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Soil structure, its dynamics and its relevance to soil functions: feedbacks with soil biology and impacts of climatic conditions and soil management

Soil structure and its stability determine soil physical functions and chemical properties such as water retention, hydraulic conductivity, susceptibility to erosion, and redox potentials. These soil physical and chemical characteristics are fundamental for biological processes, among them root penetration and organic matter and nutrient dynamics. The soil pore network forms the habitat for soil biota, which in turn actively reshape it according to their needs. The soil biota, root growth, land management practices like tillage and abiotic drivers (e.g. wetting/drying cycles) lead to a constant evolution of the arrangement of pores, minerals and organic matter. With this, also the soil functions and properties are perpetually changing. The importance of the interaction between soil structure (and thus soil functions) on one side and soil biology, climate and soil management on the other, is highlighted by recent research outcomes, which are based on advanced imaging techniques, novel experimental setups and modelling approaches. Still, present studies have barely scratched the surface of what there is to discover.

In this session, we invite contributions on soil structure, its formation and alteration and its associated soil functions. Special focuses are on feedbacks between soil physical or chemical processes and soil biology as well as the impact of mechanical stress exerted by heavy vehicles deployed under land management operations, which are linked with each other through a dynamic soil structure. Further, we encourage submissions that integrate complementary measurement techniques, explore new modelling concepts or aim at bridging different scales.

Convener: Loes van Schaik | Co-conveners: Thomas Keller, John Koestel, Frederic LeutherECSECS, Ludmila Ribeiro Roder, Saoirse Tracy
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Fri, 30 Apr, 15:30–17:00

Chairpersons: Frederic Leuther, Ludmila Ribeiro Roder, Loes van Schaik

5-minute convener introduction

Ulrich Weller

Ever since mankind has started to dig up the earth for planting, we are concerned with soil structure. For a long time digging the soil and breaking it into pieces was the only way to get insight into its architecture. Many valuable things were learned by this way: how the stability of the structure depends on the constituents, which soils are accessible for roots. To study the soil constituents in detail and in their natural ensemble has only begun about 90 years ago with the establishment of micromorphology. Thus, describing the soil by looking at its pieces has a 100 times longer history.

The new endeavor started with looking at the solid constituents of soil. The arrangement gave a new insight on processes, and enabled to describe the development of minerals, the activity of soil fauna and the diffusion of substances. It was in a rather descriptive manner that the light of microscope was shed on the soil structure.

With the introduction of X ray CT a new chapter was opened. Now it became possible to generate sufficient data for a quantitative analysis of the soil space. And with that the study of a new aspect of soil structure became feasible: the description of the pore space. Most of the functions of soil architecture are directly related to the pore space, thus a quantitative tool to describe this feature was required to understand the influence of pore space architecture on soil functions. The possibility to quantify pore space has meanwhile gotten a new tool: a standardized quantitative evaluation routine together with a comprehensive and growing library of evaluated soil structure images.

Here we are. We have to go on. To study dynamics of structural development is still tedious and can only be achieved by getting small glimpses at points in time.

New techniques occur. As is X ray CT for pore space, imaging techniques for the composition and arrangement of the solid phase evolve. They will give rise for new quantitative descriptions of soil forming processes.

Yet all this insight has to be digested and put into meaningful concepts. To profit from the wealth of information on pore space dynamics we have to implement models that can deal with a dynamic pore space. For soil hydraulics such a model is in development. It shows a clear dependency of the soil’s properties on the structure. With this, the importance of soil structure forming and preserving in agricultural management can be stressed.


How to cite: Weller, U.: Looking for soil structure, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11147, https://doi.org/10.5194/egusphere-egu21-11147, 2021.

Marine Lacoste et al.

The structure of soils, i.e. the macroscopic organization of aggregates and pores, conditions the storage and transport of water and gas in the soil, and strongly determines the physico-chemical environment of soil organisms (plants, micro and macro-organisms). The description of the soils structure dynamics constitutes a major issue in the current context of global change, at the scientific, environmental and agronomic level. However, few tools are available to monitor this dynamic non-destructively and in situ. We therefore propose to develop a new method based on the analysis of acoustic emissions (AE) spontaneously emitted by soils during the evolution of their structure. A laboratory feasibility study was conducted to explore the links between variations in soil structure and the AE emitted during soil desiccation.

Two undisturbed soil columns (8 cm in diameter, 5 cm high) were sampled in an agricultural field (near Chartres in France), in the surface horizon of a Glossic Retisol. These cylinders were air dried (20°C during 9 days), and the AE produced during drying were monitored using piezoelectric sensors place at the soil surface. The concomitant soil structure changes were followed through 3D images, acquired by X-ray tomography (CIRE platform, INRAE, Nouzilly) all along the experiment. These images, with a resolution of 168 µm, were used to characterize the pore network (porosity, surface density, connectivity, etc.).

The dynamics of the EAs recorded during the drying of the samples is comparable for the two samples: the AE rates are maximum at the start of the experiment and then reach a plateau. Changes in soil structure follow the same dynamics, e.g. considering porosity or surface density of the pores. If we analyze the relationship between the signals recorded by the surface sensors (EA rate) and the porosity, we observe a linear relationship (R² of 0.79). This relationship, although encouraging, remains to be consolidated by additional results.

To go further, it is also necessary to define the necessary conditions to perform such a measurement in situ, and to improve the acoustic signal processing to characterize the EA produced during soil desiccation. Indeed, a major objective of our work is to differentiate, thanks to EAs, the various factors responsible for the evolution of soil structure (physical and biological), by determining their "acoustic signature".

How to cite: Lacoste, M., Giot, G., Seger, M., and Cousin, I.: Passive acoustic emissions: a dynamic tool to monitor soil structure variations?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12184, https://doi.org/10.5194/egusphere-egu21-12184, 2021.

Giorgio Capello et al.

Adopting integrated measurement techniques may enhance our understanding of hydropedological processes within the critical zone. To investigate lateral subsurface flow due to lithological discontinuities, a ponding infiltration test, two GPR surveys, and soil penetration resistance (PR) measurements were conducted on a 1 m2 plot in a vegetated area located in the university campus of Doua (Lyon, France). A GPR grid with 0.2 m intervals was established. In the center of the grid, around the root system of a hawthorn shrub, an infiltration test was conducted using an automated single-ring infiltrometer proposed by Concialdi et al. (2020), to infiltrate a shear-thinning viscous solution (1 g L−1 Xanthan gum powder). The viscous solution was expected to fill preferential pathways due to the roots, with limited infiltration into the soil matrix, and thus reveal complex geometries or macropore networks in highly heterogeneous soils. To create three-dimensional (3D) representations of the infiltrated solution, two GPR surveys were carried out just before and 20 min after the infiltration test, using a GSSI (Geophysical Survey System Inc., Salem, NH) SIR 3000 system with a 900 MHz antenna. A total of 24 radargrams were collected in time mode by moving the antenna along the survey lines and recording the markers position along the survey line intersections. After the second GPR survey, PR was measured at each of the 36 intersection points of the grid using an electronic hand-pushed cone penetrometer. The cone had a 30° angle and a base area of 1 cm2, inserted into the soil at a constant speed of 2 cm s−1 to a depth of 0.8 m. These measurements were aimed to highlight contrasting penetration resistance characteristics between different soil horizons. We also determined the soil bulk density from 24 undisturbed soil cores (~ 100 cm3) collected at different depths from 0 to 50 cm. Finally, an auger was used to extract a 0.69-m-depth soil core for the direct observation of lithological heterogeneities.

Differenced radargrams from pre- and post-infiltration surveys allowed to detect the 3D infiltration bulb, which was vertically elongated and irregularly shaped, but with an evident horizontal divergence between the depth of 20 and 30 cm. Below 30 cm depth, a significant increasing of soil PR and BD (respectively higher than 2.5 MPa and 1.50 g cm-3, between 30 and 50 cm depth) was detected, indicating the presence of a underlying layer, which was also identifiable by visual observation of the soil core. This dense layer impeded water flow. Consequently, the liquid solution partially diverged laterally and accumulated upside this layer, and partially infiltrated into the dense layer along preferential flow paths in correspondence with the plant root system, as detected by the 3D GPR diagram. Summing up and considering every aspect, this study allowed to identify water perching above a shallow restrictive layer for a better understanding of the water dynamics of the investigated soil. This study shows the benefits to couple different types of soil physics approaches to relate hydrological processes to the soil hydraulic and mechanical properties.

How to cite: Capello, G., Biddoccu, M., Di Prima, S., and Lassabatere, L.: Combining new techniques to investigate water dynamics above a shallow restrictive layer., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12220, https://doi.org/10.5194/egusphere-egu21-12220, 2021.

Maik Lucas et al.

Cover crops are known to increase macroporosity and pore connectivity, thus having a beneficial effect on soil hydraulic properties such as saturated hydraulic conductivity, However, cover crop species typically used encompass a variety of contrasting root architectures and their effects on small-scale pore properties are difficult to quantify.

Here we explore the influence of five different cover crops (annual ryegrass, Austrian winter pea, dwarf essex rapeseed, oats, and oilseed radish) on soil structure with X-ray µCT. Undisturbed samples were taken from an experiment with these cover crops on Kellogg Biological Station (Michigan, USA) in October 2019. Two soil columns with a diameter of 5 cm were taken in 5 - 10 cm depth from each of three replicated plots per plant species and scanned with X-ray µCT at a resolution of 18 µm.

These images will be used to characterize pore structure in terms of pore size distribution, pore connectivity. In addition, a new imaging protocol will be used, which combines existing ones with a random forest classifier to segment image features such as pores, biopores and roots simultaneously.

First, the results reveal that different cover crops indeed result in different pore characteristics.  The fibrous root system of oats leads to the highest volume of narrow macropores and increased their connectivity, while the tap root system of dwarf essex rapeseed mainly effected wide macropores.  The highly diverse root system of Australian winter pea increased a wide range of pore sizes and thus resulted in the highest visible porosity.

The current study is funded by a grant from USDA Organic Transition program

How to cite: Lucas, M., Nguyen, L., Guber, A., and Kravchenko, A.: The effect of cover crops on soil structure is mainly driven by root architecture, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13448, https://doi.org/10.5194/egusphere-egu21-13448, 2021.

Gheorghe Stegarescu et al.

Cover crops are widely known for their capacity to improve the soil biological properties and soil structural stability. Nevertheless, the cover crop residues quantity necessary to improve these soil properties is not yet really known. A 30-day incubation experiment was conducted to explore the effect of oilseed rape (Brassica napus) residues (ORR) as a cover crop on the soil aggregate stability of sandy loam soil. The fresh ORR was mixed with the soil at different rates starting from 1.0 to 6.0 g C kg-1 of soil. The experiment consisted of five treatments: bulk soil (I), soil mixed with ORR at a rate of 1 g C kg-1 of soil (II), soil mixed with ORR at a rate of 2 g C kg-1 of soil (III), soil mixed with ORR at a rate of 4 g C kg-1 of soil (IV), soil mixed with ORR at a rate of 6 g C kg-1 of soil (V). During 30 days of incubation the soil moisture, soil water stable aggregates, and microbial substrate induced respiration rates were measured. The aggregate stability significantly increased after 30 days only in the treatment with 1 g C kg-1 of soil. In turn, the ORR applied at a rate of 6 g C kg-1 of soil significantly decreased the soil aggregate stability. The higher the ORR addition rate the lower was the soil basal respiration and substrate induced respiration. The general conclusion was that the higher quantity of ORR increased the soil moisture which subsequently created unfavorable conditions for the soil microbial activity and led to soil aggregate stability degradation. However, this conclusion must be validated in a field study where the soil moisture and temperature conditions are much more variable compared to our incubation experiment.

How to cite: Stegarescu, G., Reintam, E., and Tõnutare, T.: The influence of different cover crop residues quantities on soil structural stability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3877, https://doi.org/10.5194/egusphere-egu21-3877, 2021.

Nicolás Riveras Muñoz et al.

Biological soil crusts (biocrusts) composed of cyanobacteria, algae, lichens and bryophytes have a stabilizing effect on the soil surface. This effect is mostly studied in arid climates, where biocrusts are the main biological agent to steady and bind together soil aggregates. Nevertheless, biocrusts are also an integral part of the soil surface under semi-humid and humid climate conditions, mainly covering open spaces in forests and on fallow lands. As such, they often develop after vegetation disturbances, when their ability to compete with higher plants is increased. To better understand how biocrusts mediate changes in soil aggregate stability under different climatic conditions, we analyzed soil substrates taken under biocrust communities from four national parks in Chile using dry and wet sieving. These samples cover soils from a large climate gradient from arid (Pan de Azúcar), semiarid (Santa Gracia), mediterranean (La Campana) to humid (Nahuelbuta). 
Biocrust communities were dominated by cyanobacteria in Pan de Azúcar and Santa Gracia, bryophytes and lichens in La Campana and bryophytes in Nahuelbuta. They showed a stabilizing effect on the soil surface in three of the four investigated climates. Their presence increased the Mean Weight Diameter of the aggregates (MWD) by 102% in Pan de Azúcar, 208% in Santa Gracia and 82% in La Campana. In Nahuelbuta there was no significant increase to the condition without biocrust, because the abundance of permanent soil covering higher vegetation does not allow the effect of biocrusts to manifest. The stabilization differed between the aggregate fractions studied, being most pronounced for smaller aggregates >2 mm. The Geometric Mean Diameter (GMD) showed similar results as MWD, but with a clear effect of drying and wetting conditions, as an increase in the stability directly related to precipitation and the climatic gradient. Bulk density (BD) changed from high mean values of 1.50 g cm-3 in Pan de Azúcar and 1.63 g cm-3 in Santa Gracia (where cattle grazing was observed) to 1.16 g cm-3 in La Campana and the lowest mean of 0.62 g cm-3 in Nahuelbuta, where we observed a more developed soil structure and high organic matter content (21.58% in average). Accordingly, here we also found pronounced hydrophobicity of the soil. These preliminary findings indicate not only differences in the stability of the aggregates, but also in the state of conservation and management of the soils. Results will now be extended by further statistical analyses, which will additionally be presented at vEGU21.

How to cite: Riveras Muñoz, N., Seitz, S., Gall, C., Pérez, H., Kuehn, P., Seguel, O., and Scholten, T.: Biological soil crusts mediate changes in soil aggregate stability along a climate gradient in Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7914, https://doi.org/10.5194/egusphere-egu21-7914, 2021.

Anastasia Mishchenko et al.

The aggregate composition is one of the key characteristics of soils. Based on the use of aggregates of different sizes, one can draw conclusions about the anthropogenic load on soils in conditions of agricultural use. We investigated the aggregate composition of soil samples of the 0-20 cm layer of soils with application of four tillage techniques: plowing, energy-saving (surface tillage, without plowing), longline (surface tillage + chisel tillage), anti-erosion (chisel tillage). Stationary experience laid in 1995. The сrops were: bare fallow, busy fallow and wheat. Soil samples were sieved with a standard set of sieves:> 10; 10-7; 7-5; 5-3; 3-2; 2-1; 1-0.5; 0.5-0.25; <0.25 mm, water resistance was determined by the Savvinov method with sieves of:> 5; 5-3; 3-2; 2-1; 1-0.5; 0.5-0.25; <0.25 mm with daily water saturation prior to analysis. Rheological parameters were studied using the amplitude sweep method on a modular compact rheometer MCR-302 (Anton Paar, Austria) with a parallel plateau PP-25 measuring system.

All 24 plots with all four treatments demonstrated an excellent water-resistant structure of agro-gray soils. The soils have a good structural state in terms of agronomically aggregates content and the structural coefficient. Water resistance of the structure is excessively high and good as well. The average diameter of the aggregates is from 3.6 to 6.1 mm, the average value is 4.7 mm. This gives us an idea of the structural condition in general, but we cannot track the structural condition of plots with different treatments in the field.

The Principal Component analysis and cluster analysis was used to determine the differences in soils of different types of use. We used STATISTICA. These statistics method successfully classified soils structural relatively treatments.

The study of the rheological properties of agro-gray soils with different processing methods showed that in the zone of linear viscoelastic behavior (LV[С1] B) during all treatments, the range of LVB did not differ significantly and averaged 0.0048% deformation. Differences were noted at Shear Stress max, for the energy-saving treatment application, the τ (632.67 Pa) was lower than the other treatments, an average of 661.83 Pa for 12 repetitions. The crossover occurred at 1.48% strain for an average of 12 reps. The smallest value for the deformation at which crossover occurred (1.22%) was observed for the variant with the use of anti-erosion treatment. The highest (1.72%) for energy efficient processing.

Thus, the use application of aggregate and rheological analyses has shown the promotion of energy-saving technologies application to form a relatively favorable structural condition of the studied soils.

The work was supported by RFBR grant No 19-29-05021 mk

How to cite: Mishchenko, A., Khaydapova, D., Karpova, D., Abdulkhanova, D., and Shulga, P.: The structural state of agro-grey soil in various tillage conditions (based on aggregate and rheological analyses), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10206, https://doi.org/10.5194/egusphere-egu21-10206, 2021.

Steffen Schlüter et al.

Land use is known to exert a dominant impact on a range of essential soil functions like water retention, carbon sequestration, matter cycling and plant growth. In addition, land use management is known to have a strong influence on soil structure, e.g. through tillage and compaction. While the difference in topsoil structure between grassland and agricultural soil is huge, differences among different farming or grassland management practices can be more subtle. At the same time, soil structure is known to be a suitable indicator for many soil functions. That is, differences in carbon content or plant-available field capacity between different land uses can often be explained by different structural properties.

This impact of land use on the relationship between soil structure and biological indicators for soil processes was explored in the Global Change Exploratory Facility, a well-established (>5 years) field experiment in Bad Lauchstädt, Germany, comprising five land use types (conventional farming, organic farming, intensive meadow, extensive meadow, extensive pasture). 15 intact topsoil cores were sampled from each land use type in spring 2020 and soil structure and microbial activity were measured using X-ray CT and respirometry, respectively. Microbial activity was estimated by basal respiration at field moisture and by substrate-induced respiration with glucose solution under wet conditions. The aims of this study were to (1) quantify the impact of land use on these structural and biological soil properties and (2) to assess in how far microbial activity can be predicted by the structural properties.

Surprisingly, image-derived macroporosity did not differ between farming and grassland plots mainly due to the huge variability among compacted and non-compacted samples in the farming plots. Other pore metrics like pore distance and pore connectivity followed the same trend, whereas mean pore size was larger in the grassland plots due to more large biopores. Basal respiration increased in the order farming < meadow < pasture, whereas the order was reversed for substrate-induced respiration. The predictability of basal respiration (R2=0.29) and substrate-induced respiration (R2=0.5) with explanatory variables based on pore metrics and bulk soil properties was rather low, with root mass and bulk density being the best predictors.

How to cite: Schlüter, S., Roussety, T., Rohe, L., Guliyev, V., Blagodatskaya, E., and Reitz, T.: Impact of land-use on soil structure and soil ecological properties in a long-term field experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9723, https://doi.org/10.5194/egusphere-egu21-9723, 2021.

Patricia Ortega-Ramirez et al.

N2O emission in soils is a consequence of the activity of nitrifying and denitrifying microorganisms and potentially abiotic processes. However, the large microscale variability of the soil characteristics that influence these processes and in particular the location of anoxic microsites, limits prediction efforts. Better understanding of denitrification activity on microscopic scales is required to improve predictions of N2O emissions.

This study explored the role of soil microstructure on N2O emission. To fulfill this objective we sampled 24 soil columns (5 cm diameter, 6 cm height) in the surface layer of a same plot in a cultivated soil (Luvisol, La Cage, Versailles, France). The soil samples were saturated with a solution of ammonium nitrate (NH4NO3), and equilibrated at a matrix potential of -32 cm (pF 1.5). The emitted fluxes of N2O were measured during 7 days. At the end of the experiment, the soil columns were scanned in a X-ray micro tomograph, at the University of Poitiers. A 32 µm voxel resolution was achieved for the 3D reconstructed images.

In order to reduce noise and segment the 3D images, the same protocol was implemented for all columns. The reduction of noise consisted of passing a non-local mean filter, a non-sharp mask and a radial correction. Such combination of steps succeeded in removing both ring artifacts and the radial dependence of the voxel values. Due to the variety of material densities in the soil, a local segmentation based on the watershed method was implemented to classify the soil constituents in four classes (based on its density value): air, water and organic matter (OM), soil matrix and minerals. This method is good for detecting thin pores and avoids missclassification of voxels undergoing partial volume effect, which can lead to false organic coatings around macropores.

The soil columns exhibited a large variability of accumulated N2O after 7 days (from 107 to 1940 µgN kg-1 d.w. soil). The size of OM clusters varied between a couple and up to thousands of voxels. No correlation was found between the emission of N2O and the porosity, nor between the N2O emission and the connectivity of the air phase. Based on the premise that the less accessible is the oxygen to the OM, the bigger should be the N2O emission of the soil column, we proposed and computed a microscopic spatial descriptor, Igd, based on the notion of the geodesic distance between clusters of OM and air for each soil column 3D image. We expect to find a correlation between Igd and the N2O emission.

How to cite: Ortega-Ramirez, P., Pot, V., Laville, P., Schlüter, S., Hadjar, D., Basile-Doelsch, I., Henault, C., Caurel, C., Mazurier, A., Lacoste, M., and Garnier, P.: Role of soil microstructure on the emission of N2O in intact small soil columns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12438, https://doi.org/10.5194/egusphere-egu21-12438, 2021.

Galina Denisova et al.

Phosphorous is one of the most important elements for plant life, its supply is limited, so supporting the balance of phosphorous is considered to be a global challenge for the 21st century[1]. In the majority of soils, a vast amount of organic and mineral phosphorous is contained in immobile and insoluble compounds. Intensive tillage, even without fertilizers, may provide plants with resupply of phosphorous, but it leads to negative ecological consequences. [2] There is large amount of total phosphorous (0,15 - 0, 35% P2O5) in Chernozem of Kursk Region, and about 50-70% of it is organic compounds. [3]

We investigated soils with different land use: mowed grassland, soil under the wood line, soil of perennial fallow, tillage and no-till farming. The main soil is Vermic Chernozems (WRB).  Every soil sample was divided into four groups of different-sized aggregates (> 5 mm, 5-2 mm, 2-1 mm and < 1 mm) by Savvinov dry sieving method. We determined the content of organic carbon, mobile phosphorous, organic phosphorous, mineral phosphorous and total ratio of phosphorous and other elements in each group.

Cultivation increases the content of mobile phosphorous because of mineralization process. However, it leads to content reduction of organic matter. Moreover, it significantly changes the structure: the amount of aggregates larger than 5 mm increases. The content of mobile phosphorus in natural soil depends on the size of aggregates, and its amount decreases with decreasing size of aggregates. After cultivation, this trend changes, and mobile phosphorus is shared almost evenly among all groups of aggregates. Most of the mobile phosphorus is in the soil with no-till farming.

When the structure is damaged, the phosphoric state of the soil changes, which will lead to changes in the nutrition of plants.


1) Yang X., Chen X., Yang X., 2019. Effect of organic matter on phosphorus adsorption and desorption in a black soil from Northeast//

2)Агрохимическая характеристика почв СССР. Почвенно-агрохимическое районирование / Всесоюзная академия сельскохозяйственных наук им. В.И. Ленина (ВАСХНИЛ), Почвенный институт им. В.В. Докучаева ; Отв.ред. Андрей Васильевич Соколов, Николай Николаевич Розов . – Москва : Наука, 1976 . – 363 с.

3)Макаров М.И. Фосфор органического вещества почв. – М.: ГЕОС, МГУ, 2009. – 397

How to cite: Denisova, G., Karpova, D., and Abdulkhanova, D.: Phosphorous in air-dry soil aggregates of Chernozem in different types of human-induced landscapes (Kursk region), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13080, https://doi.org/10.5194/egusphere-egu21-13080, 2021.

Jin Ho Lee et al.

Bioenergy crop cultivation is suggested as one of the promising options to increase soil organic carbon (SOC) stock, and thereby sequester atmospheric carbon dioxide. Yet, the increase in SOC varies greatly depending on the cropping system, with high plant diversity in particular appearing to be positive for carbon storage. This is recently linked to, among other things, the formation of a pore architecture favorable for microbial function and the storage of microbial degradation products. However, little is known about whether this observation holds true for a wide range of soil textures. Therefore, the objective of this research was to compare the abundance of pores with different sizes and SOC contents in soils with contrasting texture and plant diversity. Soil cores and surrounding soil samples were taken on seven long-term field experiments of monoculture switchgrass and restored prairie sites in Michigan, USA. In addition to texture and SOC analyses in disturbed soil samples, undisturbed cores with a diameter of 5 cm were scanned by micro-computer tomography (µCT) at a resolution of 18 µm. These will be used to analyze pore characteristics.

such as pore size distribution.

Results reveal, in highly sandy soil, high plant diversity was less effective to form narrow mid-size pores, and thus did not enhance SOC, while numerically higher SOC contents were observed in the restored prairie of less sandy soil, having higher abundance of mid-size pores compared to the monoculture. In conclusion, in the highly sandy soil, restored prairie with plant diversity was less effective to form pores in the mid-size range, and thus it couldn’t enhance the capability of C sequestration.

How to cite: Lee, J. H., Lucas, M., Guber, A., and Kravchenko, A.: Pore architecture and soil carbon accrual in soils under monoculture switchgrass vs. prairie soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14035, https://doi.org/10.5194/egusphere-egu21-14035, 2021.

Yair Mau et al.

Soil salinity and sodicity present serious risks to agriculture, in the face of dwindling freshwater resources and changing rainfall patterns. As a finite resource of crucial importance, soils must be protected from irreversible degradation. However, very little is known about how soils respond to adverse conditions in the long run, in particular regarding salinity and sodicity. As a proxy for soil stability and health, we will discuss what (little) is known about the irreversible deterioration of saturated hydraulic conductivity (Ks), subjected to water of varying levels of salinity and sodicity. We present novel soil column experiments measuring Ks hysteresis, for three soils of varying clay content. We then present a mathematical framework that allows us to make sense of the hysteresis in Ks, and that helps us understand the pivotal role of a soil's history of salinization and sodification in determining future Ks behavior. Most importantly, our model gives specific guidelines of what to measure in order to best characterize a soil's partial decline in Ks. We will focus on the role of reversal curves as the key to unlock a full characterization of the Ks hysteresis. With the help of weighting functions, we will show that our modeling framework is able to describe soils of any texture and clay mineralogy, making it both versatile and useful.

How to cite: Mau, Y., Kramer, I., Adeyemo, T., and Bayer, Y.: Making sense of irreversible soil salinization and sodification, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9235, https://doi.org/10.5194/egusphere-egu21-9235, 2021.

Frederic Leuther and Steffen Schlüter

The ploughing of soils drastically alters soil structure and at the same time reduces its stability against external stresses. A fragmentation of these artificially produced soil clods during winter time is often observed in areas with air temperatures fluctuating around the freezing point. In this study, the cumulative effects of multiple freeze-thaw cycles (FTCs) on soil structure and soil hydraulic properties were analyzed for two different soil textures, a silty clay loam with a substantial amount of swelling clay minerals and a silty loam with less swell/shrink dynamics. The soil material was brought into two different initial states: (i) undisturbed soil cores taken from the topsoil from a grassland, and (ii) cylinders repacked with soil clods taken from a ploughed field nearby. FTCs were simulated under controlled conditions in the lab, changes in soil structure ≥48 µm were regularly recorded using X-ray µCT. After 19 FTCs, the impact on hydraulic properties were measured and the resolution of structural characteristics were increased to 10 µm by subsampling.

The effect of FTC on soil structure was found to be dependent on the initial structure, soil texture and number of FTCs. Freezing and thawing induced a consolidation of the repacked soil clods taken from both field sites, resulting in a systematic reduction in pore sizes and macro-pore connectivity. The macro-pore system of the undisturbed samples was only slightly affected. Fragmentation of soil elements larger than 0.8 to 1.2 mm increased the connectivity of pores smaller than 0.5 to 0.8 mm. Frost action increased the unsaturated hydraulic conductivity of all treatments, while the water retention was only slightly affected. This leads to the conclusion that multiple FTCs enforces a well-connected meso-pore system at the expense of a fragile macro-pore system. A change in soil structure that benefits farmers but could be reduced in the face of milder winters due to global warming.

How to cite: Leuther, F. and Schlüter, S.: The impact of freeze-thaw-cycles on soil structure and soil hydraulic properties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1089, https://doi.org/10.5194/egusphere-egu21-1089, 2021.

Ludmila Roder et al.

Research over the past several decades has shown that preferential flow is more the rule than the exception. However, our collective understanding of preferential flow processes has been limited by a lack of suitable methods to detect and visualize the initiation and evolution of non-uniform wetting at high spatial and temporal resolutions, particularly in real-world settings. In this study, we investigate water infiltration initiation by tree trunk and root systems. We carried out time-lapse ground penetrating radar (GPR) surveys in conjunction with a simulated stemflow event to provide evidence of root-induced preferential flow and generate a three-dimensional representation of the wetted zone.

We established a survey grid (3.5 m × 5 m, with a local slope of 10.3°), consisting of ten horizontal and thirteen vertical parallel survey lines with 0.5 m intervals between them. The horizontal lines were downslope-oriented. The grid was placed around a Quercus suber L. We collected a total of 46 (2 GPR surveys × 23 survey lines) radargrams using an IDS (Ingegneria Dei Sistemi S.p.A.) Ris Hi Mod v. 1.0 system with a 900-MHz antenna mounted on a GPR cart. Two grid GPR surveys were carried out before and after the artificial stemflow experiment. In the experiment, we applied 100 L of brilliant blue dye (E133) solution on the tree trunk. The stemflow volume of 100 L corresponded to 63.2 mm of incident precipitation, considering a crown projected area of 201 m2 and a 1.3% conversion rate of rainfall to stemflow. Trench profiles were carefully excavated with hand tools to remove soil and detect both root location and size and areas of infiltration and preferential pathways on the soil profile.

The majority (84.4%) of artificially applied stemflow infiltrated into the soil, while the remaining 15.6% generated overland flow, which was collected by a small v-shaped plastic channel placed into a groove previously scraped on the downhill side of the tree. The 3D diagram clearly demarcated the dimension and shape of the wetted zone, thus providing evidence of root-induced preferential flow along coarse roots. The wetted zone extended downslope up to a horizontal distance of 3 m from the trunk and down to a depth of approximately 0.7 m. Put all together, this study shows the importance of accounting for plant and trees trunk and root systems when quantifying infiltration.

How to cite: Roder, L., Di Prima, S., Campus, S., Giadrossich, F., Stewart, R. D., Abou Najm, M. R., Winiarski, T., Angulo-Jaramillo, R., del Campo, A. D., Lassabatere, L., and Roggero, P. P.: Detecting stemflow-induced preferential flow pathways through time-lapse ground-penetrating radar surveys, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1697, https://doi.org/10.5194/egusphere-egu21-1697, 2021.

Jean-Phillipe Bedell et al.

Infiltration basins are among the most spread techniques for managing stormwater. Infiltration basins allow the infiltration of stormwater, which prevents their piping towards treatment systems. However, stormwater contains loads of pollutants and suspended solids that accumulate at the surface of the basin and form a sedimentary layer. That sedimentary lay may clog the infiltration basin partially, thus reducing its bulk infiltration capability. Fortunately, plants and fauna colonize spontaneously this sedimentary layer, thus preventing complete clogging and restoring soils' infiltration functions. The knowledge of the effect on restoring the infiltration function requires properly characterize fauna, notably earthworms, with the aim to predict their impact on infiltration. Besides, earthworms, considered as ecosystem engineers, are known to be good candidates for integrating soil chemical pollution.

If earthworms have been intensively studied in natural and agricultural soil, very few studies have focused on the characterization of earthworms' communities in urban soils and, in particular, in infiltration basins. This study presents the description of earthworms sampled at several places over one infiltration basins. This basin receives the stormwater collected over an industrial peri-urban catchment. The infiltration basin has been functioning for more than two decades, thus, plants and fauna have colonized the surface related to water ponding at surface and water infiltration. The sampled places were selected to follow three specific water pathways at the surface. High population variability was measured with densities ranging from 0 to 300 earthworms per square meter with the presence of adults but also juveniles. But, only endogenic and epigeic functional groups were found. The characterization of abundance, age, and species over the sampled places was correlated to water content and sediment thickness, in addition to pollutant loads.

The results show that earthworms require given edaphic conditions (including thick enough sedimentary layer) to settle. We then expect most earthworms to colonize those specific places, increasing water infiltration punctually at these places. Put all together, our findings participate in the understanding of colonization of basin infiltration by organisms and their contribution to their primary function: infiltrating water.

How to cite: Bedell, J.-P., Fernandes, G., Roques, O., and Lassabatere, L.: Characterization of earthworms in an infiltration basin for maintaining water infiltration, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7215, https://doi.org/10.5194/egusphere-egu21-7215, 2021.

sidra bibi and Loes loes.vanschaik@wur.nl

Earthworms are known as ecosystem engineers, which influence the chemical and physical properties in their own environment and thereby strongly modify soil processes. Soil structure (soil aggregates and macropores) formed by earthworms during burrowing activity may influence the soil moisture retention and water flow, enhancing infiltration into deep soil layers.

We studied the influence of anecic earthworms (Lumbricus terrestris fed on poplar leaves) on the spatial and temporal variability in water outflow and storage through a soil column. Therefore, we established a cylinder (30cm diameter, 50cm high) with silty loamy soil. At the bottom boundary, 15 fiberglass wicks drain the water from the soil column. With these wicks the water outflow is measured with a spatial and temporal resolution.  After an initial wetting of the soil, irrigation of the soil cylinder was done twice per week with a full cone nozzle, with an intensity of 36 mm/h and a duration of 20 minutes After 17 weeks 10 adult earthworms were added to the column. The research design consists of three phases (i) soil-filled column ( 14  weeks, with a gap of 4 weeks in the middle due to the corona lockdown) (ii) transition phase: initial earthworm activity (3 days) (iii) soil column with earthworm created structure (7 weeks).

After the experiment, the column was excavated carefully by layers of 4cm at a time. All of the earthworms were found back alive in the column. There was evidence of earthworm burrows down to 26 cm depth in the soil column, earthworm created aggregates were seen only in the top few centimeters.

We expected the outflow of water from the soil column to change due to the earthworm activity: on the one hand, the creation of macroaggregates was expected to increase the water retention in the soil, and on the other hand, the macropores were expected to create a stronger spatial variability in outflow and a more rapid reaction of outflow to the irrigation events. 

We observed mainly an earlier and slightly higher peak in the total outflow of the column coinciding with an earlier and higher peak in the spatial variability in the outflow of the wicks.

How to cite: bibi, S. and loes.vanschaik@wur.nl, L.: Dynamics of spatial and temporal outflow from a soil column influenced by earthworm activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15585, https://doi.org/10.5194/egusphere-egu21-15585, 2021.

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