SSS4.4 | Soil Biophysics – processes, mechanisms, and feedbacks
Soil Biophysics – processes, mechanisms, and feedbacks
Convener: Pascal BenardECSECS | Co-conveners: Ophélie Sauzet, Frederic Leuther, Samuel BickelECSECS, Sara BonettiECSECS, Dani Or
| Thu, 18 Apr, 14:00–15:45 (CEST)
Room -2.31
Posters on site
| Attendance Wed, 17 Apr, 10:45–12:30 (CEST) | Display Wed, 17 Apr, 08:30–12:30
Hall X2
Orals |
Thu, 14:00
Wed, 10:45
The physical environment of soils is continuously changing. Soil biota, root growth, land management practices like tillage and abiotic drivers lead to a constant evolution of the arrangement of pores, minerals and organic matter and herewith to modifications in the soil physical functions and chemical properties. Especially in regions with high biological activity, soil organisms induce remarkable alterations to soil structure and functions to optimize growth and reproductive conditions. Resolving the underlying mechanisms forcing such adaptive modifications and exploring the feedbacks between the drivers including the impact of management practices offers an exceptional opportunity to advance our understanding of fundamental physical and biological processes across scales.
We seek contributions linking biological processes and soil physics at any spatial and temporal scale. For example, insights on how the rhizosphere and its microbiome control fluxes beyond the pore scale; on how management practices affect soil structure and functions; on the role of biological soil curst in modifying infiltration and limiting soil erosion across vast areas of the earth’s surface; on how bioturbation shapes soil hydraulic characteristics over years and decades;

Topics of the Soil Biophysics session include but are not limited to:
1. Root growth
2. Microbial activity
3. Bioturbation
4. Virus dispersal
5. Resource allocation
6. Soil water dynamics
7. Soil structure formation
8. Biological soil crusts
9. Rhizosphere interactions
10. EPS (incl. mucilage)

The aim of this session is to highlight the potential of interdisciplinary approaches to address current and future challenges in soil science and to foster scientific exchange across disciplines.

Orals: Thu, 18 Apr | Room -2.31

Chairpersons: Pascal Benard, Samuel Bickel, Frederic Leuther
On-site presentation
Naoise Nunan, Maëlle Maestrali, Haotian Wu, Steffen Schwitzer, and Xavier Raynaud

Soil microbial communities live within a complex three dimensional pore network, the properties of which constrains microbial life and activity. The physical structure of soil, and the associated pore network, limit microbial access to resources. It also determines micro-environmental conditions (e.g. redox conditions) that can affect microbial use of the available resources and the rates at which they use energy. Whilst the distributions of different types of activities (CO2 production, enzyme activities) in the pore network have received some attention, the rate at which microbial communities use the energy available to them, i.e. metabolic power, has received little. Energy is required for most aspects of microbial functioning and the rate at which this energy is used determines the extent to microbial functioning proceeds.

Linking the energy available to the rate at which it is processed at the pore scale may help us to better understand how microbial growth and C dynamics are constrained by the physical environment in soil. In order to do so, we collected data from papers in which isotopically-labelled organic substrate was added to pores with different neck diameters and calculated the microbial community catabolic rates, the Gibbs energies of the reactions in oxic and anoxic conditions. This allowed us to estimate the distribution of microbial metabolic power in the pore network and of carbon use efficiency using the approach in LaRowe and Amend (American Journal of Science, Vol. 315, March, 2015,P.167–203, DOI 10.2475/03.2015.01). We then compare the calculations with laboratory measurements of the distribution of carbon use efficiency at the pore scale.


How to cite: Nunan, N., Maestrali, M., Wu, H., Schwitzer, S., and Raynaud, X.: How is microbial metabolic power distributed throughout the soil pore network?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10743,, 2024.

On-site presentation
Minsu Kim, Milad Aminzadeh, Samuel Bickel, Nima Shokri, and Bettina Weber

Biological soil crusts (hereafter, biocrusts) occurring in drylands modify near-surface soil properties which influences land-atmosphere interactions and exchanges of energy and matter. Yet, the impact of biocrusts on soil evaporation lacks a mechanistic understanding of the biological processes that modify the crusts’ physical properties. We used controlled laboratory experiments, field observations, and mechanistic modelling to determine the impact of biocrusts on evaporation dynamics and subsurface thermal regimes. Our experiments were conducted with bare soil and different types of biocrusts along the ecological succession of the Succulent Karoo desert, South Africa. The preliminary results highlight how different thermal and radiative properties of the crusts affect evaporation rates and heat transfer into the soil layers beneath. Furthermore, active water uptake and storage by biocrust organisms result in water redistribution, which shapes energy balance during diurnal cycles. We conclude from the mechanistic model that biocrusts can accelerate the vertical transport of substrates at the cost of evaporative water loss. Thus, biocrusts may have evolved to modify soil physical properties for balancing nutrient turnover and water usage in global drylands highlighting their crucial roles in regulating mass and energy exchanges over terrestrial surfaces.

How to cite: Kim, M., Aminzadeh, M., Bickel, S., Shokri, N., and Weber, B.: Biological soil crusts regulate evaporation dynamics and energy partitioning over terrestrial surfaces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15099,, 2024.

On-site presentation
Sara Di Bert, Konstantina Papadopoulou, Patrick Duddek, Andrea Carminati, and Pascal Benard

The hydraulic properties of the rhizosphere are essential for understanding root-soil interactions. Diverging from common assumptions in soil modelling, which often equate rhizosphere properties with those of bulk soil, research shows that the rhizosphere is distinct in its physical, biological, and chemical attributes.

There is a broad agreement on the role of mucilage and extracellular polymeric substances (EPS) in modifying soil water dynamics in the rhizosphere. However, the mechanisms of how these substances interact with the soil matrix and impact its hydraulic properties remain unclear. In this study, we assessed the forces exerted by Xanthan gum, used as a stand-in for EPS, maize root mucilage, and water - formed liquid bridges on particle pairs.

Forces were quantified for 1 microL liquid bridge between a pair of glass beads — one standing on a precision balance and the other fixed to a static stand. While the water bridges broke upon drying due to capillary forces, mucilage and Xanthan gum formed resilient filaments that maintain connectivity and tensile forces between the glass beads. The continuous recordings of weight changes by the balance provided crucial data for quantifying the force exerted on the beads during drying.

Our results show that both Xanthan gum and maize mucilage liquid bridges exert tensile strengths that are substantially greater than those of water bridges. The polymer solutions initially behave similarly to water, but the forces exerted on particle pairs deviate as the solutions dry, becoming progressively stronger. The tensile strength of water reaches around 10-1 mN, while maize and Xanthan gum are respectively 1 and 2 order of magnitudes bigger. This increase is caused by the stretching of the polymer network and the development of elastic forces.

The significant aggregating force observed in our study suggests that EPS and mucilage play a crucial role on the mechanics of the root-soil interface. They contribute to soil structure formation in the rhizoshere and to maintain root and soil contact as roots shrink in drying soils.


How to cite: Di Bert, S., Papadopoulou, K., Duddek, P., Carminati, A., and Benard, P.: The role of root mucilage and Extracellular Polymeric Substances in shaping soil structure and maintaining plant-soil contact, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6823,, 2024.

On-site presentation
Adrian Haupenthal, Patrick Duddek, Mathilde Knott, Andrea Carminati, Hermann Jungkunst, Eva Kroener, and Nicolas Brüggemann

Gas exchange in the soil is determined by the size and connectivity of air-filled pores. Root mucilage can partially reduce air-filled pore connectivity and thus reduce gas diffusivity. However, it remains unclear to what extent mucilage affects soil pore connectivity and tortuosity. The aim of this study was to gain a better understanding of gas diffusion processes in the rhizosphere by explaining the geometric alterations of the soil pore space induced by mucilage.

We quantified the effect of a root mucilage analogue collected from chia seeds without intrinsic respiratory activity on oxygen diffusion at different water contents during wetting-drying cycles in a diffusion chamber experiment. In addition, we used X-ray computed tomography (CT) imaging to visualize the distribution of air and water in the pore space, and quantified the connectivity of the gas phase. Furthermore, we used environmental scanning electron microscopy (ESEM) to visualize mucilage bridges in the dry soil samples.

Quantification of oxygen diffusion showed that mucilage decreased the gas diffusion coefficient in dry soil without affecting air-filled porosity. Without mucilage, a hysteresis in gas diffusion coefficient during a drying-rewetting cycle could be observed for fine sandy soil as well as silt and clay soils. The effect diminished with increasing mucilage content. CT imaging indicated a hysteresis in the connectivity of the gas phase during a drying-rewetting cycle for samples without mucilage. This effect was attenuated with increasing mucilage content. Electron microscopy showed that mucilage forms membrane-like liquid bridges during drying. With increasing mucilage content cylindrical structured are created and at high content interconnected structures are observed throughout the pore space, thereby progressively reducing the connectivity of the gas phase.

Our results suggest that the release of mucilage into the soil may be a plant adaptation strategy to balance soil oxygen availability and water content.

How to cite: Haupenthal, A., Duddek, P., Knott, M., Carminati, A., Jungkunst, H., Kroener, E., and Brüggemann, N.: Effects of mucilage on soil gas diffusion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16045,, 2024.

On-site presentation
Anders Kaestner

As an opaque medium, soil conceals processes beneath its surface, posing a challenge for direct observation. To overcome this limitation, scientists employ imaging techniques based on radiation types capable of penetrating the soil, offering insights into its internal structures. While X-ray imaging is the most commonly used method due to its widespread availability, our focus lies on neutron imaging, an alternative and complementary modality.

The distinctive advantage of neutron imaging lies in its heightened sensitivity to light elements, particularly hydrogen, and its greater penetration depth in many metals compared to X-rays. Hydrogen's significance emerges in studying the distribution of water and organic matter within soils. While the spatial and temporal resolution of neutron imaging falls slightly short of laboratory-based X-ray imaging, it operates within the same order of magnitude. Neutron imaging, often flux-limited, has prompted methodological advancements to enable time-series experiments in two and three dimensions on a scale pertinent to soil studies.

Our efforts have concentrated on refining methods for conducting time-sensitive experiments, and we have pioneered the concurrent use of neutron and X-ray imaging. This dual modality approach enhances the reliability of quantitative analysis by leveraging the advantages of images from the two modalities. Quantitative analysis has been a primary focus, leading to the development of correction methods that substantially enhance the accuracy of gravimetric water content quantification based on gray levels in acquired images. The exceptional sensitivity to hydrogen enables the quantification of water content even in unresolved pores, showcasing the primary advantage of neutron imaging. Incorporating advanced denoising techniques further diminishes uncertainties in the results.

Beyond imaging-related innovations, our current endeavors extend to the provision of dedicated sample environments for porous media experiments. This new equipment encompasses balances, pumps, and signal-logging devices integrated into the instrument control system. This integration improves experiment control and facilitates the logging of metadata associated with each image.

In this presentation, we offer a comprehensive overview of applications benefiting from these developments, showcasing the state-of-the-art performance of neutron imaging techniques in porous media research. Our commitment to refining methodologies, advancing quantitative analysis, and providing specialized sample environments underscores our dedication to pushing the boundaries of neutron imaging for a deeper understanding of soil processes.

How to cite: Kaestner, A.: Unveiling Subsurface Secrets: Advances in Neutron Imaging for Soil Research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15669,, 2024.

On-site presentation
Maha Deeb, Peter M. Groffman, Matthew Amato, Zhongqi Cheng, and Daniel Giménez

Green Infrastructure (GI) plays a crucial role in reducing stormwater runoff and providing ecological benefits in urban areas. Aggregation is a key process in many soil functions as it influences carbon storage, greenhouse gas emissions, nutrient cycling, hydraulic properties, and biotic activity. In this study, we investigated soil aggregation processes and stability in GI.

Soil samples were collected from six bioswale sites in New York City that had two different designs - streetside infiltration swales and enhanced tree pits. The soil samples were taken from the inlet, center, and outlet positions (relative to stormwater input) of each site. These samples were then tested for 1) macro and micro aggregate sizes; 2) distribution of soil organic carbon (SOC) and nitrogen; 3) aggregate stability; and 4) microbial biomass and activity relevant to carbon and nitrogen cycles in macroaggregates.

Our results showed that 60% g/g of the soil aggregates at these GI sites were smaller than 2 mm and had high structural stability. Microaggregates between 1-2 mm had the highest SOC and accounted for 60% g/g of all microaggregate size classes. GI aggregates are formed from the breakdown of macroaggregates into intermediate microaggregates. The newly formed microaggregates contained more stable SOC than macroaggregates and bonds within microaggregates were stronger than bonds grouping microaggregates, which is not consistent with a classical model of aggregate formation in natural soils. Microbial biomass and activity were correlated with the carbon and nitrogen content of aggregates and with GI type, allowing for the identification of microbial hot spots. These results suggest that aggregation processes in human-engineered soils included in GI play an important role in sustaining carbon and nitrogen cycles.

How to cite: Deeb, M., Groffman, P. M., Amato, M., Cheng, Z., and Giménez, D.: Characterization of soil aggregates in green bioswales in relation to carbon sequestration, aggregate stability, and microbial activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21211,, 2024.

On-site presentation
Siul Ruiz, Paul Hallett, and Dani Or

Soil bioturbation is the physical movement and alteration of soil by fauna and plants. It plays a central role in soil formation at long time scales and shapes soil structure at hydrologic time scales that affects many soil physical processes and ecosystem services. Varying biomes act as hosts to a variety of ‘ecosystem engineers’ that have developed unique strategies for generating habitats and appreciable soil biopores. For example, earthworms and plant roots generate biopores in moist soil via penetration-expansion (and some ingestion) processes. Other organisms such as ants or termites excavate soil by displacing soil particles with their limbs. We present an overview of biophysical processes associated with soil bioturbation driven by various biological agents and biomechanical  strategies (e.g. penetrators vs excavators). The study highlights the critical role of soil moisture and texture in modulating and shaping the various biomechanical strategies and activity time windows. We explore the implications that regional environmental factors play in locally favoring particular bioturbation processes, which can be used to identify the likelihood of a specific bioturbation agents occurrence in a given region. The overview highlights the relative impact of soil bioturbation on soil structure formation by comparison with conventional tillage processes (restricted to arable lands). Ultimately, this work endeavors to open discussions that can aid in reducing intensive mechanized tillage and help guide sustainable land use initiatives by capitalizing on the biological agents present in the environment.   

How to cite: Ruiz, S., Hallett, P., and Or, D.: Soil bioturbation – how habitat climatic constraints shape biophysical processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16463,, 2024.

On-site presentation
Franziska B. Bucka, Julien Guigue, Christopher Just, Saniv Gupta, Vincent J.M.N.L. Felde, Stephan Peth, and Ingrid Kögel-Knabner

Soil organic carbon (SOC) depletion is often a result of human land use, which is intensified by climate change. As SOC is closely linked to the stabilization of soil structure, the loss of SOC in a soil may induce soil structure breakdown and turnover processes that are not yet well understood.

In order to study soil structure turnover with respect to OC loss, we designed an incubation experiment with soil microcosms that allowed OC loss by leaching and microbial respiration, while avoiding any mechanical disturbance.

We incubated intact soil cores of an arable Luvisol from Loess deposits in southeastern Germany for 300 days at constant water tension and 25 °C to promote microbial activity. During incubation, CO2 release from the microcosms was monitored. A subset of the microcosms was sampled monthly to assess the effect of progressive OC depletion on the stability and architectural features of the soil structure.

The incubation resulted in a reduction of the initial OC (11.2 mg g-1) by approx. 20% and a narrower C:N ratio, corresponding to a reduced OC coverage of the mineral surfaces (1.7 m² g-1 to 0.9 m² g-1, as determined by N2-BET). Despite the OC reduction, the aggregate size distribution (as determined by both wet and dry sieving) did not change significantly, although there was a trend toward a reduction in the mean weight diameter of the aggregates. The mechanical stability of isolated soil aggregates (as determined by dry crushing) even increased slightly with lower OC content in the bulk soil. Microscopic analysis of resin-embedded soil aggregates revealed a lower bulk density in the center, suggesting a progressive carbon depletion from the outside to the inside of the soil aggregates.

These observations highlight that early stage OC depletion along with reduction of OC-covered mineral surface area, without additional mechanical influence, does not immediately lead to the degradation of soil structure. This suggests the existence of OC storage sites that are not susceptible to OC loss by leaching or microbial degradation. In contrast, the sites of initial OC loss may not contribute to the structural stability of a soil.

How to cite: Bucka, F. B., Guigue, J., Just, C., Gupta, S., Felde, V. J. M. N. L., Peth, S., and Kögel-Knabner, I.: Linking progressive SOC depletion to degradation of soil structure: Where does it fail first?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11174,, 2024.


Posters on site: Wed, 17 Apr, 10:45–12:30 | Hall X2

Display time: Wed, 17 Apr 08:30–Wed, 17 Apr 12:30
Chairpersons: Frederic Leuther, Ophélie Sauzet, Sara Bonetti
John Koestel, Jumpei Fukumasu, and David Nimblad-Svensson

It is known that soil organic carbon (SOC) is positively correlated with soil aggregation and total porosity. Similarly simple relationships between SOC content and abundance of pores in specific diameter ranges seem however elusive. In this study, we used X-ray tomography to investigate if this may be explained by treatment-specific differences in biopore forming agents, in other words soil faunal communities and root growth. We therefore compared the pore and biopore network characteristics in the topsoil of an ongoing long-term field experiment in Ultuna, Sweden, which was started in 1956. We selected three contrasting treatments that had led to significantly different SOC contents, ranging from 0.9 to 2.1% in weight, namely: a bare fallow and two cropped plots with two different fertilization treatments, mineral N-fertilizing with Ca(NO3)2 and farm yard manure (FYM). Sixteen undisturbed soil cores were sampled in eight small (ø 22.5 mm; height 65.5 mm) and eight large (ø 65.5 mm; height 74.8 mm) columns from each treatment, respectively (48 samples in total). The results of our study are in line with empirical knowledge that soil treatments associated with increased carbon contents exhibit larger porosities. However, we observed that the abundance and size distribution of biopores at different scales exhibited treatment-specific differences that cannot be explained with SOC content differences alone. Instead, they must have been caused by distinct root morphologies (or complete absence of roots) and/or by differences in soil faunal communities. Our study demonstrates that simple relationships between soil organic matter content and soil macropore network properties must not be taken for granted.

How to cite: Koestel, J., Fukumasu, J., and Nimblad-Svensson, D.: Influence of cropping and fertilization on soil macropore characteristics in a long-term field study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20510,, 2024.

Samantha Spinoso Sosa, Benjamin Hafner, Ruth Adamczewski, and Mohsen Zare

Understanding how plants regulate their hydraulic systems in response to varying soil conditions is crucial for comprehending water fluxes in the soil-plant-atmosphere continuum. This study examines hydraulic conductance in maize plants grown in loamy soil under different soil water contents. We hypothesize that plants actively adjust both aboveground and belowground hydraulic conductance in response to soil texture and moisture to balance their water loss with water uptake.

Maize plants were grown in loamy soil with varying moisture levels, simulating optimal and water-stressed conditions. Pre-germinated seeds were planted in PVC pots (10 cm diameter, 24 cm height). At different growth stages (2, 3, 4 and 6 weeks), shoots were delicately separated from the roots. We assessed both total aboveground (Kab) and belowground hydraulic conductance (Kbe). The Kbe was determined by subjecting soil and roots to incremental pressure increases in a pressure pot, collecting the sap to derive water flow at a given pressure. To calculate the total aboveground hydraulic conductance (Kab,tot), effective internal aboveground xylem hydraulic conductance (Kab,xyl), and stomatal conductance (Kab,sto), we measured transpiration, leaf water potential, temperature, and vapor pressure.

In optimal conditions (OC), our initial findings show a linear increase during the initial growth stage in both above- and belowground conductance, followed by deceleration at the late developmental stage. Significantly,  Kbe surpassed  Kab,tot by over two orders of magnitude. It's worth noting that although Kab,xyl displayed a higher magnitude in our measurements, exceeding Kbe , the Kab,sto took precedence as the primary controlling factor when considering the overall soil-plant hydraulics. Under water-stressed conditions, plants exhibited an overall increase in hydraulic conductance with growth, where Kbe once again surpassed Kab,tot by over two orders of magnitude. However,  Kab,tot values were approximately half of those obtained in OC. Notably,  Kab,xyl decreased with plant age but remained greater than  Kbe. These results provide valuable insights into the intricate interplay between root and shoot hydraulic conductance. This research contributes to our understanding of how plants dynamically regulate their hydraulic systems under varying soil conditions, contributing to the broader knowledge of the soil-plant-atmosphere continuum.

How to cite: Spinoso Sosa, S., Hafner, B., Adamczewski, R., and Zare, M.: Exploring the interplay of shoot to root hydraulic conductance in varying soil water contents, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17648,, 2024.

Cover cropping induces the formation of Mn(II) hotspots within close proximity of particulate organic matter
James O'Sullivan, Jocelyn Richardson, Andrey Guber, Michel Cavigelli, and Alexandra Kravchenko
Maysoon Mikha, Timothy Green, Tyler Untiedt, and Gary Hergret

Soil structure is an important factor in regulating soil ecological functions and soil chemical, physical, and biological properties. This study evaluated soil structural stability from three locations within the central Great Plains (USA) under different management practices.  The study sites consisted of Alternative Crop Rotation (ACR) and Long-Term Tillage (LTT) near Akron, Colorado, and Knorr-Holden (KH) near Mitchell, Nebraska.  Tillage treatments consisted of no-tillage (NT), reduced tillage (RT), conventional tillage (CT), and moldboard plow (MP). Commercial mineral fertilizer (F) was used as a nitrogen source in ACR and LTT sites while manure (M) plus F treatments were used in KH.  Soil structural stability was evaluated using four indices, aggregate stability index (ASI), mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension (FD).  At 0-15 cm depth, intensive tillage (CT and MP) in ACR and LTT, reduced (P < 0.05) ASI by 46.7%, MWD by 21.0% and GMD by 8.4% and increased FD by 0.77% compared with NT and RT treatments.  The addition of manure increased (P < 0.05) ASI by 72.2%, MWD by 65.6%, GMD by 32.8%, and reduced FD by 5.5% compared with tillage treatments in ACR and LTT.  Although FD was negatively correlated with MWD and GWD; it provides information not captured by ASI and complements MWD and GWD.  The indices presented in this study, including FD, are effective in measuring soil structural stability and should be considered further in management decisions to sustain soil resources and enhance economic returns.

How to cite: Mikha, M., Green, T., Untiedt, T., and Hergret, G.: Soil Structural Stability Influenced by Land Management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1343,, 2024.

Yi Tang and Shixing Cai

The demand for ground improvement of marine sediments has been risen in construction of offshore infrastructures, including wharves, embankments and breakwaters. In recent years, microbially induced carbonate precipitation (MICP) has developed rapidly and become an alternative technology for increasing soil strength and limiting soil erosion. Silty sand is widely distributed in offshore areas throughout the world. The high salinity of seawater may have an impact on the bacterial activity, while the fine particles in silty sand would affect the transportation of cementation solution and the formation of carbonate precipitation. In this study, attentions are paid to the application of MICP on improvement of marine silty sand properties, as well as the factors influencing the hydraulic conductivity and strength of the bio-cemented soil. Multi-gradient domestication tests on Sporosacina pasteurii were carried out to ensure the bacterial and urease activities in seawater environment. It was found that the bacterial concentration and urease activity after five-gradient domestication in seawater reached 98.5% and 92.8% of those in the deionized water environment, respectively. The permeability, unconfined compressive strength (UCS) and content of carbonate precipitation of bio-cemented specimens were measured. The MICP treatment on silty sand with seawater resulted in an increase of UCS to 700 kPa and a reduction of permeability by an order of magnitude, corresponding to a carbonate content of 8%. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to investigate the types and distributions of carbonate crystals. The results indicated the formation of calcium carbonate and magnesium carbonate crystals due to the interaction between carbonate ions and calcium and magnesium ions in seawater. The precipitations were distributed on the surfaces of soil particles and near particle contact points, affecting the soil microstructure and thus the strength and permeability. The influences of concentration and injection rate of cementation solution on the efficiency of MICP were demonstrated and the recommended values were given. This study may provide a possible solution for improvement of engineering properties of marine silty sand foundations.

How to cite: Tang, Y. and Cai, S.: Study on methodology and efficiency of microbially induced carbonate precipitation on improvement of marine silty sand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2980,, 2024.

Orsolya Szécsy, Márk Rékási, Anita Szabó, and Nóra Szűcs-Vásárhelyi

As part of a national survey, 129 soil samples were taken countrywide across Hungary, in order to be representative of both soil types and intensity of cultivation of the country. The bulk samples were taken from 20 points of the diagonals of each sampling parcel, from the 0-30 cm surface layer. Among other soil physical parameters, samples were classified into soil textures based on the Arany yarn number. Microbial measurements were selected so that they could give an overall look at the actual biological soil state.


Our goal was to find out, whether we could detect correlations between soil texture, and clay content in particular with the measured microbial parameters regarding such a heterogeneous and large group of natural soil samples.


Biological activity of the soil samples were evaluated applying three tests: fluorescein-diacetate (FDA) and sucrose (invertase) enzyme activity tests as well as substrate induced respiration (SIR) measurement. The FDA test is suitable for estimating the soil’s microbial activity. The hydrolysis of FDA is based on the process of several soil enzymes hydrolysing colourless fluorescein-diacetate added to the soil. Released coloured fluorescein can be measured by spectrophotometry. Determination of sucrose (invertase) enzyme activity is founded on quantitative measurement of reducer monosaccharides emerging from the hydrolysis of sucrose. This test provides information on the carbohydrate metabolism processes in the soil. The most important indicator of soil biological activity is the degree of soil respiration that can be measured through the quantitative analysis of the CO2 produced by the decomposition of organic matter. Substrate induced respiration (SIR) method is based on a so-called respiration answer given by the microbial biomass in the presence of an easily utilisable substrate (glucose) being in saturated concentration. Statistical analysis of the data was performed with the programme StatSoft Statistica (Version 12 and 13).


The results showed that according to the Kruskal-Wallis tests, correlations could be detected between soil texture and all three microbial parameters. Microbial activity raised in accordance with increasing clay content. It could therefore be verified that although microbiological state and activity of the soil is affected by several environmental factors, FDA and sucrose activity as well as SIR in our samples all depend on the content of clay minerals of the soil, as these can produce favourable conditions for the accumulation of enzymes. This research was funded by TDR project (KEOP-6.3.0/2F/09-2009-0006).

How to cite: Szécsy, O., Rékási, M., Szabó, A., and Szűcs-Vásárhelyi, N.: Correlations between microbial activity and soil texture in Hungarian soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8747,, 2024.

Shanshan Qi and Gangsheng Wang

Freeze-thaw cycling can influence microbial physiological states including microbial dormancy and resuscitation, and enzyme activities. These factors are essential to the mechanisms that control soil carbon and nutrition dynamics mediated by microbes. Warming-induced thawing may also cause changes in microbial functional diversity and stability. However, it remains a significant challenge to integrate these responses within microbial ecological models, which impedes the precision of carbon-nutrient-climate feedback projections. Here, we depict the dynamics of freezing and thawing soil, as well as the microbial and enzymatic functions in response to freeze-thaw processes within the Microbial-ENzyme Decomposition (MEND) model. The simulation was conducted in the Qingzang alpine grassland with field observations and comprehensive parameterization. Our findings suggest that microbial data potentially enhance confidence in model simulations. We also demonstrate that the relative substrate availability affects the trade-off between enzyme synthesis and metabolic flux. The results can deepen our understanding of microbial acclimation to freeze-thaw cycling and how they respond to soil organic carbon decomposition in permafrost ecosystems. 

How to cite: Qi, S. and Wang, G.: Freeze-thaw processes regulate microbial controls on soil organic carbon decomposition in Qingzang alpine grasslands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9003,, 2024.

Yan Jin, Jing Yan, Bridget Knight, and Wenjuan Zheng

Plant growth-promoting rhizobacteria (PGPR) are known for their ability to enhance plant tolerance to abiotic and biotic stresses, including drought and salinity. Additionally, PGPR have been shown to mediate changes in physical properties and hydrological functions of soil. In previous studies, we demonstrated that Bacillus subtilis FB17 (trade name UD1022, a PGPR), could increase soil water retention, preserve continuity of the liquid phase in drying soils, and decrease evaporation. These effects are attributed to production of extracellular polymeric substances (EPS), which are capable of mediating local/micro scale changes in water retention and flow dynamics in soil. We have since extended our study to investigate the potential influence of UD1022 on saltwater evaporation from sand. Specifically, we are comparing evaporation of saltwater, at concentrations 0 (pure water), 10 and 20 ppt, from UD1022-treated sand columns and controls (without treatment). Measurements include temporal changes in cumulative evaporation and evaporation rate, as well as recording surface salt precipitation patterns. Preliminary results from experiments with pure water and 20 ppt saltwater show significant differences in evaporation of pure water between the treated and control columns, however, treatment effects on the evaporation of 20-ppt saltwater were much less pronounced. A preliminary experiment evaluating effects of salt concentration on pellicle formation showed that biofilm formation was suppressed with increasing salinity, presumably, leading to the insignificant effect in reducing evaporation. Nevertheless, images from light and scanning electron microscopes show an earlier onset of salt precipitation on the surface of UD1022-treated sand than control sand, hinting on the potentially very complex interactions between UD1022 and salt precipitation and their effects on evaporation. Additional on-going experiments at lower salt concentrations will allow better mechanistic understanding on how PGPR may mediate changes in salt precipitation and saltwater evaporation in porous media.

How to cite: Jin, Y., Yan, J., Knight, B., and Zheng, W.: Effects of Plant Growth-Promoting Rhizobacteria (PGPR) on Saltwater Evaporation: A Case Study Using Bacillus Subtilis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14526,, 2024.

Li Lin

The presence of multiple layers of red paleosol in loess strata poses challenges due to its high hardness, which hinders easy collapse when encountering water. This characteristic significantly affects the measurement results of the collapsible amount of loess strata. However, there is currently a lack of reports on the control effect of paleosol on collapsibility, resulting in a deficiency in the theoretical basis for the scientific selection of collapsibility in these strata. This paper aims to address this gap by analyzing the differences in self-weight collapsibility between indoor and outdoor conditions under various paleosol layers in different areas and strata. The analysis is based on statistical results from immersion tests conducted in the Loess Plateau. Furthermore, the research focuses on two test sites in Xi'an and conducts large-scale immersion tests, considering measurements such as water diffusion, changes in water content, soil pressure, and cumulative collapsibility under different test conditions. The study investigates the influence of paleosol layers on water infiltration and their role in controlling total weight collapse.The final results indicate that the presence of a paleosol layer prevents collapsibility from transferring to the lower layer and inhibits water infiltration, thereby reducing total collapsibility. Discrepancies between measured and calculated collapsibility values are positively correlated with the number of ancient soil layers. This research provides valuable insights into the collapsibility mechanism of paleosol-loess strata.

How to cite: Lin, L.:  Effects of paleosol on collapsibility of loess sites under immersion test conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-209,, 2024.

The importance of soil structure data for soil erosion modelling and mapping
Surya Gupta and Christine Alewell
Markus Berli, Rose M. Shillito, Dani Or, Jeremy J. Giovando, Jay Pak, Nawa Pradhan, René A. Vermeeren, Ian E. Floyd, and Sean McKenna

Fire-induced changes in soil structure and hydraulic conductivity reduce infiltration and increase the likelihood for post-fire flooding and debris flows. Current post-fire hydrology models, however, cannot take fire-induced soil structure changes into account. The goal of this study was to review current understanding of fire-induced changes in soil structure and their post-fire persistence. Specifically, we seek to quantify how fire-induced soil structure changes affect soil hydraulic conductivity.

Changes in soil structure vary widely with the definition of structure. We focused on literature describing fire-induced changes to soil aggregate stability and onset of loss of aggregation followed by formation of surface crust. Generally, aggregate stability tends to increase with increasing soil temperature up to approximately 200°C. Beyond 200˚C, aggregate stability decreases due to changes or loss of soil organic matter (the main binding agent). Evidence suggests that aggregate stability may decrease for soil temperatures as low as 100˚C due to rupture doe to rapid water evaporation within the aggregates. The loss of soil aggregation can promote erosion or formation of surface crust from fine soil particles. Often, fire-induced soil crusts are related to high soil surface temperatures. Literature data show that fire-induced changes in soil structure may persist for a decade after the burn. We developed a conceptual model to describe soil surface structure life cycle in fire-prone ecosystems.

The effects of aggregate deterioration (and recovery) on saturated hydraulic conductivity (Ks) of the soil can be captured by the model of Bonetti et al. (2021). Calculations show that aggregate deterioration leads to a decrease in Ks by a few orders of magnitude (depending on soil texture). Additionally, post-fire soil crusting effects on infiltration were captured by calculating an effective hydraulic conductivity (Rawls et al.,1990) showing a decrease in hydraulic conductivity by one to two orders of magnitude. Moreover, results suggest that fire-induced aggregate deterioration combined with crust formation can reduce the hydraulic conductivity of a soil surface by three to four orders of magnitude. Even without explicit consideration of documented effects of wildfire on soil hydrophobicity, we illustrate the important impact of fire-induced changes in soil structure on infiltration, flooding and debris flow.

How to cite: Berli, M., Shillito, R. M., Or, D., Giovando, J. J., Pak, J., Pradhan, N., Vermeeren, R. A., Floyd, I. E., and McKenna, S.: Fire effects on soil structure and hydraulic conductivity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12707,, 2024.

“Shifting gears ain’t easy”: Why do we still focus on aggregates when describing the structure of soils?
Philippe C. Baveye
Haotian Wu, Maelle Maestrali, Maik Lucas, Xavier Raynaud, Naoise Nunan, and Steffen Schweizer

The size distribution of soil pores is an important key characteristic of soil systems influencing soil functions such as the cycling of water as well as organic matter storage and dynamics. There is a lack of information about the pore size distribution considering a wide variety of soils and whether various soil characteristics pre-dominantly influence specific pore size ranges. Especially, pores with a diameter < 100 µm serve as a key driver of soil water holding capacity and as a habitat for soil microorganisms involved in the decomposition of organic matter. Here, we aim to contribute to the identification of size patterns in the soil pore size distribution and its relationships with soil biogeochemical matter cycles. In our contribution, we will present insights into our literature-based meta-analysis approach enabling relative comparisons by the integration of pore size distributions across different soils using a water retention curve model. To disentangle the effects of soil texture, soil type, organic matter content, and land management on soil pore size distribution, we used multivariate regression, path analysis, and random forest feature importance. By building a quantitative framework of interrelated controls on soil pore size distribution, we aim to discuss the current understanding of the soil pore network and its ecological functions.

How to cite: Wu, H., Maestrali, M., Lucas, M., Raynaud, X., Nunan, N., and Schweizer, S.: Meta-analysis of soil pore size distribution and its relationship with various soil properties and land management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21045,, 2024.

Patrick Duddek, Mutez Ali Ahmed, Mathieu Javaux, Jan Vanderborght, Goran Lovric, Andrew King, and Andrea Carminati

By substantially increasing the surface area of roots available for soil resource capture, root hairs have been hypothesised to facilitate root water uptake, particularly in dry soil conditions. However, existing experimental and computational studies have shown that the effect of root hairs on water uptake cannot be generalised across soils and plant species.

The objective of our study is to investigate to what extent and under which soil conditions root hairs facilitate root water uptake. Ultimately we aim to gain a mechanistic understanding of the effect of root hairs on root water uptake across soil textures.

We scanned maize (Zea Mays L.) roots grown in two soil types (loamy and sandy soil) using synchrotron-based X-ray CT. We utilized an image‐based modelling approach to simulate water flow through the soil-root continuum by solving the flow equations numerically. This approach allowed us to incorporate rhizosphere properties (e.g. root-soil contact) and root hair shrinkage into the image-based model.

Experimental and numerical results show that under dry soil conditions (-1 to -0.1 MPa) root hairs attenuate the gradient in soil matric potential across the rhizosphere. This results in a more effective water extraction compared to a hairless root. Our model revealed that the effect of hairs is determined by soil properties (e.g. soil porosity), root hair traits (e.g. length and density) and the capacity of hairs to remain turgid under drought stress. Compared to densely packed fine textured soils, the effect of hairs is more pronounced in coarse textured soils and loosely packed fine textured soil. This is explained by the steeper hydraulic conductivity curves of these soils.

In conclusion, our results show that the effect of root hairs is determined by root-soil contact, which depends on soil properties, and root hair shrinkage.

How to cite: Duddek, P., Ahmed, M. A., Javaux, M., Vanderborght, J., Lovric, G., King, A., and Carminati, A.: Root hairs facilitate root water uptake across soil textures – a numerical study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17397,, 2024.