Orals: Fri, 2 May | Room 1.14
Field cropping practices in Canada include routine use of nitrogen (N) fertilizer, which produces substantial amounts of nitrous oxide (N2O) emissions. Adoption of improved N management practices may reduce both the amount of N applied and these N2O emissions. Using flux-tower field measurements, we investigated how dual inhibitors (urease and nitrification inhibitors with urea) reduced N fertilizer-induced N2O emissions, compared with urea only, in eastern Canada across 7 years. We also used meta-analysis (of static chamber studies) to examine how inhibitors and other enhanced efficiency fertilizers (EEFs), along with other improved N management techniques, affected fertilizer-induced N2O emissions from Canadian agricultural cropping systems. From the field study, the dual inhibitors reduced growing season N2O emissions by 22% and annual N2O emissions by 10% for high N application rates to corn (Zea mays), while N2O emissions from lower N applications to wheat (Triticum aestivum) showed no differences between the EEF and urea. Crop yields for both the corn and wheat were similar between the different N fertilizer treatments. Across Canada, the meta-analysis showed that EEFs (which include coated slow-release fertilizers and both nitrification and urease inhibitors combined and on their own), on average, reduced N2O emissions by 11%. Nitrification inhibitors (alone or in combination with urease inhibitors) averaged a 19% reduction in N2O emissions. Most of the studies used in the meta-analysis had minimal sampling through the non-growing season though, so the total annual N2O emission reductions were not evaluated and may actually be lower. The meta-analysis indicated that the most effective N management techniques for reducing N2O emissions were the use of EEFs, split application of N fertilizers and the use of organic fertilizers, with the effectiveness of these practices all strongly influenced by soil and weather conditions. The meta-analysis also found that reductions with EEFs from studies that included year-round measurements, tended to be less than studies that included only the growing season. This suggests that when improved N management practices use the same N application rates as the regular practice, more residual N may be available for non-growing season losses. As a result, when no yield benefit is noted, these improved practices should be combined with N rate reductions.
How to cite: Pelster, D., Sokolov, V., Admiral, S., Asgedom-Tedla, H., and Pattey, E.: Improved nitrogen fertilizer management practices that reduce growing season nitrous oxide emissions may increase non-growing season emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1721, https://doi.org/10.5194/egusphere-egu25-1721, 2025.
N2O is currently the single most damaging of all ozone-depleting greenhouse gases (GHG) associated with climate change, and agriculture is the primary source of this extremely potent GHG. Direct N2O emissions from agricultural fields constitute about 21 % of all greenhouse gases emitted by agriculture in Denmark. Serious efforts for N2O mitigation must be taken to limit global warming, and rigorous monitoring and correct documentation of national greenhouse gas emissions are at the forefront of this endeavor. The Danish National Inventory Report for greenhouse gases uses the Tier 1 default emission factor (EF) of 1% for mineral soils, assuming 1% of N input as fertilizer is emitted as N2O. A refinement provided by the IPCC in 2019 suggests using specific land-use categories: 1.6% for synthetic fertilizers and 0.6% for organic fertilizers in wet climates like Denmark. However, studies have shown that this distinction is unsuitable for Danish agricultural conditions, and that especially emissions from synthetic fertilizer are overestimated with both approaches.
We conducted 28 individual field trials under common Danish agricultural management throughout the country from 2022 to 2024, measuring N2O emissions in spring barley and winter wheat during their growing seasons. We were specifically interested in comparing N2O emissions from synthetic vs. organic fertilizers. The average cumulative N2O emissions of synthetic fertilizers ranged from 0.12 to 1.05 kg N2O-N ha-1 in spring barley, and from 0.08 to 1.17 kg N2O-N ha-1 in winter wheat. Average cumulative N2O emissions of organic fertilizers ranged from 0.95 to 1.41 kg N2O-N ha-1 in spring barley, and from 0.19 to 1.30 kg N2O-N ha-1 in winter wheat. All emissions were comparably low throughout trials, treatments and years. Average EF (± S.E.) for synthetic fertilizers were 0.10 ± 0.04 % (spring barley) and 0.16 ± 0.05 % (winter wheat), and for organic fertilizers 0.38 ± 0.03 % (spring barley, cattle slurry), 0.38 ± 0.06 % (winter wheat, pig slurry), and 0.37 ± 0.06 % (winter wheat, digestate) during the growing season. Our results contradict both the default and refined Tier 1 EF provided by the IPCC. In agreement with other studies, we found that N2O EF for synthetic fertilizers were lower than EF for organic fertilizers. Possible explanations for, and implications of this paradox will be discussed.
How to cite: Eller, F., Schröder Baggesen, N., Høegholm Lykke, E., Peixoto, L., O. Petersen, S., and Skov Nielsen, C.: The emission factor paradox: N2O emissions from organic fertilizer exceed those from synthetic N fertilizers on Danish agricultural soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8163, https://doi.org/10.5194/egusphere-egu25-8163, 2025.
Nitrous oxide (N2O) is an important greenhouse gas (GHG) and ozone-depleting substance. The agricultural sector is the predominant anthropogenic source of N2O, primarily due to the use of nitrogen (N) fertilizers. Thus, policies are being discussed to reduce N2O emissions across Europe. However, the scarcity of high-resolution N₂O flux data hinders our understanding of the mechanisms driving N2O emissions, and the development of effective mitigation strategies.
In this study, we measured high-resolution (10 Hz) N2O concentration over the duration of a winter wheat cropping season and calculated half-hourly N2O fluxes using eddy covariance. Our objective was to disentangle the roles of management practices, abiotic conditions, and biotic factors affecting N₂O fluxes and to track how their respective contributions change over time. Using a random forest model trained with management, environmental, and vegetation data, we applied SHAP (SHapley Additive exPlanations) analyses to investigate the drivers of N₂O fluxes.
As expected, N fertilization and soil moisture emerged as the main drivers with the largest contributions to the N2O fluxes. Moreover, the net ecosystem exchange of CO2 (NEE) was the third most important driver, highlighting the critical role of plant-microbe competition for soil N. N₂O fluxes indeed peaked during periods of low crop growth, when plant N uptake was limited, leaving available soil N accessible to N₂O-producing microorganisms. This study suggests that applying N fertilizers during periods of high crop N demand, rather than at the onset of the growing season, could significantly reduce N₂O emissions and the GHG footprint of crop production.
How to cite: Turco, F., Feigenwinter, I., Allemann, L., and Buchmann, N.: Drivers of nitrous oxide fluxes in winter wheat, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8413, https://doi.org/10.5194/egusphere-egu25-8413, 2025.
The application of nitrogen (N) fertilizers is intrinsically linked to the emissions of nitrous oxide (N2O) and ammonia (NH₃), making their mitigation a critical global concern. One effective strategy involves the use of urease and nitrification inhibitors. Over the past three years, we have conducted multiple field and pot experiments to evaluate the impact of urea combined with urease and nitrification inhibitors on N2O emissions and NH3 volatilization. These studies were performed on calcareous Mediterranean soils (pH ≥ 7.3). Our findings indicate that urease inhibitors reduced NH₃-N volatilization by 25-50%. Nitrification inhibitors significantly decreased N2O emissions. The combined application of urease and nitrification inhibitors reduced N2O emissions by up to 67% within the first two days post-application, with emissions returning to near ambient levels within four days. In contrast, N2O-N fluxes following urea application alone took approximately seven days to return to baseline levels. N2O-N emissions from the double-inhibited urea were highest following irrigation or precipitation in the weeks following N applications, yet with low values (<0.03 mg-N m⁻² d⁻¹). These results highlight the effectiveness of urease and nitrification inhibitors in mitigating N2O and NH3 emissions, contributing to more sustainable agricultural practices.
How to cite: Baram, S.: Effect of urease and nitrification inhibitors on N2O emissions in Mediterranean soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12742, https://doi.org/10.5194/egusphere-egu25-12742, 2025.
Fall bedding, a prevalent practice for potato (Solanum tuberosum) production in southern Alberta, entails fall-season soil preparations including irrigation, fertilization, plowing, and bed formation. This approach, while economically advantageous - owing to reduced labor and fertilizer costs and a decrease in other necessary preparations during fall - raises environmental concerns. Specifically, the lag between fertilizer application and crop nutrient uptake may lead to elevated emissions of carbon dioxide (CO₂) and nitrous oxide (N₂O), potent greenhouse gases.
To investigate these potential environmental impacts and assess potato yield outcomes, a field study was conducted in Lethbridge, Alberta. This experiment utilized 36 plots with different combinations of bedding approaches (fall bedding, spring bedding, and spring bedding following a winter cover crop), two irrigation levels (80% and 120% of AIMM recommended rates), and both fertilized and unfertilized conditions. Each combination was replicated three times.
Findings show that N₂O emissions are strongly influenced by fertilizer application (P < 0.005), the timing of bedding (P < 0.05) and field position (hill or furrow) (P < 0.05), with the highest emissions observed in fall-bedded plots under high irrigation and fertilization. In contrast, CO₂ emissions were less variable, although highly significant differences were observed primarily between hill and furrow positions (P < 0.0005). Furthermore, variations in bedding practices and fertilization both significantly affected tuber yields (P < 0.05), underscoring the need to balance production practices with environmental considerations in potato cultivation.
How to cite: Ball, M., Hernandez-Ramirez, G., Karimi Dehkordi, R., Appels, W., and Neilson, J.: Effects of Bedding Preparations on Potato Yield and Greenhouse Gas Emissions in Southern Alberta, Canada, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-38, https://doi.org/10.5194/egusphere-egu25-38, 2025.
Nitrous oxide emission from agricultural soils contribute significantly to global greenhouse gas emissions. Fertilizer deep placement (FDP) and reduced application rate of nitrogen fertilizer are considered as a promising strategy to mitigate nitrous oxide emissions from arable soil and increase nitrogen use efficiency of crops. This study was conducted to determine effects of FDP and, FDP with 20% reduced application rate of nitrogen fertilizer (FDP-rf) on nitrous oxide (N2O) emissions, rice yield, and soil properties in paddy soil. The study included three treatments: conventional (C), FDP, and FDP-rf. Rice (Oryza sativa L.) was transplanted on June 7, 2024 and harvested on October 15, 2024. Nitrous oxide flux for each treatment during the cultivation period showed similar patterns affected by the submerged period and fertilizer application. Emissions remained low across all treatments before the mid-term drainage period, and this trend continued during the mid-term drainage period (two weeks). Peaks of N2O flux were observed in FDP-rf and C treatments right after the mid-term drainage period, while FDP maintained consistently low emissions. Subsequently, all treatments returned to low N₂O flux levels. Following the pre-harvest drainage, N₂O flux increased across all treatments, likely due to the availability of residual nitrogen. Among the treatments, FDP exhibited the most stable and minimal N₂O emissions, indicating effective nitrogen retention and consistent control of fluxes. There was a statistically significant difference in cumulative N₂O emissions depending on the fertilization method. Conventional (C) showed the highest emissions (0.8351 ± 0.0408 kg/ha), followed by FDP (0.6259 ± 0.0562 kg/ha) and FDP-rf (0.4140 ± 0.1063 kg/ha). The total and inorganic nitrogen content in the soil varied greatly depending on the fertilization method. For total nitrogen, the highest levels were observed in the conventional (C) treatment (2.11 g/kg) on harvest time, followed by FDP-rf (1.91 g/kg) and FDP (1.23 g/kg). Nitrate levels were significantly reduced in FDP (17.7 mg/kg) and FDP-rf (26.8 mg/kg) compared to C (42.2 mg/kg). Although there was no statistical difference in ammonium levels, the highest value was observed in C (56.7 mg/kg), followed by FDP-rf (54.5 mg/kg) and FDP (43.1 mg/kg). Depending on the fertilization method, the grain yield, rice straw, root, and total biomass weight varied. For grain yield, the highest was observed in FDP (6.69 Mg/ha), followed by C (5.96 Mg/ha) and FDP-rf (5.42 Mg/ha). Fertilizer deep placement reduced N₂O emissions and improved rice yields compared to C. Fertilizer deep placement with reduced nitrogen application further decreased N₂O emissions but resulted in lower yields compared to FDP. These findings suggest that FDP could be a sustainable agricultural practice that mitigates greenhouse gas emissions while maintaining crop yields.
How to cite: Hong, C. O., Kim, S. U., and Chung, S. U.: Deep placement and reduced application rate of nitrogen fertilizer mitigates nitrous oxide emission from rice paddy soil in South Korea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14196, https://doi.org/10.5194/egusphere-egu25-14196, 2025.
Agricultural soils are a significant source of nitrous oxide (N2O) emissions, primarily driven by denitrification and nitrification pathways. Recently, emissions appeared to be strictly related to soil structure characteristics, which may also play a substantial role in the emission pathways. Among these characteristics, the extent to which soil compaction impacts N2O emissions is still debated. To investigate this, a three-year lysimeter experiment was conducted to assess N2O emissions under five cultivation systems with four replicates each: bare soil (BS), conventional (CV), conventional + cover crop (CC), conservation with shallow soil compaction (0-25 cm, CA1), and conservation with deep soil compaction (25-45 cm, CA2). Maize and grain sorghum were grown as main crops, fertilized using solid digestate (300 kg N ha-1). Continuous automatic measurements of N2O emissions were collected using a non-steady state through-flow chamber system and an FTIR gas analyzer, capturing up to seven flux measurements for each chamber per day. Daily emissions were split into four periods per year. The relative importance of nitrification and denitrification to the flux of N2O was hinted at by concurrently measuring NOx emissions and the water-filled pore space (WFPS) and soil temperature measured in the 0-30 cm profile. Additionally, 280 soil samples per year were collected in the 30-days post-fertilization from 0-5 cm and 5-15 cm depths for pH analysis and monitoring ammonia and nitrate pool dynamics. A mixed-effects model was used to test sub-daily emissions. The most pronounced N2O emissions were observed during the initial two weeks following fertilization, with maximum observed emissions highest in CC (208 g ha-1 d-1) and lowest in CA2 (53 g ha-1 d-1) for 2023. Notably, CA2 consistently exhibited lower cumulative N2O emissions, suggesting a complex interaction between management practices and soil conditions. These findings highlight the importance of soil structure and cultivation system in managing N2O emissions.
How to cite: Lewis, E., Longo, M., Rocco, S., Dal Ferro, N., Cabrera, M., Lazzaro, B., and Morari, F.: From Fertilizer to Flux: Investigating N2O Emissions in Compacted Cultivation Systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16508, https://doi.org/10.5194/egusphere-egu25-16508, 2025.
Nitrous oxide (N2O) emissions in agricultural fields exhibit substantial spatial and temporal variability, driven by complex interactions between soil water dynamics and landscape features. We conducted field experiments at two agricultural field sites (Tokkerup and Taastrup) in Eastern Denmark to quantify N2O emissions across soil water gradients. At the Tokkerup site, we quantified the effects of soil water drainage by comparing well-drained and poorly-drained areas. We installed manual and automated chambers to capture the spatial and temporal dynamics of N2O emissions, complemented by continuous monitoring of soil water tables and moisture contents with water wells and soil moisture sensors. At the Taastrup site, we investigated N2O emissions across a soil-water gradient. Twelve spatial spots were selected along a transect across the water gradient to measure N2O fluxes using an Aeris MIRA Ultra analyzer equipped with a manual chamber. Soil water wells and sensors were installed across the gradient to capture the dynamics of water table depths and soil moisture across the field gradient throughout the year. Preliminary results reveal that significantly higher N2O emissions occurred along the periphery of depressions in the field, so these transition areas acted as hot spots of N2O emissions during the crop-growing period. These findings highlight the critical role of soil water dynamics in shaping the temporal and spatial N2O emission patterns and emphasize the potential for soil water management as an important part of strategies to mitigate emissions of N2O.
How to cite: Tariq, A., Hansen, L. V., Brændholt, A., Bruun, S., and Plauborg, F.: Mapping nitrous oxide emissions across soil water gradients in agricultural fields, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13613, https://doi.org/10.5194/egusphere-egu25-13613, 2025.
Agricultural soils are the dominant source of nitrous oxide (N2O) emissions in most countries, but the spatial and temporal heterogeneity of the emission fluxes makes their quantification challenging. Here we develop a framework for estimating national N2O emissions at high spatial resolution, based on the biogeochemical-model LandscapeDNDC. We apply this framework to Germany, making use of high resolution datasets for soil type, agricultural management practices, climate and nitrogen (N) deposition. Compared to the current emission-factor (Tier-2) approach for compiling an N2O inventory, our method results in similar but slightly lower total N2O emissions at the national scale, but higher fertiliser-driven emissions, which are critical for UNFCCC reporting. It is also able to capture the effect of yearly climate variation. Spatial disaggregation of the emissions into approximately 400 districts reveals large differences at the sub-national scale, where the process-based model accounts better for local variations in soil, climate and agricultural management. We also go beyond the focus on N2O emissions and determine a full N budget for Germany, which includes the quantification of environmentally important N fluxes such as ammonia volatilisation, nitrate leaching and NO emissions.
How to cite: Smerald, A., Imhof, H., Scheer, C., and Kiese, R.: Nitrous oxide emissions and nitrogen budgets for German agricultural soils via process-based modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4034, https://doi.org/10.5194/egusphere-egu25-4034, 2025.
Rice production feeds > 50% of the world population with 250 million tonnes consumed in 2022 and is expected to continue to rise by a further ~6% by 2030. Favourable climate and soil conditions for growing temperate rice, together with low disease pressure and advanced irrigation systems enables Australia to achieve some of the highest rice yields in the world with low resource inputs. However, currently there remains a lack of complete season baseline datasets for greenhouse gas emissions from Australian rice crops. National and regionally specific greenhouse gas accounting and the global warming potential and mitigation strategies for these cropping systems remain unclear. Furthermore, recent innovative irrigation and water management practices utilizing low-cost, technology driven irrigation automation in Australia now indicates the potential to further significantly change how rice is grown. Practical implementation of alternate rice growing irrigation techniques, in which the soil is kept between 0 to -20 kPa, without water being permanently ponded during the growing season have been enabled, producing commercial crops of > 13 Mg ha-1. However, these conditions may lead to ‘tradeoff’ emissions of nitrous oxide (N2O), an even more potent greenhouse gas than the more ubiquitous methane (CH4) emissions commonly associated with rice crops. Two rice water management techniques have been compared in the 2023-2024 Austral Summer: i) Conventional drill sown (DIR) in which planted seeds are flushed with water 3-4 times until the crop has developed to the 4th leaf stage (up to 50 days after the first irrigation) followed by continuous flooding until drainage pre-harvest. ii) Water saving practise, locally known as aerobic (AER) in which the crop is flushed intermittently throughout the entire season with standing water being avoided. Methane and N2O emissions have been monitored in commercial fields using non-steady state closed chambers followed by gas chromatography (GC) and a newer laser-based method, optical feedback-cavity enhanced absorption spectroscopy (OF-CEAS). The AER system reduced seasonal CH4 emissions to 1.3 kg CH4-C ha-1 from 32 kg CH4-C ha-1 that were determined in the DIR system. Although, high N2O-N emission peaks of up to 1043 µg m-2 h-1 were recorded, associated with rainfall and fertilizer application events, total seasonal fluxes suggest that the adoption of this alternative irrigation practise can reduce the global warming potential of rice crops by 51% compared with conventional management. Because both crops were managed for yield potential, when gas emissions were related to rice productivity, yield scaled emissions were 97 kg CO2eq Mg-1 season-1 (DIR) and 47 kg CO2eq Mg-1 season-1 (AER), the lowest that have ever been recorded globally.
How to cite: Quayle, W., Marston, E., Taylor, S., and Hornbuckle, J.: Measurement of methane and nitrous oxide emissions from Australian rice grown under conventional and water saving irrigation practises., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14692, https://doi.org/10.5194/egusphere-egu25-14692, 2025.
Closed chamber measurements are still the most common approach for measuring the exchange of greenhouse gases (GHG) between soils and the atmosphere in terrestrial ecosystems. Closed chambers can either be employed as static (discrete gas sampling with syringes and subsequent gas chromatographic analysis) or as dynamic chambers (in-field connection to a portable gas analyzer for real-time gas concentration measurements). Two well-known advantages of real-time continuous gas measurements at high frequencies (seconds to Hertz) are the reduction of chamber closure periods as well as the substantially lower minimum detectable flux (MDF). During the past two decades, the technological development of portable fast response analyzers has seen tremendous leaps and new manufacturers are emerging on the scene. In our pilot study, we compared the performance of two new mid-infrared absorption spectroscopy analyzers (a MIRA Ultra N2O/CO2 and a MIRA Ultra Mobile LDS: CH4/C2H6 analyzer, Aeris Technologies, USA) with the performance of a gas chromatograph (Bruker Model 450, Bruker Corp., USA) for the quantification of CO2, CH4, and N2O fluxes under field conditions in a cropland. For the closed chamber measurements, both analyzers were connected to a single chamber, running in parallel, while simultaneously discrete gas samples were taken with a syringe at six discrete time points throughout the chamber closure times for the subsequent gas chromatographic analysis. Measurements took place at two separate days covering lower and higher soil gas fluxes. Regarding CO₂ fluxes, the results demonstrated a strong agreement between the methods, with minimal deviations for both higher and relatively smaller fluxes (normalized root mean square error, nRMSE < 12.5%). A high level of agreement between the methods was also observed for N₂O fluxes on the first measurement day, when a N₂O pulse occurred (nRMSE < 9.5 %). However, on the second measurement day, the agreement was considerably lower for very small negative fluxes. For CH₄, the agreement between methods was very low (nRMSE < 213.6%). Due to the higher analytical precision of the MIRAs, the MDFs for the closed dynamic chamber measurements were considerably lower compared to the closed static chamber measurements. This enabled the detection of significant fluxes even at very low flux rates which could not be distinguished from the background measurement noise of the closed static chamber method using GC analysis. The discrepancies between the two approaches were foremost restricted to fluxes which were below the closed static chamber MDFs. The presented results will support an informed selection of suitable gas analytical methods for measuring GHG fluxes in the field and help the soil flux research community to keep up with the rapidly developing market of portable fast-response analyzers.
(Wolfgang Aumer and Morten Möller contributed equally to this study and abstract and are considered co-first authors.)
How to cite: Möller, M., Aumer, W., Eckhardt, C., Görres, C.-M., Bruns, C., and Kammann, C.: Comparison of miniature mid-infrared absorption spectroscopy analyzers with gas chromatography for the quantification of soil greenhouse gas fluxes using the closed chamber method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18698, https://doi.org/10.5194/egusphere-egu25-18698, 2025.
The successful implementation of greenhouse gas mitigation measures requires the accurate quantification of emission fluxes in space and time. The SmartfField project comprises a unique infrastructure to measure complete N and C balances in combination with year-round measurements of N2O and other environmentally important GHG and trace gases (NH3, NO/NO2, O3, CO2, CH4). The measurement infrastructure comprises chamber and micrometeorological measurements on two experimental sites (Supersite A and B) on plot and field scale for typical Danish crop rotations, and a mobile eddy-flux and chamber system to deploy elsewhere. The overall aim is to identify greenhouse gas mitigation options which (1) can be easily integrated into existing crop rotations (2) avoid pollution swapping (nitrate leaching and ammonia emissions), (3) do not compromise crop yields, and (4) can be scaled from plot to field. In this framework, the emission factors for different amendments will be calculated, including synthetic and biological nitrification inhibitors, biochar, and rock flour, and their combined effects. The experiments will commence in 2025, and baseline measurements started in March 2024. This included soil mapping using electromagnetic induction (DUALEM-21H) and gamma ray (Medusa 2000) sensors, sensor-guided soil sampling, and soil profile descriptions. The N2O flux was measured using the LI-7820 trace gas analyser and survey chamber on field scale, and continuously with automated chambers inside and outside tractor tracks (n=5). The crop was spring barley (Hordeum vulgare), undersown with grass-clover (Lollium perenne, Trifolium pratense, Trifolium repens). These initial measurements revealed large spatial and temporal variations of soil parameters and greenhouse gas emissions. The ECa varied from 1.8-14.8 mS m-1, indicating substantial soil textural changes. The depth of the A-horizon varied between 22-30 cm, and average topsoil bulk density was higher in the tractor tracks (1.51 vs. 1.36 g cm-3). The N2O flux varied substantially within the field with a daily CV of 51%-138%. The mean daily N2O flux outside the tractor tracks was 64.3 µg N2O-N m-2 d-1, while it was 157.3 µg N2O-N m-2 d-1 inside the tracks. There is a need to account for the observed spatiotemporal variation to correctly assess mitigation measures.
How to cite: Dold, C., Værge, A. B., Lund Kasper, P., Erling-Nielsen, M., Bruun, S., Koganti, T., Bjørn Møller, A., Bimantara, D. S., and Butterbach-Bahl, K.: Unveiling the greenhouse gas mitigation potential for Danish farmers: the SmartField project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7080, https://doi.org/10.5194/egusphere-egu25-7080, 2025.
Grain production plays a critical role in ensuring national food security in China but is also a significant source of greenhouse gas (GHG) emissions, nitrogen (N) pollution, and water resource depletion. The shift in grain production centers from southern to northern China over the past four decades, driven by inter-provincial grain trade, has substantially altered the spatial distribution of carbon and nitrogen cycling processes, with important implications for agricultural ecosystems and climate mitigation strategies.
Using over 40 years of data, we show that inter-provincial grain trade in China (wheat, maize, and rice) increased more than fivefold between 1980 and 2020, from 22 to 128 million tonnes. This shift resulted in a 213% increase in N pollution and a 253% rise in GHG emissions associated with agricultural trade, alongside a 606% increase in blue water use and worsening water scarcity in northern regions. Our findings highlight that trade-driven shifts in regional production patterns, influenced by factors such as increased mechanization, population density, and urbanization, have intensified environmental challenges, particularly by increasing ammonia (NH3) and nitrogen oxide (NOx) emissions, which contribute to both GHG fluxes and air quality degradation.
To mitigate these impacts and balance food security with environmental sustainability, we propose a targeted policy intervention-a national subsidy mechanism-to compensate northern provinces for their disproportionate environmental burdens. An annual transfer of approximately US$30 million from southern to northern provinces could incentivize sustainable practices, reduce reactive nitrogen emissions, and enhance overall environmental quality while supporting agricultural productivity. Our study provides evidence-based recommendations for policymakers to develop integrated approaches that consider both GHG mitigation and nitrogen management in managed agricultural ecosystems.
How to cite: Wang, C.: Managing Domestic Trade for Sustainable Food Systems in China: Implications for GHG Fluxes and Nitrogen Emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4058, https://doi.org/10.5194/egusphere-egu25-4058, 2025.
Climate change and environmental degradation driven by greenhouse gases (GHGs) and reactive nitrogen (Nr) emissions are escalating globally. As a major emitter of both, China faces dual challenges in mitigating GHGs and Nr to achieve carbon neutrality and sustainability. This study evaluates the potential and synergies of GHG (CO2, CH4, and N2O) and atmospheric Nr pollutant (NOx and NH3) mitigation based on a multi-model framework. Our findings indicate that with a co-control solution, China could reduce GHG emissions by up to 75% and atmospheric Nr pollutants by 60% in 2050, delivering societal benefits of US$959 billion—five times the implementation costs. When both GHG and Nr control strategies are fully deployed, industry-driven emission reductions will be dominant until around 2030, coinciding with China’s carbon peak target. However, after the carbon peak, agriculture-led reductions will enhance synergies in abatement potential and cost-effectiveness. This underscores the need to shift the priority of GHG and atmospheric Nr pollution control during post-peak, to boost zero carbon and clean air in China.
How to cite: Xu, X., Zhang, X., Zhang, S., Winiwarter, W., Zhang, L., and Gu, B.: Synergies of reducing greenhouse gases and atmospheric nitrogen pollutants in China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2688, https://doi.org/10.5194/egusphere-egu25-2688, 2025.
Organic fertilization has been gaining increasing attention in recent years due to its significant soil health benefits and its alignment with European environmental and agricultural strategies. A considerable percentage (10.4% in 2022) of agricultural fields across Europe currently incorporate organic fertilizers into their management practices one or two times/year, and this proportion is projected to increase by 25% by 2030. Consequently, the environmental impacts associated with organic fertilization, particularly volatile organic compounds (VOCs) emissions, which tightly connected with air quality and health risk through their contribution to secondary pollutants, have become a critical area of study but remain poorly understood. To address these concerns, the SOFORA project was established to quantify agricultural gas emissions, including VOCs, nitrogen oxides (NOx), ammonia (NH₃), ozone (O₃) and particle matters through laboratory measurements and field campaigns. The project also aims to develop robust models to estimate emission levels resulting from the application of various types of organic fertilizers under different agricultural conditions.
During the laboratory measurements conducted as part of the SOFORA project, the dominant VOC profiles and their magnitudes were found to be highly dependent on the specific type of organic fertilizer applied. To investigate these emissions under real-world conditions, eddy covariance techniques and proton transfer reaction mass spectrometry (PTR-MS) were utilized. Field experiments were carried out in the spring and autumn of 2023 at two agricultural sites in France: a wheat field and a white mustard cover crop field. Both experiments ensured consistent crop field footprints within the measurement zones, enabling reliable data collection and an accurate representation of emission dynamics in agricultural environments.
Field measurements confirmed the short-term but significant release of gases and their potential impact on air quality following organic fertilization. VOC emissions were observed to persist for over seven days post-application for both fertilization types. Approximately 2% of the total applied carbon was estimated to be emitted as VOCs from green waste and digestates, respectively. Peak emission fluxes were approximately 85,000 μg m⁻² h⁻¹ and 53,000 μg m⁻² h⁻¹ for total VOC emissions at noon on the first day after application of green waste and digestates, respectively. VOC emissions were dominated by acetic acid, methanol, and acetaldehyde for green waste applications, and by methanol, isoprene, and acetone for digestates. These compounds are estimated to have a high potential contribution to ground-level ozone and/or aerosol formation.
Volatilisation of organic fertilizers may contribute much more significantly than expected to atmospheric burden, leading to broader environmental impacts such as air quality deterioration and nitrogen deposition. Further high-resolution measurements are needed to refine our understanding of these processes and develop strategies to mitigate potential trade-offs between sustainable soil management and environmental protection.
How to cite: Liu, Y., Lafouge, F., Feron, A., Decuq, C., Levavasseur, F., Loubet, B., and Ciuraru, R.: Organic Fertilizers Application: Impacts on VOCs and Air Quality Implications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16319, https://doi.org/10.5194/egusphere-egu25-16319, 2025.
The nutritional use efficiency (NUE) of crops is influenced by changes in soil pH caused by lime fertilizer, which also affects the nitrogen cycle. Lime application shifts soil pH from acidic to neutral, reducing nitrous oxide (N2O) emissions through the activity of nitrous oxide reductases in microorganisms, while also increasing nitrification rates due to enhanced activity of ammonia-oxidizing archaea (AOA) and bacteria (AOB). Accelerated nitrification leads to higher nitrate (NO3-) levels, which, when exceeding crop absorption capacity, pose a significant risk of leaching. This study investigated the effects of long-term NPK and lime fertilizer application on the soil nitrogen cycle using metagenomic analysis. Soil samples from plots treated with NPK alone and NPK with lime for 48 years were analyzed for metagenomic N2O gas flux, potential nitric oxide rates (PNR), and NUE. Results showed that long-term lime application significantly increased soil pH and reduced N2O emissions by 27% over 480 hours, with the most notable reduction in the first 24 hours compared to NPK-only treatment. However, NUE did not significantly improve, while PNR increased dramatically, reaching 1442% higher than in NPK-treated soils, indicating a potential risk of nitrate leaching. Metagenomic analysis revealed that nitrogen cycling pathways, including nitrification, were more active in lime-treated soils. Enhanced microbial nitrogen metabolism also increased carbon metabolism associated with degradation, suggesting a risk of soil carbon depletion via the priming effect, as evidenced by reduced total soil carbon and organic matter in lime-treated plots. The findings highlight both the benefits and drawbacks of long-term lime application. While lime improves soil pH and reduces N2O emissions, it may also increase nitrate leaching and soil carbon depletion. Further research is needed to optimize lime application for sustainable soil management.
How to cite: Park, S., Lee, J.-G., Kwon, N.-H., Lee, C., Kim, T., and Jung, J.: Long-Term Effects of Lime and NPK Fertilization on Soil pH, Nitrogen Cycling, and Carbon Depletion: Benefits and Risks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5367, https://doi.org/10.5194/egusphere-egu25-5367, 2025.
Soil heterotrophic respiration is the process by which carbon stored in soil is released into the atmosphere as CO₂ through microbial breakdown of organic matter. This process influences the balance between carbon storage and release, impacting soil carbon levels. Factors such as soil temperature, soil moisture, and the availability of organic material determine CO₂ emissions. Tillage practices alter this soil respiration process by changing soil structure, impacting on airflow, and microbial activity, which influence decomposition rates and CO₂ fluxes. Understanding these interactions is critical for sustainable farming and reducing greenhouse gas emissions from soils. This study explored the effects of different wheat establishment systems: plough (P), minimum tillage (MT), and direct drilling (DD), on the heterotrophic respiration in a long-term plot-scale experiment at Teagasc Oak Park, Ireland. Treatments were replicated four times in a randomized block design on a site where P and MT treatments were in place since 2001, with DD practiced since 2021. Measurements were taken in situ using closed chambers and a portable FTIR gas analyser (Gasmet GT5000 Terra) from September 2024 to the end of December 2024, with plans for continued monitoring beyond this timeframe. For analysis, the experimental timeline was divided into two phases: Period 1 (P1), starting from the 9th of September (following the MT event) and ending on the 10th of October (the ploughing day), and Period 2 (P2), continuing from this point to the last measurement taken in December 2024. Results demonstrated that tillage treatments significantly influenced soil respiration. During P1, MT consistently displayed higher daily CO2 emissions due to soil disturbance and incorporation of crop residues, DD and P did not differ significantly from each other. With lower temperatures in P2, MT sustained a significant greater flux compared to the other treatments, supported by its great soil moisture retention and moderate sensitivity to temperature variations (r = 0.569). While ploughing at the start of P2 P resulted in a temporary spike in CO₂ fluxes on the P plots, this diminished rapidly. With emissions strongly influenced by temperature variations (r = 0.603), this decline was further driven by a significant drop in air temperature and P's limited soil moisture retention, which may have suppressed microbial activity. This resulted in lower overall soil respiration fluxes from P compared to MT but not significantly different from those of DD in the reported time frame. Cumulative fluxes further emphasized these differences: MT recorded the highest emissions (577.39 kg CO₂-C ha⁻¹), followed by P (470.89 kg CO₂-C ha⁻¹) and DD (394.74 kg CO₂-C ha⁻¹). These findings highlight the varying impacts of tillage practices on soil carbon dynamics driven by an interaction with environmental factors such as soil moisture and temperature.
Keywords: Soil heterotrophic respiration, Tillage practices, Carbon dynamics, Greenhouse gas emissions
How to cite: Mohamed Islam, K., D. Patrick, F., Gary, L., Olaf, S., and Necpalova, M.: The effect of crop establishment system on soil heterotrophic respiration pre- and post-establishment: initial results., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17689, https://doi.org/10.5194/egusphere-egu25-17689, 2025.
Systematic evidence synthesis in soil science is crucial for developing effective climate mitigation strategies and sustainable land management practices. This study presents an integrated meta-analytical framework synthesizing three interconnected domains of soil carbon dynamics: land-use transitions, conservation management, and emerging environmental stressors. Through quantitative analysis of peer-reviewed studies, we evaluated the multifaceted responses of soil organic carbon (SOC) and associated biogeochemical processes to management interventions and environmental changes. Land-use conversion analysis suggested that grassland restoration from croplands significantly enhances SOC (16%) and total nitrogen (12%), while inducing substantial shifts in microbial stoichiometry (C:P ratio +57.9%). Conservation management practices, particularly no-tillage with residue retention, increased SOC stocks (13%) relative to conventional tillage, accompanied by enhanced microbial biomass carbon (33%) and nitrogen (64%). The implementation of grass coverage in orchards further augments these benefits, increasing microbial abundance (52.6%) and diversifying enzyme activities (15-71%). Environmental factors, including mean annual temperature, precipitation, and soil texture, emerged as critical drivers of these responses across all management interventions. Analysis of emerging stressors found that drying-rewetting cycles significantly increased soil carbon dioxide emissions (35.7%), while microplastic contamination enhanced nitrogen-cycling enzyme activities (7.6-8.0%) and SOC dynamics in polymer-specific patterns. Meta-regression analyses identified key thresholds and optimal conditions for maximizing soil carbon sequestration potential across different environmental contexts. This comprehensive evidence synthesis indicates the interconnected nature of soil carbon responses to management and environmental change, while establishing quantitative parameters for context-specific interventions. The findings provide support for policy frameworks promoting integrated approaches to soil conservation and climate-smart management strategies, particularly in vulnerable agricultural systems facing multiple environmental stressors.
How to cite: Li, Y., Shurpali, N., Xiang, Y., Zhang, Q., Li, Z., Cui, S., and Chang, S.: Evidence synthesis of soil carbon dynamics: A multi-scale meta-analysis integrating land-use change, conservation practices, and environmental stressors, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16123, https://doi.org/10.5194/egusphere-egu25-16123, 2025.
Crop harvested carbon is one of the most important components of the carbon cycle in cropland ecosystems, with a significant impact on the carbon budget of croplands. China is one of the most important crop producers, however, it is still unknown on the spatial and temporal variations of harvested carbon. This study collected statistical data on crop production at the province and county levels in China for all 10 crop types from 1981 to 2020 and analyzed the magnitude and long-term trend of harvested crop carbon. Our results found a substantial increase of harvested carbon in cropland from 0.185 Gt C yr-1 in 1981 to 0.423 Gt C yr-1 in 2020 at a rate of 0.006 Gt C yr-1. The results also highlighted that the average annual carbon sink removal from crop harvesting in China from 1981 to 2020 was 0.32 Gt C yr-1, which was comparable to the net carbon sink of the entire terrestrial ecosystems in China. This study further generated a gridded dataset of harvested carbon from 2001 to 2019 in China by using jointly the statistical crop production and distribution maps of cropland. In addition, a model-data comparison was carried out using the dataset and results from seven state-of-the-art terrestrial ecosystem models, revealing substantial disparities in harvested carbon simulations in China compared to the dataset generated in the study. This study emphasized the increased importance of harvested carbon for estimating cropland carbon budget, and the produced dataset is expected to contribute to carbon budget estimation for cropland ecosystems and the entire China.
How to cite: Ren, P., Wang, D., Xia, X., Chen, X., Qin, Z., Wei, J., and Yuan, W.: Increased harvested carbon of cropland in China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6346, https://doi.org/10.5194/egusphere-egu25-6346, 2025.
Ethiopian agriculture is under severe pressure due to erosion and degradation of arable soils. These problems are exacerbated by high livestock numbers in small-holder farming, leading to intense grazing on limited communal pastures and on crop residues. Introducing leys of perennial forage species (grasses and legumes) into soils predominately used for cereal cropping could help restore degraded soils while simultaneously providing high quality feed for livestock. To optimize perennial species selection for different soils, we studied microbial nutrient cycling responses to perennial plant inputs in six contrasting soils in Ethiopia. Two grasses, Urochloa hybrid Cayman and Megathyrsus maximus, and two legumes, Desmodium intortum and Stylosanthes guianensis, were sown in varying mixtures at three field sites in two different regions. To assess how soil microbial nutrient stoichiometry and nutrient demand changed with plant cover, we measured soil exoenzyme activity, soil microbial biomass, C, N and P stoichiometry and nitrification potentials before and after the 1.5-year field experiments. Changes in microbial nutrient limitation in response to species ratios were estimated by a combined Vector and Threshold Element Ratio model. We found variable responses for the different soils, with the largest differences between the two regions. Across all fields we saw that P-limitation of microbes decreased with increasing ratios of legumes in the perennial mixtures. We conclude that increased legume incorporation reduces P-limitation and positively affects nutrient cycling in Ethiopian soils.
How to cite: Wickander, N., Jørgensen, M., and Dörsch, P.: Effect of perennial forage species on soil microbial nutrient cycling in Ethiopian leys, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4407, https://doi.org/10.5194/egusphere-egu25-4407, 2025.
Managed grasslands are valuable from the viewpoint of the various ecosystem services they provide. They not only provide nutritious feed for the dairy cows and benefit a fertile soil but are also considered to have the potential to play a key role in greenhouse gas mitigation, particularly in terms of carbon sequestration. While grasslands on mineral soils vary anywhere from being a small sink to a source of GHGs, drained organic soils used for agriculture are a huge source of GHG emissions with net positive feedback to climate change. Continuous, year-round GHG flux measurements are therefore, necessary to assess the sustainability of dairy and beef sector under different agroclimatic conditions and soil types. These continuous fluxes represent all management practices such as fertilizer application, biomass harvesting, water table manipulation on organic soils and tillage operations and prevailing climatic conditions. We aim to present eddy covariance measured complete GHG balance of legume and nonlegume grasslands on mineral and drained organic soils under boreal conditions.
How to cite: Shurpali, N., Peltola, O., Li, Y., Rinne, J., and Virkajärvi, P.: Multi-year GHG flux measurements from grasslands on boreal mineral and drained organic soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20546, https://doi.org/10.5194/egusphere-egu25-20546, 2025.
Greenhouse gas flux studies are fundamental to understanding the net emission and removal of greenhouse gases by terrestrial ecosystems. Evidence from UK grasslands is sparse and tends to be from intensive agricultural plots.
Emerging results from a novel, 24-month study are presented. Carbon dioxide measurements were collected from grasslands across the UK, using the static chamber method. More than 20 parcels were surveyed, with habitats from a range of soil types, sward diversity and management processes, enabling a broader analysis of the variety of grasslands in England.
Carbon dioxide emissions were detected all year round, thus allowing further analysis of seasonal dynamics. The influence of wider environmental variables, such as moisture and temperature are also explored, with fluxes detected at lower soil moistures than similar studies. These studies will help us to understand the carbon sequestering potential of grassland creation for nature-based solutions as part of the Nature Returns programme.
How to cite: Hartill, J., Spiers, M., Davess, B., Izard, N., Stone, M., Elias, J., Lockwood, T., and Morecroft, M.: Greenhouse gas fluxes from established and emergent grasslands and the implications for nature-based solutions in England. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12203, https://doi.org/10.5194/egusphere-egu25-12203, 2025.
Grasslands serve a unique role in the global carbon (C) cycle and cover about 30% of the European and about 70% of the Swiss area used for agriculture. The CO2 fluxes of managed grasslands are substantially influenced by climate conditions and land management practices. The eddy covariance (EC) technique is the only approach to directly measure the net ecosystem exchange (NEE) of CO2. NEE represents the balance between two large ecosystem processes: gross primary production (GPP; amount of CO2 fixation through photosynthesis), and ecosystem respiration (Reco; amount of CO2 released via plant and soil respiration). Our study aimed to (1) investigate intra- and inter-annual changes in grassland NEE as well as regrowth after mowing/grazing events, (2) understand key drivers of GPP regrowth rates, and (3) examine grassland responses to sward renewal.
In our study, we measured EC fluxes and meteorological variables at the temperate grassland site Chamau (CH-Cha as part of FLUXNET) in Switzerland. This grassland is intensively managed, with 4-6 mowing/grazing events per year, accompanied by organic fertilization (on average 271 kg N ha-1 yr-1) and sward renewal every 7-10 years. We applied machine learning approaches such as Extreme Gradient Boosting (XGBoost) and Shapley Additive exPlenations (SHAP) analysis to address our aims, using 20 years (2005-2024) of EC flux, meteorological, and detailed management data.
Over the 20 years, a pronounced intra-seasonal course of NEE was found due to mowing and grazing, with the maximum CO2 uptake in early spring (March-April) and the largest CO2 loss in early winter (December-January). During the main growing season (April-September), the average GPP regrowth rate was 10 g C m-2 day-1. We did not find a significant trend for GPP regrowth rates over the 20 years. The most important drivers of GPP regrowth rates were air temperature and light, while water-related drivers dominated regrowth rates during summer droughts (e.g., 2015 and 2018). Nitrogen fertilization did not play a key role in GPP regrowth rates. Moreover, sward renewal years resulted in either very large CO2 losses (in 2012) or in reduced CO2 uptake rates (in 2021), most likely caused by the different timing of the renewal, i.e., February vs. August, respectively. Thus, our study provides novel insights into climate-smart management options and helps to develop mitigation strategies for current and future climate risks.
How to cite: Wang, Y., Feigenwinter, I., Hörtnagl, L., and Buchmann, N.: Impact of management on CO2 fluxes and drivers of regrowth rates in a temperate grassland during 20 years of measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6469, https://doi.org/10.5194/egusphere-egu25-6469, 2025.
Dehesa ecosystems, traditional silvopastoral systems in the Iberian Peninsula, are characterized by scattered trees and pastures extensively grazed by livestock. These systems provide critical ecosystem services, including soil organic carbon (SOC) storage, which helps mitigate the negative impacts of livestock production and might support farm economic sustainability through potential carbon (C) credits. However, accurately estimating SOC in dehesa soils is challenging due to their high spatial variability caused by scattered trees and grazing patterns, which create SOC “fertility islands” under tree canopies.
This study evaluates how different grassland management practices affect SOC storage in dehesa soils and determines optimal methodologies for estimating SOC stocks despite soil heterogeneity. Research was conducted on an organically managed farm in Alcañizo (Toledo, Spain), comparing fields with rotational and semi-continuous grazing systems, which differ in grazing frequency and resting periods. SOC and bulk density were measured in soil samples collected from 0–10, 10–20, and 20–30 cm depths on a 20 × 20 m grid. Four geospatial methods were used to estimate SOC stocks: IDW (Inverse Distance Weighting), Ordinary Kriging (OK) with 6- and 12-point radio, and soil units zonation.
Results revealed that SOC stored between 10–30 cm depth (1,724 ± 825 g C m-2) was comparable to that in the top 10 cm (1,876 ± 641g C m-2), underscoring the need to sample at least 30 cm for comprehensive SOC estimation. Trees significantly increased SOC storage by 56% and 34% in soils under the trees compared to open grassland soils in the rotational and semi-continuous management systems, respectively. Regarding management practices, the arithmetic mean of SOC stocks (0-30 cm) was slightly higher under semi-continuous management (3,861 ± 1,286 g C m²) compared to rotational management (3,339 ± 1,334 g C m²).
While SOC estimates were similar across geospatial methods and arithmetic means due to the large number of sampling points, IDW best represented SOC accumulation under trees, and soil unit-based methods identified SOC accumulation due to topography. Conversely, OK with a 12-point radius poorly captured SOC heterogeneity. The choice of geospatial estimation method significantly influences SOC stock estimates.
In conclusion, future SOC assessments in dehesa ecosystems should account for their high spatial variability by increasing sampling density and applying diverse estimation methods. This approach will improve the reliability of SOC stock estimates, aiding both ecological studies and C credit calculations.
How to cite: Cámara, J., Sánchez, S., Mendes, L. A., Estrella, M., and Benito, M.: Estimating soil organic carbon stocks in dehesa ecosystems (Toledo, Spain), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14766, https://doi.org/10.5194/egusphere-egu25-14766, 2025.
Summer irrigation in temperate managed pastures enhances aboveground productivity during soil water-limited periods, but its effects on soil organic carbon (SOC) dynamics remain insufficiently understood, with reported effects often contradictory. Our objective was to quantify the effects of summer irrigation on the short-term fate of photo-assimilated carbon (C) in the entire pasture and soil system.
Using mesocosms containing ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) that were maintained to simulate spring conditions in New Zealand, a 13CO₂ labelling experiment was conducted. After the labelling, mesocosms underwent an irrigation period during summer, followed by a post-irrigation period. The 13C-labelled mesocosms (n = 48) were sampled in sets over five sampling times: 1, 15, 140, 225 and 334 days after the last labelling event.
Over the irrigation period (15 and 140 days after the last labelling event), irrigation increased carbon losses through leaf harvest (threefold higher than non-irrigated systems) and reduced root biomass by 2000 kg dry matter ha⁻¹. At the end of both, the irrigation and post-irrigation periods, the quantity of 13C remaining in roots in the irrigated treatment was lower by 70% and 60%, respectively, compared to non-irrigated conditions. Non-irrigated conditions favoured the retention of photo-assimilated 13C in roots and in the mineral-associated organic matter size fraction (<5 µm), while irrigation promoted fine particulate organic matter formation (53-250 µm).
These findings highlight that summer irrigation accelerates carbon turnover in roots and mineral-associated fractions, potentially reducing long-term SOC storage under intensified pastoral systems.
How to cite: Carmona, C. R., Clough, T., Beare, M., McNally, S., and Qiu, W.: Summer Irrigation increases organic carbon turnover in managed pastures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1387, https://doi.org/10.5194/egusphere-egu25-1387, 2025.
In this study, we have explored effect of long-term nature protection on soil carbon storage in meadows. We have selected 30 pairs of meadows, each pair consisted from nature reserve, and neighboring commercially used meadow. In both Meadows we sample soil to 30 cm depth, and established song carbon stock. At the same time, we started plant diversity and community composition in both meadows.
Comparing carbon stock cross all pairs of meadows, natural reserve store significantly more carbon, which account for about 20 to 30% increase compare to commercially managed meadows. In general carbon stock decrease which increasing depth, but this increase was similar in both commercial as well as protected meadows. The highest carbon stock was found in dry meadows, which were followed by wet meadows, while mesic meadow stores less C and also difference between commercial and protected meadows was less pronounced. There was no difference in aboveground plant biomass between protected and cultural meadows. Protected meadows we are significantly more diverse than their commercially used counterpart, however there were no direct correlation between plan diversity and carbon stock. Based on that we assume that we assume that beside plant diversity also continuity of undisturbed soils in protected meadows, play role in soil carbon storage.
How to cite: Frouzova, J., Mudrak, O., Murindangabo, Y., Bartuška, M., and Frouz, J.: Protected meadows more diverse meadows store more carbon in soil than neighboring commercially used meadows., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6472, https://doi.org/10.5194/egusphere-egu25-6472, 2025.
In humid Africa, grassland degradation is widespread, with overgrazing as a major factor, affecting soil health and structure, and vegetation composition. Understanding this degradation is vital for targeted restoration. We assessed grassland degradation and its effects on soil properties and plant diversity in western Kenya at two contrasting sites —Kuresoi and Nyando—classified as degraded or non-degraded based on grazing intensity and land-use history. We analysed soil carbon (SOC), nutrient concentrations (TN, available P) and aggregate stability. Field measurements included soil resistance and hydraulic conductivity, alongside vegetation inventory.
The results show higher SOC and total nitrogen (TN) in non-degraded topsoil (SOC: 6.66 ± 2.21% in Kuresoi, 2.41 ± 0.51% in Nyando; TN: 0.56 ± 0.188% in Kuresoi, 0.149 ± 0.027% in Nyando) compared to degraded soils (SOC: 4.38 ± 1.37% in Kuresoi, 1.93 ± 1.22% in Nyando; TN: 0.351 ± 0.123% in Kuresoi, 0.172 ± 0.082% in Nyando); low and variable phosphorus content (Kuresoi: 3.17 ± 5.80 µg/g in degraded, 4.13 ± 8.52 µg/g in non-degraded; Nyando: 2.33 ± 2.76 µg/g in non-degraded and 3.96 ± 6.52 µg/g in degraded) across sites. We observed high aggregate stability, ranging from 61.3%–92.6%, across sites. Infiltration rates were higher in non-degraded Kuresoi (463 ± 913 mm/hr) than degraded (40.3 ± 45.6 mm/hr), with similar rates ((76.9 ± 82.1 mm/hr in non-degraded and 69.6 ±99.3 mm/hr in degraded) in Nyando. The soils were generally compacted (1.07–6.7 MPa in Kuresoi; 1.82–10.1 MPa in Nyando), with no significant differences between degraded and non-degraded soils. Species diversity indices, Shannon (H’= 2.69 ±0.39 in non-degraded Kuresoi, and 2.54 ±0.18 in degraded Kuresoi; H’ = 2.85 ± 0.32 in non-degraded Nyando, and 2.75 ± 0.21) and Simpson (D = 0.92 ± 0.03 in non-degraded Kuresoi, and 0.91 ±0.01; D = 0.93 ±0.01 in non-degraded Nyando and 0.92 ± 0.015), indicated high diversity across sites.
The findings indicate that while overgrazing driven degradation affects key soil properties such as phosphorus, compaction, and infiltration rates, some soil characteristics like aggregate stability and species diversity remain resilient. Proper grazing management, coupled with soil organic matter amendments, could improve nutrient availability, restore soil structure, and strengthen grassland resilience.
How to cite: Sibilu, H., Quinton, J., Leitner, S., and Rufino, M.: Assessing grassland soil degradation through key soil physical and chemical properties in smallholder farms of Western Kenya, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10086, https://doi.org/10.5194/egusphere-egu25-10086, 2025.
This study presents a high-resolution mapping framework for estimating GPP in grasslands over the period 2000-2022 at a spatial resolution of 30 meters. The GPP values are derived utilizing a Light Use Efficiency (LUE) model using 30-m Landsat reconstructed images coupled with 1-km MOD11A1 temperature data and 1-degree CERES Photosynthetically Active Radiation (PAR). To implement the LUE model, we used the biome-specific productivity factor (maximum LUE parameter) as a global constant. This resulted in a productivity map that did not require specific land cover maps as inputs, allowing data users to calibrate GPP values accordingly to specific biomes/regions of interest. We then derived GPP maps for global grassland ecosystems based on maps produced by the Global Pasture Watch research consortium and calibrated the GPP values using the maximum LUE factor of 0.86 gCm−2d−1 MJ-1. Nearly 500 eddy covariance flux towers were used for validating the GPP estimates, resulting in R2 between 0.48-0.71 and RMSE below 2.3 gCm−2d−1 considering all land cover classes. The final time-series of maps (uncalibrated and grassland GPP) will be available as bimonthly and annual periods in Cloud-Optimized GeoTIFF (23 TB in size) as open data (CC-BY license). Users will be able to access the maps using the SpatioTemporal Asset Catalog (http://stac.openlandmap.org) and Google Earth Engine upon publication. In the meantime, beta versions of the product can be accessed through the Global Pasture Watch Early Access data program (https://survey.alchemer.com/s3/7859804/Pasture-Early-Adopters). This dataset is the first global GPP time-series map with a spatial resolution of 30 m covering a 23 year period to our knowledge.
How to cite: Isik, M. S., Parente, L., Consoli, D., Sloat, L., Mesquita, V., Ferreira, L. G., Stanimirova, R., Teles, N., and Hengl, T.: Global Grassland Productivity Over Two Decades: 30m Bimonthly and Annual Gross Primary Productivity through Light Use Efficiency Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20008, https://doi.org/10.5194/egusphere-egu25-20008, 2025.
Semi-arid savanna grasslands in Kenya are vital for food production and rural livelihoods, with livestock grazing accounting for more than 90% of household incomes in arid and semi-arid areas. However grassland soils have become degraded in many areas due to vegetation loss and soil erosion, often caused by overgrazing. Soil degradation (depletion of organic matter and nutrient levels, disrupted soil biological process, and poor structure) reduces plant productivity and resilience to extreme weather conditions such as drought. Given that drought has been increasing in severity, duration and frequency over recent decades, this has severe implications for food security across sub Saharan Africa.
Grassland restoration often focusses on re-seeding grasses with high grazing value, but poor soil conditions may hinder successful re-vegetation. Soil processes therefore need to be restored to ensure the long-term sustainability of grazing lands. Legumes, found alongside grasses in natural grasslands, may play a key role in soil processes, particularly nutrient cycling which is likely to be important for semi-arid grassland soils as they are often highly nitrogen limited. However, while there is a significant body of research on legume-soil interactions in temperate grasslands and the tropical grasslands of Asia and Latin America, there has been little research on how the highly weathered soils and semi-arid grasslands of sub Saharan Africa function and may respond to restoration interventions.
In this mesocosm experiment, grasses were grown in native soil with and without legumes, under both droughted and well-watered conditions. This aimed to assess the impact of legumes on grassland productivity via their influence on soil processes, and whether this can mediate the effects of drought stress.
Grass biomass was higher when grasses were grown alongside native legumes than in a grass-only mix although the impact varied between grass species. This was accompanied by higher root growth and nitrogen content of plant tissue. These trends were observed in both well-watered and droughted conditions. These findings suggest that legumes play an important role in the productivity and drought resilience of grasslands, likely by helping to mitigate nitrogen limitation. Further work is needed to test these findings on a wider range of grass and legume species and improve our understanding of the mechanisms involved.
How to cite: Pearce, F.: Can legumes improve the productivity and resilience of semi-arid Kenyan grasslands via influence on soil processes?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-257, https://doi.org/10.5194/egusphere-egu25-257, 2025.
Abstract Both climate warming and increasing nitrogen deposition promote the availability of nitrogen (N) and phosphorus (P) to plants in soil, which may affect ecosystem structure and function. However, studies on the effects of nutrient enrichment on ecosystems have mostly focused on N rather than P, especially in high-altitude areas where N limits plant growth, which hinders the prediction of ecosystem changes under future climate conditions. Using a five-year experiment at an alpine meadow, we quantified the aboveground net primary production (ANPP) stability under three N levels and four P levels, including the interaction of different N and P levels. We also tested possible drivers of the ANPP stability, including plant species richness, asynchrony, dominance, and plant functional group stability. Finally, we used structural equation models to explore how different drivers affect ANPP stability. Results showed: (1) Plant growth in the alpine meadow was limited by soil available-N but not -P, and N enrichment induced P limitation on plant growth. (2) P enrichment promoted species richness, asynchrony and dominant species stability, and consequently increased the ANPP stability. (3) Species asynchrony and dominant species stability were the key mechanisms driving the variation of ANPP stability. These findings highlight the importance of understanding the balance of N and P effects on ecosystem structure and function in order to better predict the impacts of global change on ecosystem stability.
How to cite: jiang, L. and zhao, W.: Phosphorus enrichment increased community stability by increasing asynchrony and dominant species stability in alpine meadow of Qinghai-Tibet Plateau , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9977, https://doi.org/10.5194/egusphere-egu25-9977, 2025.
Grasslands play a crucial role in supplying essential resources for the livestock industry and in supporting other ecosystem services such as biodiversity preservation and soil carbon (C) storage. However, the ability of these ecosystems to maintain these services is increasingly at risk due to over-exploitation, environmental degradation, and climate change, particularly weakening their ability to effectively store C in soils. Restoring degraded grasslands is a practical and cost-effective approach to mitigating climate change by increasing soil C storage while enhancing productivity and improving ecosystem resilience. The potential for C sequestration in these ecosystems is highly variable, influenced by factors such as climate, biome type, soil depth, and management. Better management requires addressing the existing gaps in research and resources.
Using a systematic mapping approach, this project aims to build a comprehensive global inventory of studies examining the effects of different management practices on soil C. The outcomes of this approach will be used to identify well-researched areas suitable for systematic reviews, as well as knowledge gaps for further research, ultimately enhancing our understanding of the evidence in this field.
We formulated the research question to guide the systematic map protocol using the PICO framework, in line with established standards for systematic evidence synthesis. A preliminary search string was developed by integrating search terms corresponding to the Population (permanent grasslands), Intervention (varied management practices), and Outcome (soil C and related terms) categories, along with an additional category for study types (focused on farm and field experiments). A comprehensive search of both peer-reviewed and grey literature was performed across several databases, including Web of Science, Scopus, CABI, Google Scholar, and specialised platforms such as Agrotrop. Searches were conducted in English, Spanish, Portuguese, French, German, and Mongolian (the language skills of the team). Data extraction was structured into four key sections (article information, PICO categories, study characteristics, and measurable parameters), which will be used to generate tables, figures, and evidence maps to form the systematic map. The entire process of literature screening and data extraction was performed using the software Covidence.
The literature search resulted in the identification of over 30,000 references, of which approximately 3,000 were selected for further analysis following a thorough full-text eligibility criteria screening. In this presentation, we will walk through the flow diagram that captures each step of the literature search and screening process, share the data extraction table to provide insights into the outcomes, and offer a preliminary assessment at the global distribution map of studies involved. This includes an overview of the primary grassland management practices assessed. In addition, critical questions will be discussed: i) is there underrepresentation of developing countries in the literature, where vast grassland areas often suffer from intense degradation? ii) Is our knowledge influenced by a potential overrepresentation of specific forage species, management practices or climatic conditions? These findings will enhance our understanding of the existing evidence on the impact of grassland management on soil C, paving the way for a more effective allocation of future efforts and resources in this field.
How to cite: Vázquez, E., Rousset, C., Segura, C., Gilgen, A., Alfaro, M., Mendes, L. A., Dodd, M., Dashpurev, B., Bastidas, M., Rivera, J., Merbold, L., van der Meer, M., Arango, J., Cárdenas, L., Benito, M., and Chará, J.: What evidence exists relating the impact of different grassland management practices to soil carbon in livestock systems? A systematic map in progress, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16064, https://doi.org/10.5194/egusphere-egu25-16064, 2025.
Increasing soil organic carbon (SOC) stocks in grasslands is a promising strategy for offsetting greenhouse gas (GHG) emissions from cattle ranching. Previous studies have shown that certain Urochloa grasses develop an extensive deep rooting system that contributes to higher SOC accumulation in acidic soils with low fertility and aluminum toxicity. At the Alliance Bioversity and CIAT, genetically diverse a Urochloa grasses are utilized in breeding programs aimed at developing hybrids with improved adaptation to biotic (e.g., spittlebug) and abiotic (acidic soils, aluminum toxicity, drought, and waterlogging) stresses, enhanced nutritional quality, and reduced nitrous oxide from soil and methane from cattle. However, the capacity for SOC accumulation from their deep rooting ability has not yet been considered as a target trait within these breeding programs. Since these improved grasses are pivotal for sustainable livestock intensification, this study aims to evaluate the differences in the contribution of nine Urochloa genotypes to increase SOC stocks in a Mollisol of Valle del Cauca, Colombia. The field trial was established in 2016 with the planting of nine Urochloa genotypes: four cultivars/accessions (U. brizantha cv. Marandu, U. humidicola cv. Tully, U. humidicola CIAT 26146, and U. humidicola CIAT 16888), and five hybrids (cv. Mulato II, Uh08 675, Uh08 1149, Uh 72, and Uh 91) as well as a control treatment with bare soil. Each genotype was planted in 20 x 20 m plots with three replicates, and three control plots were maintained as bare soil. Six years after establishment (early 2023), soil samples were collected from each plot at four depths (0-10, 10-20, 20-60, 60-100 cm) to estimate SOC stocks using the values of SOC concentration and bulk density. We observed that SOC concentrations decreased with depth. In grass-covered plots, the average SOC concentration was 2.17% in the surface layer (0–10 cm) and 0.25% in the deeper layer (60–100 cm). In contrast, in bare soil plots, the average SOC concentration was 1.7% in the surface layer and 0.11% in the deeper layer. Results on the stocks of SOC (0-100 cm soil depth), based on equivalent soil mass, indicated that after 6 years of establishment, plots planted with Urochloa grasses showed an average value of 127.4 Mg C ha⁻¹, which is 47% more compared to 86.4 Mg C ha⁻¹ found in bare soil. We observed a clear trend with Urochloa hybrids showing a greater ability to increase SOC stocks, in the following order: Uh 91 > Uh 72 > Uh08 675 > cv. Marandu > Uh08 1149 > cv. Mulato > CIAT 26146 > CIAT 16888 > cv. Tully. For example, the Urochloa hybrid of Uh 91 had a SOC stock of 155.66 Mg C ha⁻¹, while cv. Tully had 97.17 Mg C ha⁻¹. These results highlight the potential of Urochloa grass hybrids to contribute towards mitigation of climate change. On-going Urochloa grass breeding programs should consider incorporating the trait of SOC accumulation ability together with other desirable traits of stress resistance, improved nutritional quality, and reduced GHG emissions.
How to cite: Rodriguez, L., Bastidas, M., Villegas, D., Prado, V., Benito, M., Subbarao, G., Costa Junior, C., Rao, I., and Arango, J.: Potential of different Urochloa grass hybrids to enhance soil organic carbon stocks in a Mollisol of Valle del Cauca, Colombia , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-717, https://doi.org/10.5194/egusphere-egu25-717, 2025.
Agriculture is one of the major sources of global greenhouse gas emissions, and faces challenges such as erosion, nutrient leakage, and reliance on external inputs like seeds and fertilizers. These issues are largely driven by the cultivation of annual crops with shallow roots and intensive soil disturbance. Perennial crops, such as intermediate wheatgrass (IWG), could offer a sustainable alternative by reducing emissions, erosion, and input dependency through deep and extensive roots and no-till requirements. This study focuses on IWG, producing the grain Kernza, a novel crop for food production, and investigates the climate mitigation potential of this perennial crop for a more sustainable agricultural system.
Outside Lund in southern Sweden, a 10-ha field of IWG has been established adjacent an equivalent-sized field with conventional annual crop rotation. Carbon dioxide exchange was measured continuously at both of the fields separately using the eddy covariance (EC) technique to account for the first-year’s carbon budget for each field. The cumulative net ecosystem exchange during the first crop cycle (spanning the period between the first and second sowing of annual crops at the control site), has been evaluated. Preliminary findings show that IWG has more than twice the net carbon uptake compared to the conventional annual crop after one crop cycle. Further analyses of the EC data will be undertaken, as well as incorporation of measured above ground biomass (AGB) and fossil fuel use (e.g. machinery) in the carbon budget. The results will be synthesised and presented at the conference.
How to cite: Widengren, V., Ardö, J., Holst, J., Biermann, T., and Vestin, P.: Let That Sink In- Carbon Uptake of Perennial Intermediate Wheatgrass in Southern Sweden, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1468, https://doi.org/10.5194/egusphere-egu25-1468, 2025.
Agricultural lands comprise ~40% of European land and significantly contribute to continental greenhouse and trace gas emissions1, particularly nitrous oxide (N2O), and reactive nitrogen species including ammonia (NH3) and nitrogen oxides (NOx, NOz). Within the EU's commitment to reduce agricultural greenhouse gas emissions by 30% by 2030, understanding crop variety influences on these emissions is crucial. While the release of nitrogenous gases following synthetic nitrogen (N) fertiliser application is well-documented, the impact of crop traits on emission patterns through their effects on soil properties and microbial communities remains poorly understood. Wheat, as Europe's dominant cereal crop and a global food security cornerstone, has undergone extensive breeding resulting in distinct heritage and modern semi-dwarf varieties.2 These varieties differ primarily in their expression of reduced height genes, which were introduced to support higher grain yields but consequently altered root system biomass allocation and morphology.3 Here, we present the first comprehensive assessment of how these root architectural differences influence soil N-cycling and subsequent gas emissions. Our field trials, conducted in central England, compared two heritage varieties (Red Lammas and Chidham Red) with two semi-dwarf varieties (Crusoe and Skyfall) under different N fertiliser treatments (0, 60, and 120 kg-N ha-1). Continuous gas flux measurements using multiplexed chambers coupled with FTIR spectroscopy and chemiluminescence detectors revealed >600% higher nitric oxide (NO) emissions from modern varieties during spring. Molecular analyses of rhizosphere soil showed distinct N-cycling microbial communities between variety types (Fig. 1). Seasonal dynamics indicated strongest variety effects during summer fertiliser application and early spring moisture stress periods. This research directly informs European agricultural policy by demonstrating how historical breeding decisions influence greenhouse gas emissions, while providing evidence-based strategies for variety selection and fertiliser management that could reduce agricultural nitrogen losses without compromising yield targets.
Figure 1. Predicted gene counts of microbes associated with denitrification and nitrification from rhizosphere soil of higher specific root length (SRL) taller cultivars and lower SRL semi-dwarf cultivars of wheat, quantified using shotgun DNA sequencing.
(1) Tubiello, F. N.; Salvatore, M.; Rossi, S.; Ferrara, A.; Fitton, N.; Smith, P. The FAOSTAT Database of Greenhouse Gas Emissions from Agriculture. Environ. Res. Lett. 2013, 8 (1), 015009. https://doi.org/10.1088/1748-9326/8/1/015009.
(2) Shewry, P. R. Wheat. Journal of Experimental Botany 2009, 60 (6), 1537–1553. https://doi.org/10.1093/jxb/erp058.
(3) Vergauwen, D.; De Smet, I. From Early Farmers to Norman Borlaug — the Making of Modern Wheat. Current Biology 2017, 27 (17), R858–R862. https://doi.org/10.1016/j.cub.2017.06.061.
How to cite: Purchase, M. L., Wang, D., Thorpe, A. J., and Mushinski, R. M.: Effects of Wheat Root Morphologies on Agricultural Soil Gas Fluxes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-467, https://doi.org/10.5194/egusphere-egu25-467, 2025.
As a significant greenhouse gas, nitrous oxide (N₂O) is primarily emitted through anthropogenic activities, with agriculture being the predominant source. These emissions often occur across large spatial scales. The Eddy Covariance (EC) technique stands out as one of the most advanced methods for quantifying N₂O fluxes. However, most commercially available N₂O analyzers are designed for close-path measurements. To achieve the high-frequency gas concentration data required for EC applications, these analyzers typically rely on high-flow pumps, which necessitate substantial power consumption. Consequently, the selection of monitoring sites is frequently constrained by the availability of power.
This work introduces an open-path N2O laser analyzer (Model: HT8500, HealthyPhoton Co., Ltd.) designed for future applications in EC N₂O flux measurements. The HT8500 utilizes an quantum cascade laser (QCL) to probe the mid-infrared transition of N2O at 4.54 μm. The specific absorption peak has the advantage that the density and spectroscopic effects compensate for each other, resulting in low temperature-related corrections in EC flux measurements. Laboratory experiments revealed that the HT8500 has a noise level of 0.4 ppbv at a 10-Hz sampling rate with a typical power consumption ~ 50 Watts.
A long-term field experiment based on the HT8500 over a bare agricultural field in Jinan, Shandong was conducted to test “zero-flux” measurements and computations under different meteorological conditions. Averaged hourly fluxes ranged from near zero at night to less than 0.18 mg m-2·h-1 at midday in December, which were not significantly different from zero. Compared to the laboratory detection limit of 19.29 ug N m-2·h-1, the field experiment demonstrated a detection limit of approximately 49 ug N m-2·h-1, indicating that the HT8500 analyzer maintains its low flux detection limit similar with commercial available chamber-based N2O flux measurement scenarios.
How to cite: Jiang, R., Shen, W., Wang, K., Hu, S., Wilson, D., and Wang, Y.: Detection Limit of a Low Power Open-Path Nitrous Oxide Laser Analyzer based Eddy Covariance Flux Experiment in Northern China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3921, https://doi.org/10.5194/egusphere-egu25-3921, 2025.
Nitrous oxide (N₂O) is an ozone-depleting substance with a global warming potential of 273 times greater than carbon dioxide (CO₂) for a 100-year timescale. The atmospheric concentration of N₂O has increased significantly, rising from approximately 270 ppb during the preindustrial era to over 330 ppb today. This alarming trend underscores global concerns about accurately quantifying anthropogenic N₂O sources and developing effective mitigation strategies. More than 50% of anthropogenic N₂O emissions is estimated to originate from direct agricultural activities, including land-use changes, fertilization, and manure management. In addition, agriculture may also indirectly contribute to N₂O emissions through its impact on freshwater eutrophication, which provides substrates (such as nitrate – NO₃⁻) for nitrification and denitrification processes in aquatic environments, potentially leading to N₂O production. The Intergovernmental Panel on Climate Change (IPCC) has proposed a linear correlation between NO₃⁻ concentrations and N₂O emissions to estimate global freshwater contributions to N₂O budgets. In this context, freshwater ecosystems, such as small agricultural ponds, are often considered as net sources of N₂O. However, direct measurements of N₂O dissolved concentrations and N₂O fluxes from agricultural ponds are limited. Actually, some studies have found N₂Odissolved concentration under saturation levels, leading to assume N₂O uptake from agricultural ponds. To better understand the role of agricultural ponds as sinks or sources of N₂O, we conducted a systematic literature review. Based on data from over 200 ponds associated with agricultural production we found that: there is a strong geographical bias, with most studies focusing on ponds in the northern hemisphere, and that there is non-linear relationship between dissolved NO₃⁻ concentrations and N₂O fluxes. These preliminary findings suggest that a re-evaluation of the IPCC's guidelines on N₂O emissions from inland waters is needed as local conditions strongly drive the fate of NO3- underscoring the need for further research into the driving factors behind water-atmosphere N₂O fluxes in agricultural ponds.
How to cite: Colina, M. and Kosten, S.: From Linear Assumptions to Complex Reality: Dissolved NO3- and N2O Flux Dynamics in Aquacultural Ponds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5205, https://doi.org/10.5194/egusphere-egu25-5205, 2025.
Agricultural ecosystems are significant sources of reactive trace gases, such as ammonia and nitric oxide, as well as greenhouse gases (GHGs), including carbon dioxide, methane, and nitrous oxide. These emissions contribute to global warming, air pollution, and ecosystem eutrophication. Traditional mitigation strategies, such as sulfuric acid slurry acidification in slurry storage, reduce ammonia and methane emissions effectively but face high costs, safety concerns, and restrictions in organic farming. This study explores alternative amendments for slurry, including organic acids waste i.e. cheese whey (a dairy byproduct), sauerkraut juice (a fermentation byproduct), and leonardite (a humic-rich natural material), to assess their potential for emission mitigation.
Using a controlled soil-plant mesocosm system to simulate field-like conditions under a laboratory setting, emissions of ammonia, methane, nitrous oxide, nitric oxide, and carbon dioxide were continuously monitored over nine days. Flux rates were determined using the dynamic chamber method at a temperature of 18°C and a water-filled pore space of 50%. The mesocosms were treated with either untreated slurry, slurry amended with cheese whey, sauerkraut juice, or leonardite, or left unfertilized as a control.
Results highlighted the potential of cheese whey and sauerkraut juice to substantially lower ammonia emissions by as much as 91%, with cheese whey also reducing combined GHG emissions significantly. While sauerkraut juice showed promise in reducing methane emissions, nitrous oxide emissions were elevated due to a higher ammonium content in the slurry-amendment mixture. Leonardite, though not effective in mitigating ammonia emissions, demonstrated its utility in lowering GHG emissions overall.
The findings suggest cheese whey and sauerkraut juice as promising amendments for ammonia reduction, with leonardite offering potential for GHG mitigation. However, the trade-offs observed with nitrous oxide emissions emphasize the need for further optimization to achieve a balanced mitigation strategy. These results contribute to the understanding of gas exchanges in agricultural ecosystems and promote sustainable practices by repurposing agricultural byproducts in a circular economy.
How to cite: Khan, F., Luesma, S. F., Janz, B., Dannenmann, M., Gasche, R., Gattinger, A., Qasim, W., Kiese, R., and Wolf, B.: Effect of bio-acidification and leonardite addition to slurry on ammonia and GHG emissions in soil-plant systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5833, https://doi.org/10.5194/egusphere-egu25-5833, 2025.
The denitrification process is the main process by which nitrous oxide (N2O) is generated under anaerobic conditions in rice cultivation soil. The denitrification process under anaerobic conditions is carried out by microorganisms. The denitrification process is influenced by the type and availability of carbon sources in the soil. Among the components of rice root exudate, sugars and organic acids provide essential carbon sources for soil microorganisms, and microorganisms help the physiology and growth of rice. The incubation experiment was conducted to determine the effect of sugars and organic acids contained in rice root exudates on N2O emissions from paddy soil. The soil was placed in a plastic bottle (capacity 824 cm3) mixed with glucose and acetic acid at the rates of 0.0, 0.1, 0.2, and 0.4% (wt/wt), and saturated with water to maintain anaerobic condition. Then, 0.15g of urea was added as a nitrogen source. The plastic bottles containing mixed soils were placed in the incubation under dark conditions at 25℃ for 30 days. Gas samples were collected daily during the experiment time, and daily N2O flux and cumulative N2O emissions were measured. Cumulative N2O emissions significantly decreased with increasing addition rate of glucose. Cumulative N2O emissions were 200, 8.51, 4.04, and 2.77 mg/m2/day at the glucose addition rates of 0.0, 0.1, 0.2, and 0.4%, respectively. Cumulative N2O emissions decreased more rapidly with increasing addition rate of acetic acid than that of glucose. Cumulative N2O emissions were 225, 3.02, 2.35, and 1.85 mg/m2/day at the acetic acid addition rates of 0.0, 0.1, 0.2, and 0.4%, respectively. These results suggest that acetic acid was rapidly decomposed and provided and available carbon source to microorganisms involved in denitrification, thereby promoting the process of converting nitrate (NO3-) into nitrogen gas (N2) and minimizing N2O production. In the case of the glucose treatment group, the NO3-/ N2O ratio was 1.18, 33.0, 32.6, and 31.2 and the NH4+/ NO3- ratio was 0.16, 0.13, 0.16, and 0.25 at the rates of 0.0, 0.1, 0.2, and 0.4%, respectively. In the case of the acetic acid treatment, the NO3-/ N2O ratio was 1.13, 97.9, 123, and 151 and the NH4+/ NO3- ratio was 0.15, 0.40, 0.40, and 0.75 at the rates of 0.0, 0.1, 0.2, and 0.4%, respectively. These results showed that the main emission process of N2O during the experiment period was the denitrification process rather than the nitrification process. In addition, the higher NO3-/ N2O ratio in the acetic acid treatment group compared to the glucose treatment group indicates that NO3- was converted to N2 more effectively, reducing N2O emissions.
How to cite: Chung, S. U. and Hong, C. O.: Effects of Acetic Acid and Glucose as a Carbon Source for Denitrification on Nitrous Oxide Emissions from Anaerobic Soil Condition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14265, https://doi.org/10.5194/egusphere-egu25-14265, 2025.
Nitrous oxide (N2O) fluxes exhibit a high temporal and spatial variability, making their accurate quantification challenging. Recently, the eddy covariance (EC) technique has become available for N2O measurements, providing non-intrusive spatially integrated flux data at high temporal resolution (half-hourly fluxes from 10 Hz raw data), which can give valuable insights in the underlying drivers when combined with ancillary measurements.
Since April 2022, we measure N2O fluxes by EC using a fast response closed-path N2O analyzer (Los Gatos Research, San Jose, USA) in an agricultural field in central Germany (51.49° N, 9.93° E; Reinshof, DE-Rns). The crop sequence during the study period was winter barley - white mustard (as cover crop) - sugar beet - winter wheat. Additionally, net ecosystem exchange (NEE) of carbon dioxide, ancillary meteorological and soil variables as well as plant performance were measured at the EC tower and crop management was recorded.
The N2O flux measurements over the 2.5 years showed a large temporal variability across seasonal conditions and management activities. Ten particularly large N2O emission peaks with fluxes higher than 120 and up to 950 μg N2O-N m-2 h-1 that last around three days were detected. Those peaks were induced by nitrogen (N) fertilization, rainfall, freeze-thawing or tillage events in the field. From April 2022 to September 2024, we observed cumulative N2O emissions of 3.57 kg N2O-N ha-1 and calculated an emission factor of 0.89% of applied N. We estimated that 23.4% of the cumulative N2O emissions were induced by three rainfall events and one freeze-thawing event, and were thus not directly associated with fertilizer application, while 32.2% occurred within three weeks after N fertilizations. Beside the N2O emission peaks, we observed periods with N2O uptake in 2023 and 2024 when plants showed their highest leaf area index.
This data set, providing several years of N2O fluxes at half-hourly resolution, can help us to better constraint N2O budgets of crop cultivation. Improving our understanding about the interactions of management practices and environmental conditions that lead to higher N2O emissions can help developing strategies for mitigation of N2O emissions.
How to cite: Englert, P., Markwitz, C., Abdulwahab, M. O., Cowan, N., Buchmann, N., Knohl, A., Siebert, S., and Meijide, A.: A 2.5-Year Eddy Covariance Study of Nitrous Oxide Fluxes in Winter Barley, Sugar Beet and Winter Wheat: Responses to Environmental and Management Factors, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18962, https://doi.org/10.5194/egusphere-egu25-18962, 2025.
Greenhouse gas (GHG) emissions, particularly carbon dioxide (CO₂) and methane (CH₄) from human activities, are the primary drivers of global warming. Additionally, methane contributes to ozone formation and therefore contributes to air pollution, posing risk to human health. Agriculture is a significant contributor to the global GHG emissions, with methane primarily emitted through enteric fermentation in livestock and manure management practices, while carbon dioxide largely arises from the use of machinery in various land management operations. Hence, to better understand and represent the intra - annual variability of GHG emissions within the agricultural sector, it is crucial to obtain spatial and temporal information about all contributing activities.
Within the ARTEMIS project we are further developing and refining a dynamic emission model to capture the spatio-temporal variability of anthropogenic GHG and air pollutant emissions in Germany and its surroundings. Inside the emission model the spatial allocator estimates the total yearly emissions with the gridded GHG emission inventory of TNO - CAMS for Europe and UBA - GRETA for Germany.
To account for temporal variability, different agricultural emission activities are parameterized individually. The temporal emission distribution for machinery use during land management operations gets estimated by deriving the emission timings from phenology observation data from the German Weather Service as well as using remote sensed phenology data from the COPERNICUS project. Additionally we incorporate an agricultural timer (Ge et al. 2020, 2022) developed to estimate the start of the growing season, which allows us to derive key dates such as sowing and manure application. The temporal variability of methane emissions from enteric fermentation are parameterized using literature-based emission factors linked to livestock feed intake and animal population data from national statistical agencies.
These emission datasets were integrated into a LOTOS-EUROS model simulation to demonstrate their added value. The comparison using the new dynamic emission model indicated an improved representation of intra-annual GHG concentration variability. Furthermore also the depiction of the diurnal concentration cycle showed a better alignment with measured concentrations. Additionally, evaluation against ICOS tall tower measurements revealed improvements in correlation (up to 0.06) and reductions in root mean squared error (up to 15%) between modeled and observed concentrations at nearly all stations. These findings highlight the importance of disentangling the agricultural GHG emissions into seperate subsectors, enabling a more accurate depiction of temporal variability in anthropogenic emissions. We conclude that further improving the spatio-temporal emission information should be extended on other sectors such as the industry and energy, the road traffic or the landfills as well.
How to cite: Urzí, M., Banzhaf, S., Kranenburg, R., Ge, X., Jäkel, I., Thürkow, M., Jonas, H., and Schaap, M.: Improving the temporal variability of agricultural greenhouse gas emissions for Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19451, https://doi.org/10.5194/egusphere-egu25-19451, 2025.
