Avenues for organic carbon sequestration in soils include plant-based inputs, the addition of pyrogenic carbon (biochar), and addition of composts or other additives such as manures and soil conditioners provided additionality and leakage effects are considered. Enhanced silicate weathering may hold significant potential for building up inorganic carbon stocks, while inputs from bedrock, and mediation by land use changes such as afforestation, may also increase inorganic soil carbon stocks.
This session seeks to explore how soil carbon stocks can be increased so as to simultaneously enhance agricultural productivity, mitigate negative repercussions of changing environmental conditions, and contribute to achieving carbon neutrality. In addition to organic carbon, focus will be given to inorganic carbon pools in agroecosystems and their response to management practices such as fertilisation, irrigation, liming, or other mineral additions. Alongside this, advances in methods for monitoring and modelling rates of soil carbon loss or carbon sequestration in soils will be discussed, including approaches to quantify and characterise organic and inorganic carbon in calcareous soils. We welcome contributions exploring methods of increasing both organic and inorganic carbon stocks, and studies exploring the storage, stability, and cycling of carbon within soil systems. Early career researchers are strongly encouraged to apply, and we seek submissions considering empirical, modelling, or meta-analytical approaches.
Recently, many literature reviews have focused on soil inorganic carbon (SIC) and concluded that SIC should be studied as much as soil organic carbon (SOC) to complete the soil C balance at global scale. However, as SIC has been rarely studied lately, analytical methods for measuring its carbon content and 13C in calcareous soils have not been refined. Similarly, the quantification of different SIC pools remained poorly assessed. This study aimed to illustrate the diversity of SOC and SIC pools in calcareous soils. A soil collection of 160 soil samples were selected from mostly agricultural lands in Canada, Hungary, France, Germany, Italy, and Tunisia to cover a large range of SOC and SIC contents. The carbonate composition was mainly in the form of calcite and, to a lesser extent, dolomite. The natural abundance in 13C of SOC and SIC showed a small range of values for SOC (-35 to -20 ‰, median: -27‰) signalling a predominance of C3-plants, and a large range of values for the SIC (-31 to +3 ‰; median -5 ‰), indicating a possible mixture of inorganic carbon from different sources (Hazera et al. 2025). Standard procedures to quantify SOC and SIC involving pretreatments to remove one of the C forms and/or calculations could lead to both analytical errors and substantial measurement errors (Jakab et al. submitted). Thermal analysis (i.e. Rock-Eval®, RE) has been adapted to estimate SOC and SIC contents on a non-pretreated soil sample without needing statistical post-hoc corrections (Hazera et al., 2023, in press). This RE method was applied to characterize more than 400 particle-size fractions of 65 calcareous soils i.e., particulate organic matters (POM, > 50 µm) and mineral associated organic matters (MaOM, 20-50, 0-20 and 0-2 µm). The variability of C distribution in the different fractions was more pronounced for SIC than SOC: the SOC was mainly contained in the < 20 µm and POM fractions while the SIC was distributed in all the particle-size fractions. As expected, POM fractions presented less degraded organic matter than MaOM, with higher Hydrogen index and lower Oxygen index (POM: 305 ± 63 mgHC.g-1TOC and 261 ± 37 mgO2.g-1TOC versus MaOM: 144 ± 56 mgHC.g-1TOC and 400 ± 112 mgO2.g-1TOC). Signals obtained during SIC thermal breakdown were also examined to study the SIC forms in the soil fractions. SIC signals were comparable between soil fractions for some soils, but could also vary considerably for others, suggesting a diversity in either the mineralogy or the SIC forms distributed according to the particle-size soil fractions in these soils. These preliminary results need further investigations to identify the origin of SIC e.g. by studying the isotopic signature δ13C of SOC and SIC in the soil fractions, and to determinate their sensitivity to dissolution. This communication illustrates the need to better quantify the different forms of SIC to understand its dynamics and interactions with SOC.
How to cite: Chevallier, T., Hazera, J., Sebag, D., Kowalewski, I., Gergely, J., Zachary, D., Schneider, F., Trombino, L., Manlay, R. J., Fouché, J., Yanni, S. F., Hannam, K., and Verrechia, E.: Quantifying and characterizing soil organic and inorganic carbon in calcareous soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17689, https://doi.org/10.5194/egusphere-egu26-17689, 2026.
Saline–alkali soils in coastal deltas impose major constraints on carbon stabilization, yet the mechanistic links between soil organic carbon (SOC) and inorganic carbon (SIC) under amelioration remain insufficiently understood. We conducted an in situ incubation experiment in the Yellow River Delta using low- and high-salinity soils to assess how straw inlay at 30 cm, with or without biochar incorporation in the 0–30 cm layer, regulates carbon fractions. We quantified dissolved organic carbon (DOC), particulate organic matter (POM), mineral-associated organic matter (MAOM), and both organic and inorganic carbon within each fraction. Results show that straw, biochar, and their combination consistently promoted POM accumulation and reduced DOC:SOC ratios, particularly in high salinity soils, reflecting enhanced SOM stabilization. The bulk soil and POM fraction exhibited strong positive relationships between SOC and SIC, indicating synergistic enhancement of organic and inorganic carbon pools during amelioration. In addition, DOC:SOC ratio was negatively associated with SIC, suggesting that greater inorganic carbon accumulation corresponds to lower SOM lability and supporting a role for SIC in promoting SOM stabilization. These findings provide mechanistic evidence that POC-enriching amendments can simultaneously enhance SOC and SIC pools, offering an effective pathway to improve carbon sequestration and structural resilience in coastal saline–alkali ecosystems.
How to cite: Hamad, A. A. A., Wang, X., Xu, M., and Wang, Y.: POM-Mediated Synergistic Enhancement of Organic and Inorganic Carbon in Saline–Alkali Soil Amelioration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22513, https://doi.org/10.5194/egusphere-egu26-22513, 2026.
Inorganic carbon (C) comprises a large fraction of the total C in arid and hyper-arid soils globally and therefore significantly contribute to terrestrial C sequestration. Soil inorganic carbon (SIC) derives from geological sources or from pedogenic carbonates formed by coupled biological–geochemical processes. Yet the extent to which oasis management influences and eventually reduces SIC through acidifying effects of N fertilisation and biological respiration remains poorly understood, despite the central role of oases for the agriculture and economy of arid and hyper-arid regions. We investigated SIC dynamics in southwestern Tunisia, sampling soils to 120 cm (0-5, 5-10, 10-30, 30-60, 60-90, and 90-120 cm) in three traditional and three modern oasis systems along topographic gradients (upper, midslope, and downslope positions) and beneath versus between date palms. Traditional oases are characterized by long-term organic inputs and high crop plant density and diversity, while modern oases have lower date palm density, plant diversity and greater reliance on synthetic fertilization. On average, SIC accounted for 76 % of soil total C to 120 cm depth, underscoring its role here as a dominant long-term soil C sink. The oasis types and relative tree positions did not differ in SIC contents and stocks (averaged 31.3 kg m⁻²), but uniquely distinct patterns in SIC content emerged from management–topography interactions, gypsum content, and biological activity. Modern oases showed higher SIC upslope due to limited inherent leaching, whereas traditional oases accumulated SIC together with gypsum in saline downslope positions. Carbon isotopes i.e. δ¹³CSIC values (–8 to –5‰) indicated large biological contributions, comprising up to 40% of SIC in traditional oasis systems and 20% in modern oasis systems. Soil organic C (SOC) correlated negatively with δ¹³CSIC, pointing to microbial respiration and root-derived CO₂ as primary drivers of pedogenic carbonate formation. These results highlight the dual geochemical–biological origin of SIC and the potential of oasis management to stabilize management related losses of SIC in hyper-arid regions.
How to cite: Allagui, W., Brahim, N., Allani, M., Zougari, B., Brahim, H., Bol, R., Aichi, H., and Wanek, W.: Oasis management and topography interactively shape soil inorganic carbon dynamics in hyper-arid soils., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1702, https://doi.org/10.5194/egusphere-egu26-1702, 2026.
Soil inorganic carbon (SIC) is increasingly recognized as a dynamic component of the terrestrial carbon cycle, yet its behavior in humid and semi-humid loess croplands remains poorly understood. We quantified SIC and its lithogenic (LIC) and pedogenic (PIC) fractions across 20 soil profiles (0-100 cm) in croplands of the former Yellow River Delta (FYRD), a coastal loessderived landscape shaped by historic Yellow River migrations. SIC stocks were dominated by inherited LIC (2–8 g kg⁻¹), while PIC remained smaller (<4 g kg⁻¹) but spatially variable. LIC declined by more than 50% in the northern FYRD, coinciding with lower soil pH and reduced Ca²⁺ and Mg²⁺ availability, indicating enhanced dissolution under acidifying conditions. In contrast, PIC accumulation was more pronounced along the historic river route, where elevated pH (~8.0) and higher Ca²⁺ concentrations favored carbonate precipitation. These patterns demonstrate that SIC heterogeneity in FYRD loess croplands emerges from the interplay of soil alkalinity, cation supply, and geomorphic history. The results highlight that even in humid loess agroecosystems, traditionally viewed as SOC-dominated, SIC can undergo both depletion and formation. This work contributes to a growing body of evidence that SIC is sensitive to land use and management, and should be integrated into carbon accounting frameworks, especially in calcareous coastal agroecosystems undergoing rapid transformation.
How to cite: Wang, X., Wu, L., Guo, Y., Lu, T., and Xu, M.: Spatial heterogeneity and drivers of soil inorganic carbon fractions in loess-derived croplands of the former Yellow River Delta , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22224, https://doi.org/10.5194/egusphere-egu26-22224, 2026.
Microbes alter biogeochemical cycles at spatial scales ranging from soil pores to the globe. For example, it’s increasingly recognized that microbes affect mineral weathering by influencing solubility and metal speciation. This presents an opportunity to leverage microbial processes to accelerate silicate weathering as a carbon dioxide removal (CDR) strategy. Microbially-accelerated weathering is similar to enhanced rock weathering but instead of adding crushed mineral feedstocks, microbes are added to the soil to increase weathering of native silicate minerals. Recent work has demonstrated that the addition of a particular Bacillus subtilis strain can enhance silicate dissolution in both laboratory and field environments (Timmermann et al., 2025, Global Change Biology). Here, we use the CrunchFlow reactive transport model to better understand how microbial acceleration of mineral dissolution may alter the soil weathering system, including quantifying changes in weathering rates, impacts on soil pH, and the predominant sinks of weathering products. The latter determines whether microbial-driven increases in weathering correspond with actual CDR. Our results suggest that in laboratory mesocosm experiments, microbes can accelerate the weathering of some silicate mineral by as much as 10x. We also explore the role of secondary carbonate precipitation as a key mechanism in microbially-accelerated weathering, and we consider the implications for CDR measurement, reporting, and verification.
How to cite: Lawrence, C., Timmermann, T., Weyman, P., and Fuenzalida-Meriz, G.: Microbially Accelerated Weathering for CDR: Reactive Transport Modeling to Quantify Rates and Sinks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13829, https://doi.org/10.5194/egusphere-egu26-13829, 2026.
Enhanced rock weathering (ERW) is a promising carbon dioxide removal (CDR) technology that involves spreading silicate rock powder in agricultural and silvicultural settings to trap CO2 by increasing soil alkalinity and promoting the formation of secondary carbonate minerals [1]. Many previous ERW trials have used newly mined rock for their amendments, resulting in embedded carbon emissions. To avoid these emissions, alkaline and environmentally safe mine residues could be used for ERW [2]. Here, we assess the carbon drawdown potential of two mine residues (kimberlite, serpentinite) and three newly mined agricultural amendments (basalt, metabasalt, wollastonite). We explore the use of geochemical analyses and remote sensing to monitor CO2 drawdown and the introduction of potentially hazardous transition metals into soil solids, plants, and water.
Pea (Pisum sativum L.) plants were grown in acidic soil (pH = 4.9) amended with each rock type at four spreading rates (1, 5, 10, and 50 t/ha). This growth chamber trial ran for three months, with leachate samples collected throughout, and soil samples collected at completion. Over 3 months, the alkalinity of drainage waters from pots of all amendment types significantly (p < 0.05) increased compared to controls, while soil inorganic carbon increased significantly (p < 0.05) for four of five rock types (all but metabasalt). After 3 months, visible, near infrared (VNIR), and shortwave infrared (SWIR) scans of the soils showed increased abundances of carbonate minerals on the surfaces of soil colloids in the amended pots.
Among the transition metals analyzed (e.g., Cd, Co, Cr, Ni) in drainage waters, plants, and soil solids, significant increases in concentration (p < 0.05) were only detected for nickel (10 mg/L) and only in leachates from soils amended with high amounts of serpentinite (50 t/ha), which remains below the Canadian regulatory standard (14 mg/L). Further, significant increases (p < 0.05) in nickel concentration were seen in the soil solids for both kimberlite- and serpentinite-amended pots, resulting in contamination (63 and 140 mg/kg respectively) significantly above (p < 0.05) the Canadian regulatory limit (37 mg/kg). Finally, a significant increase (p < 0.05) in nickel concentration was seen in the edible portion of the pea plants grown in soils amended with serpentinite, but the concentration remained significantly below (p < 0.05) the EU regulatory limit (10 mg/kg). The remaining drainage waters, plants and soil solids contained transition metal concentrations below regulatory limits.
While this study demonstrates the potential for CDR through ERW using mine residues, it also highlights contamination risks that need to be weighed when determining deployment strategies, locations, and amendment rates if mine residues are to be used.
[1] Paulo et al. (2021), Appl Geochem, 129, 104955.
[2] Power et al. (2024), Environ Sci Technol, 58, 43-52.
How to cite: Spence, J., Wilson, S., Rivard, B., Russel, W., Santos, R., Power, I., Thilakarathna, M., Feng, J., and Barker, S.: Assessing the Benefits and Drawbacks of Using Mine Residues for Enhanced Rock Weathering, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8243, https://doi.org/10.5194/egusphere-egu26-8243, 2026.
Quantifying carbon exchange between the land and atmosphere is crucial for estimating terrestrial carbon sinks and meeting climate goals. However, current bottom-up methods often ignore atmospheric observations and overlook the contribution of deep soil carbon. We integrated ten years of satellite XCO2 data, emission inventories, and 5,037 soil organic carbon (SOC) measurements (0–5 m depth) from the Liaohe Plain. We analyzed the spatial relationship between atmospheric XCO2 and SOC at various depths. Results show that correlations between XCO2 and SOC are weak at the point scale. However, significant correlations (p < 0.01) appear at 1–5 m depth when analyzed within a 5 km radius. The XCO2-SOC relationship varies by geological zone. Surface SOC drives short-term CO2 variations. In alluvial zones, deep SOC affects the carbon cycle through water transport. In contrast, wind erosion limits SOC accumulation in aeolian zones. Additionally, XCO2 levels correlate with environmental factors like Net Primary Productivity and precipitation. This suggests the regional carbon cycle is driven by combined climate, vegetation, and hydrological processes. This study highlights the importance of deep soil in watershed carbon cycling. It offers a new method for assessing regional carbon sinks and supporting land management strategies.
How to cite: Tang, Y., Wang, M., Rui, Q., Zhang, J., and Chen, Z.: Coupling Atmospheric XCO2 with Deep Soil Carbon in the Black Soil Region: A Multi-Source Assessment in the Liaohe Plain, China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2874, https://doi.org/10.5194/egusphere-egu26-2874, 2026.
Carbon farming aims to sequester soil organic carbon (SOC) in agroecosystems by increasing soil organic matter content to improve soil health, while contributing to reducing greenhouse gas emissions. In this context, a promising approach is the use of agroecosystem models that can inform and optimize farmer’s practices but also offer a holistic perspective to enhance both agronomic and environmental outcomes while accounting for climate change. In this study, we developed a farm-scale digital twin of 14 fields with a combined area of 80.4 ha for an arable farm in western Germany. The twin uses a spatialized version of the process-based agroecosystem model AgroC, driven by detailed soil, climate, and management data since 2009.
In its current version, the digital twin provides a reconstruction of past SOC dynamics and can be used to explore future management scenarios focused on regenerative agricultural practices, such as cover cropping, harvest residue management, and the application of organic amendments. It can thus provide decision support for optimizing carbon sequestration at the field-to-farm scale. The analysis of simulated SOC development for the past 16 years showed that simulated SOC stocks increased by 30.9 Mg C y-1 in the period 2009-2025. This is equivalent to a farm sequestration rate of 0.4 Mg C ha-1 y-1, corresponding to a relative gain of 6.5‰ y-1. To attribute the SOC sequestration achieved by regenerative management to individual practices, we compared SOC trajectories simulated for a system without regenerative management, the farm’s actual management, and each practice considered separately. Across all regenerative practices, cover cropping accounted for 4.2% of the additionally sequestered SOC, harvest residue retention for 69.7%, and organic fertilizer applications for 15.1%, with the remaining 11% attributable to interaction effects among these practices. For a moderate future climate scenario (RCP 4.5 ensemble), an additional carbon sequestration potential of 7.5±0.7 Mg C ha-1 by 2050 is predicted for a representative field under present management. Sequestration rates were found to slow after around 2028–2032 and to stagnate thereafter.
Beyond these results for current management, the digital twin provides a decision-support environment in which farmers can explore future SOC management options, such as effects of new cover crops, altered crop rotation sequences, and improved cultivars. The available options can be compared for their long-term SOC sequestration potential, and the farmer can select the strategies that fit the farm-specific objectives and constraints best. When new observations on SOC, biomass, and yield become available, the digital twin can be updated and used to reevaluate the scenarios.
In conclusion, the digital twin for carbon farming introduced here is a promising tool to identify locally adapted, farm-specific management strategies that further increase and sustain SOC and to evaluate their robustness under current and future climate conditions. These management changes may also have implications for other ecosystem services, including nutrient leaching and agricultural productivity. Our process-based approach already represents these processes, and in future work we aim to extend the digital twin to explore trade-offs and synergies between a range of ecosystem services beyond carbon sequestration.
How to cite: Bauer, F. M., Brogi, C., Herbst, M., Schullehner, K., and Huisman, J. A.: Towards a farm-scale digital twin for carbon farming: regenerative management scenarios and decision support for a German arable farm, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3403, https://doi.org/10.5194/egusphere-egu26-3403, 2026.
The accrual of stabilized soil organic carbon (SOC) can mitigate the atmospheric CO2 concentration and thus climate change. Organic carbon in the fine silt and clay size fraction (OCfine) is typically mineral-associated and thus considered relatively stable compared to the coarse fraction. The SOC saturation concept suggests that this pool has a limited storage capacity, for which the fine soil particle content constrains SOC sequestration. Therefore, fine-textured soils with low OC loading of the fine fraction are thought to have a greater potential to stabilize additional OC than soil with high OC loading and coarse-texture due to their higher available storage space. Here, we assessed soils’ potential to stabilize additional OCfine using 21 temperate agricultural soils. The soils were selected from the archive of the German Agricultural Soil Inventory to analyze SOC gradients (0.7-10.2 %) in three texture classes (sandy, loamy, clayey). After a two-years incubation, we investigated the recovery of 13C labeled litter in two size-based fractions: OCcoarse (>20µm) and OCfine (<20 µm). Our results show that the litter-derived OC retention increased significantly with initial SOC content and fine fraction OC loading. This was primarily driven by the OCcoarse fraction, which indicated that less added litter was decomposed/transformed in the presence of sufficient SOC. In contrast, litter-derived OCfine formation was negatively correlated with initial SOC and fine fraction OC loading. However, when normalized to the amount of actually decomposed litter, initial SOC and texture did not significantly affect the efficiency of OCfine formation. NanoSIMS analysis revealed that microscale organic matter patches drove litter-derived OC formation. We found large parts of litter-derived SOC allocated with likely pre-exisiting SOC patches suggesting a high importance of organo-organic interactions. All soils also had new OCfine on mineral-dominated surfaces. Furthermore, five out of six soils were still dominated by bare mineral surfaces, despite partly very high SOC contents. Taken together, those findings revealed that OC loading of the fine fraction or soil texture are not the major limiting factors of new OCfine formation. Instead, initial SOC content have a positive effect on litter-derived OC retention by retarding its mineralization. This feedback of pre-existing SOC on the dynamic and fate of new OCfine should be studied more closely from a microbiological perspective and considered in SOC models.
How to cite: Poeplau, C., Begill, N., Schiedung, M., Don, A., Hoeschen, C., Guggenberger, G., and Schweizer, S.: Is initial soil organic carbon more important than texture for the fate of carbon inputs into temperate agricultural soils?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5718, https://doi.org/10.5194/egusphere-egu26-5718, 2026.
Liming is an important agricultural practice for mitigating soil acidification and potentially reducing N2O emissions. Although lime can act as either a CO2 source or sink depending on proton donors driving dissolution i.e., strong acids vs. carbonic acid, IPCC assumes it as a 100% CO2 source. Soil leachate and shallow groundwater chemistry can reveal the dominant proton donors governing these reactions; however, previous studies have primarily focused on gas emissions alone. To address this knowledge gap, we conducted a two-month mesocosm experiment with spring barley using 13C-labeled carbonate and 15N-labeled fertilizer in acidic sandy (pH = 5.42) and clayey soils (pH = 5.45), incorporating three simulated rainfall events. Lime and fertilizer were homogeneously mixed with the soil, and gas samples were collected immediately following setup (Day 0).
In lime-treated soils, both CO2 and N2O fluxes were elevated prior to crop emergence and peaked on Day 0, whereas in control treatment, CO2 and N2O slightly increased on Day 0 and peaked after the first rainfall event. This suggests that liming and tillage stimulate initial greenhouse gas emissions. Consistent with previous studies, about 13% of lime-derived C was emitted as CO2, and N2O emissions were low (N loss < 0.1% of applied fertilizer) over the experiment period. Cumulative N2O fluxes slightly decreased in limed clayey soils but increased modestly in limed sandy soils relative to controls, suggesting soil texture and biological processes suppress N2O production during barley growth.
Calcium, magnesium and bicarbonate concentrations in leachate following the first rainfall event indicate that lime dissolution was dominated by strong acids, most likely nitric acid derived from the fertilizer inputs, with lime as a resulting net CO2 source. In contrast, during later rainfall events, lime acted as a CO2 sink. Based on δ13C-dissolved inorganic carbon, additional bicarbonate was likely generated through lime dissolution driven by carbonic acid produced during aerobic organic matter degradation in sandy soils, but by Fe- and Mn-coupled degradation in clayey soils, consistent with increased soil pH at depth. After rainfall events, CO2-lime levels remained stable in clayey soil but declined in sandy soils, while N2O fluxes increased slightly in clayey soils but remained consistently low in sandy soils. This pattern corresponds to higher bicarbonate and nitrate concentrations in leachate from clayey soils compared with sandy soils, suggesting that soil texture regulates aerobic and anaerobic microbial processes, which in turn affect lime dissolution. By linking lime dissolution, alkalinity production, and soil physical controls on gas and solute transport, our results show that soil texture fundamentally regulates liming-driven carbon and nitrogen cycling across the soil-gas-shallow groundwater continuum, highlighting the need for an integrated perspective to better assess the impacts of liming in agricultural systems.
How to cite: Chen, N.-C., Adnew, G. A., Ambus, P. L., Abalos, D., Liang, Z., and Kim, H.: Soil Texture-Greenhouse Gas-Leachate Linkages Reveal Liming Effects on C and N Cycling , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6322, https://doi.org/10.5194/egusphere-egu26-6322, 2026.
Accurate monitoring of soil organic carbon (SOC) is essential for the development of national greenhouse gas inventories as well as for the assessment of strategies implemented to maintain and increase SOC stocks in agricultural systems. Limited access to high quality SOC data across large spatial and temporal scales remains the main barrier for scientists, policy makers and practitioners to make informed decisions about soil management. To address this knowledge gap, the Thünen Institute of Climate-Smart Agriculture conducted the German Agricultural Soil Inventory (BZE-LW), with the first campaign carried out between 2010 and 2018 and the second campaign initiated in 2022. During the first campaign, 3,104 arable, grassland, and permanent crop sites were sampled on an 8×8 km grid and analyzed for SOC contents and stocks, along with additional soil parameters, down to a depth of 1 m. In addition to soil sampling, annual farm management data were collected via questionnaires. The second campaign, which involves resampling of the same sites, enables to quantify and explain changes in SOC contents and stocks at the decadal scale. Based on the most recent results (n=587), minor changes in SOC contents were observed in cropland soils. Average SOC stocks declined significantly in 0–30 cm (−1.6%) and 0–50 cm (−2.7%) with a statistically insignificant increase of 0.9% in the top 10 cm. Grassland soils showed more pronounced SOC losses, with significant declines in both 0–30 cm (−5.9%) and 0–50 cm (−5.1%). Current hypotheses attribute SOC losses to land use history, soil type, rapid climate warming characterized by a 2.1°C rise in the mean air temperature in Germany over 50 years, and farm management activities such as declining nitrogen fertilization. Conversely, increased adoption of cover cropping and reductions in tillage intensity might have partially mitigated against SOC stock losses in croplands. Disentangling these drivers while accounting for several methodological adjustments to the first soil sampling campaign are key tasks, which will serve to inform future soil monitoring efforts in Germany and beyond. To further highlight the importance of data quality, we will emphasize the methodological challenges associated with detecting SOC changes across spatial scales ranging from individual sites to regional levels.
How to cite: Golicz, K., Poeplau, C., Harbo, L. S., Schneider, F., Schiedung, M., Don, A., Heolek, S., Dechow, R., Vasylyeva, E., Heidkamp, A., Prietz, R., and Flessa, H.: Decadal trends of organic carbon in German agricultural soils – Preliminary findings from the German Agricultural Soil Inventory, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18295, https://doi.org/10.5194/egusphere-egu26-18295, 2026.
It is becoming increasingly evident that one-size-fits-all solutions are rare when it comes to enhancing soil organic carbon (SOC) stocks in agricultural soils. Instead, context-specific management recommendations are needed, guided by a detailed understanding of how different management practices interact with environmental factors, such as climate or soil type, to affect SOC stocks. Since it is impossible to test all such combinations in controlled experiments, using large datasets of on-farm data is a promising alternative. Here, we predicted crop-specific management for all sample locations of the European wide soil monitoring of SOC in agricultural soils (LUCAS Soil, n = 8,834 repeat samples from the years 2009, 2015 and 2018) using individual farm management data representatively surveyed yearly for all EU + UK regions (n = 82,000 farms per year). We will present results of how relevant agricultural practices, including crop rotation diversity, cropping intensity, fertilizer use, fertilizer type, organic farming and tillage intensity, impact SOC stocks at the European scale. In addition, the large sample size and coverage of extensive environmental gradients allows disentangling the effect of management and environmental drivers on SOC stocks. We expect that these results provide a more nuanced view of how management impacts SOC under various soil and climatic conditions, contributing to the development of context-specific management recommendations to increase SOC stocks in agricultural soils.
How to cite: Helfenstein, J., van Dijk, N., Edlinger, A., Moinet, G. Y. K., van Rijssel, S., Wadoux, A. M. J.-C., Creamer, R., Vazquez, C., and Mulder, V. L.: European-scale evidence of farm management impacts on soil organic carbon stocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7282, https://doi.org/10.5194/egusphere-egu26-7282, 2026.
A soil’s capacity to store and stabilize organic carbon (OC) is commonly attributed to its silt and clay content, which provides mineral surface area for OC interactions. Because this surface area is finite, soils are assumed to exhibit a texture-dependent limit for OC stabilization, referred to as soil OC saturation. However, this concept neglects the role of soil structure, which largely determines which mineral surfaces are actually accessible for contact with OC.
In structured soils, OC predominantly enters through soil pores. In the absence of structural turnover, these pores may represent sites of high OC content where mineral surfaces are saturated. Meanwhile, other parts of the soil matrix do not receive OC input and therefore remain well below their OC storage capacity. Based on this assumption, we hypothesize that the occasional ploughing of agricultural fields may eventually increase net soil OC stabilization. Specifically, the infrequent disruption of the soil structure could redistribute the OC more evenly throughout the soil matrix, thereby bringing previously unsaturated mineral surfaces into contact with OC.
We investigate this hypothesis by monitoring OC stocks and soil respiration (used as a proxy for OC turnover and stabilization) over several years in intact soil samples from agricultural fields that had been subjected to a single ploughing event after more than a decade. These were then compared with non-ploughed control fields. Initial results show that ploughing led to a redistribution of predominantly surface-stored OC (0-5 cm) throughout the entire plough horizon (0-20 cm). This initially resulted in increased soil respiration and microbial activity in the middle of the plough layer (10-15 cm), accompanied by a decrease in the OC content at the soil surface. After seven months, soil respiration declined, indicating the onset of OC stabilization processes. Analyses of disturbed soil samples from the same sites suggest that the physical disruption of soil structure itself played a minor role compared to the OC redistribution.
These results demonstrate that a single ploughing event can induce not only short-term OC destabilization, but also longer-term stabilizing effects, in line with our hypothesis. Ongoing and planned analyses will further assess the temporal development of OC stocks, stabilization processes, and the spatial distribution of OC within soil microsites.
How to cite: Bucka, F., Geier, F., Ramos Pencue, A., Lanthier, R., and Meyer, N.: Can occasional ploughing enhance soil organic carbon stabilization?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11656, https://doi.org/10.5194/egusphere-egu26-11656, 2026.
Agroforestry is promoted as a practice for climate change mitigation and adaptation. Alley cropping, which combines tree rows with wide alleys for agricultural crops, shows variable potential to store additional carbon (C) in soil, compared to conventional cropping, depending on tree species, tree age, distance from trees, soil properties, and sampling depth. To better understand soil carbon accumulation, it can be useful to separate soil organic matter into fractions of contrasting behaviors. However, studies quantifying C in particulate organic matter (POM) and mineral-associated organic matter (MAOM) remain scarce for alley cropping systems. The present study aimed at comparing C stocks in POM, MAOM and whole soil in the 0-80 cm soil profile, between a 10-year-old alley cropping system, a tree-free agricultural control, and an adjacent mature forest, under a northern temperate climate. A second objective was to assess the variability of C stocks as a function of the distance from the tree row. Within the alley cropping system, C stocks in the 0-10 cm soil layer were generally greater under the tree row than in the cultivated alley, with most of the additional C and N stored as POM. In the 0-10 cm soil layer, soil C stocks in alley cropping were lower than in the forest, but not statistically different from the agricultural control. In the 10-20 cm layer, soil C stocks were greater than in the control, but not statistically different from the forest. When considering the 0-20 cm soil layer, the C stock in alley cropping was numerically 34% greater than in the control, with 80.5% of the additional C stored as MAOM. This corresponded to a potential soil C accumulation rate of 1.26 Mg C ha-1 yr-1. In the cultivated soils considered in this study, soil organic matter losses may persist for decades following deforestation or grassland-to-cropland conversion, but implementation of alley cropping in these soils could offset soil C losses.
How to cite: Maillard, É., Rivest, D., Laganière, J., Angers, D. A., and Chantigny, M. H.: Carbon stocks in whole soil and soil organic matter fractions in an alley cropping system under a northern temperate climate, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12244, https://doi.org/10.5194/egusphere-egu26-12244, 2026.
Agricultural management measures that promote carbon sequestration in soils are essential for both climate change mitigation and adaption. Crop roots are the primary source of soil organic carbon (SOC) as belowground carbon (C) inputs —namely root biomass C and rhizodeposition C— persist in soil longer than C derived from above ground crop residues and organic soil amendments and they explore deeper soil layers. Therefore, selecting varieties of main crops with increased belowground C (BGC) inputs has been proposed as a viable option to enhance SOC stocks without compromising yield.
Despite this potential, there is limited understanding of how root biomass C and rhizodeposition C vary among modern commercial crop varieties. Moreover, data are lacking on how these belowground C inputs are influenced by diverse pedoclimatic conditions, and few studies assess C allocation in deep soil layers.
To address this gap, we implemented an in situ multiple-pulse ¹³CO₂ labeling experiment with four commercially relevant winter wheat (WW) varieties, which were selected based on a previous study with 10 varieties on 11 European sites (Heinemann et al., 2025). This replicated field study was carried out across four European countries—Austria, Lithuania, Spain, and Switzerland—to quantify net belowground C inputs after harvest. The WW varieties were isotopically labelled multiple times during their active growth phase. Following harvest, soil and roots were sampled using soil coring to a depth of 1 m. Bulk isotope analysis was performed on soil and each root fraction to quantify net rhizodeposition C.
Results show mean total BGC inputs across all sites and varieties of 1.59 ± 0.07 Mg ha-1. Rhizodeposition C accounted for 55% of total BGC, peaking in the 15–30 cm soil layer, which contained 81% of total BGC. After accounting for site effects, varieties showed different belowground carbon allocation strategies: some varieties exhibited relatively greater allocation to root biomass, whereas others showed comparatively higher rhizodeposition.
Our results will also integrate aboveground biomass and grain yield data to assess whether selecting specific genotypes can simultaneously support food production and enhance SOC build up.
Note: This study was part of the European Joint Programme on Soil (EJP Soil) project MaxRoot-C.
REFERENCES
Heinemann, Henrike, et al. "Optimising Root and Grain Yield Through Variety Selection in Winter Wheat Across a European Climate Gradient." European Journal of Soil Science 76.2 (2025): e70077. https://doi.org/10.1111/EJSS.70077
How to cite: Fernández Balado, C., Juchli, T., Toleikiene, M., Veršulienė, A., Hirte, J., Mayer, J., González Pérez, J. A., and Hood-Nowtony, R.: Is it possible to enhance belowground carbon inputs to soil through variety selection? A Case Study in Winter Wheat Using a ¹³CO₂ Multiple-Pulse Labelling Approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21537, https://doi.org/10.5194/egusphere-egu26-21537, 2026.
Hydrochar has emerged as a promising soil amendment within climate-smart agriculture due to its potential to improve soil properties and contribute to carbon (C) sequestration. However, while hydrochar is often regarded as a relatively recalcitrant material, substantial uncertainties remain regarding its short-term stability in soil and its interactions with native soil organic carbon (SOC), particularly under contrasting soil moisture conditions. Addressing these knowledge gaps is essential to better assess the role of hydrochar in soil C cycling and its implications for soil C stability.
In this study, we investigated the short-term mineralization dynamics of hydrochar and its effects on SOC decomposition through a 45-day laboratory incubation experiment. A Cambisol was amended with chicken-manure-derived hydrochar at four agronomically relevant application rates (3.25, 6.5, 13, and 26 t ha⁻¹) and incubated under two contrasting soil moisture regimes simulating well-irrigated (60% water holding capacity, WHC) and moderate water-deficit conditions (30% WHC). Soil respiration was periodically quantified on incubation days 1, 3, 7, 11, 16, 23, 30, 37, and 45, and the isotopic composition of emitted CO₂ (δ¹³C–CO₂) was determined using a GasBench interface coupled to an isotope ratio mass spectrometer. Combined with isotopic signatures of soil and hydrochar, these data allowed partitioning of CO₂ sources, estimation of hydrochar-derived CO₂ contributions, and assessment of priming effects on native SOC.
Across both moisture regimes, total soil respiration increased consistently with increasing hydrochar application rate throughout the incubation. Concurrently, δ¹³C–CO₂ values became progressively less negative at higher hydrochar doses, indicating an increasing contribution of hydrochar-derived C to total CO₂ emissions. Source partitioning confirmed that the proportion of CO₂ originating from hydrochar increased with application rate, with this effect being more pronounced and temporally consistent under well-irrigated conditions. These results demonstrate that hydrochar is not inert in the short term and can undergo measurable mineralization shortly after soil incorporation.
Priming effect analysis revealed a clear interaction between hydrochar dose and soil moisture. Under well-irrigated conditions, low hydrochar doses induced a tendency towards positive priming, whereas higher doses resulted in neutral or negative priming effects. In contrast, under water-deficit conditions, positive priming emerged predominantly at higher hydrochar application rates, increasing with dose. These patterns suggest that hydrochar-mediated stimulation or suppression of SOC mineralization is strongly context-dependent and governed by both amendment rate and water availability.
Overall, our findings challenge the common assumption of hydrochar recalcitrance by demonstrating its short-term degradability and its capacity to modulate SOC dynamics. The results highlight that hydrochar application can not only contribute directly to CO₂ emissions through its own mineralization but, depending on dose and moisture conditions, may also enhance native SOC decomposition. These insights are critical for refining assessments of hydrochar-based soil management strategies and their implications for soil C stability under future climatic scenarios.
How to cite: Knicker, H., Moreno Racero, F. J., Wissel, H., dos Anjos Leal, O., and Brüggemann, N.: Short-term mineralization of hydrochar and its interaction with native soil carbon under contrasting moisture conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5702, https://doi.org/10.5194/egusphere-egu26-5702, 2026.
Biochar has been widely used for soil improvement, but uncertain results persist due to diverse biochar characteristics, soil properties, and crop responses. Therefore, the effects of biochar on crop yields and soil quality were evaluated using effect sizes from 1011 paired data points from field trials, based on a global meta-analysis method. The results indicated that biochar with a higher total phosphorus concentration (≥1.0%), total carbon concentration (≥70%), specific surface area (≥50 m2 g-1), and biochar application rates of 10–30 t ha-1 are optimal for improving crop yields. Biochar made from manure (effect size, 42%) exceeded that made from ligneous (22%) or cereal (12%) material. Porous, acidic, or young soil types are optimal for biochar application, while sandy and clay soils are preferred over loam soil. Soils with lower available nitrogen (<80 mg kg-1), phosphorus (<10 mg kg-1), potassium (<120 mg kg-1), pH (<4.5), and cation exchange capacity (<10 cmol kg-1) were more effective. The effect of biochar on yield is higher for cash crops (oil plants: 37%, vegetables: 28%) compared to food crops (legumes: 26%, maize: 20%, wheat: 12%), with no significant effect observed on rice. Finally, biochar increases crop yields by improving soil quality through enhanced levels of soil organic carbon, total nitrogen, ammonium-nitrogen, nitrate-nitrogen, and soil pH while reducing soil bulk density. Our research enhances understanding of the relationships between biochar, soil, and crops, aiding researchers, manufacturers, and farmers in making informed decisions regarding biochar selection, planting locations, and crop choices. However, it remains unclear to what extent machine learning can accurately predict crop yield or SOC when biochar is applied to soil. In our study, Random Forest (RF) and Multilayer Perceptron Neural Network (MLP- NN) models were employed to predict crop yield and SOC with 297 paired data from field trials. The results indicated that the RF model (test R2 = 0.83) did not differ significantly from the MLP- NN model (test R2 = 0.84) in predicting crop yield. However, the RF model (test R2 = 0.87) performs significantly better than the MLP- NN model (test R2 = 0.53) in predicting SOC. The most influential features for crop yield were found to be the biochar application rate (15%), initial SOC (13%), biochar pH (10%), and biochar TP (10%). In contrast, the variation of SOC was primarily influenced by latitude (26%), biochar application rate (22%), initial SOC (15%), and biochar pH (13%). Furthermore, both crop yield and SOC variation were influenced by multiple factors, not solely one, and their impacts were not necessarily linear. This study suggests that the optimization of biochar pH and phosphorus content, along with the regulation of its application rate in sandy or clay- rich soils, can simultaneously enhance both crop yield and SOC. In the future, we hope to develop a decision support system with prediction, different scenarios, and consultation capabilities based on geospatial location.
How to cite: Xu, Z.: Global Potential Effects Analysis of Biochar on Crop Yields and Soil Quality, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6121, https://doi.org/10.5194/egusphere-egu26-6121, 2026.
Pyrogenic carbon (PyC) is widely regarded as a persistent component of soil organic carbon, yet how small amounts of vertically redistributed PyC influence organo mineral interfaces in subsoils remains unresolved. Here we combine a ten year field ageing experiment along a 200 cm soil profile with electrochemical assays, spectroscopy, and nanoscale microscopy to link PyC electron transfer capacity to mineral association with depth. Redistributed PyC retains electron accepting and donating capacities in subsoils despite low concentrations, and exhibits faster electron transfer kinetics. Retention is grounded in oxidative surface transformation, enriching quinone and phenolic oxygen redox moieties and mineral complexing oxygen groups. Nanoscale observations of deep subsoil PyC show oxidised surfaces with organo mineral coatings associated with Fe and Ca bearing phases, consistent with a coupled redox and sorptive interface rather than passive persistence. Surface oxygenation links PyC mediated electron exchange to mineral protection and may extend reactive interfaces into subsoils, where lower oxygen availability and reduced microbial activity could preserve functionality. These findings suggest that field aged PyC contributes to redox coupled mineral stabilisation in subsoils and provide a basis for predicting when effects scale with reactive Fe across soil types.
How to cite: Wang, Y., Su, L., and Shang, J.: Oxidised pyrogenic carbon sustains electron transfer capacity and organo mineral coupling in subsoils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16076, https://doi.org/10.5194/egusphere-egu26-16076, 2026.
Crop breeding is attracting attention as a potentially effective strategy to enhance soil organic carbon (SOC) stocks, thereby mitigating climate change as well as improving soil physical health and the sustainability of arable cropping systems. We used the new soil-crop model USSF (Uppsala model of Soil Structure and Function) to investigate the potential of variety selection to increase SOC whilst maintaining or even improving yields in spring-sown barley under Nordic agro-environmental conditions. USSF combines a generic crop growth model with physics-based descriptions of soil heat and water flow and transpiration by plants, with a model of SOC turnover that considers the effects of physical protection and microbial priming on the rates of decomposition of SOC.
Data on soil water contents, soil temperatures and above-ground biomass and grain yields were obtained during two growing seasons (2022 and 2023) in both drought and control treatments for two varieties of spring barley (“Annelie” and “Feedway”) grown on a loamy soil in Uppsala, Sweden. In 2022, above-ground biomass was not significantly different between the two varieties, whereas grain biomass was significantly larger in Feedway. No effect of the drought treatment on crop growth was detected for either variety. Crop growth was poorer in 2023, which was attributed to a colder spring and a drier summer. In this second year, Feedway had both larger above-ground biomass and grain yields than Annelie, and also showed a significant effect of the imposed drought treatment on both of these crop growth parameters, whereas Annelie did not.
Eight crop parameters in USSF were treated as uncertain. Thirty “acceptable” parameter sets for each variety were identified by calibrating the model against the field measurements using the GLUE method. The USSF model could satisfactorily match the data in both drought and control treatments using a common parameterization. The results of this model calibration strongly suggested that the main difference between the two varieties of spring barley is that Feedway develops a deeper root system. This allowed for a better water supply, especially in the late summer drought period during grain-filling in 2023, leading to better crop growth, larger yields, harvest indices and return of crop residues.
We are currently performing long-term (30-year) simulations for historical and future climates to evaluate the potential effects of cultivating these two varieties on SOC stocks and grain yields under contrasting weather and climatic conditions.
How to cite: Jarvis, N., Coucheney, E., Vico, G., Suizu, M., Colombi, T., and Keller, T.: The potential of crop variety selection to enhance soil organic carbon stocks and yields: a soil-crop modelling study for spring barley in a Nordic climate, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7564, https://doi.org/10.5194/egusphere-egu26-7564, 2026.
Globally 13% area is under Lateritic soils characterized by compact, vesicular honey-comb structure with low silica-to-sesquioxide ratios resulting in low water and nutrient retention capacity, making them challenging for sustainable crop production. Degraded general health of these soils makes them unusually vulnerable to shifts in management practices. Soil health can be closely tagged with tillage regimes and residue handling in cropping systems since these practices drive microbial turnover and stabilise organic matter. When aligned with conservation agricultural (CA) practices, the improvement is often surprisingly rapid in lateritic profiles, especially the secondary laterites where disrupted aggregates and depleted carbon stocks react quickly to reduced disturbance and a consistent surface mulch. Given this background, a field experiment was initiated in 2022 in secondary laterites to evaluate the effect of varying tillage treatments and residue management practices on soil carbon pools and biochemical properties in rice-wheat cropping system during the transitional phase of CA adoption. The results from the study showed that zero-tillage (ZT) coupled with retained-residues (RR) significantly enhanced Walkley black carbon (WBC) at top soil (15 cm) by 0.33% within three years, whereas, for conventional tillage (CT), WBC content was reduced by 1.55% from initial values. The CA practices also resulted in higher soil respiration rate and favourable bulk density, suggesting an increased microbial turnover and organic matter decomposition. Furthermore, ZT and RR exhibited significant increments in labile pools of organic carbon viz. permanganate oxidizable organic carbon (23-25%), microbial biomass carbon (36-40%) and in soil enzymatic properties viz. dehydrogenase (6-10%), urease (38-42%), acid (58-64%) and alkaline phosphatase (40-44%) respectively, over those under CT. In contrast, traditional CT was recorded with higher soil compaction, reducing microbial activity and overall biochemical quality indices. System yield was also found to be highest under ZT with RR. ZT coupled with RR reduced the carbon footprint over CT due to higher carbon sequestration. The findings indicate that CA with proper residue management can strengthen soil biochemical health, system productivity, and overall sustainability in lateritic soils of tropical and subtropical regions. Their limited buffering capacity, coupled with a tendency for rapid degradation, means that these soils often exhibit a relatively swift positive response when disturbance is reduced and surface residues are maintained.
How to cite: Rana, S., Swain, D. K., Bhattacharya, P., and Dey, P.: Soil health responses, nutrient turnover, and carbon footprint dynamics during early adoption of conservation agriculture in secondary laterites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2239, https://doi.org/10.5194/egusphere-egu26-2239, 2026.
Acidification of stored manure and on‑farm anaerobic digestion have been identified in Canada as beneficial management practices (BMPs) that can mitigate climate change by reducing greenhouse gas (GHG) emissions. The objective of this study was to assess the effects of these technologies on manure agronomic value, soil physicochemical properties, and nitrous oxide (N₂O) emissions.
Field experiments were established in 2024 at two contrasting sites classified as a silty clay loam and a sandy loam. Five treatments were applied in a randomized design with three replicates per site: undigested manure, digestate, acidified digestate (pH 6.5), mineral fertilizer, and an unfertilized control for a total of 30 plots. During the growing season, soil samples (0–20 cm) were analyzed for pH, major nutrients (N, P, K, Ca, Mg, S), and trace elements (Cu, Zn, Fe, Mn, Al). Treatments were applied in spring and after forage harvests. Before each application, manure samples were analyzed for density, pH, and total major and trace element concentrations.
To quantify N₂O emissions, non–steady‑state chambers were installed in spring and remained in place throughout the season. Chambers were sampled weekly, and gas concentrations were measured using a gas chromatograph with an electron capture detector. Forage yield was measured for each plot, and plant tissues were analyzed for total major and trace elements using ICP‑OES.
Soil pH ranged from 5.8 to 6.6 in the silty clay loam and from 5.9 to 6.8 in the sandy loam. Manure‑based treatments emitted 1.2 to 3.9 times more N₂O than the mineral fertilizer treatment, except in the silty clay loam in 2024, where manure treatments (excluding the control) produced similar emissions. The acidified digestate treatment consistently generated the highest N₂O emissions among manure treatments.
In sandy loam plots, N₂O production was 1.3 and 2.6 times higher in the undigested manure and acidified digestate treatments, respectively, compared with the silty clay loam. Cumulative N–N₂O losses were also greater in 2025, particularly for the acidified treatment (73% higher), while increases in the control and mineral fertilizer treatments were more moderate (28% higher).
Forage yields were higher in 2025 than in 2024. In the silty clay loam, yields followed the order: digestate > acidified > mineral > undigested > control, ranging from 1.8 Mg ha-1 (control) to 2.8 Mg ha-1 (digestate). A similar trend occurred in the sandy loam, where the acidified treatment produced the highest yields, followed by the digestate.
Overall, the results show that treated and acidified manure applications improved forage yield relative to mineral fertilizer in both soils. However, the acidified treatment also increased N₂O emissions, suggesting that its reduced pH may require a longer stabilization period before field application. This aspect will be examined in the coming years. Additional project data will also help identify BMPs that can effectively reduce N₂O emissions on Canadian farms.
How to cite: Royer, I., Bertrand, N., and Talbot, G.: Impact of manure anaerobic digestion and acidification of digestate on soil quality and GHG emissions , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15551, https://doi.org/10.5194/egusphere-egu26-15551, 2026.
Agroforestry systems are increasingly implemented in temperate regions due to their wide range of environmental benefits, including their potential to sequester carbon in both woody biomass and soil. This study examines an organic syntropic alley-cropping system for fruit and nut production, established in 2019 on sandy loam in Brandenburg, Germany. The site consists of 1 m-wide north-south-oriented tree rows amended with 15 t ha‑1 of organic manure at establishment, bordered by a mulch layer, and alternating with 10 m-wide rows of forage crops (a grass-alfalfa mixture). The control side represents the previous managment regime.
To assess the stability of soil organic carbon (SOC), we measured the amount of SOC in the fine particulate fraction (<63 µm), the percentage of water-stable aggregates and their concentration of soil organic matter (SOM), the binding strength of SOM to the mineral matrix, and the slaking index (SI). We further compared these data with microbial biomass and community composition.
Our results show an increase in intra-aggregate SOM with stronger binding to the mineral matrix and reduced slaking potential in the tree strip compared to the crop alley and cropland control. This corresponds with a significantly higher microbial biomass and an increase of total fungi as well as in the bacterial genus Streptomyces, both of which are assumed to play a role in soil aggregate stabilization. In contrast, the tree row had no influence on carbon storage or soil structure within the crop alley.
How to cite: Büks, F., Toups, J., and Beule, L.: Enhancement of stable carbon pools and slaking resistance in a temperate organic syntropic alley-cropping system on sandy loam, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11902, https://doi.org/10.5194/egusphere-egu26-11902, 2026.
Metropolitan authorities, governing territorially contiguous areas where urban, peri-urban, and agricultural land uses coexist, play a key role in steering territorial trajectories through spatial planning and incentive-based policies. To effectively implement climate strategies, they require a clear understanding of how land-use patterns and management practices across agricultural, natural, and urban spaces may evolve and affect soil organic carbon (SOC) stocks and tree carbon storage. In line with climate commitments such as the European Green Deal and local climate–energy action plans, metropolitan authorities are required to develop strategies that combine greenhouse gas emission reductions with enhanced SOC sequestration. While increasing SOC and biomass carbon is widely recognized as a climate mitigation strategy, land-use change and management practices can also drive SOC losses and CO₂ emissions, depending on the trajectory adopted. Existing models that quantify SOC dynamics under different agricultural management practices, as well as methods estimating carbon stock changes based on land-use conversion factors. However, the combined effects of SOC fluxes, land-use change, and management in mixed urban–rural areas are rarely modelled within a single, spatially framework, particularly urban expansion’s impact on soils. Scenario-based SOC modelling is key to guiding decisions for achieving carbon-neutrality.
This study evaluates SOC and biomass carbon fluxes under four land-use and management scenarios co-developed with territorial planning stakeholders from the Rennes Metropolitan Area (north-western France). The study area covers 705 km² and includes agricultural and natural land (510 km²) and urban areas (195 km²). The first scenario follows current trends, with continued urban expansion and unchanged agricultural practices. The second assumes moderate improvements in farming practices and reduced conversion of agricultural soils to urban land. The third represents a transformative trajectory characterized by a strong increase in permanent grasslands at the expense of arable land, enhancing SOC storage. The fourth, maximalist scenario converts all agricultural land to forest to estimate the upper bound of SOC and biomass carbon sequestration. These scenarios were assessed relative to the current situation to simulate changes in soil and tree‑biomass carbon stocks by 2050. Models of varying complexity were used to address uncertainties associated with long‑term projections.
Initial results indicate that all scenarios increase SOC and biomass carbon stocks; however, the first two remain insufficient to offset projected metropolitan greenhouse gas emissions by 2050. Even under the most ambitious scenarios, results highlight those urban green spaces alone cannot achieve carbon neutrality. Rural soils constitute the main SOC sink at the territorial scale, but they are also associated with significant emissions, particularly from grazing systems, underscoring the need for ambitious soil management strategies and cross-territorial compensation mechanisms.
How to cite: Amelin, J., Michot, D., Cannavo, P., and Walter, C.: Soil organic carbon dynamics under land-use and management scenarios in a metropolitan urban–rural territory, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13707, https://doi.org/10.5194/egusphere-egu26-13707, 2026.
Increasing soil organic carbon (SOC) stocks in agricultural soils can enhance soil health, support higher crop productivity with fewer inputs, and contribute to offsetting greenhouse gas emissions. SOC can be increased through carbon-farming practices, such as cover crops, residue retention, and carbon-rich organic amendments. However, SOC changes are difficult to monitor at relevant temporal and spatial scales, and existing modelling and data-driven approaches often struggle to capture the complex interactions between management, soil, and future climate conditions.
In this poster, we provide details on the implementation of a farm-scale digital twin, defined as an accurate and dynamic representation of a real-world agricultural system that is consistently updated, evaluates future scenarios, and provides actionable insights for stakeholders. The current version of the digital twin supports decision-making for carbon farming and agricultural management while accounting for key interactions within the soil-crop-atmosphere continuum. It is built on the process-based agroecosystem model AgroC, which couples SoilCO2 for water, heat, gas, and solute transport in a one-dimensional soil column, SUCROS for organ-specific crop growth, and RothC for soil carbon turnover. The digital twin was applied to 14 fields of varying size (1.5–15 ha) from a farm in western Germany. Field-specific crop rotation, seeding and harvest dates, fertilization, and application of mushroom compost were implemented in close collaboration with the farmer, enabling simulation of SOC dynamics over periods of 5 to 16 years depending on field data availability.
Although within-field soil heterogeneity can be represented using spatially distributed simulations, each field was modelled using a single soil unit, as regional soil maps indicated relatively homogeneous conditions. This assumption was supported by Electromagnetic Induction (EMI) measurements performed on two representative fields in August 2025. For model validation, SOC data from previous years were available for eight fields. Additionally, ten fields were sampled between August and November 2025 at 56 locations, resulting in 164 soil samples for which SOC was estimated via the loss-on-ignition method. Further validation was performed using harvest data. The digital twin simulations well matched measured values, and it was confirmed that the sustainable practices implemented by the farmer had positively influenced SOC trajectories over the study period. Other unique information could be provided to the farmer, such as the rate at which SOC would decrease if regenerative practices were interrupted or the relative importance of individual actions in each field, with residue retention being the most prominent.
Taken together, these results show that the developed farm-scale digital twin allows to account for complex interactions within the soil–crop system, can provide holistic, tailored analyses with the potential to not only support SOC management, but also adapt agricultural practices to climate change, improve water regulation, and enhance soil ecosystem functions for sustainable agriculture.
How to cite: Brogi, C., Bauer, F. M., Herbst, M., Schullehner, K., and Huisman, J. A.: Towards a farm-scale digital twin for carbon farming: site-specific implementation, validation, and potential for future projections, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3399, https://doi.org/10.5194/egusphere-egu26-3399, 2026.
Soil organic carbon (SOC) sequestration is a key nature-based climate solution, with carbon credit markets offering a financial incentive to practices that enhance SOC stocks. Market credibility, however, hinges on baseline methodologies, the counterfactual scenario used to measure the additionality of carbon stored. Most protocols rely on static baselines that assume SOC remains constant without intervention, overlooking the dynamic effects and interaction of climate, land use, and management practices over time.
We critically discuss static versus dynamic baselining approaches in SOC crediting systems. Dynamic baselining frameworks, incorporating empirical SOC trends, process-based modeling, and environmental covariates, offer time-varying reference scenarios that better reflect real-world SOC dynamics and reduce overcrediting.
We discuss the implications for carbon market integrity, environmental additionality, and stakeholder confidence, highlighting challenges such as data availability, computational demands, and uncertainty quantification. Practical strategies for integrating dynamic baselines into crediting standards are outlined, balancing scientific rigor with operational feasibility.
By synthesizing current evidence and frameworks, this work provides actionable guidance for policymakers, standard-setters, and project developers seeking to enhance the credibility and effectiveness of SOC sequestration as a climate mitigation strategy.
How to cite: Brown, R. and Kilner, C.: From Static to Dynamic: Rethinking Baselines in Soil Organic Carbon Markets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4827, https://doi.org/10.5194/egusphere-egu26-4827, 2026.
Calcareous soils are widespread in many regions of the world, including the Mediterranean basin, and are characterized by the presence of inorganic carbon (SIC), predominantly in the form of calcium carbonate (CaCO₃). Although long considered stable and inert, SIC is now understood as dynamic and its presence, concentration, and composition influence agricultural soil functioning and carbon storage. Carbonate dissolution and precipitation are sensitive to agricultural practices. For instance, nitrogen fertilization induces soil acidification and gradually deplete SIC stocks, resulting in carbon losses through CO₂ emissions (Raza et al., 2024). Beyond their role in buffering soil pH, carbonates have also been reported to contribute to soil aggregation, soil organic matter stabilization, and nutrient availability (Zamanian et al., 2024). Therefore, a better understanding of SIC dynamics would support the development of sustainable agricultural practices to enhance the conservation and resilience of calcareous soils (Dina Ebouel et al., 2024; Raza et al., 2022). In response to environmental and climatic challenges that necessitate rapid adaptation of agricultural practices, greater integration of stakeholder perspectives and needs into soil research agendas has been widely encouraged (Cimpoiasu et al., 2021). Establishing shared understanding of the challenges enables to align research questions with real-world conditions, enhancing the relevance of recommendations for practice changes. In the frame of the PRIMA European project “Sharing-Med”, which aims to characterize Mediterranean soils, a survey is being undertaken to investigate farm advisors’ perceptions, concerns, and knowledge regarding SIC. The objective is to relate these perspectives with scientific knowledge to identify future research priorities specifically relevant to Mediterranean calcareous agricultural soils. By march 2026, a total of twenty semi-structured interview, will have been conducted in southern France, complemented by an online questionnaire disseminated to agricultural advisors across the broader Mediterranean region (including Spain, Italy, Greece, and others). Insights derived from this survey will subsequently be discussed with the scientific community to refine and prioritize SIC research directions.
References
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Dina Ebouel, F. J., Betsi, T. B., and Eze, P. N. 2024. Soil inorganic carbon: A review of global research trends, analytical techniques, ecosystem functions and critical knowledge gaps. CATENA 242:108112. https://doi.org/10.1016/j.catena.2024.108112.
Raza, S., Miao, N., Wang, P., Ju, X., Chen, Z., Zhou, J., and Kuzyakov, Y. 2020. Dramatic loss of inorganic carbon by nitrogen-induced soil acidification in Chinese croplands. Global Change Biology 26:3738–3751. https://doi.org/10.1111/gcb.15101.
Zamanian, K., Taghizadeh-Mehrjardi, R., Tao, J., Fan, L., Raza, S., Guggenberger, G., and Kuzyakov, Y. 2024. Acidification of European croplands by nitrogen fertilization: Consequences for carbonate losses, and soil health. Science of The Total Environment 924:171631. https://doi.org/10.1016/j.scitotenv.2024.171631.
How to cite: Temple, C., Fallot, A., and Chevallier, T.: SIC dynamics in Mediterranean agricultural soils: Characterizing farm advisors’ perception to inform research agendas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2802, https://doi.org/10.5194/egusphere-egu26-2802, 2026.
Drylands contain most of the global soil inorganic carbon (SIC), yet its sources and vulnerability are poorly constrained. We measured SIC content and its radiocarbon (14C) at 55 dryland sites across Asia and Europe to investigate the origins of SIC and its environmental factors. In the top 10 cm, SIC generally increased with aridity, but extremely dry sites with low soil organic carbon (SOC) often had low SIC, implying that low vegetation input limits both SOC accumulation and pedogenic carbonate formation. The Δ14C of topsoil SIC was positively related to the Δ14C of SOC and declined with aridity, consistent with reduced influence of modern C sources. SIC content was linked mainly to net primary productivity (NPP) and SOC, whereas Δ14C-SIC was controlled primarily by soil pH, which governs carbonate dissolution and precipitation reactions. Thus, a greater imprint of modern carbon is found in carbonates of less alkaline surface soils, either indicating a greater potential for forming new pedogenic carbonates or greater isotopic exchange. At a subset of sites on the Chinese Loess Plateau and the Inner Mongolia Plateau, soil samples were collected across multiple depth intervals. SIC contents remained relatively constant with depth, whereas Δ14C-SIC decreased, indicating reduced contributions of recent carbon to SIC. We estimate that carbonates reflecting the influence of modern C sources accounted for about 30% of topsoil SIC but only about 10% in subsoils. These results show that dryland subsoils retain older, more stable, and likely geogenic carbonates, whereas topsoils contain younger pedogenic carbonates that are more influenced by and potentially vulnerable to environmental change.
How to cite: Wang, H., Huang, J., Maestre, F. T., Lu, N., Wang, C., Chen, W., Zhao, G., Zhang, Y., Bramble, D. S. E., Schrumpf, M., Dippold, M. A., Zaehle, S., Fu, B., and Trumbore, S.: Limited imprint of modern C sources on soil inorganic C, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17779, https://doi.org/10.5194/egusphere-egu26-17779, 2026.
Soil organic carbon (SOC) sequestration in deep soil (below 30 cm depth) is considered a promising strategy for climate change mitigation and has recently attracted increasing global attention. However, studies on the accumulation potential and mechanisms of newly added residue-derived C in deep soil remain limited, particularly using 13C-labeled residue under in-situ conditions. Residue-derived C accumulates through two pathways: as mineral-associated organic matter (MAOM) through chemical protection, or as particulate organic matter (POM) through physical protection. These accumulation mechanisms are influenced by soil depth-dependent properties such as carbon saturation of clay minerals, as well as by residue quality. This study aims to evaluate the C accumulation potential of newly added residue across soil depth via MAOM accumulation and POM persistence in Andosols, and to assess how different residue quality affects these pathways. To compare the residue-derived C accumulation potential across soil depths, we conducted a 1-year in-situ incubation experiment on Andisols cropland in Japan. Soil of each depth (10, 50, and 90 cm depth) was mixed with 13C-labeled maize leaf, stem, and root residue (C/N ratio = 21–39) at 2 g C kg−1, and buried at the corresponding depth. After 3, 6, and 12 months, buried samples were collected and fractionated into free particulate organic matter (fPOM; < 1.7 g cm−3), occluded POM (oPOM; < 1.7 g cm−3,> 53 μm), and mineral-associated organic matter (MAOM; > 1.7 g cm−3, < 53 μm), and residue-derived C in each fraction was quantified. After 12 months, the remaining proportion of residue-derived C in bulk soil was significantly highest in 90 cm (36–43 %), followed by 50 cm (32–36 %) and 10 cm depth (22–25 %), indicating that the deep soil of Andisols has a higher accumulation potential of newly added residue-derived C across all residue quality than topsoil. Residue-derived C in MAOM was highest in 90 cm depth (0.58–0.71 g C kg−1), followed by 50 cm (0.52–0.64 g C kg−1) and 10 cm depth (0.37–0.46 g C kg−1) after 12 months, and negatively correlated with carbon saturation statuses of soil. These results indicate the high accumulation of residue-derived C via mineral association in deep soil which has lower C saturation. Furthermore, root residue-derived C in oPOM remained higher in deep soil than in topsoil, while it was not observed for leaf- and stem-derived C in oPOM after 12 months. It should indicate that oPOM persistence can provide an additional accumulation pathway for root residue in deep soil. Overall, we found that the deep soil of Andisols has a higher C accumulation potential than the topsoil, through enhanced MOAM formation and POM persistence.
How to cite: Yasuno, H., Lyu, H., Tanaka, H., and Sugihara, S.: High C accumulation potential of deep soil via mineral association in Andisols, Japan., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8901, https://doi.org/10.5194/egusphere-egu26-8901, 2026.
Understanding how land management influences soil carbon dynamics and greenhouse gas fluxes is essential for evaluating realistic carbon dioxide removal potential. However, soil carbon changes are difficult to detect against large background stocks, often requiring long-term field studies, and gains may be offset by increased emissions of other greenhouse gases, particularly nitrous oxide. Few land-based mitigation projects have the capacity to measure these processes in sufficient detail. Together, these limitations introduce considerable uncertainty when estimating the true climate benefit of soil-based approaches. Here we introduce the Exeter Soil Carbon Sequestration Lab (ExSEQ), which has been established to address these challenges.
Central to the facility are two large-scale, environmentally controlled growth chambers at the University of Exeter. Temperature, light, CO2, and humidity are precisely regulated, allowing crops to grow in soil under realistic yet highly controlled climatic conditions and a continuously 13CO2-enriched atmosphere. We have successfully grown pasture species and arable crops through their full life cycles under continuous stable-carbon isotope labelling at 500‰. This level of enrichment allows accurate tracing of plant-derived carbon into soils and enables precise quantification of new soil organic matter formation, even when newly added carbon represents less than 0.5% of the total SOM pool.
ExSEQ supports continuous, high-frequency measurement of CO2, CH4, and N2O fluxes, together with isotopic characterisation of both gases and soil carbon. Fluxes are monitored without opening the chambers, preventing dilution of the isotopic signal and allowing simultaneous quantification of new SOM inputs, losses of existing soil carbon, and full greenhouse gas budgets to assess net climate mitigation outcomes.
While no laboratory can fully replicate the complexity of field systems, ExSEQ operates at a realistic scale and enables rapid screening of potential interventions across contrasting soils, climates, and plant–soil systems. The facility offers considerable potential to advance understanding of the effects of different fertilisers, soil amendments (e.g. enhanced rock weathering, biochar, biostimulants), and management practices (e.g. tillage intensity, pasture sward biodiversity, grazing management). ExSEQ provides a highly adaptable experimental platform deployable across a wide range of land management scenarios and aims to promote collaboration across academic institutions and industry.
How to cite: van Groenigen, K. J., Friggens, N. L., Kuempers, B., and Hartley, I.: The Exeter Soil Carbon Sequestration Lab (ExSEQ)): Advancing Quantification of Soil Carbon Dynamics and Climate Mitigation Potential, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12904, https://doi.org/10.5194/egusphere-egu26-12904, 2026.
The need for soil carbon measurements is increasing as global efforts to combat climate change intensify. Soil health, soil fertility and climate change mitigation are drivers for ongoing analytical testing. Accurate and precise soil carbon data for applications such as carbon credit programs is crucial for transitioning from estimated based approaches to direct measurement technologies. This study evaluates the precision of soil carbon measurements using the Elementar soli TOC® cube, focusing on the critical factors of sample grain size and sample weight.
We analyzed two different soil samples, ALP SRS-1810 and ALP SRS-2308, using the DIN EN 17505 standard for temperature-dependent differentiation of carbon fractions, including TOC, ROC, and TIC, without the need for time-consuming acid pre-treatment. Samples were ground and sieved to various grain sizes, from <2.00 mm down to <0.10 mm, and then analyzed in different weights ranging from 0.025 g to 1.0 g. Our results show a clear trend: precision, as measured by the absolute standard deviation (SD), significantly improves with decreasing grain size and increasing sample weight. However, the data also reveals a sweet spot that balances sample preparation effort with measurement precision.
Based on our findings, a sieve size of 0.25 mm to 0.50 mm combined with a sample weight of 0.1 g to 0.25 g provides a highly efficient and effective working range (Figure 1). This combination delivers very good to excellent precision (relative standard deviation, SD rel. < 1.80%) while minimizing the labour and time associated with excessive grinding and weighing. The soli TOC® cube's ability to handle this optimal range, along with its automated sample feeder, makes it an ideal instrument for high-throughput laboratory analysis, providing reliable and reproducible soil carbon data that exceeds required precision specifications.
How to cite: Preece, C., Corell, P., and Loos, A.: Quantification of soil carbon with the Elementar soli TOC® cube: the impact of sample weight and grain size on precision , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11159, https://doi.org/10.5194/egusphere-egu26-11159, 2026.
The presence of surface oxygen vacancies (Vo) has proven critical in enhancing the reaction and activation processes for the selective oxidation of hydrogen sulfide (H₂S) and carbon dioxides (CO₂). However, achieving efficient H₂S and CO₂ removal at ambient temperatures remains a significant challenge. In this study, we report the synthesis of a copper-iron impregnated titanium oxide (Cu-Fe/Vo-TiO₂) catalyst designed to address this challenge through a facile impregnation method. The objectives of this research were to synthesize and characterize novel multi-metal catalyst and evaluate the feasibility of its application to remove H2S and CO₂ in room temperature. 1) The synthesized novel multi-metal catalyst was characterized. 2) The effects of multi-metal catalyst, initial H2S and CO₂ concentration on the behavior of fixed-bed column, and reusability of novel catalyst was investigated. 3) A possible reaction mechanism of novel multi-metal catalyst was proposed through diverse chemical analysis. This study successfully demonstrated the development of Cu-Fe/Vo-TiO₂ as a highly efficient catalyst for H₂S and CO₂ removal at ambient temperature. The synergistic interactions between Cu and Fe species, driven by the electron-donating properties of oxygen vacancies, enabled efficient H₂S and CO₂ adsorption, activation, and conversion. This study establishes Cu-Fe/Vo-TiO₂ as a robust and energy-efficient catalyst for ambient-temperature desulfurization, with significant potential for industrial applications.
How to cite: Choi, J.: Decarbonization and desulfurization using Cu-Fe/Vo- TiO2 in ambient temperature , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2642, https://doi.org/10.5194/egusphere-egu26-2642, 2026.
Biochar is a stable carbon-rich material produced from carbon-rich biomass in the absence of air or under oxygen-limited conditions. A plethora of feedstocks can be used to produce biochar including wood-based materials, organic wastes (i.e. sludges, manure), plant-based materials (i.e, leaves, seeds, husks) as well as food-waste residues or by-products. In addition, pyrolysis conditions such as temperature, heating rate, duration and the scale the pyrolysis system, also vary considerably. Therefore, biochars differ widely in their physical and chemical characteristics. Biochar is recommended as a soil amendment due to its ability to enhance the physicochemical characteristics of soil and support crop growth.
Biochar influences soil in various ways. It can raise pH, enhance cation exchange capacity, increase extractable nutrients, modify microbial communities and soil processes, and improve physical traits like bulk density and structure, supporting better plant growth. This study reviews the factors that influence the interaction of soil and biochar in terms water retention. The analysis shows that biochar generally reduces soil bulk density and improves water retention, especially in coarse‑textured soils where field capacity, wilting point, and available water increase substantially. Effects are smaller in medium soils and minimal in fine soils.
How to cite: Manarioti, M. V. and Pelekis, P.: Factors affecting water retention in biochar-amended soil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13384, https://doi.org/10.5194/egusphere-egu26-13384, 2026.
As greenhouse gas emissions continue to rise, contributing to global warming, land-based CO2 removal through enhanced carbon storage could help in climate mitigation efforts. Biochar, produced by pyrolysis of biomass under O2-limited conditions, has gained attention for its potential to stabilise soil carbon. However, in natural ecosystems microbes access multiple carbon sources (e.g. soil organic matter, biochar, plant litter,) meaning that total CO2 fluxes alone are insufficient to assess biochar effects on soil carbon dynamics. To address this, we investigated how biochar addition affects the fate of multiple carbon sources using isotopic partitioning to improve understanding of priming and source-specific CO2 emissions.
Two soils, a fine-textured pasture soil and a coarser-textured arable soil, were incubated with biochar produced from naturally enriched Miscanthus at three pyrolysis temperatures (350, 450, and 700 °C). Control and biochar-treated soils (2% w/w), with and without 13C-labelled plant litter, were incubated for 200 days with repeated measurements of CO2 fluxes and isotopic signatures. Isotopic partitioning separated litter-derived CO2 from background CO2 (soil + biochar), and soil- and biochar-derived CO2 were further partitioned using no-litter treatments. A sensitivity analysis was conducted to assess the robustness of litter-derived CO2 estimates.
Biochar pyrolysis temperature strongly influenced total CO2 emissions: 350 °C biochar substantially increased total cumulative CO2 emissions in both arable (58%) and pasture (99%) soils, whereas higher-temperature biochar (450, 700 °C) produced smaller increases. Isotopic partitioning showed that biochar-derived CO2 decreased with increasing pyrolysis temperature in both soils. In arable soil without litter, soil-derived CO2 changed little (0-8%) across biochar treatments, indicating that higher total CO2 emissions were driven primarily by biochar-derived CO2 rather than enhanced native soil carbon decomposition (i.e., priming). In contrast, pasture soil without litter, showed a stronger priming response, with soil-derived CO2 increasing by 41–45% across biochar treatments relative to the control. Adding litter reduced biochar-induced differences in total CO2 emissions in pasture from 57–99% to 3–8%, but not in arable soil. Litter-derived CO2 was not affected by biochar treatments in either soil.
Overall, our results suggest that, in the short term, biochar effects on total CO2 emissions are largely driven by priming effects and biochar decomposition rather than the decomposition of new plant material. However, these effects were soil-specific and changed with litter addition, underlining the need for soil- and context-specific evaluation when assessing the stability and climate benefits of biochar additions.
How to cite: Hiniduma Gamage, K. A., Hartley, I., Lindstrom Friggens, N., Bore, E., and Van Groenigen, K. J.: Biochar-induced Priming Effects Depend on Soil Type and Fresh Carbon Inputs , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13774, https://doi.org/10.5194/egusphere-egu26-13774, 2026.
Soil organic carbon (SOC) stocks in European croplands are declining, and increasing demand for biomass to substitute fossil fuel–based products may further exacerbate this trend. Cereal straw represents a substantial and still underutilized biomass resource; however, its additional removal may intensify SOC losses. This study quantifies the impact of increased straw removal on SOC stocks in German croplands and evaluates the potential of biochar (BC) produced from cereal straw to compensate for these losses.
SOC dynamics were modelled for 1,115 cropland sites using soil and management data from the first German Agricultural Soil Inventory. Seven scenarios representing different levels of straw removal and BC application were simulated using a model ensemble combining three allometric approaches for carbon input estimation with the RothC soil carbon model.
Annual straw harvest from German croplands could theoretically be tripled to 26.3 million Mg straw (dry matter). Removing all additionally harvestable straw (17.4 million Mg) reduced mean carbon inputs to cropland soils by 21% and resulted in an average SOC loss of 8.9 Mg C ha⁻¹ within 100 years. During the first 20 years, SOC stocks declined by 0.10 ± 0.20 Mg C ha⁻¹ a⁻¹, corresponding to additional emissions of 4.2 million Mg CO₂ a⁻¹ at the national scale compared to business-as-usual. Although SOC losses decreased over time, they persisted beyond 200 years and were more pronounced on clayey than on sandy soils.
In contrast, converting straw to BC and applying it to the same cropland soils led to an SOC increase of 16.7 Mg C ha⁻¹ within 100 years, equivalent to a net carbon sink of 25.6 Mg C ha⁻¹ and negative emissions of 93.9 million Mg CO₂ ha⁻¹. An average BC application rate of 4.9 Mg C a⁻¹ increased SOC by 10.8 million Mg CO₂ a⁻¹ relative to business-as-usual, corresponding to approximately 10% of Germany’s current annual agricultural greenhouse gas emissions. Accounting for SOC losses due to straw removal reduced cumulative SOC gains over 100 years by 25%.
Our results demonstrate that additional straw harvesting can undermine SOC stocks and climate mitigation efforts, whereas BC application from cereal straw has substantial potential to offset these losses. However, climate mitigation strategies relying on agricultural residues should integrate SOC losses from biomass removal to avoid overestimating the mitigation potential of BC systems.
How to cite: Helfrich, M., Seitz, D., Dechow, R., and Don, A.: Biochar from Cereal Straw Can Offset Soil Carbon Losses from Increased Straw Harvest in German Croplands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19411, https://doi.org/10.5194/egusphere-egu26-19411, 2026.
Conventional biochar from woody biomass (woodchips, sawdust, bamboo etc.) and crop residues (rice husk, wheat straw, coconut shell etc.) enhances long-term soil carbon (C) storage with slow-release soil fertiliser input. However, the soil response to food waste biochar application is yet to be established. In order to optimise food waste biochar as a soil amendment product, a comparative meta-analysis of food waste biochar to other established conventional biochar types is needed. This study compares the effect of feedstock type and pyrolysis temperature on biochar physical-chemical properties, chemical stability and aromaticity to infer how food waste biochar may alter soil properties.
Data was synthesized from 33 peer-reviewed articles on food waste and 50 on conventional biochar. Feedstocks were categorised into cooked food waste, fruit-vegetable peels/seeds, woody biomass and crop residues. Pyrolysis temperatures were classified as slow (300 to 500oC), fast (550 to 650oC) and flash (700 to 1000oC). Pairwise comparison of feedstock types was achieved by Welch’s t-test and Cohen’s d effect size to assess impacts of temperature on biochar properties.
Pyrolysis temperature predominantly governs biochar properties, with minimal impact from feedstock choice. Lack of significant differences (p > 0.05) and low-to-high effect sizes were observed in moisture content (d = 0.10 – 1.08), surface area (d = 0.12 – 0.35), ash content (d = 0.19 – 0.74) and pH (d = 0.02 – 0.75) at fast temperature regime in most food waste and conventional biochar pairwise comparisons. Food waste biochar was similar to conventional biochar in total potassium (p > 0.05; d = 0.06 – 0.25) at slow temperature regime but a significant difference and large effect sizes (p < 0.05; d > 0.5) in total nitrogen was observed between food waste and conventional biochar at the three temperature regimes. Food waste biochar had lower total C content across all temperature regimes compared to conventional biochar (p < 0.05; d > 0.5) but showed similarity in fixed C at flash temperature. In addition, most food waste biochar clustered in the coal and anthracite regions of the van Krevelen diagram at flash pyrolysis temperature, indicating lower H/C (0.0 – 1.2), O/C (0.0 – 0.76) ratios that signify enhanced aromatic C and potential for long-term stable C. Overall, these findings show that food waste feedstocks differ in nitrogen content compared to conventional feedstocks – which are high in total C –, with resulting biochar capable of enhancing N availability in soil. Despite limited field and laboratory data on the potentials of food waste biochar on enhancing soil C stocks and associated soil co-benefits, evidence suggests that pyrolysis temperature can be used to optimise food waste biochar for total C, fixed C and porosity to match the soil carbon stock potential of conventional biochar. The N and K content variations amongst food waste and conventional feedstocks emphasises the potential to engineer biochar production from co-blend of food waste and crop residues to produce balanced nutrient content for targeted soil fertility management.
How to cite: Agbarakwe, S. P., da Costa, T., and O'Rourke, S.: Comparative Meta-Analysis of Physical and Chemical Properties of Food Waste and Conventional Biochar, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21246, https://doi.org/10.5194/egusphere-egu26-21246, 2026.
This study evaluated whether compost produced by agricultural residues-mixed livestock manure could improve crop productivity and soil quality while reducing inorganic fertilizer use and nitrous oxide (N₂O) emissions in upland cultivation of autumn Chinese cabbage (Brassica rapa L.). Direct incorporation of crop residues often provides limited benefits due to slow decomposition and nitrogen immobilization; therefore, residues were aerobically co-composted with livestock manure and applied in combination with inorganic fertilizers. The results showed that treatments receiving the agricultural residue–manure compost significantly increased cabbage growth and yield. In particular, the treatment combining compost with 50% the recommended inorganic fertilizer rate produced higher yields than the 100% inorganic fertilizer treatment alone. Compost application improved soil chemical properties, including higher pH, organic carbon, available phosphorus, and exchangeable base cations, and enhanced nitrogen uptake and nitrogen use efficiency. Moreover, cumulative N₂O emissions were reduced by about 21% in the 50% rate inorganic fertilizer plus compost treatment compared with inorganic fertilizer alone. Overall, these findings indicate that co-composted agricultural residues and livestock manure can serve as an effective soil amendment, maintaining high crop productivity while lowering greenhouse gas emissions and reducing reliance on inorganic fertilizers, thereby supporting more sustainable nutrient management in upland cropping systems.
Acknowledgments
This study was supported by (2026) the RDA Fellowship Program of National Institute of Agricultural Sciences, Research Program for Agriculture Science and Technology Development (Project No. RS-2022-RD010368), Rural Development Administration, Republic of Korea.
How to cite: Yun, J.-J., Park, J.-H., Jeon, S.-H., Hong, S.-J., Roh, A.-S., and Shim, J.-H.: Effects of Agricultural Residues-Mixed Livestock Manure on Chinese Cabbage Growth and Nitrous Oxide (N2O) Emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8841, https://doi.org/10.5194/egusphere-egu26-8841, 2026.
Posters virtual: Wed, 6 May, 14:00–18:00 | vPoster spot 2
EGU26-20534 | ECS | Posters virtual | VPS17
Irrigation activates soil inorganic carbon dynamics in a calcareous mediterranean agroecosystemWed, 06 May, 14:54–14:57 (CEST) vPoster spot 2
The implementation of irrigation is a key management practice in arid and semi-arid regions to sustain agricultural productivity. Irrigation modifies the soil carbon cycle [1], [2] but its effects on soil inorganic carbon (SIC) have received far less attention than those on soil organic carbon. However, SIC constitutes most of the soil carbon stock in calcareous soils of these regions. Understanding how irrigation interacts with SIC dynamics, governed by carbonate dissolution and precipitation processes, is crucial to assess soil carbon stability and its response to management changes.
This study compares two contrasting management scenarios, rainfed maize and irrigated maize, and evaluated how irrigation affected the dynamics of the SIC in an experimental plot in Navarra (northern Spain) historically cultivated with rainfed wheat. We quantified SIC and SOC contents in bulk soil and in coarse (>50 µm) and fine (<50 µm) fractions of the tilled layer (0–30 cm) of a calcareous soil (⁓40% CaCO₃), together with the isotopic signatures of SOC (δ¹³C-SOC) and SIC (δ¹³C-SIC) along the first 7 years of the trial, as direct assessment of SIC isotopic signatures provides a more reliable estimate of pedogenic carbonate contributions than commonly used mixing equations, avoiding biases associated with C3–C4 crop changes [3].
After 7 years, it was found that the accumulated SOC inputs were higher in irrigated maize (24.0 Mg C ha⁻¹) than in rainfed maize (14.8 Mg C ha⁻¹). Therefore, irrigated maize showed an increase in SOC stocks of +7.1% [4]. With regard to total SIC, ⁓24% of soil carbonates were found in the coarse fraction and ⁓16% in the fine fraction. No differences were observed between treatments, either in total SIC or in the coarse fraction, but there were differences in the fine fraction of irrigated maize compared to rainfed maize (-1%).
Clear differences in δ¹³C-SIC were however observed between treatments. In bulk soil, δ¹³C-SIC decreased from −3.80‰ under rainfed maize to −4.14‰ under irrigated maize. In the coarse fraction, the shift was more pronounced, from −3.70‰ to −4.95‰, while intermediate changes were observed in the fine fraction (from −3.94‰ to −4.20‰). These isotopic shifts indicate that irrigation, together with increased organic matter inputs, activated carbonate dissolution–precipitation cycles, thereby increasing the relative contribution of pedogenic carbonates.
Furthermore, the preferential accumulation of SIC in the coarse fraction may be related to the formation of pseudo-sands driven by carbonate cementation within aggregates [5], highlighting the need to adjust ultrasonic energy during particle-size fractionation.
Overall, our results demonstrate that irrigation triggers SIC dynamics in calcareous agricultural soils, promoting carbonate dissolution and precipitation processes even in the absence of significant changes in total SIC content, and emphasize the importance of jointly considering SOC and SIC to accurately interpret pedogenic carbonate formation under contrasting agricultural management regimes.
References
[1] Ball et al. (2023), https://doi.org/10.1016/j.soilbio.2023.109189
[2] de Soto et al. (2017), https://doi.org/10.1016/j.geoderma.2017.03.005
[3] de Soto et al. (2024), https://doi.org/10.1016/j.catena.2024.108362
[4] Antón et al. (2022), https://doi.org/10.3389/fsoil.2022.831775
[5] Rowley et al. (2018), https://doi.org/10.1007/s10533-017-0410-1
How to cite: Conte, A. P., Antón, R., Enrique, A., de Soto, I. S., and Virto, I.: Irrigation activates soil inorganic carbon dynamics in a calcareous mediterranean agroecosystem, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20534, https://doi.org/10.5194/egusphere-egu26-20534, 2026.
