This joint session focuses on soil C and N cycling and related soil functions and processes, with particular emphasis on two soil domains that remain comparatively understudied: grassland soils and subsoils.
Contributions addressing grassland soils examine how management and restoration practices such as grazing regimes, fertilisation strategies, legumes, and silvopastoral systems, affect soil C sequestration, N cycling, and greenhouse gas emissions, and how these processes respond to broader drivers such as climate variability and grassland degradation.
Studies focusing on subsoils (below ~30 cm or the B-horizon) explore deep soil C and N dynamics, soil physical properties, soil–plant–atmosphere interactions, and the role of subsoils in long-term carbon storage, nutrient and water regulation, and ecosystem resilience. By integrating research across soil depths and land-use systems and managements, this session provides a holistic view of how management influences soil functions relevant to climate change mitigation and sustainable land management.
More than half of the soil water and nutrients are allocated below a 30 cm soil depth. Yet, this reservoir is hardly included in soil management strategies and is sometimes not even accessible to plants due to root-restricting layers. Here, we present an overview of different research projects on (i) the coupling and decoupling of subsoil biogeochemistry from topsoil processes under different management practices, (ii) the option to manipulate subsoil access through biopores and deep-rooting plants, and (iii) the success of subsoil management through compost injection and burial of straw for the cropping of rainfed (barley, maize) and flooded cereals (paddy rice), respectively. We show that plants are key to connecting top- and subsoil processes, but that it takes decades to centuries for subsoil processes to reach new steady-state equilibria. The interactions between sub- and topsoils, however, can be disentangled using stable and geogenic isotope tracing techniques, such as δ¹⁸O and ⁸⁷Sr/⁸⁶Sr, and can be utilized for management via biological or mechanical techniques to lower the physical resistance of soil to plant growth. Intelligent management of subsoil offers new options for making land use more resilient to climate change and for maintaining high productivity and sustainability with lower long-term fertilizer requirements.
How to cite: Amelung, W., Yang, H., and Bauke, S.: Biogeochemistry and sustainable management of the subsoil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7970, https://doi.org/10.5194/egusphere-egu26-7970, 2026.
Understanding the vertical distribution of soil biota is essential for predicting soil functioning, nutrient cycling, and ecosystem responses to environmental gradients such as elevation and climate. We studied the depth distribution of soil macrofauna, nematodes, and soil microbes (using phospholipid fatty acid analysis, PLFA), together with basic soil parameters, along an elevational gradient from approximately 90 to 2700 m a.s.l. in a temperate climate (Europe) and a tropical climate (Papua New Guinea). Soil profiles were sampled using hand-dug soil pits to a depth of 1 m.
The density of all faunal groups as well as microbial biomass decreased with increasing soil depth; however, the depth patterns varied among elevations. Soil biota reached the greatest depths at the lowest part of the gradient, particularly in alluvial soils characterized by a deep A horizon, and also at sites close to or above the tree line where A horizon was also quite deep. These results indicate that both soil development and elevation-related environmental constraints strongly influence the vertical distribution of soil organisms, highlighting the importance of considering soil mainly A horizon depth and landscape position when assessing biodiversity and ecosystem processes along elevational gradients.
How to cite: Frouz, J.: Vertical distribution of soil biota along elevation gradient in temperate and tropical climate., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6895, https://doi.org/10.5194/egusphere-egu26-6895, 2026.
The volume and connectivity of the soil macropore network play a key role in soil functioning. Cylindrical pores formed by biotic processes, known as biopores, are essential components of the network because they are typically continuous over longer distances and connect different soil regions. They are therefore fundamental to near-saturated hydraulic and gas-exchange properties, to delineating habitats for soil fauna, and to low-resistance pathways for root growth to deeper soil layers. So far, detailed studies quantifying soil macropore network morphologies have predominantly focused on topsoils. Little is yet known about macropore networks in the subsoil with respect to soil depth, land use, and soil management, especially at depths greater than 0.5 m. This study addresses this knowledge gap by examining the average and variability of macropore network morphologies and the distribution of biopores across different soil horizons down to 1.5-2 m at three agricultural sites located in Belgium, Germany, and Switzerland. Each site included three sampling pits, two in croplands under two contrasting management systems (e.g., conventional tillage vs. reduced tillage) and one in adjacent grassland. Eight undisturbed 250 cm³ aluminium soil cores were sampled from every soil horizon identified in the respective sampling pits, as well as from the transition area between the A and B horizons, resulting in a total of 434 samples [3 sites × 3 pits × (5 – 7) horizons × 8 replicates]. X-ray computed tomography was performed at a voxel resolution of 90 µm. All imaged air-filled macropores were segmented, and cylindrical pores were extracted as biopores. The effects of soil depth, land use, and cropland management on the imaged pore and biopore network morphologies and on the variability of pore structure across soil horizons will be investigated using linear mixed-effect models. We hypothesize that i) the variability of the soil macropore network morphology will decrease with depth; ii) the diameter and volume of biopores will decrease with depth; and iii) the effects of land use and management will be limited to the uppermost B subhorizon. The results from this study provide insight into how land use, agricultural management, and soil depth influence soil macropore structures, which is crucial for understanding and predicting subsoil health, specifically soil functioning related to air, water, and solute transport properties, and soil habitat quality for roots and fauna.
How to cite: Fu, Y., Koestel, J., and Weller, U.: Quantifying soil macropore morphology and biopore distribution at different subsoil horizons in European agricultural soils using X-ray CT, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9667, https://doi.org/10.5194/egusphere-egu26-9667, 2026.
Deep soil horizons represent a major but still poorly understood component of the soil carbon pool, despite their important contribution to long-term carbon storage and climate regulation. While carbon dynamics in topsoils have been extensively studied, much less is known about the mechanisms controlling carbon processing and stabilization at depth, particularly the role of microbial functioning and soil structure. This study investigated how microbial carbon use efficiency (CUE) varies with depth in a temporary agricultural grassland soil profile (10, 30 and 60 cm) under temperate conditions in Lusignan, France. Measurements were performed in both bulk soil and biostructures. Microbial CUE was estimated using two independent approaches (13C-based CUE and 18O–H₂O-based CUE), while microbial functional diversity was characterized using MicroResp and organic matter quality using Rock-Eval pyrolysis. Results showed contrasting depth-related patterns depending on the method used. 13C-based CUE increased with depth, with consistently higher values in biostructures than in bulk soil. In contrast, 18O-based CUE declined along the soil profile. Organic matter became progressively more stable and chemically mature with depth, while microbial communities shifted towards assemblages adapted to lower substrate availability and higher organic matter complexity. Variations in soil physical and chemical properties, organic matter quantity and quality, and microbial community structure therefore strongly depended on depth and the presence of biostructures, and jointly controlled microbial efficiency. These findings show that carbon storage in deep soil horizons depends strongly on microbial efficiency, soil structure and organic matter quality, and can be enhanced by management practices that increase carbon inputs and promote biostructure formation.
Keywords: Subsoil carbon storage, Deep soil horizons, Land management practices, Microbial communities
How to cite: Zi, Y., Jeay, L., Nunan, N., Chabbi, A., and Rumpel, C.: Microbial processes controlling organic carbon storage along deep soil profiles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21406, https://doi.org/10.5194/egusphere-egu26-21406, 2026.
Land cover changes exert growing pressure on soils and can modify their physical structure and hydraulic behaviour. While the influence of land cover on erosion, compaction, and biological activity in the upper 30 cm is well documented, much less is known about how far these effects extend into deeper horizons. Here, we analyse depth-dependent variations in structural and hydraulic properties for soils of comparable texture under cropland, grassland, and forest. We used the EU-HYDI database, comprising 6,014 profiles and over 18,000 samples across Europe (36% with LUCAS land cover information). Samples were grouped by texture classes (using a modified version of the HYPRES texture triangle) and land cover independently of soil profile. For each texture X land cover combination, we fitted generalized additive models (GAMs) with depth, including random effects for data source to account for heterogeneity in analytical methods and sampling protocols. Results reveal significant differences in bulk density and θsat up to 60 cm, with consistent patterns (cropland > grassland > forest for bulk density; cropland < grassland < forest for θsat). These results show that land cover impacts are not restricted to the topsoil, highlight the lack of subsoil data, particularly for fine-textured soils and forested sites and underscores the importance of harmonized measurement procedures to improve comparability in soil hydrological studies.
How to cite: Lengrand, A., Javaux, M., Koestel, J., and Vereecken, H.: Effects of land cover on subsoil physical and hydraulic properties, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12659, https://doi.org/10.5194/egusphere-egu26-12659, 2026.
In the northwestern Amazon region livestock farming typically involves extensive grass-only pastures that do not receive nitrogen (N) fertiliser. Over time, nutrient depletion leads to degradation in vast areas of pasture, with severe economic and ecological consequences. Our project investigates the impact of integrating legumes (e.g., Arachis pintoi) and grasses with biological nitrification inhibition (BNI) capacity on the N cycle in the soil–plant system. The study was conducted on seven farms in the Caquetá department of Colombia, in pasture plots that had been under the present pasture type for 5 to 30 years. We quantified plant biomass yields, N uptake and biological N2 fixation. In topsoil (0-0.1 m) the ammonium and nitrate content was measured and the gross N fluxes quantified using the 15N pool dilution method. The results revealed that the presence of legumes and the species of grass significantly affected the N cycle in the soil-plant system. Higher forage yield and higher mineral N in soils were observed in grass-legume than grass-alone pastures. This was likely due to the N2 fixation capacity of the legumes, which derived more than 70% of their N from atmosphere. The yield benefit in grass-legume pastures was more pronounced when the legumes were combined with the high BNI capacity grass (Urochloa humidicola). Ammonium was the dominant soil mineral N form in all pasture types, and gross and net nitrification tended to be lower in soils from pastures with high BNI capacity grass (P ≤ 0.10). Reduced nitrate production indicates a lower risk of nitrate leaching and N₂O emissions. Data on the impact of pasture type on total soil organic carbon and N contents are under evaluation. To our knowledge, this is the first study to examine the role of high-BNI grasses under low-input farming conditions, combined with legumes to mitigate N deficiency in pastures. Our findings illustrate a pathway towards sustainable intensification through biological interventions, with the potential to reduce soil degradation and harmful N losses across large areas of tropical pastureland.
How to cite: Oberson, A., Allemann, L., Arango, J., Frossard, E., Giraldo, A., Sotelo, M., Vázquez, E., Velásquez, J. E., and Villegas, D. M.: Sustainable intensification of tropical pastures: Optimize nitrogen supply through integration of legumes and grasses with biological nitrification inhibition?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18826, https://doi.org/10.5194/egusphere-egu26-18826, 2026.
Pastures contain a fine-scale mosaic of grass-only (GP) and mixed (grass–legume–forb; MP) patches, whose functional traits shape belowground C inputs and ecosystem respiration (ER). These traits make ER sensitive to drought and frequent grazing, yet their combined effects across patch types remain poorly understood.
To address this, we conducted a 2×2 rainfall × grazing factorial in GP and MP in a field-based temperate pasture climate-manipulation experiment, quantifying the effects of drought, frequent grazing, and their combination on ER, its temperature and moisture sensitivity, and plant C-use efficiency (AGB/ER). Rainfall was based on 30-year records, and grazing simulated via one or three harvests per season. ER was measured during spring, summer, and autumn 2023–2024, and structural equation modelling identified the key pathways by which biophysical factors regulate ER in each patch type.
Highly productive MP, compared to GP, consistently exhibited higher ER (spring: 0.17 vs. 0.11; summer: 0.32 vs. 0.17; autumn: 0.41 vs. 0.12 g C m-2 hr-1), greater C-use efficiency (3.2 ± 0.63 vs. 0.09 ± 0.02), higher apparent temperature sensitivity (Q10: 1.46 vs. 1.22), and weaker moisture constraints. However, this higher functioning came with greater vulnerability: under combined drought and frequent grazing, ER declined non-additively and more sharply in MP (–14.5%, –42.8%, –67.3%) than in GP (–4.6%, –34.2%, –11.2%). C-use efficiency dropped by 80% in MP but remained stable in GP, accompanied by larger reductions in AGB and Q10. Mechanistically, ER in MP was plant-biomass driven, whereas in GP it was microbial-substrate driven, with both indirectly constrained by moisture and temperature-induced soil drying.
These results show that the higher productivity of MP comes at the cost of greater ER vulnerability to drought–grazing stress, offering guidance for grazing management and strengthening predictions of pasture C–climate feedbacks.
How to cite: Tiwari, P., Macdonald, C. A., Wright-Osment, N., Kusai, N. A., Power, S. A., and Pendall, E.: Productivity at a price: mixed pastures show higher ecosystem respiration vulnerability to drought–grazing stress than grass-only patches, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-350, https://doi.org/10.5194/egusphere-egu26-350, 2026.
Grasslands represent a vast resource, covering >40% of the Earth’s land surface, supporting biodiversity, reducing erosion risks, and storing carbon (C) in soils. Yet they are increasingly threatened by land-use intensification, land degradation, and climate change. In response to these multiple pressures, numerous scientific studies have examined how grasslands function and what their environmental and socio-economic roles are across diverse climatic, soil, and management contexts. To provide an integrated overview of this complexity, we developed the first systematic global map that synthesises scientific knowledge from field experiments investigating how grassland management practices influence soil C in livestock systems1.
For this global synthesis, 31215 scientific studies in five languages were screened from several major databases (e.g., Web of Science, Scopus, CABI). Each publication was assessed using strict inclusion and exclusion criteria to ensure the reliability of the data retained1. We extracted and mapped information on management practices, from grazing and fertilisation to irrigation, plant composition, and biochar addition, as well as on soil C measurement types (e.g., concentration, stock, sequestration rate), pedoclimatic contexts, and experimental approaches (e.g., study duration, randomisation).
Between 1991 and 2024, the number of studies investigating the effects of grassland management on soil C increased exponentially. Most research has been conducted in temperate, high or upper-middle-income regions, particularly in China, the United States, and parts of Europe, while major gaps persist in Africa and tropical regions. Research has primarily focused on grazing (presence/absence, stocking density), fertilisation, and plant community management. More than half of the studies relied on established agricultural plots, using a space-for-time substitution approach (i.e. comparing long-term management sites to infer temporal trends).
This global map highlights both areas with relevant knowledge and knowledge gaps: key practices such as silvopastoral systems or grazing duration remain understudied. Gaining a deeper understanding of the effects of management practices on C sequestration and soil C fractions, particularly at depths beyond the top 30 cm, is essential to refine models and enhance the accuracy of global C stock estimates.
The compiled dataset represents a valuable resource for the scientific community. It can support future meta-analyses or the identification of knowledge gaps that merit further investigation.
Acknowledgements
This research was developed within the framework of the European Joint Program for SOIL, "Managing and Mapping Agricultural Soils for Enhancing Soil Functions and Services" (EJP SOIL), project CARBOGRASS, funded by the European Union Horizon 2020 research and innovation programme (Grant Agreement No. 862695).
Reference
1. Rousset, C., Segura, C., Gilgen, A. et al. (2024). What evidence exists relating the impact of different grassland management practices to soil carbon in livestock systems? A systematic map protocol. Environmental Evidence, 13, 22. https://doi.org/10.1186/s13750-024-00345-2
How to cite: Rousset, C., mendes, L., van der Meer, M., Rivera, J. E., Segura, C., Bastidas, M., Gilgen, A., Alfaro, M., Dodd, M., Dashpurev, B., Merbold, L., Chará, J., and Vazquez, E.: Grasslands and soil carbon: What can livestock management practices teach us? A global map of scientific knowledge, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9710, https://doi.org/10.5194/egusphere-egu26-9710, 2026.
Cattle slurry is widely used as organic fertilizer in temperate grasslands, but high nitrogen (N) losses during application cause emissions of greenhouse gases and air pollutants, water quality issues, and biodiversity loss. Furthermore, N balances frequently are negative, causing soil organic nitrogen (SON) mining, often accompanied by soil organic carbon volatilization and associated losses of agronomic and ecological soil functions. Low-emission slurry fertilization such as ground-level application has become obligatory in many countries, but such legal regulations as well as the individual decisions of farmers frequently are largely based on knowledge on ammonia losses only, but not on full N balances. Here, we provide a synthesis of data from experiments with 15N labelled organic fertilizers at 36 field plots, spanning a gradient of 1000 km from the Alps to Northern Germany. This approach allowed to assess effects of management intensity, climate change and different low emission application techniques on fertilizer N fates and full ecosystem N balances.
For intensive management with broadcast spreading of cattle slurry, on average almost half of the applied fertilizer N was lost to the atmosphere with a large contribution of dinitrogen emissions, while leaching of recent fertilizer N was negligible. Surprisingly, less than 10% of fertilizer N was taken up by plants, with the residual almost half of fertilizer N being stored in soil organic nitrogen. Nonetheless, grasslands were highly productive and largely met their N demand from mineralization of SON, which resulted in negative N balances and SON mining of on average 70 kg N ha-1 year-1 which increased with soil organic matter content, management intensity and experimentally induced climate change. Hence, a new paradigm for organic grassland fertilization is needed: the soil, not the plant is fertilized.
Both open slot slurry injection and traditional management with farmyard manure strongly reduced N losses compared to broadcast spreading of slurry, thereby leading to more closed N balances and counteracting N mining. However, slurry injection was more effective for acid soil rather than calcareous soil, where slurry acidification could be more promising to reduce N losses. Slurry dilution with water promoted infiltration, productivity and reduced N losses but avoided N mining only when N fertilizer amounts were maintained at the same level, which increases costs for farmers and the risk for soil compaction. In this context, slurry separation into liquid and solid phases is helpful.
In sum, we recommend either intensive grassland management with targeted low emission fertilization when productivity and fodder quality is prioritized, or extensive grassland management with grazing and fertilization with farmyard manure when soil organic matter formation and biodiversity is prioritized. Coexistence of these two diverging management approaches rather than applying medium management intensities is recommended to maximize both economical and ecological soil functions and ecosystem services at landscape scales.
How to cite: Dannenmann, M., Piatka, D., Floßmann, S., Ramm, E., Kepp, J., Han, J., and Kiese, R.: Towards more sustainable organic grassland fertilization – a synthesis based on full N balances, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20471, https://doi.org/10.5194/egusphere-egu26-20471, 2026.
Mountain pastures in the Alps are cultural landscapes that have been shaped over centuries by traditional grazing practices. These pastures harbour unique biodiversity and provide multiple ecosystem services, such as forage production and soil carbon sequestration. However, in recent decades, socio-economic changes have led to a widespread decline in mountain agriculture, resulting in pasture abandonment and woody encroachment. This study assesses how early successional woody encroachment affects soil carbon storage and nutrient dynamics along an elevation gradient.
To this end, 15-metre transects were randomly placed within non-encroached and encroached areas (with >20% cover of juvenile trees) of eight mountain pastures, which ranged in altitude from 680 to 1270 meters above sea level in the Berchtesgaden National Park in the Northern Limestone Alps in Germany. Soil samples were taken to a depth of 30 cm and analyzed for total organic carbon (TOC), total nitrogen, and available phosphorus (Olsen-P). Bulk density was also measured, and nutrient stocks were calculated.
TOC and nitrogen concentrations, as well as Olsen-P, were significantly higher with encroachment, while carbon and nitrogen stocks showed no significant differences between encroached and non-encroached transects. The effect on TOC was more pronounced in the upper soil layer; in the lower layer, elevation and aspect also significantly affected TOC levels. The magnitude of the TOC increase in encroached sites could be partially explained by soil pH. These results highlight the variable effects of woody encroachment on nutrient and carbon dynamics, which depend on the successional stage, elevation, aspect and parent material.
How to cite: Kopp, C., Stilp, L., Mutz, V., Bott, M., Panassiti, B., Ewald, J., and Rufino, M.: Soil Carbon and Nutrient Responses to Woody Encroachment in Alpine Grasslands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17042, https://doi.org/10.5194/egusphere-egu26-17042, 2026.
Stony soils are very common in non-agricultural landscapes. Yet, characterizing the hydraulic properties of stony subsoil is necessary but technically complex.
In this study, we aim to improve the characterization of stony subsoils by addressing two critical aspects: (i) the estimation of coarse fragment content and (ii) the water retention of stones. Both factors potentially influence plant available water capacity - a key input for many hydrological models - and its uncertainty, yet they are rarely quantified in deep horizons.
Our methodology involved eleven forest sites in Wallonia (Belgium), where soil pits were excavated down to 2 m depth to capture the vertical variability of soil texture, stoniness, hydraulic properties. Coarse fragment content was assessed by horizon using four approaches: two in situ methods and two laboratory-based methods applied to samples of different sizes. Additionally, we carry out measurements on stones to measure available water between field capacity and wilting point.
Preliminary results underline the importance of adapting soil sampling volume and method to the degree of soil heterogeneity to quantify stone water availability at the profile scale. Our results also indicate that certain rock types can hold up to 15 % of their volume of plant available water, challenging the common assumption that their contribution is negligible.
How to cite: Doat, A., Vincke, C., and Javaux, M.: Challenges in estimating plant available water in stony forest soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5788, https://doi.org/10.5194/egusphere-egu26-5788, 2026.
Increasing soil organic carbon (SOC) stocks while maintaining high crop productivity remains a critical challenge in paddy-based cropping systems. Widely adopted conservation practices, such as no-till and straw mulching, often show limited potential for subsoil carbon sequestration and may even reduce yields under flooded conditions. Here, we evaluate a subsoil-oriented management practice, ditch-buried straw return (DB-SR), designed to address both constraints simultaneously. Based on a 15-year rice–wheat rotation field experiment, DB-SR significantly increased SOC stocks at 0–40 cm depth by 46%. DB-SR also increased grain yield by 15% without additional fertilizer inputs. Moreover, DB-SR reduced net CO₂-equivalent emissions by 34% and increased net economic benefits by 18%, indicating clear environmental and agronomic advantages. A meta-analysis of field studies across China further confirmed that DB-SR consistently outperformed other straw return and tillage practices in promoting subsoil SOC accumulation and increasing crop yield. Overall, our findings suggest that DB-SR shows strong potential as a subsoil management strategy to enhance subsoil carbon sequestration while sustaining high crop productivity.
How to cite: Li, Z., Kan, Z.-R., Wulf, A., Zhang, H.-L., Rattan, L., Bol, R., Bian, X., Liu, J., Xue, Y., Li, F.-M., and Yang, H.: Sustainable subsoil management promotes soil carbon sequestration while sustaining crop productivity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5939, https://doi.org/10.5194/egusphere-egu26-5939, 2026.
Different soil management practices and crop species can significantly influence the plant water and nitrogen use. However, how this affects the plant nitrate (NO3-) and water use efficiency from different soil depths, particularly from deep subsoil layers, remains unclear. In this study, we aimed to investigate variations in plant water and nitrogen uptake efficiency across topsoil and subsoil layers under till and no-till soil management practices. A mixture of 2H2O and Ca (15NO3)2 was injected into the soil columns at depths of 20 cm, 60 cm, and 90 cm using customized suction cups in both till and no-till plots. During the installation of the suction cups, soil samples were taken from 10–20 cm, 50–60 cm, and 80–90 cm depth intervals for subsequent nitrate analysis. Aboveground plant tissues were sampled from winter wheat and maize at two field sites in 2025 as an initial test of the method. We plan to expand this approach to five sites across different European countries in 2026. Plant material was collected on the fourth- and eighth- days following tracer injection, including tillers from winter wheat and top leaves, cobs, and stems from maize. The experimental setup provides a promising approach for tracing plant uptake from different soil depths, especially subsoil. We anticipate that this method will help identify variations in plant water and nitrogen uptake across different soil depths and may become a method that allows more routine inclusion of the subsoil in different studies of plant water and nitrogen uptake. This work will contribute to ongoing efforts to evaluate the impacts of conventional and sustainable soil management practices on resource use efficiency.
How to cite: Li, Q. and kristensen, K. T.: Tillage effects on plant water and nitrate uptake compare topsoil to subsoil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7169, https://doi.org/10.5194/egusphere-egu26-7169, 2026.
DeepHorizon is a Horizon Europe Soil Mission project which aims to uncover hidden potential of European subsoils, an overlooked but vital component in soil functioning. Knowledge of subsoil dynamics, functions and degradation remains limited, and the pressure of unsustainable land management practices (LMPs) and climate change are increasing. To address this, DeepHorizon is leveraging multi-disciplinary collaborations across 19 international institutions to i) map subsoil properties, ii) identify sustainable subsoil management practices, and iii) develop and refine user-oriented tools to monitor and improve subsoil health.
The initial sampling campaign is underway, with 19 of our 40 sites sampled, which will be completed by the end of Autumn this year. Excavating a soil trench up to 2-meters provides comprehensive physical, chemical and biological data to capture subsoil properties including soil texture, pH, Carbon, Nitrogen and other nutrients, X-ray CT, hydraulics, root length density, fauna, microbiology and more. These data will contribute to a better representation of subsoils in existing databases and calibrate two process-based models to improve representation of subsoil functions.
These models will be validated across 100+ test sites and 3 regional case-study areas (CSA), then adapted to suit the needs of end-users through farmer- and manager-friendly tools. The project will also assess the socio-economic impact and environmental trade-offs of LMPs to generate policy recommendations and incentives to propose the sustainable management and restoration of European subsoil.
To ensure widespread impact, DeepHorizon engages land managers, researchers and policymakers through Community of Practice (CoP) and targeted outreach and communication activities. To facilitate the work planned on future test sites and case study areas, we are looking for constructive feedback, synergies, and collaborations that may be available across existing projects, institutions or individuals.
How to cite: Javaux, M., Wadoux, A., Chabbi, A., Di Bonito, M., Falsone, G., Koenig, S., Vogel, H.-J., Burgeon, V., Michaiidis, A., Miglio, E., Blanco Velasquez, F. J., and Wardak, L.: DeepHorizon: DEploying Ecosystemic solutions to imProve soil Health and uncOveRing subsoil functIons in the critical ZONe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21994, https://doi.org/10.5194/egusphere-egu26-21994, 2026.
Subsoils represent an important yet poorly studied component of terrestrial ecosystems. By storing large quantities of water, carbon and nutrients, the subsoil has the potential to support plant productivity. Especially during dry spells, which are assumed to intensify with climate change, subsoil water resources provide a valuable buffer to reduce water stress. However, deep root growth is frequently hampered by the presence of root-restricting layers, such as dense subsoil horizons. Hence, subsoil management options should be established to support plant growth.
We conducted field experiments in arable regions in Germany and South Africa to test whether soil water storage and crop water use efficiency (WUE) could be enhanced through subsoil amelioration by biological and mechanical deep loosening in combination with the incorporation of organic material.
We analyzed stable oxygen isotope (δ18O) values at different soil depths to determine water uptake depth using the Bayesian statistical model MIXSIAR. A dual-isotope approach using carbon (δ13C) and oxygen isotopes in plant biomolecules was also applied to investigate crop water use efficiency of.
The findings demonstrate that the success of subsoil management depends on soil type. In sandy soils, mechanical deep-loosening promoted root water uptake from deeper soil layers and improved biomass production. In contrast, in silty soils, only biological deep-loosening showed positive effects. However, the associated increase in biomass production intensified water stress in the crops. This effect can be mitigated by compost applications, which enhanced soil water retention and promoted root growth into deeper layers, leading to an improved water supply for crops.
How to cite: Eitelberg, L., Amelung, W., Kotzé, E., Ceronio, G., Kathlin, S., Oliver, S., and Sara Louise, B.: Impact of subsoil melioration on water use of arable crops: case studies from Germany and South Africa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10372, https://doi.org/10.5194/egusphere-egu26-10372, 2026.
Earth system models are increasingly adopting multi-layer soil frameworks to improve simulations of vertical carbon distribution. A critical parameter in these models is the e-folding depth (zτ), which quantifies the rate at which soil organic carbon (SOC) ages with depth. Specifically, zτ represents the soil depth at which carbon becomes e-times older (≈2.7 times older) than surface carbon. Despite its importance, most models assume constant zτ within biomes, leaving its spatial variability largely unclear. To test this assumption, we collected multi-layer soil samples across eight forest plots spanning a subtropical montane elevational gradient (427 to 1,474 m) and employed radiocarbon dating to quantify vertical SOC aging patterns. Our results revealed a robust exponential increase in SOC age with depth at all elevations, alongside a 66% decline in zτ from 78.6 cm at the base to 26.4 cm at the summit. This indicated that a 1-meter increase in soil depth approximately amplified SOC age by 4-fold at the lowest elevation and 44-fold at the highest position. Despite significant changes in vegetation along the elevational gradient, vegetation type did not play an essential role in controlling zτ variability. Instead, this elevational dependence of zτ was primarily driven by soil water content (22.2% of variability explained), mean annual temperature (19.7%), and soil carbon-to-nitrogen ratio (19.0%). These findings suggest zτ as an elevation-sensitive sentinel of soil carbon dynamics, urging models to incorporate its variability for projections of soil carbon persistence under climate change.
How to cite: Li, W., Wang, J., Sun, H., Wei, N., Yan, L., Zhang, J., and Xia, J.: Faster soil carbon aging with depth at higher elevations in a subtropical forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11079, https://doi.org/10.5194/egusphere-egu26-11079, 2026.
The root zone is one of the most important soil horizons through which plant obtains its needs of nutrient and water resources, especially for deep rooted plant. However, few studies exist on the multi-fractal of soil particle size distribution and its great influence on soil chemical properties and soil water status in the root zone for a deep soil profile, with most knowledge gained from shallow rooted plant. We obtained multiple soil profiles with the maximum rooting depth to 21 m, and applied single fractal and multifractal dimensions to characterize the soil particle size distribution, and explored their correlations with soil depth, soil chemistry properties and soil water. Our results found single fractal and multifractal dimensions of soil PSD and soil particle composition (clay, silt and sand content) varied with soil depth in a soil profile that can be categorized according to above and below the depth corresponding to 90% of the total root biomass as R-zone and D-zone, respectively. Soil fractal dimensions except capacity dimension (D1) and correlation dimension (D2), and clay and silt content differed significantly in the R-zone and the D-zone (p < 0.01). Correspondingly, the relationship between the soil PSD and soil chemical properties were higher in the R-zone than those in the D-zone. From the R-zone to the D-zone, the correlations between D1 and D2 and soil water content in dried soil layers changed from positive to negative. Based on these results, we concluded that more heterogeneity of soil physicochemical properties in the R-zone than the D-zone. Our findings highlight the importance and complexities of soil physicochemical properties in the root zone, some of which are valuable to characterize root function in the Critical zone and form integral components of vegetation models.
How to cite: Zhou, Z.: Using multi-fractal analysis to characterize the variability of the soil physical-chemical properties along deep soil profile through multipoint sampling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17549, https://doi.org/10.5194/egusphere-egu26-17549, 2026.
Soil enzymes are major contributors the decomposition of soil organic matter. They are believed to reflect microbial nutrient and energy acquisition strategies and limitations. Whilst enzyme activities in surface soil layers have been widely studied, activities down the soil profile have received far less attention. Here, we present the results of a meta-analysis of hydrolase and oxidoreductase activities involved in the C, N and P cycles as a function of soil depth. The aim of the analysis was to understand how the relationship between microbial communities and their nutritional environment changes with depth. We assembled a database of ~1500 soil profiles from diverse locations, soil types, land uses and climates. In order to compare activity profiles, we used Gaussian process regression, followed by hierarchical clustering. Our results show that, when expressed per soil mass, the majority of hydrolase activities decrease with increasing soil depth. Proportionally more oxidoreductase activities, however, remained stable with depth, possibly indicative of changes in microbial community resource acquisition strategies with depth. Microbial biomass specific enzyme activities tended to increase with soil depth, suggesting an increase in microbial allocation to resource acquisition in response to decreased resource (C, N and P) availability and/or an increased enzyme stabilization on mineral and organic surfaces.
How to cite: Nunan, N., El Mekdad, F., Abiven, S., and Raynaud, X.: Enzyme activities down the soil profile: a meta-analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17058, https://doi.org/10.5194/egusphere-egu26-17058, 2026.
Multi-species grassland mixtures are gaining popularity in managed grasslands, particularly as a strategy to improve soil functioning and subsequently soil health and climate regulation. However, mechanistic data on the relation between plant diversity and the greenhouse gas (GHG) balance of the soil are still sparse. We conducted a full-factorial mesocosm experiment to determine whether multi-species grassland mixtures can enhance the delivery of ecosystem services compared to traditional perennial ryegrass monocultures. Treatments included two plant communities, two soil types and three cutting frequencies - representing land use intensities under controlled conditions. We measured effects on greenhouse gas (GHG) effluxes (CO2, CH4 and N2O), above- and belowground productivity as well as functional catabolic diversity of soil microbes Linear Mixed Models (LMMs) revealed that plant community and soil type impacted all greenhouse gas effluxes, while cutting frequency only impacted CO2 efflux significantly. Multi-species grass mixtures significantly elevated primary productivity compared to perennial ryegrass monocultures, and influenced functional microbial diversity, even overriding soil type (and therefore legacy) effects on functional microbial diversity over a short timeframe. These improvements in soil functioning can improve the delivery of crucial ecosystem services such as climate regulation, food and feed production and soil habitat and nutrient cycling, which underlines the potential of species-rich grassland mixtures in multifunctional grassland farming systems. Future research should explore long-term field dynamics and validate these findings by making carbon budgets to support climate-smart management strategies.
How to cite: Tersago, R., Meersmans, J., Van Eupen, C., Aernouts, B., van Groenigen, J.-W., Desie, E., and Vancampenhout, K.: Multi-species grass mixtures enhance soil functioning in managed grassland mesocosms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-292, https://doi.org/10.5194/egusphere-egu26-292, 2026.
Grassland ecosystems form a cornerstone of terrestrial ecological security and support the livelihoods of millions of people worldwide. Under the combined influences of climate change and human activities, grassland degradation unfolds with pronounced spatiotemporal heterogeneity and marked nonlinearity, features that are particularly evident in ecological transition zones. Here, we focus on the agro–pastoral ecotone of northern China and integrate multi-source remote sensing and geospatial datasets to develop a grassland degradation assessment framework benchmarked against potential maximum net primary productivity(NPPmax). Adopting a change-pathway perspective, we identify long-term trajectory types of grassland degradation and recovery and quantitatively examine their underlying drivers. Our analyses reveal that degradation and recovery processes across the region are largely nonlinear, with abrupt, threshold-like shifts being spatially widespread. Although recovery trajectories dominate at the regional scale, a considerable fraction of grasslands remains locked in persistent moderate to severe degradation, and clear spatial differentiation emerges among trajectory types. Climatic factors primarily shape long-term trends in grassland productivity, while human activities play a pronounced amplifying role: they can accelerate rapid recovery under favorable climatic conditions, yet also precipitate sudden, localized degradation. By moving beyond single rates of change to emphasize dynamic pathways, this study deepens understanding of grassland degradation processes in agro–pastoral ecotones. Our findings underscore the importance of simultaneously accounting for climatic context and human regulation in grassland management and ecological restoration. The proposed framework and insights provide a strong scientific basis for zoned management, risk early warning, and adaptive strategies in ecologically vulnerable regions, and hold broad relevance for ecological transition zones worldwide.
How to cite: Li, W., Zhang, C., and Wang, X.: Nonlinear Grassland Degradation and Recovery Benchmarking Potential Productivity: Evidence from the Agro–Pastoral Ecotone of Northern China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3871, https://doi.org/10.5194/egusphere-egu26-3871, 2026.
Canadian grasslands are endangered ecosystems, with nearly two-thirds converted to cropland. Restoring cropland to grassland can help reintroduce biodiversity through the planting of native vegetation, increase soil carbon (С) storage, and reduce greenhouse gases through the establishment of perennial plants. However, grassland restoration is expensive and done primarily on private lands. Consequently, restoration must also benefit farmers by providing forage for livestock and creating healthy, resilient soils.
In the past, few grassland sites have been monitored long-term for soil C accumulation following restoration in the Canadian Prairie, despite the slow rate of change in soil C over time, and even fewer have examined deeper soils (beyond 30 cm).
This study addresses the following questions:
1) How do soil organic and inorganic C pools vary with depth and restoration age?
2) Do these sites also provide other important soil functions and support forage production?
To answer these questions, we sampled 18 restored grassland sites across southern Alberta and Saskatchewan, Canada, spanning a chronosequence from pre-restoration (0 years) to 24 years since seeding. Restoration practice involved a one-time seeding of a mix of native and agronomic plant species, along with exclusion from grazing during the early and mid-growing seasons (April-July) in the year following seeding. Sites were characterized based on local climate conditions and soil properties.
Soil samples were collected in May-June 2024 at depths of 0–15, 15–30, 30–60, and 60–100 cm. Soil samples were analysed for organic and inorganic C, moisture, texture, pH, and electrical conductivity. Plant surveys and biomass harvests were conducted in July 2024 to examine community composition and forage production. Climate variables were summarized using the annual heat-moisture index. Soil C and function, and vegetation responses to restoration were assessed using two complementary approaches: (1) chronosequence analysis to test space-for-time assumptions and assess temporal patterns in soil C pools, and (2) AICc-based model selection to quantify the relative influence of vegetation, climatic, and edaphic predictors.
Local climate and soil conditions played a dominant role in the rate of grassland restoration and C distribution within the soil profile, while established plant community composition was associated with changes in soil C storage and forage quality. This study provides a robust evaluation of space-for-time substitution for soil C recovery by examining organic and inorganic C responses across the one-meter soil profile using a large set of restoration sites, addressing limitations of previous studies. Together, these results improve understanding of soil and vegetation responses to restoration and provide new information for producers and policymakers supporting grassland restoration management.
How to cite: Kaliaskar, D. and Carlyle, C.: Does space-for-time substitution capture soil carbon recovery in restored dry grasslands of Canada?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4573, https://doi.org/10.5194/egusphere-egu26-4573, 2026.
Agricultural soils are significant sources of N2O, and they have been estimated to be responsible for about 60% of global anthropogenic N2O emissions. These emissions mainly originate from the application of synthetic fertilizers. Globally, 120 Tg N of new N as synthetic fertilizer is introduced to soil every year to sustain crop and grass production. Agricultural sector is responsible for 14% of the total anthropogenic greenhouse gas (GHG) emissions in Finland, from which 54% are N2O emissions. Growing season in Finland is relatively short (May-September) and all the grazing and feed production happens during those months. About 35% of Finland's cultivated arable land is cultivated with forage. With optimized management practices, such as crop species selection and timing of fertilization, N2O emissions from agricultural fields and per units of feed produced could be reduced. Since N2O is the most potent GHG, even small reductions in its emissions can yield significant climate benefits.
Introducing legumes, such as red clover (Trifolium pratense), to crop rotations reduces the need of synthetic fertilizers, due to the ability of the legumes to fix their own N via a symbiosis with rhizobia bacteria. Previous studies have shown lower N2O fluxes in red clover grass mixtures compared to monocultures and grass mixtures with other grass species. Lower levels of synthetic N fertilization also reduce indirect N2O and CO2 emissions which are generated during the fertilizer manufacturing process. In mineral soils, highest N2O emission peaks are often measured after fertilization events. The fertilizer induced emission peak can be reduced by shifting the timing of fertilization, e.g. week after harvest, when plants are in active growth phase and can utilize nutrients more efficiently.
In this research we tried to answer to two research questions: 1) Do annual N2O emissions from the agricultural field to the atmosphere decrease with increasing red clover coverage? 2) How does the timing of post-harvest fertilizer application influence subsequent N2O emission peaks? The research was conducted in a 6.3 ha agricultural field on a mineral soil, near Maaninka, eastern Finland. N2O exchange of the field was studied using the eddy covariance technique from four years of grass rotation cycle (2022–2025). Crop, soil and environmental variables were also measured to help explain the N2O exchange patterns and N dynamics. We hypothesized that delaying the fertilizer application by approx. one week after harvest decreases the resulting N2O emission peaks and that annual N2O emissions from the agricultural field to the atmosphere decreases with increasing red clover coverage. In this presentation, we highlight the changes in red clover coverage, total yield, N2O emissions originating from fertilization and the annual N2O dynamics.
How to cite: Manninen, P., Vesala, T., Peltola, O., Rinne, J., and Shurpali, N.: How timing of fertilization affects N2O emissions from a legume grassland on northern mineral soil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11005, https://doi.org/10.5194/egusphere-egu26-11005, 2026.
Drought events are increasingly threatening soil organic carbon (SOC) stability in grasslands, yet the role of grassland management in shaping drought and post-drought responses of SOC remains poorly constrained. We examined how grassland management intensity influences microbial respiration responses during drought and recovery, including the Birch effect (a pulse of soil CO2 release following rewetting of dry soils) and SOC priming (changes in SOC decomposition triggered by fresh carbon inputs). These responses were assessed in a controlled soil incubation study with experimentally imposed drought, using soils from grasslands covering a range of management types and elevations.
Grassland management strongly altered soil and root properties, including SOC content, fine-root biomass, and bulk density, and caused distinct soil microbial respiration dynamics in response to drought. Respiration was more strongly reduced by drought in soils from intensively managed grasslands, while its recovery from drought was not affected by management intensity. Similarly, the magnitude of the Birch effect following rewetting varied little among management types. In contrast, SOC priming differed strongly among sites and management regimes. Our results suggest that management-induced changes in soil structure and carbon pools modulate SOC responses to drought and subsequent carbon inputs.
How to cite: Protti-Sánchez, F., Kanis, L., Trubnikova, T., Wachter, H. A., Vindušková, O., Biasi, C., and Bahn, M.: Grassland management affects soil carbon responses to drought, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11442, https://doi.org/10.5194/egusphere-egu26-11442, 2026.
Nitrous oxide (N2O) is one of the main greenhouse gases (GHG), and it occurs particularly in agricultural soils due to fertilizer applications and livestock grazing. Cattle, for instance, excrete 75-95% of their nitrogen (N) intake. National N2O emission estimates for grazing cattle excreta are highly uncertain as they are typically calculated using global emission factors. A few countries including the U.S. and Australia use biogeochemical models to report N2O emissions from agricultural soils. In Switzerland, the biogeochemical model DayCent was successfully applied for simulations of N2O emissions from cropland with diverse crop rotations (dos Reis Martins et al. 2022; Wang et al. 2025) and mown grasslands with different mangement intensities (dos Reis Martins et al. 2024). However, it has not yet been validated for grazing pasture systems in Switzerland.
In this study, we aim to test DayCent for pasture systems in Switzerland, by a) examining how the grazing activities can be represented appropriately in the model, and b) to test the preformence of Daycent in reproducing observed N2O emissions.
Datasets from two Swiss field experiments in Posieux (Voglmeier et al. 2019; 2020) and Waldegg (Barczyk et al. 2024) were used. In both experiments, pasture N2O emissions had been measured by eddy covariance over several years (Posieux: 2013-2017; Waldegg: 2020-2023) and the pasture management like the timing of grazing and fertilising events was precisely documented. First, a sensitivity analysis of the model was performed by varying the main grazing parameter flgrem (fraction of live shoots removed by a grazing event) in DayCent. Secondly, the model was applied in two scenarios: GrazMod (using the specific grazing module of DayCent) and HarvFert (representing cattle grazing intake by harvests and excreta depositions by fertilizer applications).
For both sites, the amount of biomass N consumed by the cattle on the pasture varied between 2-30 g N m-2 yr-1 initially increasing in correlation to the flgrem value, however following a saturation curve at higher flgrem values. The amount of N excreted on the pasture was proportional to the amount of N consumed (DayCent default: 80%), which was close to the values estimated by a cattle N budget approach as used in the national GHG inventory. N2O emissions were higher for the HarvFert scenario, possibly due to a lower aboveground biomass which favors the emission loss of N. DayCent tends to underestimate the observed N2O emissions of both pastures. Further results of DayCent simulations will be shown and discussed.
How to cite: Barczyk, L. and Ammann, C.: How to model N2O emissions of grazed pastures with DayCent?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17164, https://doi.org/10.5194/egusphere-egu26-17164, 2026.
Agroecosystems integrate livestock and food production systems to meet global demands, but highly intensive management practices are often associated with soil degradation, erosion, and losses of soil carbon and biodiversity. In Mediterranean silvopastoral systems such as dehesas, grazing management plays a central role in regulating vegetation dynamics, nutrient cycling, and soil organic carbon storage. Understanding how different grazing intensities influence soil carbon stocks is therefore essential to support sustainable land management strategies in these systems.
This study examines the effects of contrasting grazing management intensities on soil carbon stocks and related soil properties within Mediterranean silvopastoral environments. Reforested areas without grazing were compared with two grazing systems characterized by different degrees of rotational intensity, allowing the evaluation of how grazing pressure and management strategies influence carbon distribution across ecosystem compartments. Field assessments to quantify aboveground and belowground carbon stocks included measurements of woody and herbaceous vegetation components, plant necromass, and soil carbon, with particular attention to spatial variability associated with tree canopy presence.
The results revealed consistent differences in soil carbon stocks among grazing management strategies, with lower grazing intensities generally associated with higher soil carbon accumulation compared to higher grazing intensity. The presence of grazing, when managed under rotational schemes, was linked to enhanced soil carbon stocks compared to unmanaged areas, suggesting positive interactions between livestock activity, vegetation turnover, and soil carbon accumulation. Tree canopy effects further influenced soil carbon distribution, highlighting the importance of spatial heterogeneity and vegetation structure in modulating soil carbon dynamics within silvopastoral systems. In addition, soil carbon stocks were closely associated with other indicators of soil fertility and nutrient cycling, reflecting broader changes in soil functioning linked to grazing management.
Acknowledgements
This work was funded by the project “Impact of grassland management on soil carbon storage-CARBOGRASS” (Project PCI2023-143386 funded by MCIN/AEI/ 10.13039/501100011033/EU).
How to cite: Mendes, L., Vázquez, E., Estrella, M., Almorox, J., Rubio, A., Cámara, J., and Benito, M.: Effects of Grazing Management Intensity on Carbon Stocks in Mediterranean Silvopastoral Systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19838, https://doi.org/10.5194/egusphere-egu26-19838, 2026.
Grasslands cover nearly 40% of the Earth’s terrestrial surface and store large quantities of carbon (C) in their soils. However, grassland-use intensification, unsustainable management practices and climate change threaten this important C reservoir. Understanding how different grassland use intensities (GUI) influence soil C stocks is therefore essential to promote C accumulation and improve grassland sustainability. Although many studies have addressed this issue in recent decades, most have been conducted at local or regional scales, limiting our ability to detect general patterns because the response of soil C to GUI is strongly context dependent. Therefore, disentangling management effects from pedoclimatic factors is crucial to improving our understanding of how grassland management influences soil C.
To address this knowledge gap, we investigated 46 grasslands across 15 sites located in Argentina, Colombia, Germany, Kenya, New Zealand, Spain and Switzerland, all sampled following a standardized protocol. Soil samples were collected at three depths (0–10, 10–20 and 20–30 cm) to quantify soil organic C and additional soil properties. Information on management practices was compiled for each grassland. Using livestock density (livestock unit grazing days ha−1 yr−1), the number of mowing events per year, and annual nitrogen fertilization (kg N ha-1 yr-1), we calculated the GUI index proposed by Blüthgen et al. (2012) which reflects the combined effects of these management practices.
Our sites span a wide climatic gradient, with mean annual temperature ranging from 0.8 to 27.4°C, precipitation from 518 to 2357 mm, and aridity index from 0.42 to 3.49. Tropical and subtropical grasslands were generally characterized by low grazing intensity and little or no N fertilization, whereas temperate sites often combined grazing, mowing and, in some cases, high N fertilizer inputs. As a consequence, we obtained a wide range of GUI index values, from 0 in unmanaged conservation grasslands to values >10 in intensively managed systems in Switzerland and Germany. Preliminary analyses suggest that both the aridity index and the GUI index may play an important role in explaining variation of soil C concentrations across sites, underscoring the importance of GUI in shaping soil C storage. Ongoing analyses incorporating additional explanatory variables (i.e. clay, bulk density, biomass production or soil pH) will provide deeper insights into the drivers of soil C dynamics in grasslands worldwide.
Acknowledgements
This research was developed within the framework of the European Joint Program for SOIL, "Managing and Mapping Agricultural Soils for Enhancing Soil Functions and Services" (EJP SOIL), project CARBOGRASS, funded by the European Union Horizon 2020 research and innovation program (Grant Agreement No. 862695). UPM was funded by Project PCI2023-143386 funded by MCIN/AEI/ 10.13039/501100011033/EU. ILRI was funded by the CGIAR Science Programs Climate Action and Multifunctional Landscapes.
Reference
Blüthgen, N., Dormann, C. F., Prati, D., Klaus, V. H., Kleinebecker, T., Hölzel, N., ... & Weisser, W. W. (2012). A quantitative index of land-use intensity in grasslands: Integrating mowing, grazing and fertilization. Basic and Applied Ecology, 13(3), 207-220.
How to cite: Vázquez, E., Rousset, C., Alfaro, M., Almorox, J., Arango, J., Banegas, N., Bastidas, M., Benito, M., Butterbach-Bahl, K., Colcombet, L., Dashpurev, B., Dodd, M., Gilgen, A., Leitner, S. M., Mendes, L., Merbold, L., Ngetich, F., Ntinyari, W., Rivera, J. E., and Chará, J.: Grassland use intensity and climate as key drivers of soil organic carbon across four continents, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17253, https://doi.org/10.5194/egusphere-egu26-17253, 2026.
Mountain grasslands play a crucial role in supporting biodiversity, grazing livestock, and regional water supply, while storing large amounts of carbon in their soils and vegetation. Grassland functioning is tightly coupled with climate and management practices, making these ecosystems highly vulnerable to global changes. The Afromontane grasslands of the Maloti-Drakensberg Mountains are among southern Africa’s most important ecological and hydrological systems, providing essential provisioning services. Despite their importance, surprisingly little is known about the impacts of global change drivers on carbon dynamics in these ecosystems. Filling this knowledge gap would improve our understanding of the extent of the Afromontane grasslands carbon sink, and help predict future carbon dynamics.
To address this gap, the NatuRA project has established a global change experiment in the Drakensberg Mountains focused on three global change drivers: warming, increased atmospheric nitrogen deposition, and changing grazing practices. The experiment spans an elevation gradient from 2000 to 3000 meters above sea level in a full factorial design made of a transplant treatment, nitrogen fertilization, and grazing manipulations. Measuring ecosystem carbon fluxes in this experimental design enables the assessment of how these drivers, individually and in interaction, affect key carbon-cycling processes.
Ecosystem carbon fluxes were measured using a closed-loop chamber system connected to an infrared gas analyzer. We measured net ecosystem exchange and ecosystem respiration, from which gross primary productivity was calculated. Pairing these results with treatment-specific microclimate data allows us to assess the amount of carbon captured by the ecosystem and evaluate how the carbon cycle responds to warming, fertilization, and grazing intensity. By revealing how multiple global change drivers interact to shape carbon dynamics in the Drakensberg Mountains, this study can provide critical evidence for predicting the future role of these ecosystems and for informing sustainable land management in a rapidly changing climate.
How to cite: Dam, A., Clark, V. R., Halbritter, A. H., Holzmann, K. L., le Roux, P. C., Vandvik, V., and Gaudard, J.: Afromontane Grassland Carbon Dynamics in a Changing World, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22428, https://doi.org/10.5194/egusphere-egu26-22428, 2026.
The agricultural sector's role in climate change is a topic of debate and uncertainty, particularly regarding the soil carbon sequestration effect of grasslands. Numerous studies have examined specific grassland sites using the net ecosystem carbon budget (NECB) approach based on the eddy-covariance (EC) method for measuring the CO2 exchange with the atmosphere and the quantification of ‘lateral’ carbon exports and imports (e.g., harvest and organic fertilizer application). Finding clear and consistent numbers is often complicated by issues of nomenclature and methodology of the carbon budget calculations and presentation in the literature or by missing information about management and lateral carbon flux details.
This review aims to synthesize current data on the NECB of European grasslands (excluding organic soils). For this purpose, a detailed search and screening of the currently available peer-reviewed literature regarding EC-based NECB of grasslands in Europe was conducted. Data for 43 different sites in 16 countries passed the screening and quality checks, totaling 147 site-years of NECB measurements. The gathered NECB data for grasslands are scattered over a large range of NECB values between about –350 and +350 g C m−2 yr−1. The overall average of −33 g C m−2 yr−1 indicates a slight carbon sink, although with a large uncertainty. We could not detect a significant spatial distribution pattern of source or sink sites. In addition, we found that sites at the same location can act as sources or sinks depending on the management practice of the fields. For an improved assessment, a more consistent and complete data reporting of all flux measurement sites would be useful.
How to cite: Ammann, C. and Schweizer, D.: Meta-analysis of the net ecosystem carbon budget of European grasslands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19975, https://doi.org/10.5194/egusphere-egu26-19975, 2026.
Grassland management practices, including frequent plant biomass removal, have intensified globally to enhance productivity. However, intensification leads to shifts in plant composition and plant–microbe interactions, with poorly understood implications for ecosystem functions, such as nutrient cycling, and their stability under climatic stress. We hypothesised that biomass removal frequency has an intermediate optimum at which plant–microbe–soil interactions stabilise ecosystem functions under drought, whereas both low and high removal frequencies reduce resilience to climatic stress. In a native managed African tropical grassland, we applied four above-ground biomass removal frequencies (1×, 2×, 3×, and 6× cuts annually). Intact soil-core mesocosms were grown under controlled conditions and subjected to drought stress in a split-plot, completely randomised design, combined with a 13CO₂ pulse-labelling approach. We determined plant productivity, photosynthetic 13C assimilation, belowground C allocation, arbuscular mycorrhizal fungi (AMF) colonisation, microbial biomass carbon (MBC), extracellular enzyme activities (EEAs), and rhizosphere microbial community structure to assess the impacts on C allocation and nutrient cycling. Under well-watered conditions, high biomass removal frequencies (3× and 6×) increased shoot productivity and 13C assimilation relative to low frequencies (1× and 2×). The EEAs (C, N, and P cycling) and proportion of 13C in rhizodeposits increased progressively with an increase in cutting frequency. Low cutting frequencies promoted fungal-dominated rhizosphere communities, particularly saprotrophic fungi, whereas high frequencies favoured bacterial dominance. Drought stress significantly reduced plant productivity, 13C assimilation and root biomass at high cutting frequencies. In addition, drought reduced 13C incorporation into total phospholipid fatty acids (PLFA) by 53% at high cutting frequencies and by 22% at low frequencies. Notably, despite significant reductions in root biomass and 13C assimilation under drought, root AMF colonisation and 13C allocation to soil AMF were consistently higher under drought and progressively increased with decreasing cutting frequency. This reflects a greater plant reliance on microbially mediated nutrient and water acquisition during drought. Overall, our results demonstrate that biomass removal frequency modulates drought impacts on rhizosphere nutrient cycling via shifts in plant functional traits, from resource-conservative (“slow”) to resource-acquisitive (“fast”) species, alongside a reshaping of soil microbial communities from oligotrophic to copiotrophic dominance. These findings highlight the inherent trade-offs between ecosystem productivity and an enhanced resilience to increasingly frequent and intense climate-change-induced stresses, underscoring the need for locally adapted management practices.
How to cite: Ngugi, M., Stock, S., Munene, R., Banfield, C., Shi, L., and Dippold, M.: Between Management Extremes: Moderation Sustains Plant Productivity, Rhizosphere Microbiome, and Nutrient Cycling in Drying Savannahs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5083, https://doi.org/10.5194/egusphere-egu26-5083, 2026.
Grassland stores approximately 20% of global soil organic carbon (SOC). While environmental conditions and management directly affect this storage, the role of functional diversity remains poorly quantified at large scales.
We conducted an assessment of functional diversity effects on SOC storage and productivity of managed grassland under climate change using the LPJmL-CSR model. We simulated low (FD-: single dominant strategy) and high (FD+: multiple strategies present) functional diversity under two climate scenarios (SSP1-2.6 and SSP3-7.0) from 1901 to 2100.
Results show substantial differences between scenarios. Under SSP1-2.6, SOC declined in FD- but remained stable in FD+. In contrast, under SSP3-7.0, SOC increased in both scenarios due to CO2 fertilization and increasing temperatures. For both climate scenarios FD- remained approximately 30% lower than FD+ by 2100. Productivity showed similar spatial and temporal patterns. Regional analysis revealed distinct mechanisms. In tropical climates, removing subordinate functional types reduced total productivity despite increased growth of remaining species, while in temperate regions, prevented adaptation to warming led to productivity breakdown.
Examining the underlying mechanism showed that functional diversity underpins the grassland communities’ potential to adapt to climate change allowing them to compensate for negative effects and acting as an insurance against climate change. To our knowledge, these results confirm findings from local-scale empirical experiments at the global scale for the first time. These findings have implications for carbon farming practices, where maintaining functional diversity could enhance long-term carbon sequestration potential.
How to cite: Wirth, S. B., Müller, C., Taube, F., Heinke, J., Tietjen, B., and Rolinski, S.: Functional diversity and grassland soil carbon stocks under climate change: Insights from global modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12265, https://doi.org/10.5194/egusphere-egu26-12265, 2026.
Grasslands cover a substantial part of the global ice-free land area (~40%) and they store about one third of the terrestrial carbon stock globally. These ecosystems and their significant carbon stocks are very susceptible to climate change and are often extensively managed for human use. This management, including grazing, cutting and fertilising is known to have an impact on carbon (C) and nitrogen (N) fluxes with implications for greenhouse gas (GHG) emissions and surface and groundwater pollution. In the Republic of Ireland, grasslands cover roughly 60% of the land area and the agricultural sector is the largest emitter of GHGs and contributes roughly 38% of national emissions. It is therefore critical to be able to understand and predict the interactions between management and GHG budgets. Land surface models can be an invaluable tool in this endeavour, allowing us to test a multitude of management practices and their interactions as an in sillico experiment.
We investigate the ecosystem C and N budgets as affected by long-term management of grasslands in the form of N addition (fertilizer, slurry i.e., organic N) and grazing over 50 years using the QUINCY LSM. Based on local management data, we test different N application rates across time (between 50 and 300 kg N ha-1 year-1) in combination with different grazing intensities (0.5 to 5 livestock units ha-1) and timing of grazing at four Irish grasslands. We show that applying yearly fertilizer amounts exceeding 150 kg N ha-1 does not significantly increase grassland aboveground net primary productivity (ANPP) and most N entering the system is lost through leaching and nitrous oxide (N2O) emissions, while no or very low N addition combined with grazing results in decreasing C storage We further use the resulting N addition and grazing scenarios to identify best potential practices for balancing C storage, GHG emissions and grassland productivity. Beyond providing insights into C and N cycling processes in managed grasslands, our study also points to a pathway for using complex process-based models to guide management practices and policy.
How to cite: Seitz, J., Lampard, E., Mirzaei, M., Murphy, R., Saunders, M., Gill, L., Murray, Á., Dunne, E., and Caldararu, S.: Forecasting carbon and nitrogen cycling from intensively managed grassland systems using the QUINCY land surface model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13743, https://doi.org/10.5194/egusphere-egu26-13743, 2026.
