SSS5.2 | Carbon sequestration in soils: organic and inorganic mechanisms of increasing soil carbon stocks as a pathway to net zero and improved soil functioning
Carbon sequestration in soils: organic and inorganic mechanisms of increasing soil carbon stocks as a pathway to net zero and improved soil functioning
Including Arne Richter Awards for Outstanding ECS Lecture
Co-organized by BG8
Convener: Chris McCloskeyECSECS | Co-conveners: Felix Seidel, Laura SchneeECSECS
Orals
| Wed, 17 Apr, 14:00–18:00 (CEST)
 
Room D2
Posters on site
| Attendance Thu, 18 Apr, 10:45–12:30 (CEST) | Display Thu, 18 Apr, 08:30–12:30
 
Hall X2
Posters virtual
| Attendance Thu, 18 Apr, 14:00–15:45 (CEST) | Display Thu, 18 Apr, 08:30–18:00
 
vHall X2
Orals |
Wed, 14:00
Thu, 10:45
Thu, 14:00
Soils represent a major terrestrial store of both organic and inorganic carbon. At present soils are a net carbon sink, and building soil carbon stocks holds a potential to contribute to achieving net zero carbon. Furthermore, the accrual, stability, and cycling of carbon is fundamental to the productivity and resilience of soil systems, and preserving or even increasing soil carbon stocks is critical for allowing sustainable agricultural crop production.

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 as long as 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. Is there a threshold above which a soil profile can no longer increase its carbon stock? What determines the fate of C inputs to the soil? What are the mechanisms determining differences between soils’ capacity to stabilise C?

Session assets

Orals: Wed, 17 Apr | Room D2

Chairpersons: Chris McCloskey, Laura Schnee
14:00–14:05
Carbon sequestration and storage in soils
14:05–14:25
|
EGU24-22139
|
solicited
|
Highlight
|
On-site presentation
Sebastian Doetterl

Improving carbon storage in soils and the biosphere is a promising nature-based solution to combat climate change and is receiving more and more attention with little understanding how this can be achieved globally and in a sustainable way.

Many of our expectations in finding nature-based solutions rely on vast, less developed–but nevertheless populated and rapidly changing– regions of the Global South. At the same time, concepts and assumptions about which solutions work for increasing long-term carbon capture in soil systems are based on knowledge gathered largely from the Global North in often fundamentally different environmental settings and development history. 

In my talk I will illustrate with examples from the socio-ecological context of the African Tropics how these knowledge gaps and our lack of understanding of tropical carbon cycling mislead us into thinking that we can find easy solutions in the Tropics to mitigate climate change. I will highlight how the interactions of weathering and erosional disturbance can influence and dominate biogeochemical cycles in soils and discuss some directions where geochemical proxies that are available at the global scale can be useful for improving the spatial and temporal representation of tropical carbon storage and turnover.

How to cite: Doetterl, S.: Soil carbon sequestration in sub-Saharan Africa – Great expectations, limited potentials?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22139, https://doi.org/10.5194/egusphere-egu24-22139, 2024.

14:25–14:35
|
EGU24-221
|
ECS
|
On-site presentation
Sara M. Pérez-Dalí, Águeda Sánchez-Martín, Jorge Márquez-Moreno, Jose A. González-Pérez, Layla M. San-Emeterio, and José María de la Rosa

The application of organic amendments, both traditionally utilized (e.g., compost) and more recent innovations (e.g., biochar), to degraded agricultural soils is being driven by international initiatives in the current context of global change, such as the "4 per mil initiative". The main goal is to achieve sustainable soil quality restoration, contributing to carbon (C) sequestration, while also providing a practical use and value addition to agro waste products. Despite the generally recognized benefits of such applications on soil productivity and physical properties [1,2], their effects on soil C cycling and sequestration are not as comprehensively understood. Results exhibit considerable variability depending on the type of amendment and the specific soil, emphasizing the need for a more in-depth investigation in this area [3]. Therefore, the aim of this study was to analyze the effects of contrasting organic amendments on soil carbon stability.

To accomplish this, two soils commonly employed in humid grasslands of the northern region and rainfed agriculture in the southern region of the Iberian Peninsula, respectively, were amended in triplicate at 10% (w/w) with wastewater sludge biochar, olive pomace biochar , white poplar wood biochar, rice husk biochar, cow manure digestate, a mixture of cattle manure and straw digestate (CM&SD), green compost (GC), and a mix of GC and OPB. A control was also established for each type of soil. After inoculating all the vessels with 1 mL of a standard microbial solution, respiration rates (CO2 emissions) were measured every 6 h over 100 days using an automated respirometer (Nordgren Innovations, Sweden) under controlled conditions (25°C; 60% water holding capacity). The data obtained were plotted against the incubation time by an exponential curve to discern the C stability through fast and slow C pools.

Our findings revealed significantly enhanced stability of recalcitrant carbon (slow C pool) in both soils treated with biochars, particularly in the case of RHB and WB. These amendments substantially extended the mean residence time of the slow C pool (MRT2) by a factor of six to nine. The overall trend observed for the studied amendments was as follows: biochar >> green compost >> digestates > native soil carbon. In contrast, the alkaline rainfed soil exhibited a faster carbon turnover rate compared to the grassland soil, resulting in a lower C MRT2.

Acknowledgements:  The Spanish Ministry of Science and Innovation (MCIN) and AEI are thanked for funding the project RES2SOIL (PID2021-126349OB-C22). The European Joint programme EJP SOIL from the EU Horizon 2020 R&I programme is thanked for funding the subproject EOM4SOIL (Grant agreement Nº 862695).

References:
[1] De la Rosa, J.M., Pérez-Dalí, S.M., Campos, P., Sánchez-Martín, Á., González-Pérez, J.A., Miller, A.Z., 2023. Agronomy, 13, 1097.
[2] Doblas-Rodrigo, A., Gallejones, P, Artetxe, A., Merino, P., 2023. Sci. Total Environ., 901, 165931.
[3] De la Rosa, J.M., Rosado, M., Paneque, M., Miller, A.Z., Knicker, H., 2018. Sci. Total Environ., 613-614, 969-976.

How to cite: Pérez-Dalí, S. M., Sánchez-Martín, Á., Márquez-Moreno, J., González-Pérez, J. A., San-Emeterio, L. M., and de la Rosa, J. M.: Effects of Contrasting Organic Amendments on Carbon Stability and Soil Carbon Dynamics in Acidic and Alkaline Soils , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-221, https://doi.org/10.5194/egusphere-egu24-221, 2024.

14:35–14:45
|
EGU24-11164
|
ECS
|
Highlight
|
On-site presentation
Florian Schneider, Daria Seitz, Felix Seidel, and Axel Don

In order to estimate a feasible carbon (C) sequestration potential in European agricultural soils, we need to know the area where additional measures that increase soil organic carbon (SOC) can be implemented and the corresponding SOC accrual rates. In this study, we focus on the former and identify areas where promising SOC increasing practices can be implemented on European agricultural soils.

The practices considered include a higher share of agroforestry, cover crops replacing bare winter fallows, reduced tillage instead of ploughing and the integration of perennial legumes and leys into crop rotations. Open-access data of European Farm Structure Surveys as provided by EUROSTAT at NUTS2 level serve as a reference for the intensities at which the measures are already implemented in Europe. It was assumed that only the further spread of these measures could potentially sequester additional C in soils.

We argue that the adoption of reduced tillage is the practice that covers by far the largest area relevant for potential C sequestration in soils under current food, feed, and fibre demands. The replacement of bare winter fallow with cover crops is restricted to regions with sufficient growing degree days to allow a second crop after harvest. The introduction of more woody features like hedgerows and alley cropping to agro-ecosystems, as well as the integration of more perennial legumes or leys in present crop rotations creates the need for land reallocation and likely compromises agricultural productivity.

Overall, we conclude that reduced tillage may emerge as the most promising practice for atmospheric C sequestration in European agriculture despite its reported relatively low SOC accrual rate per hectare. Trade-offs between C sequestration in soils, agricultural production and agricultural demand warrant further inter-disciplinary attention.

How to cite: Schneider, F., Seitz, D., Seidel, F., and Don, A.: Areas available for potential carbon sequestration in European agricultural soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11164, https://doi.org/10.5194/egusphere-egu24-11164, 2024.

14:45–14:55
|
EGU24-8970
|
On-site presentation
|
Alexander Prechtel, Simon Zech, and Nadja Ray

Background: Carbon storage and turnover in soils depend on the interplay of soil architecture, microbial activities and soil organic matter dynamics. For a fundamental understanding of the mechanisms that drive these processes, not only the exploitation of advanced experimental techniques down to the nanoscale is necessary, but also spatially explicit and dynamic image-based modeling at the pore scale.
We present a modeling approach which is capable of transferring microscale information into macroscale simulations at the profile scale. This enables the prediction of future developments of carbon fluxes and the impact of changes in the environmental conditions linking scales.
We consider a mathematical model for CO2 transport across soil profiles (macroscale) which is informed by a pore-scale (microscale) model for C turnover. It allows for the dynamic, self-organized re-arrangement of solid building units, aggregates and particulate organic matter (POM) based on surface interactions, realized by a cellular automaton method, and explicitly takes spatial effects on POM turnover such as occlusion into account. We further include the macroscopic environmental conditions water saturation, POM content, and oxygen concentration.

The coupled simulations of macroscopic transport and pore scale carbon and aggregate turnover reveal the complex, nonlinear interplay of the underlying processes. Limitations by diffusive transport, oxygen availability, texture dependent occlusion and turnover of OM drive CO2 production and carbon storage.

Zech, Prechtel, Ray (2024): Coupling scales in process-based soil organic carbon modeling including dynamic aggregation. J. Plant Nutr. Soil Sci.

How to cite: Prechtel, A., Zech, S., and Ray, N.: Coupling scales in process-based soil organic carbon modeling including dynamic aggregation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8970, https://doi.org/10.5194/egusphere-egu24-8970, 2024.

14:55–15:05
|
EGU24-10379
|
On-site presentation
Pengzhi Zhao, Daniel Fallu, Sara Cucchiaro, Ben Pears, Andreas Lang, Paolo Tarolli, Sebastian Doetterl, Jeanette Whitaker, Tony Brown, and Kristof Van Oost

Agricultural terraces, being among the volumetrically largest and most common man-made landforms, have been widely implemented to support essential soil ecosystem services, e.g., erosion control, soil nutrient, and water retention, and have had an essential impact on soil organic carbon (SOC) stock and its exchange with the atmospheric C. However, the direction and magnitude of this impact remain highly uncertain. By integrating the broad-scale field observations of 14 terrace sites across the EU with a global data synthesis, we demonstrate that the effectiveness of terracing-driven SOC sequestration potential is intricately controlled by climate conditions that govern in-return soil properties.

Our findings reveal that the terracing practices represent a promising land management strategy for enhancing SOC sequestration, but also that risks of SOC loss exist when building terraces under arid climate, where they could be potentially very beneficial to crop productivity and SOC storage. We recommend that future terrace construction should integrate water and nutrient recycling techniques to ensure soil moisture and nutrient availability, enhancing land productivity and maximizing SOC sequestration potential. Our data suggest that promoting the recovery of the lost topsoil C during terrace construction through increasing C inputs and C use efficiency, i.e., straw return and nutrient amendment is an efficient way to counteract initial SOC losses.

How to cite: Zhao, P., Fallu, D., Cucchiaro, S., Pears, B., Lang, A., Tarolli, P., Doetterl, S., Whitaker, J., Brown, T., and Van Oost, K.: Climate conditions control the SOC sequestration potential of agricultural terraces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10379, https://doi.org/10.5194/egusphere-egu24-10379, 2024.

15:05–15:15
|
EGU24-19022
|
On-site presentation
Shinya Iwasaki, Kosuke Hamada, Kazutoshi Kinjo, Yudai Yamaura, Yoshifumi Terajima, and Toshihiko Anzai

Achieving increased or sustained crop yields while minimizing environmental impact is a pressing challenge in agricultural science. Enhanced Rock Weathering (ERW) has emerged as a novel negative emission technology that accelerates natural geological processes of carbon (C) sequestration by applying crushed silicate rocks, specifically basalt, to croplands. However, field-scale evaluations to demonstrate carbon sequestration potential and agricultural co-benefits have been limited. This study quantitatively assessed the carbon and nitrogen (N) flow resulting from basaltic rock application in sugarcane and upland rice cultivation in a sub-tropical agroecosystem.

Two types of experiments were conducted on Ishigaki Island, located in the subtropical zone of Japan, where the annual rainfall and annual temperature were 2,500 mm and 24.0 ℃, respectively. Firstly, an outdoor field experiment on sugarcane cultivation was conducted. The following six treatments were applied with four replicates using a completely randomized block design: bare soil (no sugarcane), control without any amendment, lime application, manure application (10 Mg C ha−1), basaltic rock application (10% by weight), and a combination of manure and basaltic rock. Soil water at the 0.6 m depth, which we defined as leaching water, was collected from all plots using the porous cup method and subjected to dissolved C and N analysis. Secondly, an indoor lysimeter experiment was conducted on upland rice cultivation to understand the comprehensive flow of C and N, including greenhouse gas emissions. The following four treatments were assigned with three replicates to 12 concrete lysimeters with 2 m2 and 1 m depth: control without any amendment, torrefied plant residue (1% by weight), basaltic rock application (10% by weight), and a combination of torrefied plant residue and basaltic rock.

In the outdoor field experiment, continuous monitoring of soil volumetric water content and electric conductivity showed that the weathering of basaltic rock was enhanced by solid-liquid contact. Soil pH increased by the basaltic rock application the same as lime application. Similarly, the acidification of leaching water was buffered in the basaltic rock application treatments. Consequently, the inorganic carbon concentration in leaching water was higher in the basaltic rock application treatments than in the control and lime application treatments. Although there were no significant differences in the plant height of sugarcane, the number of leaves and Single Photon Avalanche Diode (SPAD) increased by basaltic rock application. Similarly, the indoor lysimeter experiment observed higher pH and dissolved inorganic C concentrations in leaching water. Although carbon dioxide flux increased by basaltic rock application in the first month, it was decreased in the crop growing period. These results indicated that the ERW application has a C sequestration potential and co-benefit on crop production. The annual C and N budget and further discussion will be presented in the session.

How to cite: Iwasaki, S., Hamada, K., Kinjo, K., Yamaura, Y., Terajima, Y., and Anzai, T.: Enhanced rock weathering application on sub-tropical agroecosystems for carbon sequestration and sustainable crop production, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19022, https://doi.org/10.5194/egusphere-egu24-19022, 2024.

15:15–15:45
|
EGU24-11742
|
ECS
|
solicited
|
Arne Richter Awards for Outstanding ECS Lecture
|
On-site presentation
Daniel Evans

Terrestrial environments and their ecosystems demand healthy, sustainable, and resilient soils. Over the past couple of decades, significant efforts have been made to safeguard global soils, yet the materials and resources responsible for soil formation have been widely overlooked.  The transition from bedrock to soil – a zone often described as ‘soil parent material’ – holds an exciting yet untapped potential for helping us address some of the largest environmental challenges, including climate change and the biodiversity crisis. In this award lecture, I will present a strand of my research programme ‘Building Tomorrow’s Soils’ which seeks to establish how soil parent materials enhance the sustainability, health, and resilience of soil systems. First, with a focus on carbon sequestration, I will highlight how the bedrock–soil transition zone has the potential to be a long-term store of organic carbon. I will then present research which shows that some soil parent materials release petrogenic (i.e. rock-derived) organic carbon into soils. These understudied inputs of organic carbon to soils are currently absent from most, if not all, soil carbon models, which threatens our ability to optimize soil carbon management in the long-term. Finally, I will argue that developing a mechanistic understanding about this transition zone – this underexplored material which is neither rock nor soil in structure and function, but a blend of both – requires a similarly cross-disciplinary approach.

How to cite: Evans, D.: Digging into the Future: The transition between bedrock and soil as an underexplored frontier zone in geoscience, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11742, https://doi.org/10.5194/egusphere-egu24-11742, 2024.

Coffee break
Chairpersons: Chris McCloskey, Felix Seidel
16:15–16:20
Advances in understanding carbon stabilisation and destabilisation in soils
16:20–16:40
|
EGU24-9216
|
solicited
|
Highlight
|
On-site presentation
Christopher Poeplau, Rene Dechow, Neha Begill, and Axel Don

Accrual of soil organic carbon (SOC), and especially the formation of mineral associated organic carbon (MAOC), has a large theoretical potential to act as sink for atmospheric CO2. For reliable estimates of this potential and efficient policy advice, the major limiting factors need to be understood. The positive correlation between the content of fine mineral particles (silt + clay) and the content of MAOC is widely used to estimate a general maximum MAOC storage capacity of soils, based on the notion that mineral surfaces get C saturated. However, recent literature raised doubts about the concept of C saturation and it remains unclear, if and to what extent the mineral capacity of soils to stabilise C limits SOC accrual. Here, using large scale soil datasets and the model RothC, we provide two independent lines of evidence, that the upper boundary line of the correlation between MAOC and silt and clay does not resemble a maximum mineralogical SOC stabilisation capacity. 1. In coarse-textured soils, the C loading of the silt and clay fraction was found to strongly overshoot the mentioned upper boundary line and thus exceed previous C saturation estimates. 2. A global modelling exercise revealed that only for 28.8 % of all soils, local net primary production (NPP) would be sufficient to reach a C loading of 80 g C kg-1 silt and clay, which is currently assumed to be the maximum capacity of soils to stabilise C. This proportion decreased strongly with increasing silt and clay content, which revealed that high C loadings can hardly be reached in more fine-textured soils. We conclude that SOC accrual is mainly limited by C inputs and strongly modulated by texture, mineralogy and climatic conditions. Taken together, those factors could be used to be formulate an ecosystem capacity to stabilise SOC. However, a potential C saturation point of MAOC appears still unknown and of no relevance for strategies of climate mitigation via SOC sequestration.

How to cite: Poeplau, C., Dechow, R., Begill, N., and Don, A.: Net primary production rather than saturation of mineral surfaces limits soil carbon sequestration , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9216, https://doi.org/10.5194/egusphere-egu24-9216, 2024.

16:40–16:50
|
EGU24-3492
|
On-site presentation
Jeanette Whitaker, Kelly Mason, Ashley Taylor, Pengzhi Zhao, Tim Goodall, Rob Griffiths, Niall McNamara, and Dafydd Elias

Mineral-associated organic matter (MAOM) forms from plant or microbial-derived compounds and comprises the largest reservoir of soil organic carbon (SOC) globally.  Most SOC is associated with soil minerals and mineralogy is considered a primary control on SOC persistence due to variations in mineral reactivity. However, most mineral-associated SOC is microbial in origin thus microbial residue formation, through the processing of plant inputs, may also control SOC dynamics. Current understanding suggests that litter quality controls the formation of MAOM with high-quality litter producing more microbial residues which are then stabilised on mineral surfaces. We hypothesized that inputs of high-quality litter would lead to a net increase in MAOM stocks, relative to low-quality litter, through more efficient formation of MAOM and less priming of existing SOC.  We also hypothesised that soil mineralogy would act as the primary control on the formation of MAOM relative to litter quality. To test our hypotheses, we amended an agricultural soil with common soil minerals (Kaolinite, Montmorillonite and unamended control) and incubated these amended soils in the laboratory with two surface-applied 13C labelled litters of contrasting qualities (high quality - White Clover and low quality - Winter Wheat). During the incubation, litter decomposition and priming were quantified by δ13CO2 analysis. After 4 months, mineral stabilisation of litter-C, the amounts of particulate organic matter (POM) remaining and litter-C assimilated into microbial biomass were all quantified, along with characterisation of the soil microbial communities. Soil mineralogy strongly influenced the efficiency of MAOM formation, with Montmorillonite-amended soils respiring less litter-C and stabilising more as MAOM. High quality litter led to less (not more) efficient production of MAOM due to soil microbial community shifts associated with lower carbon-use efficiency. Low-quality litter enhanced priming of pre-existing SOC, counterbalancing the effect of litter quality on MAOM stocks.  Taken together, our findings demonstrate that soil mineralogy was the primary control on MAOM formation and that litter-microbial interactions determine the effect of litter quality on MAOM.  These findings refute the hypothesis that high-quality plant litters form MAOM most efficiently and demonstrate that mineral and microbial interactions regulate the formation of stable SOC.

How to cite: Whitaker, J., Mason, K., Taylor, A., Zhao, P., Goodall, T., Griffiths, R., McNamara, N., and Elias, D.: Microbial and mineral interactions decouple litter quality from soil organic matter formation , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3492, https://doi.org/10.5194/egusphere-egu24-3492, 2024.

16:50–17:00
|
EGU24-8770
|
ECS
|
On-site presentation
Neha Begill, Axel Don, and Christopher Poeplau

The hotly debated concept of carbon (C) saturation in mineral soils not only affects our understanding of soil organic matter (SOC) dynamics but also holds critical implications for negative emissions strategies. Many recent studies have indicated that soil’s capacity to store and stabilize C in mineral form depends on the initial SOC content, i.e., the soil C saturation deficit. According to these studies, low-C soils are suggested to have a higher potential for SOC storage compared to high-C soils. In light of these considerations, our hypothesis presents a different viewpoint, suggesting that initial C content in soils mainly affects the absolute loss of old carbon (following first-order kinetics), while it will not significantly impact the soil’s ability to stabilize new C. To investigate this experimentally, we selected soils from the first German Agricultural Soil Inventory with varying C contents (0.7–14.5%) and three different soil textures (light to heavy). These soils were then incubated in air-tight glass jars, where the same amount of 13C labeled litter was added, along with an unamended control of each sample. After two years, soils were dried and physically fractionated into mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) using a size-cutoff of 20µm to find and δ13C as well as total SOC was measured. Here, we will present the first results from this lab incubation experiment, providing further systematic insights into whether the amount of initial carbon content or the ‘saturation C’ deficit truly affects the SOC dynamics with varying amounts of C contents in it.

How to cite: Begill, N., Don, A., and Poeplau, C.: Influence of initial soil carbon content on the stabilization of new carbon: a 2-year lab incubation study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8770, https://doi.org/10.5194/egusphere-egu24-8770, 2024.

17:00–17:10
|
EGU24-4695
|
ECS
|
On-site presentation
Anna Gunina, Ying Wang, and Yakov Kuzyakov

Most of the organic carbon (C) in soil is linked to various degrees with the mineral matrix, which includes the formation of aggregates and the association of organic C with clay minerals and Fe and Al hydro(oxides). Both mechanisms ensure the physical stabilization of organics against microbial decomposition and the stability of the soil system. The present work analyzed the processes of C stabilization, and C flows between the aggregate size classes of macro- and macroaggregates and density fractions (free and occluded light (FL, OL), occluded dense (OD) and mineral (MF)) based on the 13C natural abundance approach using 73 published works and looked at the two groups of factors: i) internal (edaphic soil properties) and ii) external (type of land use and climate).

The global pattern showed the relative enrichment of 13C in silt + clay fraction for 0.4‰ and MF for 0.25-0.6‰ compared to bulk soil. In contrast, organics in micro- and macroaggregates and FL and OL fractions were 13C depleted, reflecting the fast decomposition of these pools and input of fresh plant-derived organics. The difference in 13C enrichment between the OL and MF fractions was 1.3‰, whereas between macroaggregates and silt+clay fraction 0.6‰, showing that density fractionation could more accurately reflect the intensity of organic C processing by microorganisms and fractions are more homogeneous in composition than aggregates.

The 13C enrichment in silt + clay and MF increased with the clay content; the difference between the 13C enrichment for OL and both dense fractions and macroaggregates and silt + clay fractions rose. Forests, grasslands, and croplands showed the same trend of increasing 13C enrichment with decreasing aggregate size classes; grasslands and croplands showed higher enrichment of silt+clay associated C (~0.3‰ relative to bulk soil) than forests. Under grasslands and forests, 13C enrichment in OD and MF was higher than in agriculture, showing deep microbial processing of organic matter without structure disturbance. The differences in 13C enrichment of organic matter between the aggregate size classes (0.6-0.9‰) and density fractions (2.5-3‰) were higher under subtropical and tropical climates, compared to temperate and Mediterranean, reflecting more intensive recycling of organic matter by microorganisms.

C flows between the aggregates followed the trend from macroaggregates to silt+clay fraction and from large macro- to microaggregates, reflecting the well-known sequential formation of soil structure and macro aggregates' role in stabilizing plant residues. More intensive C flows were found from FL to MF, compared to the C flow from OD to MF, pointing to the importance of plant-derived organics and microbial metabolites for the formation of MF. Thus, the global pattern of organic C transformation identified that the 13C natural abundance approach could be used for a broad range of automorphic soil types and can open a new perspective for the estimation of processes of C recycling and reveal the intensity of microbial processes depending on the land use, soil edaphic factors and climate.

How to cite: Gunina, A., Wang, Y., and Kuzyakov, Y.: 13C natural abundance approach for analysis of steps of organic carbon transformation in soil: application for various ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4695, https://doi.org/10.5194/egusphere-egu24-4695, 2024.

17:10–17:20
|
EGU24-1152
|
ECS
|
On-site presentation
Robin Schäfferling, Lilli Zeh, Patrick Wordell-Dietrich, Alina Azekenova, Alexandra Koller, Kenton Stutz, Karl-Heinz Feger, Stefan Julich, Goddert von Oheimb, and Karsten Kalbitz

Dead wood has important functions in forest ecosystems. It is a biodiversity hot spot, serves as a storage of water and stores 8% (73 +- 6 Pg) of the world’s forest carbon (Pan et al., 2011). The fate of this carbon (C) is still highly debated particularly concerning its influence on soil organic matter (SOM) and its contribution to the forest soil’s C sink. The aim of this research is to investigate how downed beech dead wood affects the stable soil C pool of temperate beech forests, and how this depends on soil moisture.

The research was conducted in a near natural beech forest near Leipzig, Germany (Dübener Heide) and is part of the BENEATH-Project. We sampled three sites representing a soil moisture gradient, i.e. dry, intermediate (i.e. moist) and wet conditions. Undisturbed soil cores were taken from these sites in three depth (0-10 cm, 10-20 cm and 20-30 cm) beneath dead wood at an advanced stage of decay. Reference soils were sampled at a distance of about 2 m. Soil moisture and soil temperature are constantly monitored. We applied a physical fractionation scheme to identify the effects of dead wood on differently stable SOM fractions. The samples were separated in the free light fraction (F-LF), the occluded light fraction (O-LF) and the heavy fraction (HF) via density fractionation using sodium polytungstate solution (ρ =1,6 g cm-³). For each fraction, the organic C and N contents were determined.

Our results indicate a positive influence of dead wood on SOC stocks in the dry and wet regions of our soil moisture gradient. In the intermediate region of the soil moisture gradient, dead wood has no or even a negative effect on SOC stocks. Changes in the SOC content under dead wood compared to the reference soil occurred manly in the F-LF and HF fraction at 0 cm and 10 cm depth. The observed pattern of dead woods effect on SOC along the moisture gradient is suggested to be a result of the relationship between soil moisture and microbial activity. According to the literature, we assume that the microbial activity should be highest in the intermediate moist soil and to some extent inhibited under either wet or dry conditions. In this case, it is not the input but the rate of decomposition that changes with soil moisture, resulting in a different net increase in SOC. To test our hypothesis, we attempt to estimate the theoretical time of effective microbial decomposition per year based on soil moisture and soil temperature data for our three sites. Correlation analysis will be used to test this indicator of microbial activity for the effect of dead wood on SOC.

Our results should sharpen the picture of the dead wood’s role for long-term C stabilization in forest soils and how this process is affected by differences in the soil moisture status. They will give implications for climate mitigating forest management.

How to cite: Schäfferling, R., Zeh, L., Wordell-Dietrich, P., Azekenova, A., Koller, A., Stutz, K., Feger, K.-H., Julich, S., von Oheimb, G., and Kalbitz, K.: Soil moisture determines dead wood effects on soil organic matter in temperate beech forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1152, https://doi.org/10.5194/egusphere-egu24-1152, 2024.

17:20–17:30
|
EGU24-12698
|
ECS
|
Highlight
|
On-site presentation
David Emde, Christopher Poeplau, Axel Don, Stefan Heilek, and Florian Schneider

Land-use change (LUC) in agricultural settings is common both historically and under more recent climate-smart agriculture guidelines aimed at reducing the impact of agriculture on the climate. Recognising that conversion of perennial grasslands to annual cropland results in a large, but potentially reversible, loss of soil organic carbon (SOC) such guidelines often call for increasing the overall area under grassland. To date, the magnitude and direction of SOC change following LUC has been fairly well accounted for, but the time it takes to reach a new SOC equilibrium is not well understood. While broad scale emission reporting best practices (e.g. IPCC) suggest that SOC equilibrium is reached approximately 20 years after LUC, there is a growing body of knowledge that supports a centennial timescale in temperate or boreal climates. With data from the first German Agricultural Soil Inventory alongside extensive per-site land-use histories, we established SOC change timelines that show that not only does SOC take much longer than 20 years to reach equilibrium but it reaches equilibrium at vastly different rates depending on the direction of LUC. Sites converted from cropland to grassland took 83 years (95 % CI: 79 to 90 years) to reach SOC equilibrium whereas sites converted from grassland to cropland took 180 years (95 % CI: 151 to 223 years). In order to map the effects of historic LUC on SOC stocks in temperate agroecosystems with similar grassland and cropland SOC stocks to Germany, we applied these timeline models to comparable sites from the HILDA+ global LUC database (Winkler et al., 2020); a global reconstruction of annual land use and land cover at a 1 km spatial resolution from 1899 to 2019. Compiled from a range of open data sources (remote sensing, reconstructions, and census data) the HILDA+ dataset offers insights into relatively fine scale LUC dynamics that follow known socioeconomic drivers over the past 120 years. Using this dataset, we determined that 112 Million ha, or 3.5 % of the total agricultural area worldwide, was comparable to German agriculture in terms of SOC and growing conditions, and 11 % of that land (12.6 Million ha) had undergone LUC from cropland to grassland or vice versa since 1899. After accounting for duration on a per-cell basis, areas having undergone LUC from cropland to grassland (7.5 million ha) accounted for a 86.2 million Mg C increase over the past 120 years. Conversely, areas having undergone LUC from grassland to cropland (5.1 million ha) accounted for a -55.0 million Mg C decrease in SOC. The overall net increase of 31.2 million Mg C corresponds to about 5‰ of total SOC stocks across all agricultural land with pronounced regional differences. We conclude that land-use change histories of at least one century should be considered when interpreting present-day, and predicting future, SOC dynamics.


Winkler, K., Fuchs, R., Rounsevell, M. D. A., & Herold, M. (2020). HILDA+ Global Land Use Change between 1960 and 2019 [dataset]. PANGAEA. https://doi.org/10.1594/PANGAEA.921846

How to cite: Emde, D., Poeplau, C., Don, A., Heilek, S., and Schneider, F.: The centennial legacy of land-use change on organic carbon stocks of temperate agricultural soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12698, https://doi.org/10.5194/egusphere-egu24-12698, 2024.

Cover crops and carbon sequestration in soils
17:30–17:40
|
EGU24-17654
|
ECS
|
On-site presentation
Ferdinando Binacchi, Murilo Veloso, Cimélio Bayer, Christopher Poeplau, Carsten Mueller, Franz Buegger, and Andreas Gattinger

Diversification of no-till cropping systems through the inclusion of leguminous crops can be a sustainable means for enhancing both the bioavailability as well as the persistence of soil organic carbon (SOC). Therefore a comprehensive assessment of long-term soil organic matter (SOM) dynamics is crucial to realize the potential of sequestering atmospheric carbon dioxide, while concomitantly restoring the productivity and functionality of degraded soils. In the current study, soil samples were taken from a 39 years old subtropical trial at seven soil increments until one meter depth. Treatments included five maize-based cropping systems, with increasing shares of leguminous cover crops, with or without nitrogen (N) fertilizer applications to the maize plants. Varying degrees of labile and recalcitrant SOC were distinguished by means of thermal analysis as well as through physio-chemical fractionation, yielding contrasting results in shares of carbon accumulation across conceptual pools. While thermally recalcitrant SOC (combusted at temperatures between 400˚C and 800 ˚C) represented a small percentage of total C accrual, chemically recalcitrant SOC (silt and clay fraction resisting sodium hypochlorite oxidation) reported both a large share of total C content, as well as a high C accumulation. Although limited overlap among C pools from the two fractionations was found, irrespective of C detection method, systems with higher shares of leguminous cover crops reported highest SOC stocks. Interestingly, including additional leguminous cover crops contributed in storing as much SOC as systems with N fertilization, but the depth at which SOC sequestration occurred varied between fertilized and non-fertilized systems. While SOC stocks in the 0-30 cm depth correlated positively to total C inputs from crop residues in both fertilized and unfertilized systems, SOC stocks in the subsoil (30-100 cm depth) only correlated (p<0.05) to inputs from leguminous cover crops in non-fertilized systems.

Moreover, shifts in δ¹³C signatures across the five physically separated C fractions (silt+clay, recalcitrant SOC , stable aggregates + sand, dissolved organic carbon and particulate organic matter), were used to calculate contributions of C₃ leguminous C inputs in mixed C₃/C₄ cropping systems and study pathways of SOC dynamics.  

Overall, the study reports high potential of leguminous cover crops to contribute to SOC build-up in subtropical Oxisols, especially through the association of labile organic matter to soil minerals.

How to cite: Binacchi, F., Veloso, M., Bayer, C., Poeplau, C., Mueller, C., Buegger, F., and Gattinger, A.: Distribution of soil organic carbon across contrasting fractionation techniques - results from a long-term field trial with increasing shares of leguminous cover crops, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17654, https://doi.org/10.5194/egusphere-egu24-17654, 2024.

17:40–17:50
|
EGU24-9389
|
ECS
|
Highlight
|
On-site presentation
Laura Reinelt, Nicole Christin Maack, Henrike Heinemann, and Axel Don

An increased use and optimised management of cover crops is a promising way to promote soil organic carbon accrual in agricultural soils. However, data is lacking on aboveground and especially root biomass of important cover crop species depending on the length of their cultivation window and on climatic conditions. We sampled aboveground and root biomass in a German field trial covering twelve common cover crop species and eight commercially available seed mixtures in 2021, a year with a rather wet summer, and 2022, a year with a rather dry summer. Each species and mixture were sown at three different dates and were sampled in early November, after having grown for 8 to 14 weeks.

Root and shoot biomass differed significantly between species, years and sowing dates. Oil radish, Phacelia, Bristle oat and Italian rye-grass had the highest root biomass. Cover crop mixtures did not have significantly higher aboveground or root biomass than single species. Aboveground biomass was 60% lower in 2022 compared to 2021 and root biomass on average 52% lower. Biomass generally decreased substantially with later sowing dates, by up to 80%. In 2021, the root to shoot ratio decreased by on average 41% from the earliest to the latest sowing date.

Based on the results of our study, management recommendations can be given regarding the selection and management of cover crop species for soil carbon accrual. Our data is also useful for more accurate mechanistic modelling of the soil carbon dynamics under different agricultural management scenarios. We conclude that there is a large optimisation potential for cover crop cultivation in Europa that could reveal a significant soil carbon sequestration potential.

How to cite: Reinelt, L., Maack, N. C., Heinemann, H., and Don, A.: Cover crop´s carbon inputs to soils via aboveground and root biomass as affected by species, mixtures and sowing date, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9389, https://doi.org/10.5194/egusphere-egu24-9389, 2024.

17:50–18:00
|
EGU24-5359
|
ECS
|
On-site presentation
Julia Fohrafellner, Katharina Keiblinger, Sophie Zechmeister-Boltenstern, Rajasekaran Murugan, Heide Spiegel, and Elena Valkama

Cover crops (CC) offer numerous benefits to agroecosystems, particularly in the realm of soil organic carbon (SOC) accrual and loss mitigation. However, uncertainties persist regarding the extent to which CCs, in co-occurrence with environmental factors, influence SOC responses and associated C pools. We therefore performed a weighted meta-analysis on the effects of CCs on the mineral associated organic carbon (MAOC), the particulate organic carbon (POC) and the microbial biomass carbon (MBC) pool in arable cropland. Our study summarized global research of comparable management, with a focus on climatic zones representative of Europe, such as arid, temperate and boreal climates. 
    In this meta-analysis, we included 71 independent studies from 61 articles published between 1990 and June 2023 in several scientific and grey literature databases. Sensitivity analysis was conducted and did not identify any significant publication bias. The results revealed that CCs had an overall statistically significant positive effect on SOC pools, increasing MAOC by 4.8% (CI: 0.6% - 9.4%, n = 16), POC by 23.2% (CI: 13.9% - 34.4%, n = 39) and MBC by 20.2% (CI: 11.7% - 30.7%, n = 30) in the top soil, compared to no CC cultivation. Thereby, CCs feed into the stable as well as the more labile C pools. The effect of CCs on MAOC was dependent on soil clay content and initial SOC concentration, whereas POC was influenced by moderators such as CC peak biomass and experiment duration. For MBC, e.g., clay content, crop rotation duration and tillage depth were identified as important drivers. 
    Based on our results on the effects of CCs on SOC pools and significant moderators, we identified several research needs. A pressing need for additional experiments exploring the effects on CCs on SOC pools was found, with a particular focus on MAOC and POC. Further, we emphasize the necessity for conducting European studies spanning the north-south gradient. 
    In conclusion, our results show that CC cultivation is a key strategy to promote C accrual in different SOC pools. Additionally, this meta-analysis provides new insights on the state of knowledge regarding SOC pool changes influenced by CCs, offering quantitative summary results and shedding light on the sources of heterogeneity affecting these findings.

How to cite: Fohrafellner, J., Keiblinger, K., Zechmeister-Boltenstern, S., Murugan, R., Spiegel, H., and Valkama, E.: Cover Crops Affect Pool Specific Soil Organic Carbon in Cropland – a Meta-analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5359, https://doi.org/10.5194/egusphere-egu24-5359, 2024.

Posters on site: Thu, 18 Apr, 10:45–12:30 | Hall X2

Display time: Thu, 18 Apr 08:30–Thu, 18 Apr 12:30
Chairpersons: Chris McCloskey, Felix Seidel, Laura Schnee
X2.120
|
EGU24-1321
|
ECS
Mollie Lowrie, Mark Schuerch, Jack Lacey, and Daniel Magnone

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.

X2.121
|
EGU24-3039
Effect of topsoil dilution on stabilization of plant derived carbon
(withdrawn after no-show)
Maire Holz, Bryan Salzmann, Rainer Remus, Valerie Pusch, Eva Mundschenk, Mathias Hoffmann, and Jürgen Augustin
X2.122
|
EGU24-9335
|
ECS
|
Antonia Zieger, Klaus Kaiser, and Martin Kaupenjohann

Andosols are commonly subdivided according to silandic and aluandic features. Both subgroups are considered to be end members of the Andosol genesis. Silandic Andosols are characterized by organic matter (OM) strongly bound to imogolite-type material (ITM), while Aluandic Andosols mainly consist of aluminium-OM complexes (Al-OM complexes). According to current theory, silandic and aluandic properties are direct results of primary weathering, assuming two separate lines of genesis.

Our previous results, however, suggest that silandic horizons can transform into aluandic over time, resulting in additional carbon accumulation. This is likely caused by dissolved organic matter (DOM) entering the subsoil with the percolating soil solution, masking dissolved aluminium as soluble Al-OM complexes. This promotes the dissolution of ITM, releasing aluminium. The latter reacts with DOM, inducing the formation of insoluble, Al-OM complexes, which then precipitate.

To test this hypothesis, we conducted a long-term percolation experiment with material of an Ecuadorian Andosol formed in a homogeneously tephra deposit. This soil exhibits aluandic properties in the topsoil and silandic properties in the subsoil. Ions, pH, and DOC in the feed and eluate solution were monitored over a period of 18 months. The convection-dispersion-equation as implemented in HYDRUS-1D was used to model the percolation experiment as a one-dimensional standard reactive solute transport.

Our results revealed a strong carbon accumulation of 14 g·kg-1 in the silandic material after 18 months, with the vertical transport of Al-OM complexes only explaining up to 33 % of the carbon accumulation. The HYDRUS-1D model revealed that sorption of DOM dominates at the beginning of the experiment and explains up to 40 % of carbon accumulation (including vertically transported Al-OM complexes). For the silandic material, the results indicate that up to 91% of the carbon accumulation are due to ITM dissolution and subsequent formation of insoluble Al-OM complexes.

In summary, our findings support the hypothesis, that ITM dissolution and the subsequent formation of Al-OM precipitates significantly contribute to the increase in carbon concentration in the silandic material, while the above aluandic material did not change.

How to cite: Zieger, A., Kaiser, K., and Kaupenjohann, M.: Andosol genesis: Transition from silandic to aluandic properties and the related changes in organic carbon storage, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9335, https://doi.org/10.5194/egusphere-egu24-9335, 2024.

X2.123
|
EGU24-7294
|
ECS
Soil carbon stabilization and potential stabilizing mechanisms along elevational gradients in alpine forest and grassland ecosystems 
(withdrawn)
Adugna Feyissa Gubena and Xiaoli Cheng
X2.124
|
EGU24-17497
|
ECS
Miyanda Chilipamushi, Claudia von Brömssen, Tino Colombi, Thomas Kätterer, and Mats Larsbo

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.

X2.125
|
EGU24-1635
|
ECS
Marcus Schiedung, Pierre Barré, and Christopher Poeplau

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.

X2.126
|
EGU24-7280
|
ECS
The role of dissolved organic matter chemodiversity in driving bacterial and fungal community patterns at a continental scale
(withdrawn)
Jian Wang, Helena Osterholz, Edith Bai, and Chao wang
X2.127
|
EGU24-9176
Sobia Bibi, Hassan Ahmad, Wolfgang Wanek, Mohammad Zaman, Magdeline Vlasimsky, Maria Heiling, Reinhard Pucher, and Gerd Dercon

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.

X2.128
|
EGU24-2696
|
ECS
Lucie Hüblová and Jan Frouz

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.

X2.129
|
EGU24-6188
|
ECS
|
Highlight
Ciriaco McMackin, Luisa Minich, Wiesenberg Guido, Burgos Stéphane, and Egli Markus

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.

X2.130
|
EGU24-10155
|
ECS
Giulia De Luca, Eszter Sugar, Nándor Fodor, Tamás Árendás, Péter Bónis, and Renáta Sándor

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.

X2.131
|
EGU24-10695
Györgyi Gelybó, Giulia De Luca, János Balogh, Nándor Fodor, Szilvia Fóti, Eszter Sugár, and Renáta Sándor

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.

X2.132
|
EGU24-13777
|
ECS
Koya Kobayashi, Maki Asano, and Kenji Tamura

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.

X2.133
|
EGU24-18626
|
ECS
|
Highlight
Gaétan Pique, Basile Goussard, and Andréa Géraud

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.

X2.134
|
EGU24-21376
Soil organic carbon persistence: a comparison between Dry Forest and Mangrove ecosystems
(withdrawn)
Gerardo Ojeda, Francy Ceballos-Burgos, Yolvi Prada, and Jörg Bachmann
X2.135
|
EGU24-18494
|
ECS
Olga Vindušková, Gaby Deckmyn, Kateřina Jandová, and Veronika Jílková

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.

X2.136
|
EGU24-802
|
ECS
Gebreyes Gurmu Debele, Kenzemed Kassie, and Tsegaye Getachew

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.

X2.137
|
EGU24-2352
|
ECS
Experimental study of the effect of tillage gradient along the slope transect on soil respiration rates under agricultural fields of Indian Himalaya
(withdrawn after no-show)
Sankar Mariappan, Suresh Kumar, Lekh Chand, Madhu Madegowda, Deepak Singh, and Sadikul Islam
X2.138
|
EGU24-7311
|
ECS
Microbial necromass decomposition and stabilization in soilBai
(withdrawn)
Chao wang, Xu Wang, and Edith Bai
X2.139
|
EGU24-2917
|
ECS
Evidence for the formation of recalcitrant carboxyl-rich alicyclic molecules (CRAM) in an organic soil profile
(withdrawn after no-show)
Jeewan Gamage, James Longstaffe, Naresh Thevathasan, Sameer Al-Abdul-Wahid, Paul Voroney, and Adam Gillespie
X2.140
|
EGU24-7874
|
ECS
|
Sean Adam and Conrad Jackisch

To gain a better understanding of changes in soil carbon stocks and composition it is essential to have data on relevant soil properties with high temporal and spatial resolution. However, traditional laboratory analysis can be both time-consuming and expensive, ultimately limiting data availability. Mid-DRIFTS (Diffuse Reflectance Infrared Fourier Transformed Spectroscopy in the mid-IR range) is a cost-effective alternative to conventional analytical methods. It enables the simultaneous inference of multiple soil properties, such as soil organic carbon, nitrogen and phosphorus content, soil texture, and cation exchange capacity, from measured spectra. This makes it a valuable analytical tool for soil monitoring.

To successfully integrate mid-DRIFTS into a soil monitoring concept, a spectral library representative of the target is required as the basis for multivariate or machine-learning-based calibration models. Here, we want to present the initial results obtained using the BDF-SSL, a soil spectral library we created as the foundation for integrating mid-DRIFTS in agricultural soil monitoring in Saxony, Germany. The library's core consists of nearly 300 spectra obtained from retention samples from agricultural soil monitoring sites in Saxony, which were collected over the past 20 years.
We focused on the inference of soil carbon content, including three thermally derived carbon fractions (TOC400, ROC, TIC900) we measured according to DIN19539 by combustion. Additionally, we calibrated models for a wide range of other soil properties, such as soil texture, nitrogen and phosphorus content, elemental concentrations and cation exchange capacity. We used both Partial Least Squares Regression (PLSR), Cubist, and the Memory Based Learner (MBL) to calibrate the models.

Both Cubist and MBL consistently outperformed PLSR. Our models show high predictive accuracy for the carbon fractions, total nitrogen and phosphorous contents, cation exchange capacity and texture. In addition, we are also able to predict several elemental concentrations, such as Fe, Al, or Ni contents with high accuracy. Our results show that mid-DRIFT can be used to enhance spatial and temporal coverage of soil monitoring, allowing not only for more accurate estimations of soil carbon stocks and sequestration rates, but also for the rapid estimation of several other soil properties.

How to cite: Adam, S. and Jackisch, C.: Rapid analysis using Diffuse Reflectance Spectroscopy can enhance Soil Carbon Monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7874, https://doi.org/10.5194/egusphere-egu24-7874, 2024.

X2.141
|
EGU24-9072
A transition from arbuscular to ectomycorrhizal forests halts soil carbon sequestration during subtropical forest rewilding
(withdrawn)
Ruiqiang Liu and Xuhui Zhou
X2.142
|
EGU24-2329
|
ECS
Yifeng Zhang

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.

X2.143
|
EGU24-12025
|
ECS
|
Highlight
Sílvia Poblador, Lucía Álvarez, Bárbara Díaz, Marc Felip, Francesc Sabater, Arthur Vienne, and Sara Vicca

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.

X2.144
|
EGU24-17426
|
ECS
Christhel Andrade Diaz and Lorie Hamelin

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 MgCO2e) than HPO (563 MgCO2e) 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 MgCO2e for HPO and 10,707 MgCO2e 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.

X2.145
|
EGU24-14590
|
ECS
Ahmed Al Rabaiai, Daniel Menezes-Blackburna, Said Al-Ismailya, Rhonda Janke, Ahmed Al-Alawi, Mohamed Al-Kindi, and Roland Bol

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 (SO42-) 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.

X2.146
|
EGU24-13751
|
ECS
|
Sirjana Adhikari, M A Parvez Mahmud, Ellen Moon, and Wendy Timms

Organic waste-derived biochar has been proven to have a significant potential for soil improvement, with recent results from this group showing evidence for improved water holding capacity, carbon stability and exchangeable cations. However, to contextualise these benefits it is important to consider environmental impacts during each stage of life cycle for the product.

In this study, a cradle-to-gate life cycle assessment (LCA) was performed, comparing a common use for garden organics (composting) to two alternative scenarios. One involved converting over-sized compost screenings (otherwise considered waste) to biochar as a supplementary product from the process, and the other involved converting garden organics directly to biochar as an alternative product.

LCA was conducted using ReCiPe2016 impact assessment method in OpenLCA software. Data for assessment were collected from the participating industries and Ecoinvent database. Sensitivity analysis considering different transport distances was carried out and finally an optimum transport distance with the lowest environmental impacts was recommended. Additionally, physico-chemical characterisation and carbon stability assessment were conducted to provide a comprehensive idea about the overall benefits of organic waste-derived biochar for soil and climate.

Our results revealed that global warming was increased from 675 kgCO2eq during composting of garden waste to 1017 kgCO2eq where over-sized screenings of compost is converted to biochar as a value-added product. Direct conversion of organic waste to biochar showed reduced global warming impact of 428 kgCO2eq compared to the previous two scenarios. Among 16 environmental impact indicators studied, the magnitude of 10 impact indicators increased with transport distance, while the remaining six indicators were not influenced by transport distance.

Soil application of biochar from organic waste has multiple co-benefits, that can be short and/or long term. Nevertheless, this study emphasises that research focused on agricultural application of biochar needs to be coupled with LCA or other holistic assessments for a comprehensive evaluation of net environmental impacts and benefits that consider the processes involved in sourcing of feedstock, biochar production, transport, and application.

How to cite: Adhikari, S., Mahmud, M. A. P., Moon, E., and Timms, W.: Assessing the environmental benefits of biochar application in agriculture: Insights from lifecycle assessment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13751, https://doi.org/10.5194/egusphere-egu24-13751, 2024.

X2.147
|
EGU24-1004
Comparative effect of incorporated and surface spread crop residues, poultry manure and their biochars on soil health indicators along a soil profile 
(withdrawn after no-show)
Tanvir Shahzad, Rummana Basit Mir, Umme Aiman Fiaz, Huma Shahid, Fiza Arshad, and Muhammad Sanaullah
X2.148
|
EGU24-9202
|
ECS
Haichao Li, Elias S. Azzi, Cecilia Sundberg, Erik Karltun, and Harald Cederlund

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.

Posters virtual: Thu, 18 Apr, 14:00–15:45 | vHall X2

Display time: Thu, 18 Apr 08:30–Thu, 18 Apr 18:00
Chairpersons: Chris McCloskey, Felix Seidel, Laura Schnee
vX2.12
|
EGU24-18070
|
ECS
|
Sam Walrond, Jeanette Whitaker, Caroline Peacock, and Nick Ostle

Reversing the trend of decreasing soil carbon stocks is important to help mitigate current environmental challenges. Improving knowledge on the mechanisms that control the stabilisation and persistence of soil organic carbon will provide a foundation to tackle the issue. This includes the mechanisms controlling the stability of organomineral associations, considered to be the most persistent pool of soil carbon. Uncertainties remain in how the composition of carbon involved in mineral associations can control the persistence of this soil organic carbon (SOC) pool.

With the mineral associated pool being dominated by soil carbon derived from microbial necromass, composition of microbes and their cell components will have a significant impact on organomineral stability. This study aims to investigate whether differences in cell wall composition between fungi, gram-positive and gram-negative bacteria, contribute to contrasting stability of the organominerals synthesised using necromass of these microbial groups.

Organominerals composed of ferrihydrite and montmorillonite minerals and three types of necromass were synthesised and tested for their stability. This was done using chemical washes that bring about desorption (NaOH) and oxidation (NaOCl) of the necromass C. Solid fraction C and N were measured before and after chemical wash treatments to determine the extent of organic carbon (OC) destabilisation, and Fourier transform infrared (FTIR) spectroscopy was used to semi-quantitatively assess changes in OC functional groups before and after destabilisation.

Results indicate that organominerals containing fungal necromass have greater stability compared to organominerals containing gram-positive and gram-negative bacterial necromass. The most stable fraction within organominerals was C rich and did not comprise N-containing necromass components. The results imply that necromass derived from soil fungi could enhance the persistence of the mineral-associated pool of SOC.

How to cite: Walrond, S., Whitaker, J., Peacock, C., and Ostle, N.: Stability of microbial necromass in soil is controlled by necromass chemical composition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18070, https://doi.org/10.5194/egusphere-egu24-18070, 2024.

vX2.13
|
EGU24-19605
|
ECS
Niharika Sharma, Mohammad Atif Khan, Priyamvada Dubey, Chhavi Nath Pandey, Sanjeev Kumar, and Vikrant Jain

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.