Tidal wetlands sequester around ~4.8-87.2 Tg of carbon per year¹ and represent approximately 25% of the global carbon sink, as a result of high inputs of organic matter and slow below-ground decomposition. The rate of carbon storage is hypothesised to be linked to the composition, particularly the relative oxidation, of soil organic carbon and the relationship with the sediment mineral matrix. The complex and dynamic biogeochemical processes governing tidal wetland carbon are not yet fully understood and therefore, the aim of this research was to understand how the composition of organic material varies across a tidal wetland and how this in turn is related to source, mineralogy and salinity.

Topsoil (0-20cm) and subsoil (20-40 cm) samples were collected from three marshes along a transect representing a salinity, inundation and elevation gradient and were analysed to assess the variations of SOC source, prevalence and composition, as well as the influence of salinity and sediment mineral composition on SOC stabilization.

SOC in the saline environments was highly oxidised with a low oxidation potential and thus had a particularly stable composition. In contrast, the carbon in the freshwater marsh was significantly less oxidised and thus demonstrated a greater potential for CH₄ and CO₂ emission. Carbon isotope (δ¹³C) and C:N analysis revealed that the SOC in all sites was produced in-situ by C3 plants, but highlighted differences between the photosynthetic pathway of the vegetation in each marsh. The freshwater marsh carbon was also more δ¹³C depleted, indicative of methane-consuming organisms and we hypothesise this variation in production pathway links to oxidation state.  

The compositional stability of SOC affected overall concentrations with the highest concentration of SOC in the first 20 cm of sediment in the high saltmarsh (between 0.35% and 5.34% w/w) and the lowest concentration of SOC in the lower 20-40 cm of sediment of the freshwater marsh (0.4% - 2.7% w/w). SOC prevalence is also positively associated with Fe-Al clay minerals, which was the dominant sediment type in the saltmarshes, whereas the freshwater marsh was predominantly siliceous sediment.

We conclude that the relative stability and concentration of SOC is greatest in the saltmarshes compared to the freshwater marsh. This aligns with emerging theory that mineral association is an important pathway of SOC stabilisation, and that salinity may exhibit a positive effect on cation bridging between organic material and mineral surfaces.

Acknowledgements: This project received funding from the National Environmental Isotope Facility (# 2656.0424).

References: Mcleod, E., Chmura, G. L., Bouillon, S., Salm, R., Björk, M., Duarte, C. M., Lovelock, C. E., Schlesinger, W. H., and Silliman, B. R.: A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2, Frontiers in Ecology and the Environment, 9, 552–560, https://doi.org/10.1890/110004, 2011. 

How to cite: Lowrie, M., Schuerch, M., Lacey, J., and Magnone, D.: A demonstration of the compositional stability of saline-hosted sedimentary carbon in a coastal wetland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1321, https://doi.org/10.5194/egusphere-egu24-1321, 2024.

Examining soil carbon losses across various time scales is essential for understanding the potential of soil carbon stabilization. It allows for considering these losses in estimating the net changes in carbon stocks. The soil's intrinsic physical and chemical properties, particularly those associated with the mineral phase, have been suggested to regulate soil organic carbon (SOC) losses. However, the relationship between these properties and SOC losses remains to be determined in long-term experiments. A 600-day incubation experiment was conducted on sieved soil samples (<2 mm) and intact cores (volume=~200 cm³) collected from an arable field in Bjertorp in southwest Sweden with large variations in soil texture and SOC to determine the respiration rate through chamber alkali trap respirometry using a Portable conductivity meter. After the incubation experiment, soil properties (carbon, nitrogen, and pH) were also measured. In addition, previously determined soil texture, oxalate extractable aluminum (Alox), and iron measurements were used to explain the results of the incubation experiment. The ratios between Alox and SOC and Alox and clay content were used as proxies for the protection of SOC. Preliminary results from the sieved soil samples indicate that the respiration rate (µg C-CO₂ g^-1 SOC h^-1) was positively correlated to the Alox:SOC  and clay:SOC ratio. These findings can be interpreted as the absence of SOC protection by Alox and/or clay complexes or interactions. The conclusions drawn from this study suggest the need for additional exploration into the intricate dynamics that influence the fate of soil organic carbon (SOC) associated with mineral phases when assessing carbon stocks.

How to cite: Chilipamushi, M., von Brömssen, C., Colombi, T., Kätterer, T., and Larsbo, M.: The role of oxalate-extractable aluminum in regulating soil organic carbon decomposition in agricultural topsoil in humid continental climates: Insights from a long-term incubation field-scale study., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17497, https://doi.org/10.5194/egusphere-egu24-17497, 2024.

Soil organic carbon (SOC) is significantly affected by land use change (LUC), which can lead to either SOC losses or gains. In consequence, LUC is a major controlling factor of total SOC contents and its dynamics. In general, LUC from forest or grassland to permanent cropland results in losses of SOC, while the reverse can result in long-term gains. Several methods have been developed to assess distinct SOC pools. This includes particle size separation, thermal analysis and soil reflectance spectroscopy. The responses of such defined SOC pools to LUC have rarely been studied comprehensively, while doing so is a straightforward way to reveal their biogeochemical relevance. Here we used 23 sites covering six different LUC (i.e. forest-cropland, grassland-cropland, grassland-forest, cropland-grassland, cropland-forest and cropland-perennial Miscanthus) to assess SOC pool changes. We used particle size fractionation to obtain coarse (>50µm) and fine (<50µm) fractions and Rock-Eval 6 analysis to estimate active and stable SOC pools. Additionally, we used mid-infrared spectroscopy (Diffusive Reflectance Infrared Fourier Transformed Spectroscopy (DRIFT)) on bulk soils and particle size fractions to determine the relative SOC composition.

All methods identified kinetically different SOC pools across all LUC. The fine particle size fraction, representing a stabilized and slow cycling SOC pool, was more responsive to LUC compared to the stable pool estimated using Rock-Eval. Assessing the relative changes of total SOC and organic carbon contents of the fractions across all LUC, showed that the fine particle fraction follows closely the total SOC changes (R²=0.91 with slope of 0.77). In comparison, the stable pool extracted by Rock-Eval was less dynamic (R²=0.72 with a slope of 0.43). Absolute changes in bulk SOC were well described by the absolute organic carbon change of extracted Rock-Eval pools (active: R²=0.99 and stable: R²=0.91), while organic carbon changes of the particle size fractions were less sufficient to describe bulk SOC changes (coarse: R²=0.77 and fine: R²=0.33). The SOC composition, determined by DRIFT, revealed that changes in the relative composition of fast cycling aliphatic to slow cycling aromatic compounds can well explain relative total SOC changes (R²=0.81). This shows that three conceptually different methods (physical, thermal and spectroscopic) are suitable to determine SOC pool changes for a large diversity of LUC, but the sensitivity of the individual pools can differ strongly, depending on the method.

How to cite: Schiedung, M., Barré, P., and Poeplau, C.: The impact of land use change on soil organic carbon pools: A multi-method assessment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1635, https://doi.org/10.5194/egusphere-egu24-1635, 2024.

Climate change poses a significant threat to soil quality and global food security, with projections indicating potential crop yield declines of 17% by 2050. Simultaneously, agriculture contributes to an estimated 24% of all greenhouse gas (GHG) emissions. The dynamics of carbon (C) and nitrogen (N) play a pivotal role in GHG emissions and soil C sequestration, yet further research is needed on how management practices influence these dynamics.

To address these challenges and provide data can facilitate efficient resource utilization in agricultural production, an incubation experiment was conducted to provide data on the impact of management options on C sequestration and GHG emissions from agricultural soils. The experiment took place in 850 mL glass jars under controlled conditions at 60% water-filled pore space and a temperature of 25°C. Composite soil samples, derived from a moderately fertile soil (2-3% SOC) from Grabenegg, Austria, at a depth of 0-15 cm, were subjected to five treatments: 1) control, 2) labeled urea, 3) inhibitor and labeled urea, 4) biochar + 15N labeled urea, and 5) inhibitor and biochar and labeled urea.

The 15N-labeled urea (5% atom excess) was applied at a rate of 150 kg N ha-1, while biochar was applied at 2% of the soil by dry mass basis. A neon inhibitor which includes NBPT to limit nitrogen loss into the atmosphere as ammonia and DCD to reduce leaching, were applied at a rate of 4 mL per 100g urea as instructed by the manufacturer. All treatments were replicated four times. Soil and gas samples were collected on days 1, 3, 8, 15, 24, 31, 38, 45, 52, and 59 after treatment application. Gas samples were collected over a two hour period each day. Soil samples were analyzed for pH, soluble organic C, and mineral-N (NH4+, NO3-), while gas samples were analyzed using a gas chromatograph (GC) for NO2, CO2, and CH4.

Preliminary results indicate that the addition of biochar increased soil C content, aligning with expectations from prior studies and that the addition of the inhibitor had a discernible impact on the pathways of nitrogen in the study samples. The use of isotopic methods and GHG measurements can furnish critical data supporting the most efficient use of resources for both climate mitigation and adaptation.

How to cite: Bibi, S., Ahmad, H., Wanek, W., Zaman, M., Vlasimsky, M., Heiling, M., Pucher, R., and Dercon, G.: Carbon Sequestration and Mitigation of Agricultural Greenhouse Gas Emissions through management: Insight from an incubation experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9176, https://doi.org/10.5194/egusphere-egu24-9176, 2024.

Soil contains three times more carbon (C) than the atmosphere and biosphere combined. It therefore represents an important tool for removal of carbon dioxide (CO₂) from the atmosphere and its long term sequestration. However, in the current climate crisis, C that is already stored in soil reservoir represents a potential threat because different fractions of C in soil have different stability against the rising global temperatures. C is stored in soil in the form of soil organic matter (SOM) which is a mixture of many different organic components. Based on different properties we can divide SOM into two pools. The first pool is represented by small fragments of dead biomass referred to as free particulate organic matter (FPOM). The other pool is comprised of organic matter, usually chemically transformed or converted to microbial necromass, which is in various ways associated with soil mineral matrix. This pool is referred to as mineral associated organic matter (MAOM). It is assumed that MAOM becomes C saturated during soil development because it is limited by the amount of available mineral surfaces. FPOM, on the other hand, does not saturate and can therefore play an important role in later stages of soil development. Beside this some OM is stored in organic horizons in forest floor (Oe layer), which we expect will have similar pattern as FPOM. However, there is scarcity of studies that examine this assumption. In this work we studied the hypothesis that soils in different stages of development will differ in the amount of C stored in FPOM and MAOM fractions. On top of that, we assumed that this difference will be affected by the dominant tree species growing on the soil and the effect of tree species and soil age will not always be additive. We tested this hypothesis by analyzing C storage in soil and amount of C in FPOM and MAOM using two types of soils - recultivated spoil heap (immature soil) and forest soil in the surrounding area (mature soil). Plots with only one type of tree species (spruce or alder) in 3 replications were present on each of these soil types. Our results show that different tree species have different effects on the amount of C stored in mineral soil and Oe layer in immature and mature soils. In mineral soil more, C was sequestered under alder on recultivated heap, while in the surrounding area no difference between tree species was found. In Oe layer more C was sequestered under spruce in both types of soils. Soils did not differ in the amounts of FPOM and MAOM present in soil, but they did differ in the amount of C stored in these fractions. In young soil, MAOM fraction stored more C under alder than spruce. For mature soil the opposite was true. For FPOM fraction no significant effect of tree species or soil age was found but in young soil higher C storage in FPOM was found under alder compared to spruce.

How to cite: Hüblová, L. and Frouz, J.: Sequestration of soil organic matter in broadleaf and coniferous forests in soil at various stages of pedogenesis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2696, https://doi.org/10.5194/egusphere-egu24-2696, 2024.

Peatlands are the Earth's largest natural terrestrial carbon reservoir, storing more than 40% of all soil organic carbon. Despite their significance, damaged peatlands emerge as a major source of greenhouse gas emissions, contributing to nearly 5% of global anthropogenic CO₂ emissions.

Peatlands have been drained in the Three Lakes region (Switzerland). These drainage efforts were initiated to develop agricultural land use and enhance the overall quality of life in the region. While the drainage improved living conditions, it also accelerated peat decomposition. This accelerated decomposition gave rise to a loss of soil, reaching up to 4 meters at specific locations, and drastically increased CO₂ emissions.

Various strategies have been developed to reduce CO₂ emissions from degraded peatland. Backfilling—the deposition of a mineral layer on the soil— is one promising method to mitigate CO₂ emissions. Backfilling disconnects the peat from the surface soil by a mineral layer. CO₂ emissions from the peat are diminished, while the surface soil can still be used for agricultural purposes.

Peatlands contain very old carbon preserved by water-logged conditions that limited carbon decomposition. We measured rates and radiocarbon (C14) signals of the CO2 emissions at three locations in the Three Lakes Region to compare the amount and age of carbon emitted from drained and drained-backfilled peatland soils. First results show that the backfilled peatland soils emit less and younger CO₂ than peatland soils having no backfilling. The covered peatland still continues to degrade, however at a slower pace. The overed peat contributes to about 50% of the measured CO2 emissions from the transformed sites. Further investigation will be needed to identify the spatio-temporal variability and the influence of other factors such as the groundwater table level.

How to cite: McMackin, C., Minich, L., Guido, W., Stéphane, B., and Markus, E.: Transformation and backfilling of peatland soils and effect on CO2 emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6188, https://doi.org/10.5194/egusphere-egu24-6188, 2024.

Agricultural crop production plays a key role in satisfying the increasing food demand of our ever-growing population. However, continuous production and certain land use practices often result in the depletion of soil quality. This revelation developed a need to improve soil fertility by enhancing carbon sequestration and storage in our cultivated fields using different methods.

Even though the application of green manure crops can significantly increase the amount of carbon stored in the soil while improving its water storage capacity and protecting the surface from erosion, it is still not a widespread method in Hungary due to usual water shortage during their sowing and germination periods. Furthermore, different soil management techniques can also alter the quality and carbon sequestration potential of our soils. The objective of our study is to determine how soil management and the usage of catch crop cover may affect crop productivity.

A maize-oat bicultural field trial with two different soil management techniques (conventional ploughing and reduced tillage) combined with four types of cover crops (fallow, trefoils-buckwheat mixture, phacelia and oilseed radish) was established in 2020. Changes in soil water content and temperature were continuously monitored at three depths (5, 25 and 45 cm), while leaf area index (LAI) and chlorophyll content (SPAD) were measured periodically. At the end of the vegetation periods measurements regarding crop quality and quantity were executed as well. Furthermore, soil respiration and additional (soil penetration resistance, SWC, VIgreen index) measurements were carried out during the study period, these results will be presented in a separate poster (Effect of cover cropping and soil tillage on soil CO₂ emissions).

Our results showed that differences between treatments regarding management techniques and cover crops are more characterized in maize than in oat.

How to cite: De Luca, G., Sugar, E., Fodor, N., Árendás, T., Bónis, P., and Sándor, R.: Impact of cover crops and conventional and reduced tillage on plant productivity in a bicultural maize-oat cropping system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10155, https://doi.org/10.5194/egusphere-egu24-10155, 2024.

It has long been in the focus of research interest how cover cropping affect water regime of the soil. However, its simultaneous effect on CO₂ emission, i.e. soil respiration is not so widely reported. We examined an agricultural experiment set up as a maize-oat rotation under conventional and reduced tillage tillage and four different cover-cropping treatments (fallow, oilseed radish, mixture, phacelia) in Martonvásár (Hungary). Soil respiration measurements were carried out using infrared gas analyzer in 5 replicates per treatment plot (tillage-main-crop-cover crop combinations). Measurements covered two years in the different main crops and also in cover crops. A total of 10 measurement campaigns were organized in 2021 and 2022, which covered both main crops and cover crops. Meteorological parameters were measured in a nearby automatic meteorological station.

Besides soil respiration measurements ancillary measurements have been carried out to better characterize soil status. Using a penetrologger soil penetration resistance, using handheld sensors, soil water content measurements and soil temperature was recorded. Also, point scale continuous soil water content profile measurements were carried out. At each plot, vegetation was characterized using the VI green index derived from RGB imagery and periodically chlorophyll content (SPAD) and leaf area index was recorded. Here we analyze soil respiration, VI green soil temperature and soil water content measurements. The results showed differences between tillage treatments and between main crops. For further results please see abstract “Impact of cover crops and conventional and reduced tillage on plant productivity in a bicultural maize-oat cropping system”.

How to cite: Gelybó, G., De Luca, G., Balogh, J., Fodor, N., Fóti, S., Sugár, E., and Sándor, R.: Effect of cover cropping and soil tillage on soil CO2 emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10695, https://doi.org/10.5194/egusphere-egu24-10695, 2024.

The process of organic horizon formation is reflected in the quantity and quality of the mineral materials contained. In the highland of mountains in northern Japan, thick organic horizons develop due to heavy snowfall. The organic horizons are rich in 2:1 clay minerals from Asian dust originating from the Eurasian Continent and active Al and Fe derived from volcanic ash. Organic matter in the organic horizons is present in separation or associations with these clay minerals or active Al and Fe. These organo-mineral associations make different biogeochemical properties between relatively free and mineral-associated organic matter in its dynamics, even in the organic horizons, because minerals can protect organic matter from microbial decomposition. Evaluating the biogeochemical arrangements of organic matter and minerals is valuable to understanding organic matter dynamics in the organic horizons containing rich minerals. The objective of this research is to evaluate the organo-mineral associations in the organic horizons in the snowy mountains of northern Japan using density fractionation.

The organic horizon samples were collected from three mountains. Two selected mountains (Mt. Chokai and Mt. Kurikoma) are volcanoes, and the other is a non-volcanic mountain (Mt. Makihata). Samples in Mt. Chokai were taken from each soil horizon from two soil profiles of snow meadow soils and one of dwarf bamboo and dwarf pine soil. In Mt. Kurikoma, one soil profile of a snow meadow was selected. One soil profile and two surface soils (5-15 cm) of snow meadow were collected in Mt. Makihata. Freeze-dried organic horizon samples were shaken with 1.6 g cm-3 SPT and grass beads at 16 h and 120 rpm. Recovered floating materials were sieved at 0.5 mm to remove coarse, fresh plant roots. The fraction larger than 0.5 mm was termed course light fraction (cLF), and the smaller fraction was termed small light fraction (sLF). The residue heavier than 1.6 g cm-3 was  heavy fraction (HF). Isolated fractions were freeze-dried and observed by SEM. Organic carbon and total nitrogen of isolated fractions were measured by an elemental analyzer.

The mass recovery ranged from 91.5 to 97.0%. A lower recovery rate was observed in the upper horizons, presumably due to losses attributable to higher dissolved organic carbon contents. Each isolated fraction separated by density and size showed different physicochemical properties. cLF mainly consisted of fresh roots. Decomposed plant residue was found in sLF. In HF, structures of highly decomposed plant residues combined with minerals were observed. Lower C/N of HF compared to cLF and sLF in Mt. Chokai indicated more decomposed organic matter associated with minerals. These results showed that even in organic horizons, organic matter had different physicochemical properties depending on their associations with minerals. This study highlights the importance of focusing on minerals in evaluating organic matter dynamics in organic horizons affected by aeolian dust. The stability of organic matter bound to minerals in organic horizons needs further evaluation.

How to cite: Kobayashi, K., Asano, M., and Tamura, K.: Organic matter characteristics in density fractionation of organic horizons with Asian dust and volcanic ash in snowy mountains of northern Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13777, https://doi.org/10.5194/egusphere-egu24-13777, 2024.

Agricultural land is a major contributor to human greenhouse gas emissions, but it is also affected by climate change. At the same time, the recent 4p1000 initiative has identified cropland as having important the potential to sequester atmospheric carbon in the soil.
However, there is currently a lack of robust and accurate tools to assess the carbon budget of cropland at plot level and over large areas. This lack is due to the heterogeneity of the landscape, characterised by a wide range of soil and climatic conditions and many agricultural practices. However, these tools are needed to better understand the contribution of cropland to greenhouse gas emissions and to properly identify the most efficient levers for sequestrating carbon in the soil.
In this study we propose a modelling framework to estimate carbon budgets at plot scale and over large areas. This approach assimilates optical remote sensing products with high spatial and temporal resolution into a crop model (SAFYE-CO2). This model allows the estimation of CO2 fluxes as well as crop productions (biomass and yield) of the main crops and the cover crops. This information is then used as input to a soil model (RothC) to estimate the carbon storage following the introduction of the cover crops into the soil.
This framework is validated using CO2 flux measurements from the ICOS network and cover crop in situ biomass data.
This approach is in line with the search for the 'monitoring, reporting and verification' tools that is needed today to drive the agricultural transition, to enable sustainable agriculture that provides sufficient production in a changing climate, while identifying the best practices to use agricultural land as a way of achieving net zero carbon targets.

How to cite: Pique, G., Goussard, B., and Géraud, A.: Combining remote sensing products with crop and soil models to estimate changes in soil organic carbon on cropland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18626, https://doi.org/10.5194/egusphere-egu24-18626, 2024.

Even though priming effects (PE) could reduce soil organic C gains from enhanced ecosystem productivity under global change, the PE has been introduced to few models only recently. Both particulate organic matter (POM) and mineral-associated organic matter (MAOM) decomposition may be increased by DOC (dissolved organic carbon) inputs via the priming effect (PE) which is stronger in less-protected fractions (i.e., POM) and is also influenced by the DOC input quality. In our previous study, we showed that spruce litter leachates induced a higher PE than root exudates and could track their utilization by fungi and bacteria using isotope labelling, 13C-PLFA and 13C in respired CO2 and soil C fractions (Jílková et al. 2022)

Here we use components from the KEYLINK model to develop a model that can be optimized using data from the experiment of Jílková et al. (2022) and used to predict outcomes of ongoing follow up incubation experiments using 13C-labelled spruce and beech litter leachates and root exudates on soils and fractions alone. We use this approach to test our understanding of the mechanisms of the microbially-driven soil C turnover under contrasting quality of DOM inputs.

How to cite: Vindušková, O., Deckmyn, G., Jandová, K., and Jílková, V.: Modelling priming effect to explain the effect of DOC input quality on soil C turnover, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18494, https://doi.org/10.5194/egusphere-egu24-18494, 2024.

ABSTRACT

Nowadays, due to high population pressure more fragile lands are put into farming which then leads to low crop yield, loss of biodiversity and above all contributing to increased greenhouse gas emissions. This two year study (2020-2021) evaluated the potential of legume green manure (GM) species in improving soil fertility and barley yield, and their ability to effectively sequester soil organic carbon (SOC) towards reducing greenhouse gas emissions. The GM crops; lupine and vetch were planted during the main rainy season on the land that previous barley crop was harvested and left bare and fallow. The green manures crops were chopped and ploughed under at their 50% flowering stage and the main test crop, barley was introduced during the next cropping season. The treatments included (i) vetch GM, (ii) vetch GM + 23N + 20P, (iii) lupine GM, (iv) lupine GM + 23N + 20P, (v) fallow, (vi) fallow + 46N + 20P laid down in RCBD design with three replications. The N rate used was half when integrated with the GM species but full dose with the fallow system, whereas P was full dose. Results showed that barley grain & biomass yields were increased by 3.7 to 39.8% and 10.66 to 38.58%, respectively due to the application of the GM crops. The highest grain yield (4.1 t ha^-1) and biomass yield (10.1 t ha^-1) were recorded from vetch + NP application while the least grain yield (2.94 t ha^-1) & biomass yield (7.24 t ha^-1) were registered from the traditional fallow system. Green manure addition has brought 25 to 95.41% SOC relative change in the top 0-20cm soil depth compared with the traditional fallow system. Since both GM species are legumes, they added more N to the soil alongside with storing more C in the soil so that C: N ratio was also not affected. The highest carbon sequestered was from sole application of vetch GM (26.18 t C ha^-1 yr^-1) followed by vetch + NP applications (22.82 t C ha^-1 yr^-1). Lupine GM alone sequestered 9.24 t C ha^-1 yr^-1 and lupine + NP sequestered 6.86 t C ha^-1 yr^-1. The carbon balance in the fallow and fallow + NP combinations were negative (-0.98 and -1.40 t C ha^-1 yr^-1, respectively) indicating that there was C loss to the atmosphere. Therefore, application of vetch and lupine GMs with and/or without inorganic fertilizer integration had positively contributed towards improving the yield of barley and sequestering more C as compared to the local fallow practice.

How to cite: Debele, G. G., Kassie, K., and Getachew, T.: Improving Carbon Sequestration and Yield of Barley (Hordeum vulgare) through Combined Application of Green Manure and Mineral Fertilizers under Cambisols in Ethiopian Highlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-802, https://doi.org/10.5194/egusphere-egu24-802, 2024.

Given that microbial mediated input of crop residues and their humification products may be more conducive to the transformation and sequestration of soil organic matter. The study aims to use ¹³C¹⁵N double labeling tracing technology in incubation experiments to quantify the differences in the fate and distribution contribution of the C and N of crop residues and their decomposition products under the mediation of different exogenous microorganisms with different life strategies in soil organic matter (SOM) and dissolved organic matter (DOM). The study utilized exogenous microorganisms, such as Trichoderma reesei, Trichoderma harzianum, and Phanerochaete chrysosporium (K-strategists), as well as Bacillus subtilis (r-strategist). Additionally, a combination microbial treatment comprised of Trichoderma harzianum, Phanerochaete chrysosporium, and Bacillus subtilis was also employed. The study also aims to reveal the variation patterns of soil active organic carbon and humic carbon components in response to different exogenous microorganisms. The main conclusions of the study are as follows:

• The addition of exogenous k-strategy microorganisms was more favorable than r-strategy microorganisms in mediating the increase in soil SOM contribution of crop residues derived C and N.Trichoderma treatments were more adept at mediating crop residues derived dissolvd organic carbon, and k-strategy microorganisms were more likely to stimulate soil production of dissolved nitrogen. Although the combination microbial treatment was the most effective at translational immobilization of crop residues in SOM, the Trichoderma reesei treatment had the best ability to increase soil organic carbon content by mediating crop residues translational immobilization with the lowest depletion of SOM. In addition, the addition of K-strategy microorganisms was more effective than r-strategy microorganisms in increasing the content of labile organic carbon and humic carbon fractions in the soil.
• Fungimediated humification products was significantly better than bacterial and no microbe mediated for translational immobilization in soil, and the fungal treatments contributed more to DOM and stimulated soil deriving dissolved nitrogen. The Trichoderma reesei treatment was the most effective in immobilizing the carbon and nitrogen dereived from humification products. Fungi mediated humification products was superior to bacteria in boosting labile organic carbon and humic acid fractions. The Trichoderma reesei treatment was the most effective in boosting contents of easily oxidizable organic carbon, microbial biomass carbon and humic acid carbon, whereas the combination microbial treatments significantly increased fvlic acid carbon and substantially reduced PQ values in the early part of the experiment, and the three fungal treatments were effective in increasing fvlic acid carbon in the later part of the experiment.

In summary, these conclusions provide a theoretical basis for seeking suitable microbial regulation of farmland management measures to improve SOM transformation and humification effects and provide practical reference for scientifically guiding agricultural production and soil carbon sequestration and fertilization.

How to cite: Zhang, Y.: The impact of microbial-mediated crop residues and their humification products on transformation of soil organic matter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2329, https://doi.org/10.5194/egusphere-egu24-2329, 2024.

Climate change is progressing at an alarming pace. In order to limit global warming to the agreed-upon 2°C in the United Nations Paris Agreement, we require both rapid decarbonization and the implementation of negative emissions technologies (NETs), that actively remove carbon dioxide (CO₂) from the atmosphere and ensure stable long-term carbon storage. In this context, enhanced silicate weathering (ESW) has been proposed as a NET based on a nature solution. ESW aims to accelerate the natural uptake of atmospheric CO₂ during the weathering of silicate rocks by grinding them, increasing their reactive surface and speeding up the process. This NET is particularly interesting as it does not compete for space with other economical activities. For instance, in agroecosystems, ESW is already considered a promising NET, offering multiple co-benefits for crop production when spreading silicate minerals on arable soils (i.e. increase in crop yields, restoration of soil base cations and micro- and macronutrient stocks). Besides agricultural land, urban soils can also be suitable for ESW. The application of ESW in city parcs and gardens presents an opportunity to increase the capture of atmospheric CO₂, while also favoring vegetation growth (lawn, shrubs and flowers) and potentially enhancing resistance to drought and pests.

EMBARCARB is a pilot project that aims to increase soil carbon sequestration and improve the vegetation status in two parcs of the city of Barcelona (SE Iberian Peninsula), during an extremely dry year. Moreover, the project also aims to compare the carbon sequestration capacity of soils with weathering of silicate rocks and concrete demolition fines, thus reusing construction debris and strengthening the circular economy of the region. Here, we explore the preliminary results of the project and give a first estimation of the weathering rates and the capacity of such NETs to enhance soil carbon sequestration in the green areas of the cities.

How to cite: Poblador, S., Álvarez, L., Díaz, B., Felip, M., Sabater, F., Vienne, A., and Vicca, S.: Enhancing soil carbon sequestration in the parks of the city of Barcelona , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12025, https://doi.org/10.5194/egusphere-egu24-12025, 2024.

Crop residues play a key role in supplying renewable carbon for the envisioned future greenhouse gas-neutral economy. However, their harvest is often limited below their technical potential to avoid soil organic carbon (SOC) stock losses. Nevertheless, the use of crop residues in the bioeconomy often involves the generation of a coproduct rich in recalcitrant carbon that can be reintegrated into soils to maintain SOC stocks. Yet, the environmental implications of such a strategy beyond those on climate change remain uncertain and contingent on specific contexts. Here, we present a novel framework that integrates a recalcitrance-adapted SOC model with a consequential life cycle assessment (LCA) to comprehensively evaluate the spatially explicit long-term SOC evolution and environmental impacts associated with returning various bioeconomy coproducts to croplands. The study spans diverse contexts, including temperate (France) and tropical (Ecuador) regions and five environmental impact categories, assessing the conversion of crop residues into maritime fuels, here hydrodeoxigenated pyrolysis oil (HPO) and cryogenic liquefied biomethane (bio-LNG), generating biochar and digestate as coproducts, respectively. The simulations were performed for >60,000 and >15,000 simulation units in France and Ecuador, employing adapted versions of AMG and RothC, respectively, under the RCP4.5 climate pathway in both regions. Results revealed that after 100 years, compared to a reference scenario where crop residues are directly incorporated into soils, biochar allows harvesting 100% of crop residues without any SOC losses in both French and Ecuadorian contexts. In contrast, digestate demonstrates a more limited potential, reaching 50% in France and 0% in Ecuador. This is referred to as the C-neutral harvest rate, which allows a surplus potential of 71-125 PJ in France and 113 PJ in Ecuador. The LCA revealed environmental benefits for all five impact categories for HPO and three categories for bio-LNG, per tonne of crop residues. Despite bio-LNG representing higher net avoided emissions (946 MgCO_2e) than HPO (563 MgCO_2e) per tonne of crop residues, the scaled results for the national C-neutral harvest rate showed the opposite trend with net avoided emissions of 11,912 MgCO_2e for HPO and 10,707 MgCO_2e for bio-LNG. Further, the scaled results revealed increased eutrophication impacts in marine water in the bio-LNG case, reflecting the nitrogen emissions associated with digestate, which is responsible for N₂O, NH₃, and nitrate losses to water. Yet, these can be mitigated with simple solutions such as treating digestate with nitrification inhibitors, microbial enrichment, or acidification at spreading. Moreover, biochar could be applied in tandem with digestate to create synergies from the nutrient-fertilizer effect of digestate and reduced C and N mineralization properties of biochar. In conclusion, defining a C-neutral harvest rate emerges as a pivotal strategy, ensuring a harmonious balance between SOC maintenance and net environmental impacts across diverse scenarios, emphasizing the potential of integrating bioeconomy practices with soil carbon management.

How to cite: Andrade Diaz, C. and Hamelin, L.: Tradeoffs between long-term SOC storage and overall environmental impacts of supplying crop residues to the bioeconomy: where, when, how and what does it depend on? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17426, https://doi.org/10.5194/egusphere-egu24-17426, 2024.

This study aimed to enhance the quality of biochar for applications in arid lands by employing elemental sulfur (S, 0.013%) as an acidifying agent and compost (10%) as a biological activator. The addition of elemental sulfur significantly reduced the biochar pH, with the most substantial decrease from 8.1 to 7.2 observed when co-amended with vermicompost was used. Elemental sulfur markedly increased the water-soluble concentrations of calcium (Ca) by 147% and 105%, as well as magnesium (Mg) by 929% and 447% in compost and vermicompost, respectively. This suggests a decline in biochar basicity due to acid mineral dissolution and desorption. Sulfate (SO₄^2-) levels showed the greatest increase when compost was co-applied with sulfur, indicating more efficient oxidation in this treatment. FT-IR analysis revealed increased carbonyl groups (C=O) and decreased alkyne (C≡C) groups in compost and vermicompost-treated samples, while sulfur treatment resulted in the decrease of hydroxyl groups, but only in the presence of vermicompost. SEM-EDX analysis demonstrated changes in the elemental composition and microscale pore structure of biochar samples after incubation with sulfur. Sulfur amendments stimulated substrate-induced respiration, particularly in biochar amended with sulfur (BS, 0.011 ug CO₂- C/g/h) and biochar with vermicompost (BV, 0.18 ug CO2- C/g/h) treatments. Microbial diversity (Shannon H) significantly increased in compost treatments with sulfur amendment from 3.08 to 4.52, while it decreased in vermicompost from 4.25 to 4.02. Vermicompost treatments (BV, BVS) exhibited higher microbial evenness (0.27 and 0.28) and equitability (0.67) diversity indices. The bacterial community structure was significantly influenced by all treatments, with sulfur reducing the abundance of Proteobacteria by 30% in the presence of compost and 8% with vermicompost, while increasing the abundance of Actinobacteria by 18% and 4% for compost and vermicompost treatments, respectively.Multivariate principal component analysis (PCA) indicated that soluble sulfate was associated with specific sulfur-oxidizing bacterial clusters, which were differentially expressed under different compost treatments. Integrating biochar with sulfur and compost emerges as a promising sustainable technology for managing alkalinity, enhancing soil fertility, and improving agricultural productivity in arid regions.

How to cite: Al Rabaiai, A., Menezes-Blackburna, D., Al-Ismailya, S., Janke, R., Al-Alawi, A., Al-Kindi, M., and Bol, R.: Improving Biochar Suitability for Arid-Land Use: Impact of Elemental Sulfur and Compost on Acidification and Biological Activation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14590, https://doi.org/10.5194/egusphere-egu24-14590, 2024.

Estimating the long-term stability of biochar in soil often relies on extrapolating mineralization data from short-term laboratory incubations. Various models such as single first-order (SFO), double first-order (DFO), triple first-order (TFO) and the power model have been employed for this purpose, all of which have an inherent assumption that biochar is completely biodegradable. However, recent insights challenge this assumption by highlighting that biochar consist largely of highly condensed aromatic structures, which have been proposed to be essentially inert. If biochar were resistant to microbial degradation it would make sense if this was reflected in the choice of model used. Therefore, our aim was to assess whether the proposed inert pool models (SFO+I and DFO+I) fit the data better compared to existing models (SFO, DFO, TFO and power model) using a recently compiled extensive dataset. We hypothesized that models incorporating an inert pool would fit better (or at least comparably well) to incubation data compared to the existing models and give more reliable long-term predictions. As a way of assessing the model’s predictive ability, we fitted them to progressively shortened incubation times derived from the longest biochar incubation data sets available, and then evaluated how well they extrapolated to the full measured range. Our results indicated that the proposed DFO+I model did indeed fit better than the both DFO and TFO models. Moreover, predictions of BC100 (% of carbon remaining after 100 years) by the inert pool models and by the power model displayed stronger correlations with the biochar stability indicator (H/C ratio) than both SFO and DFO models, which aligns with our initial hypothesis. However, the power model in general outperformed all other models, including the inert pool models, with the highest number of best fits. From our extrapolation exercise, it is clear the DFO model, which has been most widely used to date, substantially underestimated biochar stability in the longer term while the inert pool models tended to overestimate it. This uncertainty appears to be quite severe when fitting inert pool models to incubation data from non-pyrolysed materials. By comparison, the power model appeared to be more robust when estimating biochar persistence in soils. From these results we cannot conclusively confirm nor reject the idea of inert pool models. It is possible that an inert-pool model is the more suitable choice for extrapolating biochar decomposition data. However, it is clear from their tendency to overestimate stability of biodegradable materials. Our current understanding is hampered by the fact that the incubation data set available contains a high proportion of biochars produced at relatively modest temperatures and by a lack of chemical/structural characterization of the incubated biochars. Future research could remedy this by providing better information on the degree of aromatic condensation/proportion of inertinite in incubated biochars samples. For now, we recommend the power model as the most robust option.

How to cite: Li, H., Azzi, E. S., Sundberg, C., Karltun, E., and Cederlund, H.: Assessing inert pool models for estimating long-term biochar stability in soil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9202, https://doi.org/10.5194/egusphere-egu24-9202, 2024.

Carbon storage in soils is a significant nature-based solution for adaptation and mitigation of climate change. However, soil carbon storage varies with the change in land cover and the association of organic matter with differently sized soil aggregates. To compare the effects of these parameters on the carbon cycling of soils, we have analyzed the soil carbon content and greenhouse gas emissions from soils under different land cover in Gujarat, India. We sampled forest soils from regions covered with dry deciduous trees, moist trees, forest fires, and forest conversion to agriculture. We further sampled grassland soils in the areas showing matured grasses, harvested grasses, salinity-affected grasses, grazing-affected grasses, and the grassland region impacted by the invasion by Prosopis juliflora species. We classified some of these land features as a result of climatic disturbances (increase in salinity, invasion by Prosopis, forest fire) and others as anthropogenic disturbances (cattle grazing, harvesting, agriculture). Physico-chemical properties and greenhouse gases emitted from soils were measured using handheld probes and chamber methods, respectively. Laboratory analysis of soil carbon and its isotopes was performed for bulk soils and the soil density-size fractions (particulate fractions, sand-sized fractions, clay and silt size fractions, and recalcitrant organic matter fractions). Our analysis reveals the change in carbon emissions and carbon storage in soils of arid-moist stretch in Gujarat is caused by different land cover and management practices. The presence of aboveground biomass has a significant control on the carbon storage capacity of soils highlighting the importance of afforestation and ecosystem restoration in building up the soil carbon stock. Carbon emissions were also higher in soils with large aboveground vegetation; however, this mainly represents soil microbial respiration and thus indicates healthy soil and rich pedo-biodiversity. Most of the carbon in grassland soils was associated with silt and clay-sized particles whereas the carbon content in forested soils is higher within sand-sized particles. Soils from both grasslands and forests acted as a sink for atmospheric methane except for soils from grazed grasslands, indicating the importance of grazing management in grassland ecosystems. Climatic stressors like an increase in salinity and Prosopis invasion showed no significant impact on soil carbon stock and greenhouse gas emissions and behaved similarly to harvested grasslands or dry-deciduous forests. Forest fire, on the other hand, can change the texture and carbon and nitrogen association in the soils. Conversion of forests to croplands has the most detrimental impact on soil carbon storage and can lead to loss of stored carbon in the form of high greenhouse gas emissions. Forest land conversions should, therefore, also consider this aspect of forest conversion in its management plan.

How to cite: Sharma, N., Khan, M. A., Dubey, P., Pandey, C. N., Kumar, S., and Jain, V.: Soil carbon storage and greenhouse gas fluxes in forested and grassland ecosystems of Gujarat undergoing anthropogenic and climatic disturbances, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19605, https://doi.org/10.5194/egusphere-egu24-19605, 2024.