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. Alongside this, advances in methods for monitoring and modelling rates of soil carbon loss or carbon sequestration in soils are key to inform political, agronomical, and geo-engineering approaches. 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.
Session assets
Understanding changes of soil organic carbon (SOC) contents is important to estimate the role of soils as emission sinks or sources. Agricultural land use has led to substantial losses of SOC and recent projections indicate continuous decreases on a European scale, while main drivers remain elusive. The German Agricultural Soil Inventory is currently resampling around 3,000 sites to determine decadal SOC changes. Here we present the trends in SOC stocks of the first 800 analysed sites. We identified significant losses of SOC stocks in cropland and grassland soils by approximately 4% in the upper half meter. Most SOC was lost from overall carbon rich soils. Our analysis will extend to the role of past land use changes and management to identify key drivers of SOC dynamics. In addition, mid-infrared spectroscopy will be used to explore the role of SOC quality and composition for determining the decadal SOC changes. Recently, we used compositional information, for example the relative composition of aliphatic to aromatic compounds, to identify SOC change direction at land-use change sites. A large spectral library is being built to extend this approach to the national Soil Inventory and thereby improve our biogeochemical understanding of bulk SOC trends and establish new indicators of such.
How to cite: Schiedung, M., Harbo, L. S., and Poeplau, C.: Changes in soil organic carbon stocks and quality on a national scale – Decadal trends of the German Agricultural Soil Inventory, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6891, https://doi.org/10.5194/egusphere-egu25-6891, 2025.
Afforestation of agricultural land is one of the main nature-based solutions to reduce emissions of CO2 to the atmosphere while possibly increasing soil carbon (SOC) stocks. However, information on high-resolution temporal dynamics in SOC are scarce. SOC sequestration after afforestation of former cropland has commonly been studied by the chronosequence approach. The advantage of such space-for-time substitution for estimating slow SOC change processes must be balanced against the spatial variation introduced. However, no previous studies extended the chronosequence approach with multiple repeated inventories for comparison and validation of observed SOC dynamics.
We conducted a long-term combined chronosequence/resampling study in a former cropland area afforested with oak (Quercus robur) and Norway spruce (Picea abies) over the past 50 years. Soil sampling was carried out in 1998, 2011 and 2022 in the same oak and spruce afforestation chronosequences to reveal inferred and true temporal trends in forest floor and mineral soil SOC to 25 cm depth. Sampling in adjacent cropland and a 200-year-old forest served as references for the overall SOC sequestration rates. The C sequestration in woody biomass was quantified to estimate the contribution of SOC stocks to ecosystem C sequestration. The objective was to study the decadal patterns in post-agricultural SOC change in afforested oak and Norway spruce by i) comparing chronosequence trends in forest floor and top mineral soil C stocks within and across the three sampling campaigns, ii) quantifying current rates of SOC stock change at stand level based on multiple sampling campaigns.
Forest floor C stocks followed a non-linear trend and levelled off after about 30 years towards 8.6 ± 1.2 Mg C ha-1 for spruce and 3.4 ± 0.9 Mg C ha-1 for oak. The chronosequence trajectory was largely validated by resampling, and decadal rates of forest floor C sequestration approached 0 after about 40 years. Chronosequence trends in topsoil SOC were similar for oak and spruce and increased across the three inventories by 0.29 ± 0.05 Mg C ha-1 yr-1 to a C stock equivalent to 75% of that in the 200-year-old forest after about 50 years. However, there was no detectable topsoil SOC change along the three chronosequences based on individual inventories. Repeated sampling revealed further temporal and species-specific dynamics. SOC sequestration rates in the periods 1998-2011 and 2011-2022 were positive in most stands, and particularly increased with stand age in the spruce stands older than 20 years. Norway spruce also sequestered most C in biomass.
We conclude that contrasting temporal change in forest floor and mineral soil C sequestration rates indicates a shift in C source-sink strength over 50 years. Three decades of forest floor C sequestration is shifted to increasing mineral soil C sequestration, and sequestration rates in both soil compartments were greater in Norway spruce than in oak. The chronosequence approach across all three inventories provided the best estimate of mineral soil C trajectories since afforestation, but repeated sampling revealed significant stand- and species-specific dynamics in soil C change even within a homogeneous former cropland area.
How to cite: Vesterdal, L., Rosas, Y. M., Mueller, C. W., and Yu, M.: Soil carbon sequestration after afforestation of former cropland: oak and Norway spruce chronosequences repeatedly sampled after 13 and 22 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6100, https://doi.org/10.5194/egusphere-egu25-6100, 2025.
Forestation is regarded as an effective strategy for increasing terrestrial carbon sequestration. However, its carbon sink potential remains uncertain due to the scarcity of large-scale sampling data and limited knowledge of the linkage between plant and soil C dynamics. Here, we conduct a large-scale survey of 163 control plots and 614 forested plots involving 25304 trees and 11700 soil samples in northern China to fill this knowledge gap. We find that forestation in northern China contributes a significant carbon sink (913.19±47.58 Tg C), 74% of which is stored in biomass and 26% in soil organic carbon, while soil inorganic carbon contributes minimally. Further analysis reveals that the biomass carbon sink increases initially but then decreases as soil nitrogen increases, while soil organic carbon significantly decreases in nitrogen-rich soils. A tradeoff between organic carbon (biomass + soil organic carbon) and inorganic carbon dynamics is also observed along water gradient. These results highlight the importance of incorporating plant and soil interactions, modulated by nitrogen and water supply in the calculation and modelling of current and future carbon sink potential.
How to cite: Hong, S. and Song, Y.: Tradeoffs between soil and plant carbon sink after forestation along water and nitrogen gradients, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4926, https://doi.org/10.5194/egusphere-egu25-4926, 2025.
Carbon sequestration in soils has been proposed as a strategy to mitigate greenhouse gas emissions in the agricultural sector. However, there is still much uncertainty regarding how carbon is sequestered and accumulated in soils. We conducted a six-month soil incubation study amended with 13C-labelled plant litter to investigate carbon sequestration along a hillslope in southeast Norway. The field, cultivated with cereals, exhibits a natural gradient in soil organic matter (SOM) content, pH and soil moisture. Eight rain exclusion shelters (excluding ~50% of the rain) were installed along the gradient for four months, after which soils were sampled to investigate the impact of soil conditions and short-term drought on carbon sequestration. Carbon and nitrogen contents, as well as stable isotope ratios, were measured in bulk soil and in particulate organic matter/mineral-associated organic matter fractions at both the beginning and the end of the incubation. 13C-CO2 was measured continuously throughout the incubation and used for allocating 13C to a two-pool model. Exoenzymatic activity was also measured to provide insights into nutrient cycling in the soil. Litter decomposition was found to be highest in soils with low SOC, high pH and low moisture.
How to cite: Kjær, S. T. and Dörsch, P.: Assessing carbon sequestration along a natural carbon gradient impacted by short-term drought , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6221, https://doi.org/10.5194/egusphere-egu25-6221, 2025.
The potential for soil carbon (C) sequestration strongly depends on the availability of plant biomass inputs, making its efficient use critical for designing net zero strategies. Here, we compared different biomass processing pathways and quantified the long-term effect of the resulting exogenous organic materials (EOMs) on soil organic carbon (SOC) storage. We estimated C losses during feed digestion of plant material, storage of manure, composting and anaerobic digestion of plant material and manure, and pyrolysis of plant material based on literature values. Then we applied the widely used SOC model RothC with newly developed parameters to quantify SOC storage efficiency, i.e., accounting for both processing losses and decomposition losses, of the different EOMs. Based on simulations for a 39-year long cropland trial in Switzerland, we found that the SOC storage efficiency is higher for plant material directly added to the soil (16 %) compared to digestate and manure (3 % and 5 % respectively). For compost, the effect was less clear (2 % ̶ 18 %; mean: 10 %) due to a high uncertainty in C-losses during composting. In the case of biochar, 43 % of the initial plant C remained in the soil, due to its high intrinsic stability despite C-losses of 54 % during pyrolysis. To provide robust recommendations for optimal biomass use, additional considerations such as nutrient availability of EOMs, environmental impacts of soil application, and life cycle assessments for the entire production processes should be included.
How to cite: Keel, S. G., Budai, A., Elsgaard, L., Hardy, B., Levavasseur, F., Liang, Z., Mondini, C., Plaza, C., and Leifeld, J.: Efficiency of plant biomass processing pathways for long-term soil carbon storage, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2248, https://doi.org/10.5194/egusphere-egu25-2248, 2025.
Soil degradation is one of the most significant challenges in modern agriculture. The loss of humic substances leads to a decrease in soil fertility and resistance to water and wind erosion, making soils more prone to the impacts of global climate change. One of the key strategies to combat soil degradation is the implementation of soil conservation practices aimed at increasing organic matter content in the soil.
Under conditions of a long-term stationary field experiment on typical low-humus chornozem, the effect of microbial products — plant residues biodecomposers — on the sequestration of labile carbon compounds in the soil under prolonged monoculture maize cultivation was investigated. An increase in the labile carbon content in the soil was observed in variants using the biodecomposers Ecostern Classic and Ecostern Bacterial + Ecostern Trichoderma by 0.11% and 0.18%, respectively, compared to the control. The obtained data on the increase in labile carbon content were confirmed by the dynamic determination of the organic matter transformation coefficient, the increase of which indicates enhanced microbiological processes in the soil and the predominance of organic matter synthesis processes over its mineralization. Thus, when biodecomposers were used, this indicator was significantly higher than in the control throughout the study period.
Focusing on the survival of the fungal bioagent from the Ecostern Classic and Ecostern Trichoderma products in the soil, the dynamics of the Trichoderma genus fungi population were monitored. The results showed an increase in the population of this micromycete in variants with the application of Ecostern Classic by an average of 19 thousand CFU/g of soil and, with the combined application of Ecostern Bacterial and Ecostern Trichoderma, by 34 thousand CFU/g of soil, compared to 28 thousand CFU/g of soil in the control. This indirectly indicates the survival of this bioagent included in the bioproducts.
During the determination of the soil eco-physiological diversity index using the BIOTREX technology (Community-Level Physiological Profiling method), it was found that in the control soil samples, the index was 3.66, whereas with the use of biodecomposers, it increased to 4.87–5.61, depending on the studied variant. Additionally, according to the BIOTREX assessment, the use of biodecomposers not only enhanced soil biodiversity but also improved its biological activity. The application of biodescomposers ensured an increase in maize grain yield compared to the control by 3.2 t/ha in the variant with Ecostern Classic and by 1.76 t/ha with the combined application of Ecostern Bacterial and Ecostern Trichoderma.
It was found that the application of a biodecomposer on corn residues accelerates their transformation and ensures the sequestration of labile carbon compounds. Microbial decomposers also enhance microbiological processes in the soil, leading to a predominance of organic matter synthesis over its mineralization, which is crucial for mitigating soil degradation.
How to cite: Khomenko, T., Bolokhovska, V., Bolokhovskyi, V., Lunhul, A., Zhurba, M., Yakovenko, D., Bukhonska, Y., and Boroday, V.: The Effect of Biological Decomposers on Soil Carbon Sequestration to Mitigate Soil Degradation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8320, https://doi.org/10.5194/egusphere-egu25-8320, 2025.
Carbon capturing using modified agricultural practices appears to be a prominent strategy for climate mitigation, because the accrual of soil organic carbon (SOC) and its maintenance also provide many agronomic advantages. Previous studies have estimated the global SOC capturing potential as the gap between the mineral-associated organic carbon (MAOC) capacity—considered the upper limit for long-term SOC accrual—and current MAOC stocks, providing promising results. State-level estimates of SOC capturing potential using this methodology can better inform policy on how to maximize C capturing. Here we aimed at quantifying the current potential for SOC capturing in agricultural soils in Israel. Gridded geographical information on soil texture and land use was compiled for an area of 390,000 ha, encompassing field crops (180,000 ha), orchards (90,000 ha) and rangeland (110,000 ha). A bulk density-texture function was derived from published literature; and the typical capacitance for MAOC of the soils in Israel was estimated at a value of 48 g C kg-1 silt+clay based on samples of the organic-rich top-soils in planted forest sites. The MAOC capacity to a depth of 20 cm in all the agricultural soils of Israel was estimated at a total of 25.1 Mt C (92 Mt CO2-eq). Field crops were associated with the highest capacity followed by rangeland and orchards. In the field crops, the regions with the highest capacity were the Northern Valleys where clay-rich soils are abundant and the semi-arid Negev region, where the expansive agricultural land area compensates for the abundance of sandy soils. Sporadic information published from trials on field crops in the Northern Valleys and the Negev show that current SOC there only amounted to 41% and 30% of the estimated MAOC capacity for those sites (respectively). While the low SOC filling in the semi-arid Negev might carry promise for a large capturing potential, it also raises questions whether the hot climate does not further limit SOC to values below the MAOC capacitance. For orchards, scant data exists regarding current SOC levels. However, we propose that the possibility of storing SOC in deeper soil layers in orchards might offer substantial carbon storage potential at the national scale, a topic still requiring investigation. Overall, despite the uncertainty involved in this work, our study provides a foundational framework for policymakers to develop carbon management strategies in Israel, while highlighting knowledge gaps to guide future research.
How to cite: Yalin, D., Mlelwa, W., Rotenberg, E., Yakir, D., Eshel, G., and Grünzweig, J. M.: Estimating the total soil organic carbon capturing potential of agriculture in Israel to inform country-wide carbon policy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15768, https://doi.org/10.5194/egusphere-egu25-15768, 2025.
The formation of mineral-associated organic matter (MAOM) from plant litter decomposition is pivotal for climate change mitigation. However, the way in which plant litter of varying qualities influences MAOM formation and decomposition, particularly regarding the quantity of litter inputs, remains largely unclear. This study aimed to determine how the quality (C/N) of straw (low-quality (high-C/N) wheat (Triticum aestivum L.) versus high-quality (low-C/N) milk vetch (Astragalus sinicus L.)) and its quantity (input level) affect MAOM formation and decomposition. We conducted a 420-day laboratory incubation experiment using low-quality wheat versus high-quality milk vetch straws added to artificial soil (pure quartz vs. soil with reactive minerals (sandy soil: 5% clay, 10% silt, and 85%)) at input levels of 0, 3, 6, 18, 26, 31, and 35 g C kg-1 soil. Contrary to the Microbial Efficiency-Matrix Stabilization theory, our research indicates that adding high-C/N (low-quality) wheat straw addition led to a significantly greater MAOM content than milk vetch. Notably, the MAOM stabilization efficiency declined at high input levels (26, 31, and 35 g C kg-1 soil) for wheat than for milk vetch. This is further supported by the evidence that reactive minerals slowed the decomposition rate of high-C/N (low-quality) wheat straw more effectively than that of low-C/N (high-quality) milk vetch. Moreover, the lower C:N ratio of the MAOM fraction, the reduced C:N ratio of dissolved organic matter (DOM), and a higher fluorescence index of DOM (higher values indicating greater contribution of microbial sources) after adding wheat straw than adding milk vetch straw suggest the significant role of plant-derived organic matter in MAOM formation. Our findings disclose that reactive minerals preferentially protect high-C/N (low-quality) litter over low-C/N (high-quality) litter through direct interaction with plant-derived organic matter, providing a critical pathway for MAOM formation distinct from microbial assimilation. This study highlights the key role of high-C/N (low-quality) straw in the efficient and long-term stabilization of soil C within agricultural practices.
How to cite: Ji, X., Colinet, G., and Feng, W.: High-C/N straw inputs lead to higher mineral association organic matter than low-C/N straws, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6738, https://doi.org/10.5194/egusphere-egu25-6738, 2025.
As part of the EU-Interreg project ‘Blue Transition – How to make my region climate resilient’, this study targets the climate change resilience of organic matter stocks and soil fertility in agricultural soils in a study region in Lower Saxony, Germany. The Federal Institute for Geosciences and Natural Resources together with the regional water authority (Water authority of Oldenburg and East Frisia) investigates options to adapt agricultural management practices to change the trajectory of the observed organic matter losses at many agricultural sites in the region.
Considered adaptations include the optimization of fertilizer application, tillage practices, crop rotations and choices in catch crop as well as a one-time deepening of the topsoil layer depth by 5 cm to increase the soil volume for potential organic matter accumulation.
The long-term development of carbon stocks is estimated by simulating the carbon and nitrogen dynamics in the soil in response to site-specific soil and weather conditions, management practices and adaptations thereof. The dynamics are modeled using the Soil-Vegetation-Atmosphere-Transfer-Model Daisy. The model analysis highlights the potentials and limitations of different management adaptations. It also shines a light on the implications for the pollution of groundwater resources by nitrate leaching as a byproduct of efforts to increase soil carbon stocks.
How to cite: Bahlmann, L., Stadler, S., and Stange, C. F.: Fostering Soil Organic Matter Stocks by Adapting Agricultural Management Practices – A Model Analysis , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15842, https://doi.org/10.5194/egusphere-egu25-15842, 2025.
Healthy soils with high carbon content not only enhance agricultural productivity but also serve as significant carbon sinks, by sequestering atmospheric carbon dioxide. Understanding soil organic carbon dynamics is paramount for devising effective climate change mitigation strategies. In our study we analyzed the effect of a continuous dissolved organic matter (DOM) input in a Luvisol under three different land uses: grassland (GR), miscanthus (MI) and bare fallow (BF). We wanted to test if we could observe a maximum carbon content in the smaller fraction (<20μm), comparing our results to our calculations based on regressions for theretical saturation limits taken from the literature. We used a DOM-rich solution and irrigated the samples twice per week for 6 weeks. The GR and MI treatments surpassed the calculated theoretical limit by approx. 20%, contrary to BF which only reached approx. 70% of this theoretical limit. By the end of week 4, even though the carbon input was never interrupted, we observed a limited microbial respiration. It implies that the microbial communities might have focused on POM transformation, contrary to the expectation of them choosing the provided DOM. We also analyzed the change in available specific mineral surface area (SSA) through the experiment and detected a decrease for all the treatments, in line with the results for carbon content. Finally, we calculated the approximated leached carbon for each treatment. Our findings challenge the conventional notion of carbon saturation and underscore the importance of considering soil management practices and environmental conditions, contributing to advancing knowledge in soil carbon dynamics and emphasizing the critical role of adequate soil management in building a sustainable and climate-resilient future.
How to cite: Bucka, F. B., Cantorán Viramontes, A. R., Just, C., Guigue, J., and Wiesmeier, M.: Pushing the Limits of Soil Organic Carbon Storage: The Role of Land Use in Soil Carbon Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15512, https://doi.org/10.5194/egusphere-egu25-15512, 2025.
Soil fauna can have strong effects on the formation and persistence of soil organic matter (SOM). However, whether these effects are consistent across land uses and modulated by climate change remains unknown. Moreover, experiments on faunal taxa other than earthworms are very scarce.
We thus performed litterbag exclusion experiments in the Global Change Experimental Facility, Germany, in two land uses (agriculture/grassland) and two climate treatments (ambient/future). Litterbags accessible to either macro-, meso-, and microfauna, meso- and microfauna, or microfauna only were filled with soil and 13C-labeled maize litter and incubated in replicated plots for ~4 months. At the end of the experiment, we fractionated the soils into less (particulate organic matter) and more persistent (mineral-associated organic matter) SOM, and performed elemental and isotopic analyses.
Our results indicate that the conversion of litter into more persistent SOM was fostered in treatments accessible to meso- and macrofauna but not in those accessible to microfauna only, with this effect being most pronounced for the treatments accessible to mesofauna. Processes such as feces production by earthworms and springtails, which dominated the sites, could have fostered the formation of persistent SOM via stimulating microbial growth and necromass production, which is enriched in persistent SOM. This effect was insensitive to climate change and only perceivable in agriculturally managed soils, in which faunal abundance was lower than in grassland soils. These findings highlight mesofauna as strong regulators of SOM persistence, indicate density-dependent, positive effects of soil fauna on SOM persistence, and hint to a partial insensitivity of these effects to future climates.
How to cite: Angst, G., Hinkelthein, L., Schädler, M., Lochner, A., Scheu, S., and Eisenhauer, N.: Soil mesofauna increases the persistence of soil carbon in agriculturally managed soils under ambient and future climates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8176, https://doi.org/10.5194/egusphere-egu25-8176, 2025.
Peat soils in Western Europe play a crucial role in carbon storage and agriculture. However, these two functions are often incompatible, as draining of peatlands, to convert them into agricultural land, leads to emissions of stored carbon, turning these carbon reservoirs into significant carbon sources. In the Three Lakes region of Switzerland, peatlands have been drained for agriculture for the last about 100–150 years. While drainage has improved agricultural use of these peatlands, it has also accelerated peat decomposition, leading to the loss of more than 2 meters of peat thickness and causing substantial CO2 emissions.
Currently, there are no effective and sustainable measures to regenerate peatlands, aside from reflooding. In Switzerland, backfilling has emerged as an alternative approach to potentially reduce CO2 emissions without ceasing agricultural activities. Backfilling involves the deposition of mineral material from various sources onto the soil to disconnect the peat from the surface, thereby maintaining agricultural production while protecting the already degraded organic soils.
This method has been used for over 50 years in the region to improve access for machinery in areas prone to waterlogging caused by peat mineralization, but little research has been conducted on its long-term effects on the carbon cycle or overall soil functioning. With this study, we aim at better understanding the impact of backfilling on the carbon cycle in managed peatlands. To achieve this, we measured CO2 emissions and their radiocarbon content (14CO2) at three locations in the Three Lakes region to assign the source of the respired organic C. In addition, the quality (DRIFT) of soil carbon from drained and drained-backfilled peat soils was determined.
Initial summer measurements showed that CO2 emissions were over 40% higher in drained peatlands compared to their backfilled counterparts. The 14C content of the carbon respired also differed, with older carbon released from the original peatlands (up to -193 ‰, indicative of ~ 1,500 years) than from the backfilled sites (up to -115 ‰, ~ 800 years). Incubation experiments revealed that CO2 emissions predominantly originated from deeper horizons (>40 cm), which were richer in carbon and less degraded. Comparing the original drained peat to the peat buried beneath the backfilling, we observed lower carbon content and fewer easily degradable compounds in the buried peat. Compounds such as aliphatics were largely replaced by more resistant materials, like phenolics. The difference in emissions is then, primarily attributed to the quality and quantity of the remaining carbon, which is mainly dependent on the state of peat degradation at the time the backfilling was implemented. These findings highlight the critical role of the quality and quantity of the remaining carbon stock in this system. While backfilling may help reduce CO2 emissions by altering carbon availability in peat soils, it cannot fully stop the degradation process. Further research is needed to investigate spatio-temporal variability, potential peat compaction, and the influence of factors such as the groundwater table and the composition of the mineral layer.
How to cite: McMackin, C., Minich, L., Burgos, S., Hagedorn, F., Wiesenberg, G. L. B., and Egli, M.: Is Backfilling a Sustainable Alternative to Reduce CO2 Emissions from Swiss Degraded Peatlands?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5775, https://doi.org/10.5194/egusphere-egu25-5775, 2025.
Productive perennial grassland systems can increase soil carbon (C) storage compared to annual cropping systems, but the effect of species mixture composition as a means to optimize soil C input and stabilization and aboveground biomass yield at low nitrogen (N) fertilizer inputs remains unexplored.
In a field experiment, we measured aboveground yield and soil C inputs in 2-species mixtures with grasses or forbs combined with red or white clover, and in multi-species mixtures with 6 and 18 species including all 3 plant functional groups (grass, forb, legumes). All mixtures were fertilized with 75 kg N ha-1 yr-1. Monoculture perennial ryegrass plots were established at low and high N application rates (75 and 300 kg N ha-1 yr-1). We assessed aboveground yield and the input to belowground C pools (i.e., root C and rhizodeposited C) using isotopic labelling with 13C and a tracer mass balance approach. Further, we measured the allocation of the rhizodeposited C into newly formed mineral-associated organic C (MAOC) and particulate organic C (POC) fractions and related these to root traits. Lastly, we quantified selected amino sugars as proxies for bacterial and fungal necromass along a species richness gradient (1, 2, 6, 18).
The mixtures with red clover (including the multi-species mixtures) had an aboveground yield between 19.0 and 20.8 t DM ha-1 (830 – 890 g C m-2), matching the yield of the high-fertilized monoculture perennial ryegrass. The 2-species mixtures with white clover yielded on average 27% lower than mixtures with red clover. Mixtures with higher species richness than 2 yielded similar aboveground biomass as the 2-species mixtures with red clover. The multi-species mixture, consisting of 6 productive, resource-acquisitive species, resulted in a total soil C input to 1 m depth of 425 ± 30 g root C m-2 and 70 ± 10 g rhizodeposited C m-2, which was higher than all other treatments. Red clover, tall fescue and chicory secured high root C, while white clover, perennial ryegrass and plantain contributed with high C rhizodeposition. The 18-species mixture had lower total C input to soil compared to the 6-species mixture, likely due to several extra species diluting the effect of the 6 productive species used in the 6-species mixture. Legumes (low C:N ratio in root biomass) increased the proportion of MAOC of total rhizodeposition, while grasses (high root length density and root surface area) increased total C rhizodeposition and the proportion of POC. Further, the mixtures with legumes had a higher content of fungal and bacterial microbial necromass in the soil at the end of the growing season compared to monoculture perennial ryegrass. This indicates that the stabilization potential of rhizodeposted C can be enhanced by mixtures with legumes compared to monoculture grasslands.
Our results showed how grassland mixture composition can 1) increase total C input to soil without compromising high aboveground yield, 2) regulate the relative proportion of MAOC and POC from root-derived C, and 3) increase microbial necromass formation and the potential persistence of newly formed soil C.
How to cite: Mortensen, E., Peixoto, L., Enggrob, K., Abalos, D., and Rasmussen, J.: Soil C storage in productive grassland mixtures: the role of species traits and mixture composition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11866, https://doi.org/10.5194/egusphere-egu25-11866, 2025.
Soil organic carbon (SOC), a vital component of soil organic matter, plays a critical role in soil productivity, stability, and mitigating CO2 emissions. Factors such as climate, mineralogy, and vegetation influence SOC cycling, but its distribution patterns in Mediterranean arid croplands remain unclear. Using a spatiotemporal modeling approach, researchers analyzed a multi-year dataset of topsoil organic carbon concentrations from over 31,000 cropland sites in Morocco. These data were linked with environmental variables, including climate, vegetation, topography, and soil characteristics, to identify the drivers of spatiotemporal SOC changes.
The analysis revealed a low median SOC concentration of 11.71 g C kg⁻¹, with significant variability (Q1 = 8.46, Q3 = 16.24 g C kg⁻¹). Bioclimatic factors, particularly temperature seasonality and annual mean temperature, accounted for 57% of the variation in SOC content, along with contributions from vegetation and precipitation. This national dataset provides new insights into the environmental drivers of SOC variability in Morocco's arid croplands, shedding light on the mechanisms of SOC gain and loss and informing discussions about carbon cycling in arid soils and their response to climate change.
How to cite: Bayad, M., Gerard, B., Chehbouni, A., J. Hawkesford, M., Wai Chau, H., Bouray, M., Hamma, A., El Akrouchi, M., and Biswas, A.: Change Drivers and Spatial Distribution of Soil Organic Carbon Concentrations in Croplands of Morocco, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19648, https://doi.org/10.5194/egusphere-egu25-19648, 2025.
Herbivory is a key ecosystem process in terrestrial systems that influences belowground processes. In forest environments, insect herbivory alone can lead to the loss of 2-15% of foliar biomass annually. When plants experience aboveground herbivory, they may change the amount of carbon allocated to the soil via their roots, either by increasing or decreasing root exudation and turnover. These changes in carbon allocation can influence the structure and activity of the root-associated microbial communities. Similarly, herbivory by mammals can affect soil communities by changing the input of easily accessible C through contributions like plant litter and excrement. However, how plants manage C allocation above and belowground in response to mammalian versus insect herbivory remain poorly understood. Therefore, we assessed if plants differentially respond to mammalian vs. insect herbivory via changes in the quantity of C entering the soil in root exudates, resulting in shifts in soil biotic communities with consequences for C cycling and storage. To do this, we carried out a field-based 13C pulse chase experiment in a temperate forest, in which we subjected 3-year-old oak seedlings (Q. robur) to simulated herbivory by insects and mammals followed by 13C enrichment. Following plant assimilation of the labelled carbon (13C) we tracked carbon allocation to root exudates, leaves, roots, rhizosphere soil, soil fauna and continuously monitored soil 13CO2 efflux for five days. During the two-month experimental period, conducted on 36 seedlings, we observed that soil carbon efflux increased over time across all treatments. This is likely because plants were at a later stage phenologically, better able to assimilate C and therefore more C available to allocate belowground. Further results are being analysed and will be presented at the conference. Quantifying these cascading and interactive above-ground, below-ground effects is a research priority given global change-induced changes in invertebrate communities, current forest management strategies and rates of change in mammal populations.
How to cite: Ferreira Maia, L., Langridge, H., Kritzler, U., Johnson, D., E. Hidalgo, D., and Griffiths, H.: The effects of mammal and insect herbivory on above and belowground C allocation by tree seedlings in a temperate forest, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20331, https://doi.org/10.5194/egusphere-egu25-20331, 2025.
Soil management practices have led to a generalized decarbonization of agricultural soils' organic matter and carbon contents. Whereas mulching application of large amounts of organic matter (OM) on the soil surface, the incorporation of massive amounts of organic matter into the soil profile (e.g. 40-120 m3 ha-1) has been much less common, and has only been studied in a limited capacity, with effects varying depending on soil type, climate and origin of the incorporated lignocellulosic material. Large amounts of carboniferous materials applied to soil can provoke nutritional disequilibria, and potential nutritional deficiencies for plants. However, it has been shown that sweet potato (Ipomea batatas) may be able to overcome N limitation, though the exact mechanism is not clear.
In a field experiment in Catalonia, we applied an equivalent of 150 t ha-1 ramial chipped wood (RCW) simultaneously with sweet potato cultivation. The experiment was set up in two adjacent in arable fields with a cold semi-arid climate (yearly precipitation ~ 400 mm) with contrasting previous management: one field had been abandoned for 15 years, while the other had been managed with regenerative farming techniques including organic manure application, limited tillage, and green cover since 2006. RCW was applied in March, sweet potato was planted in May, and the plants were harvested in October. Using a combination of techniques including mass balances of C and N in fine earth and large (> 2 mm) organic fractions, plant nutritional analysis, and 15N stable isotope natural abundance method, we examined C and N dynamics in the soil and plant nutrition.
RCW incorporation increased both C and N in the plots where applied (Figure). However, absolute and relative gains were much greater in the regenerated plots, and the recovered C and N was much greater in the regenerated plots. Sweet potato N nutrition was not seen to be influenced by soil chemical properties (N fractions), pointing to other non-identified nutrition sources. Sweet potato leaf 𝛿15N also changed dramatically between samplings (March and October), indicating a change in N source.
These first results give some indications about the potential for rapid soil recarbonization in soils under different management and crop appropriateness to make this transition.
How to cite: Romanya, J., Cerdà-Péczely, L., Marcs, E. A. N., González -Coria, J., Jaime-Rodríguez, C., Pérez-Llorca, M., Solà-Bosch, N., and Pérez-Ferrer, A.: Harnessing massive application of lignocellulosic inputs to fallow and regenerated soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2078, https://doi.org/10.5194/egusphere-egu25-2078, 2025.
Incorporation of biochar, a carbon (C) dense and stable (over centuries or millennia) product of pyrolysis of organic material, into soil (particularly agricultural soil) has been proposed as a potential method of atmospheric carbon dioxide removal (CDR). However, assessing the impact of biochar application on agricultural soils, particularly over time, will be key to understanding the wider impact on ecosystem function. Here, using one of the longest running biochar field experiments in the UK, we evaluate the soil biological, physical and chemical impact of biochar 13 years after the initial application, at a plot (bulk soil from 50 t ha-1 biochar application vs control) and ‘charosphere’ scale (soil brushed from the biochar surface, and the biochar surface itself), as well as the impact of field exposure on biochar C stability and textural properties.
The organic C density of the biochar plots (4.89 kg C m-3) was higher than the control (3.32 kg m-3) plots, confirming the persistence of both biochar and soil derived organic C. Stable polycyclic aromatic carbon (SPAC) content, a measure of the long-term chemical stability of biochar C, of the original (non-field aged char) and field aged biochar was determined by hydropyrolysis (HyPy). The original biochar had a higher SPAC content compared to the field aged biochar, driven by one outlier, suggesting the initial biochar may have been heterogeneous in its quality and stability. Gas chromatography-mass spectrometry analysis of the HyPy-released labile fraction showed no compositional changes among samples with similar SPAC contents, indicating negligible degradation.
16S and ITS rRNA sequencing revealed divergent trends in the beta diversity of bacterial and fungal communities. The 16S bacterial community associated with the biochar surface differed from the bulk control and biochar soils and soil brushed from the biochar surface. Conversely, the ITS fungal community was different in the bulk control soil compared to biochar associated soils (bulk biochar, soil brushed from the biochar surface and the biochar surface itself). Soil pH and nitrogen (N) availability seemed to be the drivers of differences in soil properties, with pH significantly higher in the soil brushed from the biochar surface (pH 6.67) and biochar (pH 6.79) itself than the bulk soil (pH 5.22 and pH 5.30 for the control and biochar bulk soil, respectively), while extractable and available N was highest in the soil brushed from the biochar surface.
Overall, we show that, after 13 years, biochar application had a positive influence on soil C stocks. The chemical stability of the biochar had diminished by very little, with even the low quality (low SPAC content) char persisting. Soil function at a bulk soil level was relatively unchanged between control and biochar plots. However, at the charosphere (biochar surface) level, changes in the composition of the fungal and bacterial community may drive some changes in function, likely driven by soil pH and the biochar’s ability to retain nutrients, specifically N. The results presented here reinforce the durability of biochar application to soil as a CDR method, in the medium term.
How to cite: Brown, R., Li, W., Uguna, C., Meredith, W., Stevens, L., Chadwick, D., Snape, C., and Jones, D.: Understanding the legacy impact of biochar on soil function and carbon stocks – evidence from a 13-year field experiment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16585, https://doi.org/10.5194/egusphere-egu25-16585, 2025.
Long-term field experiments on the soil C cycle are essential for understanding C dynamics in agricultural soils. However, such studies are limited in the humid tropics. This study quantifies the effects of chemical fertilizer application, organic matter application, and their combinations on soil C sequestration. Data was obtained from 4 sites of the 45-year long-term field experiments in Thailand. Furthermore, a structural equation model (SEM) was employed to visualize the relationships among organic matter application, soil carbon, basic chemical properties, and cassava yield.
Compared to the control without any application, soil carbon sequestration was 2.0 ± 2.1 and 2.8 ± 2.0 Mg C ha⁻¹ (0.2 m depth) for chemical fertilizer and crop residue incorporation, respectively. The largest soil C sequestration occurred when chemical fertilizers were combined with organic matter application. Specifically, when chemical fertilizer was combined with crop residue incorporation or compost application, soil C sequestration reached 5.6 ± 3.1 and 10.1 ± 6.5 Mg C ha⁻¹ (0.2 m depth), respectively. These findings underscore the importance of C contributions from crop biomass and direct C inputs from organic matter.
SEM showed that the effects of chemical fertilizer and organic matter application on soil C concentration in clayey soils were predominantly observed in the 0–0.2 m and 0.2–0.4 m surface layers. Conversely, treatment effects were significant in sandy soils at all depths up to 1.0 m. The increase in soil C in sandy soils also significantly improved basal soil fertility, such as soil pH, available phosphorus, and exchangeable potassium, resulting in higher cassava yields. In contrast, no significant relationship was found between soil C concentration and cassava yield in clayey soils.
Currently, soil C dynamics models for agricultural lands in low-latitude regions, such as Southeast Asia, are primarily based on databases from high-latitude areas (e.g., the RothC model). The findings from this study are expected to contribute to developing tropical-specific C dynamics models for agricultural lands in low-latitude regions. Furthermore, the standard set by the Intergovernmental Panel on Climate Change (IPCC) for calculating soil carbon sequestration (30 cm from the surface) may be insufficient for sandy soils, highlighting the importance of evaluating carbon sequestration at deeper soil layers.
How to cite: Iwasaki, S., Tancharoen, S., and Luanmanee, S.: Carbon Sequestration and Soil Fertility Management in Sandy and Clayey Soils Revealed by Over Four Decades of Long-Term Field Experiments in Thailand, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17561, https://doi.org/10.5194/egusphere-egu25-17561, 2025.
Biochar (BC) application in croplands aims to sequester carbon and improve soil quality, but its impact on soil organic carbon (SOC) dynamics is not represented in most land models used for assessing land-based climate mitigation, therefore we are unable to quantify the effects of biochar applications under different climate conditions or land management. To fill this gap, here we implement a submodel to represent biochar into a microbial decomposition model named MIMICS (MIcrobial-MIneral Carbon Stabilization). We first calibrate and validate MIMICS with new representations of density-dependent microbial turnover rate, adsorption of available organic carbon on mineral soil particles, and soil moisture effects on decomposition using global field measured cropland SOC at 285 sites. We further integrate biochar in MIMICS by accounting for its effect on microbial decomposition and SOC sorption/desorption and optimize two biochar-related parameters in these processes using 134 paired SOC measurements with and without biochar addition. The MIMICS-biochar version can generally reproduce the short-term (≤ 6 yr) and long-term (8 yr) SOC changes after adding biochar (mean addition rate: 25.6 t ha-1) (R2 = 0.79 and 0.97) with a low root mean square error (RMSE = 3.73 and 6.08 g kg-1). Our study incorporates sorption and soil moisture processes into MIMICS and extends its capacity to simulate biochar decomposition, providing a useful tool to couple with dynamic land models to evaluate the effectiveness of biochar applications on removing CO2 from the atmosphere.
How to cite: Han, M., Zhao, Q., Li, W., Wang, Y.-P., Ciais, P., Zhang, H., and Goll, D. S.: Modeling biochar effects on soil organic carbon on croplands in a microbial decomposition model (MIMICS-BC_v1.0), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1431, https://doi.org/10.5194/egusphere-egu25-1431, 2025.
Biochar, a stable carbon(C)-rich material produced via biomass pyrolysis under oxygen-limited conditions, has become a topic of increasing scientific interest for its potential to improve soil health and sequester carbon, thereby contributing to climate change mitigation. Maize stover, a globally abundant and often underutilized agricultural byproduct, represents a promising feedstock for biochar production, facilitating waste reduction and soil improvement. However, a deeper understanding of the dynamics of maize-based biochar in soil, including its C storage potential, stability, and effect on nutrient cycling, is crucial for optimizing its application in sustainable agricultural practices. This study aimed to develop a cost-effective, highly C-efficient and accessible laboratory-scale biochar production method using readily available porcelain crucibles and a high-temperature muffle oven, with the goal of applying it to 13C-labelled maize stover for the creation of 13C-labelled biochar.
Maize stover was pyrolyzed at temperatures ranging from 250 °C to 550 °C (in 50 °C increments) for 1 hour. The impact of temperature on biochar recovery rate, pH, electrical conductivity, and molecular stability via mid-infrared spectroscopy (MIRS) was investigated. Results showed that the biochar recovery rate decreased with increasing temperature, stabilizing at ~30% at higher temperatures (>500 °C). Biochar pH increased with temperature, reaching pH ~11 and suggesting potential implications for soil acidity amelioration. MIRS analysis indicated optimal biochar stability at around 500 °C, crucial for long-term C sequestration, based on maximized aryl-C (C=C) absorption at 1620–1540 cm−1, minimized aliphatic C (C-H), and reductions in C=O stretching (1650–1800 cm−1) and O-H stretching (3000–3200 cm−1). Minimal variation among replicates highlights the method's high reproducibility and reliability for standardized lab-scale biochar production and comparative studies of biochar stability and soil interaction.
Further analysis, including elemental composition (C, N, H, and O), is underway to characterize the produced biochar and validate these findings. Based on these findings, the Soil and Water Management and Crop Nutrition (SWMCN) Laboratory team prepared a stable C isotope-labelled (13C) maize stover for biochar production. Utilizing 13C-labelled maize stover as feedstock will enable precise tracking of biochar-derived C in the soil, offering valuable insights into its fate and role in soil C dynamics. This isotopic labelling approach will enhance the understanding of biochar’s role in soil C cycling and support the development of evidence-based sustainable and climate-smart agricultural practices.
How to cite: Hafiza, B. S., Bibi, S., Wanek, W., Vlasimsky, M., Mitchell, J., Rabello, M., Heiling, M., Toloza, A., Dercon, G., and Burnett, J.: Cost-Effective Maize Stover Biochar Production for Enhanced Soil Carbon Sequestration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6864, https://doi.org/10.5194/egusphere-egu25-6864, 2025.
Increasing the fertility of sandy soils is a worldwide problem. A field experiment investigated the combination of two of fertility increasing methods, the application of biochar (BC) and a plant growth-promoting rhizobacteria inoculum in acidic and calcareous sandy soils from the temperate region. The treatments studied were BC alone; BC with inoculum; inoculum on BC carrier; and inoculum on conventional carrier at four dose levels. BC levels were 3, 15 and 30 t/ha. As a test plant maize was sown. Based on the chemical and biological changes observed in the soil, BC was the more decisive factor in the treatments. BC increased the pH and nitrification in acidic soil and the P and K availability in both soils. The survival of inoculated bacteria was better when it was added with BC. In acidic soil the small dose of BC inhibited arbuscular mycorrhizal fungal infection, probably due to its toxic organic contaminants. The growing season was extremely dry thus, the treatments did not affect maize yield, but the increase in total above-ground biomass showed that the combined application of BC and inoculum is more beneficial than their separate application.
Acknowledgement: This work was funded by the Norway Grant HU09-0029-A1-2013 entitled “Combined application of biochar and microbial inoculant for deteriorated soils.”
How to cite: Rékási, M., Szili Kovács, T., Tünde, T., Kutasi, J., Molnár, M., and Uzinger, N.: Effect of biochar as inoculum carrier on the fertility of sandy soils , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9730, https://doi.org/10.5194/egusphere-egu25-9730, 2025.
Enhancing soil organic carbon (SOC) accumulation is vital for improving agricultural productivity, soil health, and climate change mitigation, particularly in alkaline Indian soils with severe SOC deficiency. Amorphous Al (Am-Al) would be the major factor regulating SOC in volcanic and humid regions, and biochar has shown promise in improving SOC accumulation in temperate and tropical regions. Yet, their mechanisms and feasibility as amendments for enhancing SOC accumulation remain underexplored, especially in alkaline soils. This study investigates the effects of Am-Al and rice-husk biochar on the stabilization and mineralization of newly added plant materials in the alkaline Indian cropland soil (Inceptisol, 0-15 cm, pH: 8.8, SOC: 5.2 g kg−1, clay: 21%) through a one-year incubation experiment at 25℃ and 60% of water holding capacity. Treatments included Am-Al (Al(OH)3·mH2O; pH: 7.0, oxalate extractable Al: 58 g kg−1, BET specific surface area (SSABET): 290 m2 g−1; 10 g kg−1 soil) and biochar (formed at 550℃ for 4 hrs; SSABET: 180 m2 g−1; 10 g kg−1 soil) with and without washing (pH 9.2 and 6.9), with combination of plant residues (13C-labeled maize residue; 350 g C kg−1; 34% of 13C; <1 mm powder; 1 g kg−1 soil). The amounts and 13C ratios of respired CO2 and SOC during incubation were measured to quantify the mineralization and remaining added residues. The qualitative changes were monitored using 13C NMR and pyrolysis-GCMS.
Am-Al significantly reduced residue mineralization within the first 14 days, resulting in 27% versus 33% residue-derived CO₂ emissions for soils with and without Am-Al, respectively. Although this retardation diminished after 14 days, the legacy effect resulted in higher residue-derived C after one year, mostly in the <100 μm fraction (>90%). Am-Al preferentially stabilized plant residues directly, as indicated by a higher odd-over-even predominance of n-alkanes, reflecting a stronger plant contribution to lipids than microbial contributions. Minimal qualitative changes in residue decomposition patterns were observed in soils with and without Am-Al, as indicated by similar C functional group compositions. It suggests that stabilization may be primarily driven by adsorption rather than changing decomposition pathways, with some preferential stabilization of carbohydrate C (-C-O-) indicated by its smaller decrease among all functional groups. Biochar-amended soils also showed significant increases in remaining residue-derived C compared to controls. Still, they were lower than Am-Al treatments after one year, with stabilization effects becoming significant only in the later stages of incubation (post-day 168). This delayed effect is likely due to substrate substitution for soil microbes from residue to biochar rather than preferential stabilization. These findings highlight the divergent mechanisms of Am-Al and biochar in enhancing SOC accumulation, with Am-Al offering stronger stabilization from early stages and biochar contributing during later stages. Also, SSA may not be the only primary factor regulating the effectiveness of Am-Al and biochar in influencing SOC stabilization. This research underscores the potential of these amendments for SOC management in alkaline, low-carbon soils.
How to cite: Zhong, R., Lyu, H., Nishiki, A., Seki, M., Sugihara, S., and Watanabe, T.: Divergent impact of amorphous aluminum hydroxide and biochar on enhancing organic carbon accumulation in low-carbon alkaline Indian soil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15185, https://doi.org/10.5194/egusphere-egu25-15185, 2025.
Enhanced rock weathering (ERW) has emerged as a promising strategy for atmospheric CO2 removal via promoting inorganic carbon (IC) sequestration. Despite its impact on IC accrual that has been extensively studied and modelled, the lack of understanding of its impact on the largest terrestrial C stock - organic carbon (OC), and the overall C fluxes throughout the weathering stages impede the long-term assessment of ERW in C sequestration. Here, we conducted a 6-month microcosm study using fresh basalt (fine size) and weathered basalt (coarse and fine size) to simulate the impacts of basalt on C fluxes with weathering progressing in a temperate cropland topsoil. We also incorporated 13C-labeled straw to understand their effects on the turnover of new straw-derived organic matter (OM) and the native OM. Our findings show that both fresh and weathered basalt treatments increase IC through the release of exchangeable cations, with the fresh basalt contributing more exchangeable Mg and the weathered basalt shifting toward exchangeable Ca dominance as olivine minerals deplete. The fresh basalt treatments lead to a significant loss of soil OC, driven by soil alkalinity. Nevertheless, they concurrently reduce CO2 emissions by promoting IC accrual in soils and the leaching of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). With the progress of weathering, the alkalinity effect diminishes. The weathered basalt (fine size) treatments demonstrate improved OC retention for both native soil organic matter (SOM) and straw-derived OM. This is accompanied by the reduced DOC and DIC leaching, attributed to increased specific surface area (SSA), low pH and SOM stabilization through Ca. However, the IC accrual can be labile to fresh biomass inputs, which enhance CO2 emissions and deplete the accumulated IC in bulk soils and DIC leaching. These findings suggest that in soils with continuous biomass inputs, the benefits of ERW (e.g. basalt) throughout the weathering stages lie in reducing OC loss driven by weathered ERW materials rather than sustaining IC accumulation, which can be easily lost by environmental fluctuations in temperate zones.
How to cite: Lei, K., Bucka, F. B., Teixeira, P. P., Buegger, F., and Koegel-Knabner, I.: The enhanced rock weathering stages determine the fluxes and interactions of soil inorganic and organic carbon pools, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8352, https://doi.org/10.5194/egusphere-egu25-8352, 2025.
Enhanced rock weathering (ERW) is a promising carbon dioxide removal (CDR) technology, capable of removing up to 95 t CO2 ha-1 yr-1 from the atmosphere. In recent research, not only natural rocks but also industrial by-products, such as blast furnace slag (BFS) and mine tailings (MT), have been found to exhibit ERW potential, highlighting the need for comprehensive evaluations of their effects. While the CDR potential of ERW is mainly assessed by the increase in soil or leachate inorganic carbon, its impact on soil organic carbon (SOC) dynamics remains underexplored. To address this gap, we conducted a 290-day greenhouse experiment to evaluate the effects of BFS and MT, representative industrial by-products, on SOC dynamics. The experiment consisted of a factorial design with three replicates, with or without plants (alfalfa, Medicago sativa L.), and applying BFS and MT at a rate of 60 t ha-1. SOC dynamics were analyzed through temporal changes in SOC fractions, including free particulate organic carbon (fPOC), occluded particulate organic carbon (oPOC), and mineral-associated organic carbon (MAOC). Additionally, we measured soil pH, available nutrients (NH4+, NO3-. and P2O5), microbial biomass carbon (MBC), and microbial activities (hydrolase and oxidase). Results showed decreased total SOC in BFS and MT after 290 days. The SOC fraction dynamics showed distinct temporal dynamics. The fPOC content declined rapidly within 122 days and continued to decrease slowly thereafter. In contrast, oPOC and MAOC showed minimal or statistically insignificant changes over time. Microbial parameters, including MBC and enzyme activities, significantly increased in response to BFS and MT applications. These results indicate that the high levels of (3127.3 mg kg-1), Na (4.0 mg kg-1), and Mg (12.6 mg kg-1) contained in BFS and MT stimulated microbial activity, thereby promoting the decomposition of labile SOC fraction (fPOC). Despite the SOC loss, BFS and MT significantly enhanced above- and below-ground plant biomass carbon. This augmented plant growth suggests the potential for increased carbon (e.g., plant residues) input to the soil, which may counterbalance the reduced SOC. These results highlight a complex interplay between ERW materials, soil microbes, and plant growth. To further explore these interactions, we plan to use synchrotron micro-CT to investigate the spatial arrangements between ERW materials, soil carbon, and microbial activity.
How to cite: Park, Y. L., Ok, Y., Hyun, J., Seo, I., and Yoo, G.: Soil Organic Carbon (SOC) Fraction Dynamics Influenced by the Enhanced Rock Weathering with Blast Furnace Slag and Mine Tailings, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19373, https://doi.org/10.5194/egusphere-egu25-19373, 2025.
A significant approach for reducing the effects of climate change is carbon sequestration, which is the process of absorbing and storing atmospheric carbon dioxide. The potential for carbon sequestration to lower greenhouse gas concentrations has significant effects on human welfare and ecological services. The present study was designed to assess carbon storage and sequestration by using the InVEST model in Chandigarh, India. The study highlights the effects of carbon sequestration on ecosystem services and human well-being. While increases in CO2 levels may boost crop yields, they pose significant risks to long-term climate stability. Enhancing carbon storage in an urban environment can notably improve air quality and mitigate climate change impacts. In addition, carbon sequestration has a critical role in soil formation and nutrient cycling, which is essential for maintaining ecosystem health. The findings reveal a significant increase in built-up areas and a reduction in green spaces despite regulations implemented by authorities. The InVEST model results indicate a decrease in carbon storage from 5.8 × 10⁵ Mg in 2013 to 4.9 × 10⁵ Mg in 2023. This shift resulted in a decline in carbon storage and negative carbon sequestration. Total carbon sequestration for this period was -8.2 × 10⁴ Mg, suggesting carbon emissions exceeded sequestration. Chandigarh experienced a notable decrease in green cover and agricultural land, with built-up areas increasing by 21% from 2013 to 2023. Further, economic analysis through net present value indicated a financial loss for the city due to higher carbon emissions outweighing sequestration. It advocates the implementation of participatory sensing to raise awareness and prioritize multifunctional landscapes, ensuring sustainable ecosystems and mitigating adverse effects on ecosystem services. The results emphasize the simultaneous use of carbon sequestration as a socioeconomic and environmental instrument, supporting a well-rounded strategy that gives equal weight to ecological sustainability and community well-being. The present study contributes to the larger conversation on sustainable urban development in India by offering helpful information to environmental stakeholders, politicians, and urban planners.
How to cite: Paswan, N. G. and Pathak, S.: Carbon Sequestration and its Effects on Ecosystem Services and Human Welfare, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1330, https://doi.org/10.5194/egusphere-egu25-1330, 2025.
Soil carbon sequestration (SCS) is a promising approach to mitigate climate change by enhancing carbon storage in soils while simultaneously improving soil functioning. Despite its potential, the effectiveness and sustainability of SCS strategies are highly variable, contingent on location-specific environmental and management contexts, and are often constrained by risks of reversibility and potential soil quality degradation. This underscores the urgent need for robust, data-driven frameworks to guide the prioritization and implementation of SCS strategies, ensuring long-term benefits while minimizing trade-offs.
This study introduces an innovative multicriteria decision-support tool designed to evaluate and prioritize SCS strategies in croplands, considering their carbon sequestration potential, environmental co-benefits, and socio-economic implications. A comprehensive review of 264 meta-analyses was conducted, focusing on the impacts of 13 SCS strategies, grouped into seven families: crop diversification, land management, mulching, organic amendments, fertilization, biochar application, and agri-technologies. The developed tool integrates seven key performance indicators (KPIs): ease of implementation, SOC increase potential, co-benefits, negative effects, costs, permanence of carbon in soil, and additional crop yield. The prioritization tool integrates quantitative and qualitative data into a scoring matrix, providing a robust framework to evaluate the multifaceted impacts of SCS strategies. It accounts for variability in data quality and uncertainty, allowing users to adapt the weighting of KPIs to align with specific goals. This allows the identification of Pareto-efficient strategies that maximize SOC sequestration while minimizing trade-offs, supporting the adoption of contextually relevant SCS strategies in agriculture.
Preliminary results highlight biochar application and agroforestry as promising strategies, with average SOC stock increases of 34% and 32%, respectively, followed by crop rotation (20%), fertilization techniques (16%), cover cropping (12%), and mulching (8%). Biochar demonstrates particularly high sequestration rates (0.03–66 MgC ha⁻¹ y⁻¹), alongside substantial improvements in soil properties, such as porosity, aggregate stability, and water-holding capacity, and a 25% average enhancement in crop productivity. By systematically synthesizing evidence and scoring SCS strategies across multiple dimensions, this study bridges the gap between theoretical knowledge and practical implementation of SCS strategies. The tool facilitates targeted decision-making, promoting research and investment in the most effective and sustainable practices, advancing the integration of soils into climate change mitigation strategies.
How to cite: Andrade Diaz, C. and Hamelin, L.: Advancing soil carbon sequestration solutions: A decision-support tool for achieving net-zero goals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11591, https://doi.org/10.5194/egusphere-egu25-11591, 2025.
The harmful effects of air pollution on human health and well-being are well-studied. However, research on the effects of air pollution on the non-human environment is still sparse. We add to this by investigating the causal effect of particulate matter (PM2.5) on vegetation and soil invertebrates throughout Europe. To do so, we exploit the quasi-random variation in air pollution concentration caused by thermal inversion episodes in an econometric instrumental-variable setting, with the help of a dedicated new dataset of thermal inversion episodes across Europe. With this econometric technique, we can estimate the causal effects of an increase in air pollution on soil variables taken from the LUCAS database. We focus particularly on processes related to carbon sequestration. A pollution-induced reduction in soil carbon sequestration constitutes a reduction in ecosystem services which can be monetised by estimating the additional economic damages arising from this carbon cycle feedback and the climate change impacts it causes. Results from a preliminary analysis in the UK suggest that a 1 ug increase in PM2.5 concentrations would imply a reduction in topsoil carbon sequestration of up to 2 MtC across England, which is substantial compared to annual UK CO2 emissions of around 80 MtC. These results indicate that the effect of air pollution on soil biota and soil carbon sequestration might be a major overlooked damage which is to a large extent caused by the combustion of fossil fuels. Consequently, accounting for this effect allows us to economically quantify the co-benefit of increased soil health and carbon sequestration that arises from reducing fossil fuel emissions through climate change mitigation policies.
How to cite: Schaumann, F., Basaglia, P., and Drupp, M.: Quantifying the effect of air pollution on soil carbon sequestration using an EU-wide thermal inversions dataset, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17737, https://doi.org/10.5194/egusphere-egu25-17737, 2025.
Climate and land-use change induce dynamic disequilibrium in C cycling (Luo & Weng TREE 2011) as does soil erosion (Doetterl et al. ESR 2016) and soil meliorations, e.g. deep tillage (Alcantara et al. GCB 2016, Schiedung et al. GCB 2019). The effect of disequilibria on decadal trends of SOC in arable soils is demonstrated in controlled, long-term field experiments, which include desurfacing as well as meliorative fractional deep tillage (mFDT). Our results show that soil systems well below equilibrium state induce a fast, significant and sustainable CO2 sink effect. Especially mFDT offers a realistic, practical option for 4p1000 as it increases crop yields and soil fertility in arable soils simultaneously.
How to cite: Sommer, M. and Gerriets, M.: Soils as CO2 sinks? - The importance of dynamic disequilibria in soil systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3455, https://doi.org/10.5194/egusphere-egu25-3455, 2025.
Soil organic matter (SOM) plays a pivotal role in enhancing soil's physical and biological properties, contributing to improved crop productivity and long-term agricultural sustainability. Among the components of SOM, humic acid (HA) is particularly important due to its capacity to enhance soil structure and promote nutrient availability. While previous studies have primarily focused on the impact of naturally derived HA on soil properties, this study investigates the effects of HA on soil aggregation and stability under different fertilizer regimes. The experiment was conducted during the summer cropping season with maize (Zea mays L.) grown under both organic and synthetic fertilizer treatments. The organic fertilizer treatment involved the incorporation of barley (Hordeum vulgare L.) and hairy vetch (Vicia villosa R.) residues five days prior to maize cultivation, whereas the synthetic fertilizer treatment applied recommended rates of NPK fertilizers in accordance with Korean agricultural guidelines. Results showed that the organic fertilizer treatment significantly improved soil aggregation and stability, as indicated by the mean weight diameter (MWD) of soil aggregates (p < 0.05), compared to the synthetic fertilizer treatment. This enhancement was largely attributed to the increased quantity and quality of HA derived from organic inputs. The organic treatment yielded nearly double the amount of HA compared to the synthetic treatment. Additionally, the organic treatment demonstrated a 140% increase in MWD and a 40% higher total phenolic content than the synthetic counterpart. Furthermore, maize cultivated under organic treatments exhibited significantly higher macronutrient absorption (p < 0.001), an 11% increase in above-ground biomass, and a 21% increase in grain yield compared to synthetic fertilizer treatments. These findings suggest that the incorporation of fresh organic residues can effectively enhance HA characteristics in soil, thereby improving soil structure and promoting sustainable crop productivity.
How to cite: Lee, J., Park, S., Kwon, N.-H., Lee, C., Kim, T., and Jung, J.: Humic Acid-Driven Soil Stability and Nutrient Absorption: Comparing Organic and Synthetic Fertilization in Maize Production, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5420, https://doi.org/10.5194/egusphere-egu25-5420, 2025.
Soil organic carbon (SOC) is important for soil health and its accrual is discussed for carbon sequestration. The SOC fraction stabilized by mineral associations is of special interest, but limited reactive mineral surfaces comprise a natural boundary. The potential upper limit of soils to store SOC as mineral-associated organic carbon (MAOC), the mineralogical capacity, cannot be directly measured as MAOM formation is the result of a complex interplay between mineral properties, plant litter input, and microbial growth and transformation. Accordingly it, depends on a variety of environmental drivers. Current approaches use boundary line regression to identify the dependency of the mineralogical capacity on texture, mineral type, and other environmental conditions and thereby suffer from data sparsity and neglect interactions among the different drivers.
To exploit multiple sources of data and combine them via common and expert knowledge, we developed a parameter learning framework that combines machine learning and mechanistic modeling. The spatial distribution of parameters (e.g. mineralogical capacity or litter decomposition rates) of a mineral and microbial explicit mechanistic model is inferred using a hybrid neural network, where the mechanistic model forms the final layer. The neural network learned the mechanistic parameters from observations of SOC and MAOC, using environmental covariates like texture, climatological and vegetational conditions as inputs. Influences from mineral properties and other environmental conditions can thereby be separated in an informed way.
Bootstrapping and analyzing the distribution of mechanistic parameters revealed that relying solely on SOC observations from the Land Use and Land Cover Survey (LUCAS) is insufficient for stable results. Thus, the output space was further constrained by penalizing unrealistic predictions, using MAOC and other sparse observations, and restricting the degrees of freedom in the framework. The posterior parameter combinations per site were thereby limited, which reduces equifinality and assures physical consistency of all model parts.
Results of the distribution of the mineralogical capacity, steady state MAOC/POC and sensitivities on mineral and environmental conditions can inform the carbon sequestration and soil health community about areas of interest. As rates of change and respective sensitivities are also of high interest, the framework should be extended in the future with a dynamic mechanistic model.
How to cite: Roßdeutscher, L., Chettouh, M. A., Paina, M., Reichstein, M., Schrumpf, M., and Ahrens, B.: Disentangling the Effects of Minerals and Other Environmental Factors on Soil Carbon Stocks, and Capacity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18721, https://doi.org/10.5194/egusphere-egu25-18721, 2025.
Afforestation is an efficient strategy used to promote soil organic carbon (SOC) sequestration. Though the effects of afforestation on SOC sequestration have been investigated worldwide, the underlying mechanisms remain to be further explored. We adopted a space-for-time approach by comparing maize field and plantation forest at a regional scale in subtropical China, and explored the mechanisms underlying the effects of afforestation on SOC sequestration. Amino sugars and lignin phenols were used as biomarkers to indicate soil microbial and plant residual carbon. SOC stock was significantly promoted 20 years after afforestation with an accrual rate of 301.7 ± 43.3 g C m-2 yr-1. According to the 13C mass balance method, new carbon contributed 28.9 ± 2.8% of SOC pool in the plantation forest with the contribution much higher in the topsoil than in the subsoil horizon. The turnover time of SOC was comparable across the soil profile from 0 to 45 cm depth with the average being 130.8 ± 26.6 years. Afforestation promoted particulate organic carbon (POC) content more pronouncedly in the topsoil than in the subsoil horizon, but promoted bulk SOC and mineral-associated organic carbon (MAOC) content similarly across the soil profile from 0 to 45 cm depth. In the topsoil, microbial residue played a key role in stimulating SOC accumulation following afforestation, with the roles of lignin and mineral protection being much minor. In the subsoil, the roles of microbial residue and mineral protection in stimulating SOC accumulation were comparable, with the role of lignin being minor. For both POC and MAOC accumulation following afforestation, the role of microbial residue was much higher than that of lignin or mineral protection. The findings demonstrate that microbes may play a key role in promoting soil carbon accumulation following afforestation in the subtropical region.
How to cite: Li, D.: Key role of microbes in promoting soil carbon accumulation following afforestation in a subtropical region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1230, https://doi.org/10.5194/egusphere-egu25-1230, 2025.
The “42 plots of Versailles” site is a long-term bare fallow established in 1928. Over the course of almost 100 years, these plots have been carefully maintained without vegetation and enriched annually with various fertilizers and amendments (16 types x 2 replicate plots + 10 control plots), and sampled throughout the period. In particular, the control plots offer the opportunity to use elemental analysis to monitor the kinetics of soil organic carbon (SOC) evolution in the absence of carbon inputs.
Zimmermann fractionation (Zimmermann et al., 2007, DOI : 10.1111/j.1365-2389.2006.00855.x) is a granulo-densimetric separation protocol that separates SOC into 5 fractions: dissolved organic carbon (DOC), coarse particles > 63 µm consisting of particulate organic matter (POM) and “heavy” coarse matter containing sand and aggregates (S+A), and fine particles < 63 µm consisting of oxidation-sensitive fine fraction (sSOC) and oxidation-resistant organic matter (rSOC).
These 5 fractions are expected to have distinct mean residence times; in particular, the rSOC fraction is seen as a stable fraction, with aged carbon whose quantity changes little or not at all over time; conversely, the POM fraction is composed of very labile carbon. When applying this fractionation to control samples from the 42 plots at different times, we therefore expect to see strong variations in the size of the labile compartments, and on the contrary very little variation in the stable compartments.
In this study, we compare the results of this fractionation on 5 control plots at various dates (notably at the start of the experiment in 1929; at the present in 2021, which is the latest sampling date; and intermediate dates), in order to verify whether Zimmermann fractionation is indeed capable of separating SOC fractions with very distinct kinetics.
How to cite: Delahaie, A., Pouteau, V., Plessis, C., and Chenu, C.: Can secular stable soil organic carbon be isolated? An assessment of Zimmermann fractionation using a long-term bare fallow., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6311, https://doi.org/10.5194/egusphere-egu25-6311, 2025.
Understanding how different soil types and land management practices can increase the quantity of carbon stored in soil is increasingly important for climate change mitigation efforts. Determining the total organic carbon (TOC) content in soils provides information on the soil health, carbon sequestration potential and soil fertility. This information allows improvements in agricultural applications, environmental monitoring and other land management practices. Another recent application for TOC analysis is assessing the quality and carbon sequestration potential of biochar, a carbon rich material produced via pyrolysis of biomass for the purpose of transforming the biomass carbon into a more stable form. Biochar has emerged as a potentially promising soil amendment as it captures carbon that would otherwise be released into the atmosphere and can improve soil fertility and improve water quality.
The Elementar soli TOC® cube has been developed for the measurement of total organic carbon (TOC) and total inorganic carbon (TIC) but also the residual oxidizable carbon (ROC). The soli TOC cube uses temperature ramped differentiation of the carbon factions with a crucible-based sample feeding system, gas switching and dynamic furnace. Alongside standard applications using a 3-step temperature programmes e.g. EN 17505, the soli TOC® cube also has the option for flexible programmes with up to 5 temperature steps offering new possibilities for differentiating carbon fractions or species and for studying the temperature-dependent decomposition of carbon compounds.
We present results from the new 5 - step temperature ramping method that gives users the ability to run flexible temperature programmes under combustion or pyrolytic conditions with up to five target temperatures between 150 and 900 ℃. Other adjustable parameters include the switching time between combustion and pyrolysis, temperature ramping time and temperature hold times. This enhanced flexibility gives the opportunity to address new scientific questions with an unrestricted analysis of the different carbon fractions.
How to cite: Preece, C., Alt, F., and Loos, A.: Flexible temperature-dependent differentiation of carbon fractions with the Elementar soli TOC® cube , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10997, https://doi.org/10.5194/egusphere-egu25-10997, 2025.
