, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8135, https://doi.org/10.5194/egusphere-egu21-8135, 2021.
In grassland ecosystems nitrogen (N) inputs are mainly attributed to fertilizer applications for increasing herbage productivity and to excreta of grazing animals. Cattle, for instance, excrete 75-95 % of the N intake. Accordingly, dung and urine patches of grazing animals form hotspots of nitrate leaching and gaseous N emissions as ammonia (NH3) or the important greenhouse gas nitrous oxide (N2O). Global default emission factor (EF) values for N2O, 2.0 % for grazing based nitrogen inputs (EF3) and 1.0 % for nitrogen inputs via fertilizer applications (EF1) have been suggested by IPCC. However, some countries like New Zealand, Canada or the Netherlands have established country-specific EFs showing considerable regional differences.
In the present research study, we examine N2O emissions of a pasture field in Switzerland in relation to possible drivers. Field scale emissions by eddy covariance are measured in parallel to patch-scale N2O fluxes from controlled applications of urine, dung and fertilizer. The patch-scale fluxes are measured by a manually operated chamber ('fast-box') connected to an online gas analyzer. Besides estimating EF values on annual and seasonal basis, relevant factors that might control N2O fluxes like environmental conditions (weather parameters, soil moisture, soil temperature), vegetation characteristics (height, composition, nitrogen and carbon content) and pasture management (patch age, grazing, fertilization, cut events, interactive effects) are analyzed.
We present and discuss results of the first measurement year 2020. Three artificial urine applications during summer and autumn were performed. They show peak N2O fluxes of 279-1718 μg m-2 h-1 directly after application that decrease to near-background fluxes within 19-43 days. Using a simple linear interpolation of measured N2O fluxes, EF values of artificial urine patches vary between 0.57 and 2.44 % indicating a seasonal variability of N2O fluxes.
How to cite: Barczyk, L., Kuntu-Blankson, K., Calanca, P., Six, J., and Ammann, C.: Quantification of N2O fluxes and EF values in a pasture using chamber and eddy-covariance technique, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14398, https://doi.org/10.5194/egusphere-egu21-14398, 2021.
Agriculture represents 14% of global anthropogenic greenhous gases (GHG) emissions, 46% of this amount being due to N2O emissions from soils (UNEP, 2012). N2O is a powerful GHG (IPCC, 2013) and its emissions from agricultural soils are related to physical-chemical parameters which depend on climate (temperature, rain…), soil properties (Robertson et al., 1989) and farming practices (irrigation, tillage, fertilization…) (Tellez-Rio et al., 2015). The IPCC Tier 1 emission factor remains widely used to estimate annual N2O budgets from agricultural soils by taking into account the annual amount of N input only. However, not taking into account the environmental controlling factors may introduce high uncertainty in N2O budget estimation. Our study aims at highlighting the key drivers of N2O emissions from two agricultural sites in the South West of France and at proposing an improved, simple and accessible methodology to estimate N2O budget at crop plot and seasonal scale. For this purpose, we benefited from a unique long time series of daily N2O fluxes (from 2011 to 2016) measured with 6 closed automated chambers on two ICOS sites with contrasted agricultural management (FR-Lam and FR-Aur).
N2O annual budget vary from 1.04 to 7.96 kgN ha-1 yr-1 for winter wheat and maize crop, respectively. The effects of fertilization, rain and irrigation, plant development, spring mineralization and deep tillage on N2O emissions were investigated. Significant correlations between rain combined with fertilization and plant development, deep tillage or spring mineralisation was found with R² of 0.91, 0.99 and 0.85, respectively. We took advantage of these results to develop an empirical model, including N input quantity, residual N, leaf area index and water input in order to estimate seasonal and annual N2O budget. At the seasonal scale, the model output matched well with the observed budget, with a R² and a RMSE of 0.87 and 0.33 kgN ha-1 at FR-Lam and of 0.92 and 0.12 kgN ha-1 at FR-Aur, respectively. It also gave good statistical scores at the crop year scale with a R² of 0.96 and a low RMSE of 0.43 kgN ha-1 when binding data from both sites. Using the IPCC Tiers 1 methodology gave lower and more scattered results with a R² of 0.46 and a RMSE of 1.46 kgN ha-1. For sites where N2O fluxes are not monitored, that new methodology may be an alternative and a more precise methodology than the IPCC Tiers 1 approach. It has also the advantage to require only few and accessible input variables.
IPCC, 2013. Climate Change 2013: The Physical Science Basis. Cambridge University Press, Cambridge.
Robertson et al., 1989. Aerobic denitrification in various heterotrophic nitrifiers. Antonie van Leeuwenhock., 56, 289-299.
Tellez-Rio et al., 2015. N2O and CH4 Emissions from a Fallow–wheat Rotation with Low N Input in Conservation and Conventional Tillage under a Mediterranean Agroecosystem. Sci. Total Environ., 508, 85–94.
UNEP, 2012. Growing greenhouse gas emissions due to meat production.
How to cite: Bigaignon, L., Le Dantec, V., Zawilski, B., Granouillac, F., Fieuzal, R., Claverie, N., Lemaire, B., Brut, A., Ceschia, E., Mordelet, P., Delon, C., and Tallec, T.: Towards improved N2O budgets estimation from 10 site-years measurement and analysis of key drivers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14676, https://doi.org/10.5194/egusphere-egu21-14676, 2021.
Nitrous oxide (N2O) is a potent greenhouse gas (GHG), with a global warming potential (GWP) of 265 relative to carbon dioxide (CO2) and a lifespan of over 100 years. Where N input from fertilizers exceeds plant demands, hotspots of N2O can be produced releasing short-lived pulses of N2O from the soil that exhibit disproportionately high rates of emissions relative to longer periods of time, known as hot moments. Hotspots and hot moments of N2O are sensitive to changes in agricultural management and the environment making it difficult to accurately quantify N2O emissions with low uncertainties. This study investigates the methods used to quantify N2O emissions in time and space, using both static chambers (SC) and eddy covariance (EC) techniques.N2O fluxes were measured from both techniques from an intensively managed grassland site under four fertilizer applications of calcium ammonium nitrate (CAN) in 2019. EC measurements of N2O were gap-filled by using a simple linear empirical model that incorporated environmental and management data. SC N2O fluxes were calculated using the arithmetic method and Bayesian statistics via Markov Chain Monte-Carlo (MCMC) simulations to account for the log-normal distribution of fluxes measured. N2O emissions were weakest in winter for both techniques (-3.27 µg N2O-N m-2 hr-1 for SC and -3.9 µg N2O-N m-2 hr-1 for EC). Following fertilizer application, daily averaged N2O emissions peaked in March (538.89 µg m-2 hr-1 for SC, 491.18 µg m-2 hr-1 for EC) and April (117.91 µg m-2 hr-1for SC and 306.90 µg m-2 hr-1 for EC). Delayed peaks in N2O emissions following fertilizer application occurred in June (101.03 µg m-2 hr-1 for SC and 814.76 µg m-2 hr-1 for EC) and October (417.14 µg m-2 hr-1 for SC and 313.22 µg m-2 hr-1 for EC) and these high emissions events coincided with dry periods followed by rainfall events. EC and SC measurements were most comparable when emissions were > 115 µg m-2 hr-1, when the flux footprint of half-hourly EC flux measurements overlapped with the position and time of SC measurements and when the number of chamber replicates were ≥ 15 on a given sampling day. Where the chamber sample size was small (n ≤ 5), the Bayesian method produced large uncertainties (> 25,000 µg m-2 hr-1) due to the inability to constrain an arithmetic mean from a log-normally distributed data set. Annual cumulative N2O fluxes from EC and SC by the arithmetic and Bayesian method, were 3.35(± 0.5) kg N ha-1, 2.98 (± 0.17) kg N ha-1and 3.13 (± 0.24) kg N ha-1 respectively. Emission factors from EC and SC by the arithmetic and Bayesian method were higher than the Intergovernmental Panel on Climate Change (IPCC) default value of 1%, at 1.46%, 1.30% and 1.36%, respectively. Our study highlights that disparities exist between SC and EC in quantifying N2O fluxes from a managed grassland and we recommend constraining disparities by utilizing a SC sample size > 5 and by accounting for the log-normal distribution of N2O flux data to accurately estimate N2O flux uncertainty.
How to cite: Murphy, R., Richards, K., Krol, D., Gebremichael, A., Lopez-Sangil, L., Rambaud, J., Cowan, N., Lanigan, G., and Saunders, M.: Quantifying nitrous oxide emissions in space and time using static chambers and eddy covariance from a temperate grassland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-515, https://doi.org/10.5194/egusphere-egu21-515, 2021.
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