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 and novel experimental setups. Still, present studies have barely scratched the surface of what there is to discover.
In this session, we are inviting contributions on the formation and alteration of soil structure and its associated soil functions over time. Special focuses are on feedbacks between soil structure dynamics and soil biology as well as the impact of mechanical stress exerted by heavy vehicles deployed under land management operations. Further, we encourage submissions that are integrating complementary measurement techniques or aim at bridging different scales.

Convener: Frederic LeutherECSECS | Co-conveners: Thomas Keller, John Koestel, Saoirse Tracy, Loes van Schaik
| Attendance Tue, 05 May, 10:45–12:30 (CEST)

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Chat time: Tuesday, 5 May 2020, 10:45–12:30

D2331 |
| Highlight
Emily Dowdeswell-Downey, Robert Grabowski, and Jane Rickson

Soil is a critical resource that delivers numerous ecosystem services, yet this capacity is diminished by soil erosion and further threatened by the impacts of climate change. Soil erodibility is largely overlooked when considering soils’ response to climate change. Aggregate stability is widely recognised as a key indicator of soil erodibility and is influenced by multiple physical, chemical and biological mechanisms operating simultaneously. The microbial community has been reported to respond to changing climatic conditions, yet it remains unclear how microbial change influences microbially mediated aggregation and therefore aggregate stability. The microbial community in terms of composition, activity, and growth, can change over rapid timescales in response to climate conditions. The short timescale of such microbial shifts could rapidly impact microbially-mediated soil (de)stabilisation and aggregate stability.

The aim of this work is to experimentally test whether climatic conditions, in terms of temperature and moisture content, influence the microbial community and microbially-mediated soil (de)stabilisation, in turn influencing aggregate stability and soil erodibility. A series of laboratory-controlled experiments using environmental chambers and rainfall simulation examined the effects of temperature and moisture content in both static and fluctuating treatments on two surface soils (a sandy loam and a clay loam). Treatments were conducted with single layer aggregate microcosms and multi-layered soil trays to explore aggregate-scale mechanisms and the potential upscaling to run-off processes.        

Key findings from this research demonstrate that temperature and moisture content affect aggregate stability and the importance of climate induced microbial shifts influence on microbially mediated soil (de)stabilisation. Static temperature and moisture content conditions significantly affected aggregate stability, however the effects varied dependent on soil texture. Increasing temperature significantly increased aggregate stability in clay loam aggregates, while moisture content significantly decreased aggregate stability in sandy loam aggregates. Multiple regression analysis showed that aggregate stability was best predicted by soil moisture content, microbial biomass carbon, gram-negative bacterial abundance and fungal abundance in the sandy loam. Temperature was the sole significant predictor in the clay loam. Aggregate stability was significantly lower under fluctuating conditions and higher under static conditions. Aggregate stability was not significantly different between fluctuating climate treatments representing summer and winter cycles under future emission scenarios. Although, these treatments did significantly affect the microbial community. Our results have implications for our current understanding of microbial function in terms of soil stabilisation, and the relationship between climate, aggregate stability and soil erodibility.

How to cite: Dowdeswell-Downey, E., Grabowski, R., and Rickson, J.: Temperature and moisture content influences aggregate stability: linking climate induced microbial change to aggregate (de)stabilisation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16470, https://doi.org/10.5194/egusphere-egu2020-16470, 2020.

D2332 |
Agnieszka Józefowska, Magdalena Ryżak, Justyna Sokołowska, Karolina Woźnica, Tomasz Zaleski, and Andrzej Bieganowski

Keywords: soil texture, aggregate stability, organic additives, earthworms, microbial activity,

Lubbers et al. (2017) emphasised that earthworm by creating macroaggregates increase the amount of organic carbon in the soil. Such macroaggregates contain particulate organic matter, fungal hyphae, or roots, and afterwards, during the decomposition of macroaggregates, the organic matter becomes more resistant to microbial attack (Pulleman et al. 2005). Earthworms, through feeding and burrowing, are important elements in C cycling (Curry and Schmidt 2007). However, the type of introduced organic matter (Huang et al. 2018) and abiotic factors (Six et al. 2004) are equally important in creating stable organic-mineral components as well as the presence of earthworms.

A six-month experiment was carried out to test how the soil structure (the stability of soil aggregates) behave under the influence of various organic additives. For each soil, except the reference samples, one of the listed additives was introduced, i.e. straw, straw with fulvic acid, peat (garden soil), compost, compost with active bacteria cultures and straw with fulvic acids, humus and active bacteria cultures. The research was carried out on soils with four types of texture, i.e. sandy, loamy, silty and clayey soil. In the project, three different species of earthworms commonly occurred in Polish soils were a structure-forming factor (Apporectodea rosea, Apporectodea calliginosa and Dendrobena rubillus). After the experiment, the amount of organic carbon in the soil, dissolved organic carbon, humus forms and microbiological activity of the soil were evaluated. The stability of the soil aggregates was determined using two methods: the sieve method (Kemper and Rosenau 1986) and laser diffraction method (Bieganowski et al. 2018),

Based on this research it was noted that the aggregate stability is correlated mainly with soil texture. The applied additives had the most significant influence on the transformation of organic carbon in the soil. Soil organic carbon, which may be incorporated into the soil in the form of the organic-mineral colloids, is an essential element in the balance of the carbon in nature. Among the tested additives, organic carbon from compost, peat and compost with active bacteria cultures was in the highest amount associated with fine earth particles (about 36-48%). For comparison, only less than 8.5% of the organic carbon from the straw was incorporated into the mineral part of the soil.

Two methods to measures aggregate stability are not comparable for sandy soils. In the wet-sieving method the sand fraction higher than 0.25 mm pretend to be stable aggregates.


The study was financed by The National Science Centre, Poland, grant No. 2017/01/X/ST10/00777, statistical analysis was made based the knowledge and skills achieved during the training: organized as part of the project: Integrated Program of the University of Agriculture in Kraków, which is co-financed by the European Union (POWR.03.05.00-00-z222/17)

How to cite: Józefowska, A., Ryżak, M., Sokołowska, J., Woźnica, K., Zaleski, T., and Bieganowski, A.: Determination of aggregate stability using laser diffraction method in soil with varied texture and carbon content, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8507, https://doi.org/10.5194/egusphere-egu2020-8507, 2020.

D2333 |
Jose Eugenio López Periago, Diego Soto Gomez, and Marcos Paradelo

We present a method to identify the characteristics of pressure jumps in repeated pump-driven saturation and drainage cycles in packed sand columns, i.e.,  pore pressure from zero to -80 hPa. This method is based on the registration of pore pressure oscillations using high sensitivity and rapid response tensiometers. The pressure signals were processed to identify and extract the pressure waveforms read by two tensiometers simultaneously.  Then, the waveforms were classified by k-means clustering algorithms and principal component analysis. We obtained a classification of different types of pressure waveforms that are consistent throughout successive cycles of wetting and drainage cycles. This consistency can be associated with patterns of fast capillary displacements in macropores, and ultimately, to hydrodynamic features of the structure.

How to cite: López Periago, J. E., Soto Gomez, D., and Paradelo, M.: Evidence of pressure jump signatures linked to fast air-water displacement dynamics in macropores, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22068, https://doi.org/10.5194/egusphere-egu2020-22068, 2020.

D2334 |
Shane Franklin, Yan Jin, and Bruce Vasilas

In this study we used oxygen sensitive optodes, or optical sensor devices, to observe oxygen depletion by soil microbes. Depletion served as a reference for microbial activity along three artificially constructed preferential flow paths consisting of coarse sand in the center surrounded fine sand. Following a flow event with glucose addition, images showed that oxygen depletion is greatest along the boundary between preferential flow paths (coarse sand) and the bulk matrix (fine sand). Oxygen gradients as well as nutrient gradients are commonly attributed to shaping soil bacterial communities, however, these mechanisms have not been studied in the specific soil architecture of preferential flow paths. A separate experiment was performed in which the fine sand matrix was replaced with a sandy soil containing its native microbial community. An addition of glucose and DOM was flowed through the columns containing real soil. Oxygen depletion was again monitored using oxygen sensor foils. To assess changes in the microbial community in time 16S rRNA analysis was performed on soil samples taken from different locations within the chambers. By monitoring the levels of oxygen depletion in time, we are able to gain an understanding of how this dynamic process alters microbial community structure. Additionally, zymography was performed to elucidate the locations where enzyme activity was greatest. By studying the microbial community in time along with oxygen depletion and enzyme activity, we are able to gain insight into structure-function relationships that take place within preferential flow paths. Furthering our understanding of processes taking place within preferential flow paths will allow for better estimation of how these entities function biogeochemically.

How to cite: Franklin, S., Jin, Y., and Vasilas, B.: Preferential flow induced nutrient gradients create microbial hotspots and shape bacterial community structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-892, https://doi.org/10.5194/egusphere-egu2020-892, 2020.

D2335 |
Yasushi Mori

Artificial macropores constructed of fibrous material were installed in degraded red-yellowsoils to enhance vertical infiltration of organic matter and nutrients. This can enhance vertical infiltration without cultivation which causes small particle loss from the surface soils.  Macropore and control (no macropore) plots were established and total carbon was measured at 10, 30, 50 cm depths every six months. Infiltrated soil water was sampled using a capillary force soil water sampler to measure total organic carbon and ion concentration. Results showed that soil total carbon increased in the macropore plot in spring and decreased in fall. The control plot showed few fluctuations. Total carbon concentrations in the soil water also increased in the macropore plot, which may be caused by introducing surface water into artificial macropores. In addition, nitrate nitrogen was higher in the summer in the macropore plot, representing a biological decomposition of organic matter and nutrients for plant growth. The plant biomass in the macropore plot was two times larger than that in control plot and the number of plant species also increased relative to the control plot. This vegetation represents a possible organic matter source for future soils. Finally, the carbon increment in low nutrient soils after macropore installation was calculated as 0.0036 g-C·g-soil−1·yr−1 (20.4 t-C·ha−1·yr−1), which was very successful. This study demonstrates that the relatively simple technique of installing artificial fibrous macropores can increase organic matter and recover vegetation in poorly drained soils.

How to cite: Mori, Y.: The Effect of Artificial Macropores on the Amount of Organic Matter in Soils and Plant Biomass., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5525, https://doi.org/10.5194/egusphere-egu2020-5525, 2020.

D2336 |
Sidra Bibi and Loes Van Schaik

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 will study 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 (), [LvS1] irrigation of the soil cylinder takes place twice per week with a full cone nozzle, with an intensity of 40 mm/h and a duration of 10 minutes. The research design consists of three phases (i) soil-filled column (4 weeks) (ii) transition phase: initial earthworm activity (4 weeks) (iii) soil column with earthworm created structure (4 weeks).

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

How to cite: Bibi, S. and Van Schaik, L.: Dynamics of spatial and temporal outflow from a soil column influenced by earthworm activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15232, https://doi.org/10.5194/egusphere-egu2020-15232, 2020.

D2337 |
Maoz Dor, John Koestel, Simon Emmanuel, and Yael Mishael

Soil mucilage strongly affects soil structural packing and stability. We characterized the effects of mucilage and the subsequent effect of wetting and drying on the microstructure of three agricultural soils: clayey, sandy-clay-loam, and loamy-sand soils. Soil stability measurement trends, assessed by a laser granulometry based aggregate durability index (ADI), varied between the soils. While aggregates stability of the clayey and loamy-sand soils decreased after subjecting soil samples to wetting and drying, stability increased in the case of the sandy-clay-loam soil. This observation can be explained by the high CaCO3 content in the loamy-sand soils (19.5%) which contributes to the formation of durable aggregates induced by calcite cementation. ADI values of all soils increased following mucilage amendment (0.035 w/w). Mucilage, consisting mainly of polysaccharides and lipids, may affect soil mechanical properties and structure by binding soil particles due to its adhesive properties, thus reinforcing the internal structure of the aggregates. Stability was further analyzed after subjecting the mucilage amended samples to a wetting and drying cycle, and a diverse trend was measured. While stability increased for the clayey and the loamy-sand soils, it decreased for the sandy-clay-loam soil. Mucilage is known to induce surface hydrophobicity, following its dehydration, which may lead to a decrease in the wettability of soil particles and protect aggregates from deterioration by water. However, in the sandy-clay-loam soil, the cumulative effect CaCO3 and mucilage which increases entropy overpowers the mucilage stabilizing effect.

The packing of the microstructure as a function of mucilage amendment and wetting and drying was characterized by quantifying morphological and geometrical changes within the pore-network, extracted by X-ray computed tomography (XCT). Pore volume in all soils decreased upon mucilage amendment, correlating with the observed increase in stability. However, while porosity of the clayey soil increased after wetting and drying, it decreased or remained the same in the Loamy-sand and sandy-clay-loam soil, respectively. To evaluate pore connectivity, we calculated the Euler number (c) in which smaller values (negative) indicate better pore-connectivity. Poor connectivity was assessed in the amended clayey (c=1128) and sandy-clay-loam (c=172085) soils, probably due to soil aggregation which is in correlation with porosity assessment. Following wetting and drying, connectivity improved in the clayey soil
(c=-17281), while in the sandy-clay-loam it remained poor (c=143119). As expected, pore connectivity (c<0) of the loamy-sand soil remained in all treatments. These observations are in agreement with the stability results. As stability increased in all soils following mucilage amendment, pore-volume, and connectivity decreased. Wetting and drying of the stabilized clayey soil increased porosity and connectivity. However, the decreased stability of the sandy-clay-loam soil, due to the cumulative effect of CaCO3 and mucilage, was expressed by poor connectivity and porosity. These results demonstrate the effect of mucilage amendment and wetting and drying cycle on soil structure. Finally, applying X-ray tomography and laser granulometry measurements to characterize soil structure as a function of soil amendments may shed light on how soil structure controls the storage and fluxes of water, nutrients, and gases.

How to cite: Dor, M., Koestel, J., Emmanuel, S., and Mishael, Y.: The Dynamic Effect of Root Exudates on Soil Structure – Characterization by X-ray Tomography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21422, https://doi.org/10.5194/egusphere-egu2020-21422, 2020.

D2338 |
John Koestel

Classical soil water retention curves relate tension and water content in soil. Often, the tension is equated with the equivalent diameter of the largest water-filled pores, using the capillary rise equation. This relationship is known to be an approximate one as most soils contain clay minerals that swell and shrink with wetting and drying, respectively. Most notably, cracks are created during drying which may then close again under subsequent wetting. The aim of this study was to investigate how potential soil microbial habitats are influenced under drying. I used three-dimensional X-ray imaging to quantify local volume changes and the associated evolution of the pore-network morphology in 8 undisturbed soil samples (diameter: 67 mm, height 60 mm), sampled at 4 different field sites. In general, cracks formed in all investigated samples. The crack formation corresponded to an increased volume of large pores on the expense of smaller ones. As a result, a larger and better connected macropore network led to an improved aeration of the soil matrix, adding to the increased oxygen supply associated with draining pores. This study demonstrates the large potential of non-invasive imaging methods to advance knowledge on the interaction between soil physics and soil microbiology.

How to cite: Koestel, J.: Soil drying and soil structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4563, https://doi.org/10.5194/egusphere-egu2020-4563, 2020.

D2339 |
David Nimblad Svensson, Jumpei Fukumasu, Gunnar Börjesson, and John Koestel

Soil porosity, pore size distribution and pore characteristics such as connectivity are important for a range of soil processes including ease of root growth and air and water transport. The pore structure is therefore an important part of soil fertility. The pore space is sensitive to management practices such as tillage, fertilization and cropping. Understanding how these practices influence the pore space is important for maintaining a good soil structure that is well aerated and has sufficient drainage. X-ray computed tomography has become a widely used method for studying the pore space as it offers the advantage of enabling soil to be studied in its undisturbed form. In this study it was used to compare the effects of crop growth, tillage and N-fertilizing with Ca(NO3)2 or farm yard manure (FYM). Soil samples were taken just below the surface from the long-term experiment in Ultuna, Sweden which was started in 1956. The bare fallow, FYM and Ca(NO3)2-treatment were sampled with minimum disturbance in two column sizes with inner diameters of 22.2 and 65.5 mm. Differences in pore space morphology were quantified and compared through pore size distribution and a range of connectivity measures, including the Euler number, the critical pore diameter and Gamma connectivity. Biopores were separated from non-biopores and their volume was quantified. Soil organic carbon was determined by dry combustion. Visible porosity and pores in the 150-500 µm class were significantly larger in the FYM and Ca(NO3)2-treatment compared to the bare fallow. The porosity occupied by biopores was not found to significantly differ between treatments but the biopores were found to have the largest diameters in the FYM-treatment. Despite that the organic carbon content was 1.7 times higher in the FYM compared to the Ca(NO3)2-treatment the visible porosity was similar. This may be due to the positive effects calcium has on the soil structure. The connectivity measures indicated that the FYM-treatment had the best connected pore networks. This may be partly due to the larger biopores. Ca(NO3)2 showed to be a promising alternative to increase porosity. However, as all the management practices in the long-term field study are done by hand, future studies will have to investigate if the effect is equally similar to FYM under field conditions which are subject to heavy machineries.  

How to cite: Nimblad Svensson, D., Fukumasu, J., Börjesson, G., and Koestel, J.: Influence of cropping and fertilization on soil pore characteristics in a long-term field study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4624, https://doi.org/10.5194/egusphere-egu2020-4624, 2020.

D2340 |
| Highlight
Mats Larsbo, Nargish Parvin, and Maria Sandin

The soil structure near the surface of agricultural soils changes with seasons mainly by land management together with climatic and biological factors. Quantitative analysis of post-tillage changes in soil structure and related hydraulic properties are necessary for evaluating and improving models of soil hydrological and transport processes. The objectives of this study were to quantify changes in soil seedbed structure induced by rainfall and drainage and to estimate the effects of soil texture and SOC on these changes. We collected samples from the harrowed layer of twenty-six fine to coarse textured Swedish mineral soils. Air-dried soil was placed in cylinders (5 cm high, diameter 5 cm) and exposed to simulated rainfall (5 mm h−1 for 4 h) and drainage (-50 cm pressure potential) cycles in the laboratory. We used X-ray tomography to quantify changes in pore networks in a thin surface layer and in the whole cylinder. Infiltration rates at -5 cm pressure potential were measured using a mini disc tension infiltrometer on replicate air-dried samples and on the samples included in the consolidation experiments at the final state. Total imaged specific pore volumes generally decreased from initial to final state and pore size distributions were shifted towards larger proportions of below image resolution pores (< 80 μm). There was a strong positive correlation between clay content and changes in the specific volume of pores<80 μm. Soils with high clay content and soil organic carbon (SOC) content often have strong aggregates that resist change. Nevertheless, both clay and SOC contents were negatively correlated with the changes in specific imaged pore volume. These results highlight the importance of swelling, which is largely controlled by clay content, for seedbed consolidation. In line with previous studies, when excluding coarse textured soil, the changes in surface porosity were negatively correlated with silt content. Changes in infiltration capacity were not significantly correlated to any basic soil properties. Our results suggest that shrinking-swelling should be a central part in any model for seedbed consolidation.

How to cite: Larsbo, M., Parvin, N., and Sandin, M.: Soil structure dynamics in seedbeds: Effects of soil texture and organic carbon content, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21373, https://doi.org/10.5194/egusphere-egu2020-21373, 2020.

D2341 |
Peter Surda, Lubomir Lichner, and Viliam Nagy

Abandonment of agricultural lands in recent decades is occurring mainly in Europe, North America and Oceania, and changing the fate of landscapes as the ecosystem recovers during fallow stage. The objective of this study was to find the impact of secondary succession in abandoned fields on some parameters of acidic sandy soils in the Borská nížina lowland (southwestern Slovakia). We investigated soil chemical (pH and soil organic carbon content), hydrophysical (water sorptivity, and hydraulic conductivity), and water repellency (water drop penetration time, water repellency cessation time, repellency index, and modified repellency index) parameters, as well as the ethanol sorptivity of the studied soils. Both the hydrophysical and chemical parameters decreased significantly during abandonment of the three investigated agricultural fields. On the other hand, the water repellency parameters increased significantly, but the ethanol sorptivity did not change during abandonment. As the ethanol sorptivity depends mainly on soil pore size, the last finding could mean that the pore size of acidic sandy soils did not change during succession.

How to cite: Surda, P., Lichner, L., and Nagy, V.: Effect of secondary succession in abandoned fields on some properties of acidic sandy soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21898, https://doi.org/10.5194/egusphere-egu2020-21898, 2020.

D2342 |
Yuting Fu, Lis de Jonge, Mogens Greve, Emmanuel Arthur, Per Moldrup, Trine Norgaard, and Marcos Paradelo-Perez

Organic matter decomposition is an important process in global carbon cycling and its rate is altered by various factors. Changes in land use can have a significant effect on decomposition rates, with consequences on CO2 emissions. The tea bag index (TBI) method is recognized as a simple and effective approach to investigate decomposition. Despite the fact that TBI has been globally applied, most research mainly focuses on soil microbiological aspects; the role of soil physical properties have earned less attention. Linking the soil physical properties to TBI can give us a broad understanding on how land use affects the soil microhabitat, and in turn influence carbon sequestration. Here, we measured the decomposition of green and rooibos tea in a transect from the east to west coast of Denmark across four land uses categorized into two groups (natural and cultivated). The natural group comprised forest and heath, and the cultivated group was composed of cereal and grass. Decomposition rate (k) and stabilization factor (S) were calculated after three months tea bag incubation. Soil physical properties including volumetric water content (VWC), air permeability and relative gas diffusivity (Dp/D0) were measured at matric potential of –10 and –100 kPa. The cultivated land uses had higher k and S values compared to natural systems. The S was positively correlated with VWC and negatively correlated with Dp/D0 in natural systems while no relationship was found for cultivated land. However, there was a negative correlation of k-VWC and positive correlation of k-Dp/D0 in cultivated land, suggesting an impact of soil management and anthropogenic influence on litter decomposition and carbon sequestration.

How to cite: Fu, Y., de Jonge, L., Greve, M., Arthur, E., Moldrup, P., Norgaard, T., and Paradelo-Perez, M.: Linking soil physical properties to the tea bag index for different land uses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14817, https://doi.org/10.5194/egusphere-egu2020-14817, 2020.

D2343 |
Christine Fischer, Sophia Leimer, Christiane Roscher, Janneke Ravenek, Hans de Kroon, Yvonne Kreutziger, Jussi Baade, Holger Beßler, Nico Eisenhauer, Alexandra Weigelt, Liesje Mommer, Markus Lange, Gerd Gleixner, Wolfgang Wilcke, Boris Schröder, and Anke Hildebrandt

Soil moisture is the dynamic link between climate, soil and vegetation and the dynamics and variation are affected by several often interrelated factors such as soil texture, soil structural parameters (soil organic carbon) and vegetation parameters (e.g. belowground- and aboveground biomass). For the characterization of soil moisture, including its variability and the resulting water and matter fluxes, the knowledge of the relative importance of these factors is of major challenge. Because of the spatial heterogeneity of its drivers soil moisture varies strongly over time and space. Our objective was to assess the spatio-temporal variability of soil moisture and factors which could explain that variability, like soil properties and vegetation cover, in in a long term biodiversity experiment (Jena Experiment).

The Jena Experiment consist 86 plots on which plant species richness (0, 1, 2, 4, 8, 16, and 60) and functional groups (legumes, grasses, tall herbs, and small herbs) were manipulated in a factorial design Soil moisture measurements were performed weekly April to September 2003-2005 and 2008-2013 in 0.1, 0.2, 0.3, 0.4, and 0.6 m soil depth using Delta T theta probe.

The analysis showed that both plant species richness and the presence of particular functional groups affected soil water content, while functional group richness per se played no role. Plots containing grasses was consistently drier than average at the soil surface in all observed years while plots containing legumes comparatively moister, but only up to the year 2008.

Interestingly, plant species richness led to moister than average subsoil at the beginning of the experiment (2003 and 2004), which changed to lower than average up to the year 2010 in all depths.Shortly after establishment, increased topsoil water content was related to higher leaf area index in species‐rich plots, which enhanced shading. In later years, higher species richness increased topsoil organic carbon, likely improving soil aggregation. Improved aggregation, in turn, dried topsoils in species‐rich plots due to faster drainage of rainwater.

Our decade‐long experiment shows that besides abiotic factors like texture, soil water patterns are consistently affected by biotic factors such as species diversity and plant functional types, but also properties that originate from biotic-abiotic interactions such as soil structure. Especially the effect of plant species richness propagated to deeper soil layers 8 years after the establishment of the experiment, and while originally caused by shading it was later related to altered soil physical characteristics in addition to modification of water uptake depth. Functional groups affected soil water distribution, likely due to plant traits affecting root water uptake depths, shading, or water‐use efficiency. Our results highlight the role of vegetation composition for soil processes and emphasize the need for long-term experiments to discover diversity effects in slow reacting systems like soil.

How to cite: Fischer, C., Leimer, S., Roscher, C., Ravenek, J., de Kroon, H., Kreutziger, Y., Baade, J., Beßler, H., Eisenhauer, N., Weigelt, A., Mommer, L., Lange, M., Gleixner, G., Wilcke, W., Schröder, B., and Hildebrandt, A.: Effects of biotic and abiotic indices on soil water content in a decade-long grassland biodiversity experiment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10981, https://doi.org/10.5194/egusphere-egu2020-10981, 2020.

D2344 |
| Highlight
Katharina Meurer, Thomas Keller, and Nick Jarvis

The pore structure of soil is known to be dynamics at time scales ranging from seconds (e.g. compaction) to seasons (e.g. root growth, macro-faunal activity) and even decades to centuries (e.g. changes in organic matter content). Nevertheless, soil physical and hydraulic functions are generally treated as static properties in most soil-crop models. Some models account for seasonal variations in soil properties (e.g. bulk density) due to tillage loosening and post-tillage consolidation or soil sealing, but none can account for longer-term changes in soil structure due to biological agents and processes. Here, we present a new concept for modelling soil structure evolution impacted by biological processes such as root growth and earthworm activity. In this preliminary test of the model, we compare simulations against field observations made at the Soil Structure Observatory (SSO) in Zürich, Switzerland, that was designed to provide information on soil structure recovery following a severe compaction event. In this simple application, we modelled changes in the pore size distribution in a bare soil treatment resulting from soil ingestion and egestion by earthworms and the loosening of compacted soil by casting at the soil surface. Following calibration, the model was able to reproduce the observed temporal development of total porosity, soil bulk density and pore size distribution during a four-year period following severe traffic compaction. The modelling approach presented here appears promising and could help support the development of cost-efficient strategies for sustainable soil management and the restoration of degraded soils.

How to cite: Meurer, K., Keller, T., and Jarvis, N.: A new approach to modelling soil structure dynamics and a preliminary application to structure recovery by earthworm bioturbation after heavy compaction , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3377, https://doi.org/10.5194/egusphere-egu2020-3377, 2020.

D2345 |
Sara König, Ulrich Weller, Birgit Lang, Mareike Ließ, Stefanie Mayer, Bastian Stößel, Hans-Jörg Vogel, Martin Wiesmeier, and Ute Wollschläger

The increasing demand for food and bio-energy gives need to optimize soil productivity, while securing other soil functions such as nutrient cycling and buffer capacity, carbon storage, biological activity, and water filter and storage. Mechanistic simulation models are an essential tool to fully understand and predict the complex interactions between physical, biological and chemical processes of soil with those functions, as well as the feedbacks between these functions.

We developed a systemic soil model to simulate the impact of different management options and changing climate on the named soil functions by integrating them within a simplified system. The model operates on a 1d soil profile consisting of dynamic nodes, which may represent the different soil horizons, and integrates different processes including dynamic water distribution, soil organic matter turnover, crop growth, nitrogen cycling, and root growth.

We present the main features of our model by simulating crop growth under various climatic scenarios on different soil types including management strategies affecting the soil structure. We show the relevance of soil structure for the main soil functions and discuss different model outcome variables as possible measures for these functions.

Further, we discuss ongoing model extensions, especially regarding the integration of biological processes, and possible applications.

How to cite: König, S., Weller, U., Lang, B., Ließ, M., Mayer, S., Stößel, B., Vogel, H.-J., Wiesmeier, M., and Wollschläger, U.: Systemic modelling of soil functions under the impact of agricultural management, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15243, https://doi.org/10.5194/egusphere-egu2020-15243, 2020.