SSS6.6

Along with roots, soil macrofauna such as earthworms, ants, termites, beetles and myriapods dramatically alter the physical architecture of soil with strong effects on the distribution and connectivity of pores, and therefore on key ecological functions such as water dynamics, gas exchanges, soil organic matter decomposition or storage. While most of the literature has focused on the properties of galleries and show their large variability, much less is known about the other pores produced by soil fauna (e.g., those agented between or within biogenic aggregates or those located around galleries).

Using examples from studies carried out in tropical and temperate soils, I show that the ‘trait-based’ approach in soil biology offers interesting perspectives for understanding the properties of biopores, and as a consequence of the impacts of soil fauna on water dynamics and biogeochemical cycling. Second, I show that galleries are not as stable as we imagine, indicating the need to quantify their dynamics. Finally, I show that macrofauna influence also the architecture of small pores with consequences on the dynamics of soil organic matter and other properties. To conclude, I introduce the “bioporosphere” as a new concept to integrate the complex effects of soil fauna on its functions.

How to cite: Bottinelli, N.: The bioporosphere and its role in soil functioning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9585, https://doi.org/10.5194/egusphere-egu22-9585, 2022.

Different land uses significantly affect the soil water and temperature regimes. Very different modifications of the soil surface are found especially in the urban environment, where different materials, which are used in gardening and civil engineering, are used to cover soil surface. Alternations of these regimes due to modifications of soil covers may lead to changes in soil properties. Therefore, the goal of this study was to find out how soil properties, particularly soil structure and soil hydraulic properties changed during our experiment, which has been mainly focused on the monitoring of soil water and thermal regimes under five different surface covers (bare soil, bark chips, concrete, mown grass, and unmown grass). The surface of a Haplic Chernozem (which was originally coverd by grass) was modified in the autumn 2012. Since then, climatic conditions are monitored, and soil water contents and temperatures are measured at the depths of 10, 20, 30, 40, 60, and 80 cm. In the summer 2020, after removal of the surface over, intact soil samples were taken, on which the hydraulic properties were measured using the multistep outflow method. Another set of the undisturbed soil samples was used to study soil structure using the X-Ray computer tomography. In addition, these samples were next used to prepare thin soil slides for micromorphological analyses. Along with soil sampling, the measurement of some characteristics took place directly in the field. The mini disk tension infiltrometer with a disk radius of 2.22 cm was used to measure unsaturated hydraulic conductivities for pressure head of –2 cm. The net CO2 and net H2O efflux were measured using the LCi-SD portable photosynthesis system with a Soil Respiration Chamber. The CT and micromorphological analyzes showed that while the soil under the bare surface showed small aggregates and small interaggregate pores, the soil under the grass cover was formed by large aggregates with large pores formed by roots and organisms living in soils. Soil structure under concrete or bark chips was compact with thin fractures and few pores created by organisms living in soils. However, porosity under bark chips was larger than that under concrete likely due to better conditions, i.e., larger amount of the organic matter content due to the decomposition of organic mulch. Measured soil properties reflected character of soil structure.

Acknowledgement: Study was supported by the European Structural and Investment Funds, projects NutRisk (No. CZ.02.1.01/0.0/0.0/16_019/0000845).  

How to cite: Fér, M., Nikodem, A., Klement, A., and Kodešová, R.: How various surface covers affect soil structure and hydraulic properties, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6630, https://doi.org/10.5194/egusphere-egu22-6630, 2022.

Engineered soils play an important role in urban hydrology e.g. in the functioning of green roofs and stormwater bioretention cells. Water infiltration, colloid transport, and heat transport are affected by changes in pore system geometry particularly due to the development of macropores and clogging by particles. The rate of pedogenesis is often faster than in natural soils due to higher loads of particles as well as by extreme water regimes. In the presented research we assess the temporal changes of soil structure of engineered soils in typical bioretention beds by conducting field scale and laboratory experiments. The aim is to elucidate changes in bioretention cell performance by studying the structural changes of soils at the microscale by invasive and noninvasive methods. Noninvasive visualization methods such as computed microtomography (CT), are an effective mean of soil structure assessment. X-ray CT is capable to investigate soil in terms of structure development, pore-clogging and pore geometry deformations.

Two identical bioretention cells were established in December 2017. The first bioretention cell (BC1) collects the stormwater from the roof of the nearby experimental building (roof area 38 m2). The second bioretention cell BC2 is supplied from a tank using a controlled pump system for simulating artificial rainfall. Each BC is 2.4 m wide and 4.0 m long. The 30 cm thick biofilter soil mixture is composed of 50% sand, 30% compost, and 20% topsoil. Bioretention cells are isolated from the surrounding soil by a waterproof membrane. The regular soil sampling program was initiated in 2018 in order to visualize and quantify the soil structure and internal pore geometry of samples. Undistributed samples were collected from the surface of the filter layer twice a year from each BC. The aluminum sampling cylinders had an internal diameter and height of 29 mm. Three batches of samples were taken during three years. The first set of 24 undisturbed samples was collected upon planting in June 2018, while the second set of 24 samples was taken after the end of the first vegetation period in November 2018. The second and third batches, each of 48 samples, were taken in 2019 and 2020 in the same period as in the first year.  Those collected samples were scanned by (CT) imaging.

The analysis performed by SoilJ package shows the initial decrease of macroporosity during the first season as a result of soil consolidation and subsequent further development of the soil's pore system.

How to cite: Heckova, P., Snehota, M., Koestel, J., Klement, A., and Kodesova, R.: Soil structure changes of engineered soils in bioretention cell, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5876, https://doi.org/10.5194/egusphere-egu22-5876, 2022.

Soil surface crusting is a common phenomenon on agricultural soils susceptible to rainfall drop impact. Crust affects soil hydrological properties, erosion, crop quality and yield, which implicates both agriculture and the environment. Whereas methods for determining hydraulic or basic properties of soil layers (such as thicker than 2 cm) are well established, measuring the soil characteristics of a thin crust (< 5 mm) remains a challenge. Therefore, in this study, we combine traditional lab methods and advanced techniques to test the variation in soil properties during the crust forming process. Composite samples from two soil textures were collected, dry-sieved at 8 mm, packed in soil pans and exposed to a range of rainfall amounts and two rainfall intensities, using a laboratory nozzle-type rainulator. Intact soil ring samples were collected after each rainfall event and scanned using X-ray Computed Tomography (CT) to gain more insight into rainfall-induced crust formation. Soil porosity, bulk density and the thickness of crust were derived from CT scans. Meanwhile, a scanning electron microscope (SEM) was employed to verify the variation of the crust layer thickness and soil properties. In addition, the water retention and infiltration dynamics of the developing seals were investigated with a minidisk infiltrometer placed on the crusts developed in the pans and a falling head permeameter (KSAT®) and evaporation method (HYPROP®) on soil cores taken. Shear strength was evaluated by hand vane. Disturbed soil was collected to explore variation in organic matter content and texture with rainfall. During the simulated rain events, soil loss, splash and runoff were followed as well. Overall, the purpose of this study was to reveal temporal variations of seal micro-morphology and their effect on soil properties with increasing rainfall amount. Our results showed the runoff volume and sediment mass increased, while splash and infiltration volume decreased with the increase in rainfall amount. Shear strength increased until 200 mm of rainfall. Additionally, (crust forming) rainfall amount had a rapid and strong effect on the hydraulic properties, with the unsaturated hydraulic conductivity being reduced as rainfall duration increased and the high rainfall intensity having a greater impact. These results were associated with rainfall-induced aggregate breakdown processes, which was confirmed by SEM images. It also demonstrated that crust development occurred up to at least 200 mm rainfall after cultivation. In summary, it was possible to illustrate the structural seal formation process and the temporal interrelated dominance and significance of the associated sub-processes which contribute to overcoming the challenge of testing the thin crust (< 5 mm).

How to cite: Lin, L., Yemeli Lonla, P., and Cornelis, W.: Soil properties respond to crust forming under variable simulated rainfall events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1688, https://doi.org/10.5194/egusphere-egu22-1688, 2022.

Microaggregates are structural elements of the soil smaller than 250 µm. These microaggregates are composed from diverse mineral, organic and biotic materials that are bound together during the process of pedogenesis (through a variety of ways and processes). According to the general theories, microaggregates are predominantly stabilized by organo-mineral complexes, which are relatively stable and are not easily degraded by changes in soil organic matter content as a result of land use and cultivation. At present, the relationship between soil processes and the formation of microaggregate stability needed further studies to gain a better understanding

In our study, we were looking for a quantifiable relationship between the stability of microaggregates and different soil reference groups and diagnostic properties. We examined 55 Hungarian soil profiles, which were selected on the basis of their various parameters. The stability of the microaggregate was determined by laser diffractometry (LDM) with a Malvern Mastersizer 3000, Hydro LV dispersion unit, as the ratio of dispersed to non-dispersed clay content. The measured data were sorted into a database and a statistical analysis were performed between the soils and WRB diagnostic properties of each reference group and the stability of the microaggregate. Based on our results, different significant soil groups could be identified, furthermore there is a good connection between the stability of the microaggregate and the soil reference groups. There is also a clear difference between the horizons of cultivated and uncultivated soils.

This research is supported through the common grant of the Hungarian and Polish Academy of Sciences (Grant No. NKM-2019-17) and by the Hungarian National Research, Development and Innovation Office Foundation (Grant No. OTKA K 119475).

How to cite: Labancz, V., Barna, G., Szegi, T., Bieganowski, A., Bakacsi, Z., Novák, T., and Makó, A.: Variation of soil microaggregate stability as a function of WRB reference soil groups and diagnostic properties, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8186, https://doi.org/10.5194/egusphere-egu22-8186, 2022.

Peatlands are globally significant modulators of biogeochemical cycles and important natural sources of methane. The emissions are strongly influenced by the diffusion of oxygen into the peat and the diffusion of methane from the peat to the atmosphere. The structure of peat macropore networks controls the gas transport. The characterization of peat pore structure and connectivity using complex network theory methods can give important conceptual insight into the relationship between the microscale pore space characteristics and methane emissions on a macroscopic scale. Both gas transfer in unsaturated peat and the evolution of the connected air-filled pore space can be conceptualized through a pore network modeling approach. Pores that become isolated from the atmosphere may eventually develop into anaerobic pockets, which are local hotspots of methane production in unsaturated peat.
We extracted macropore (diameter greater than 0.1 mm) networks from three-dimensional X-ray micro-computed tomography (micro-CT) images of peat samples collected from a boreal forested peatland and evaluated local and global connectivity metrics for the networks. We also simulated the soil-water retention curves of the peat samples using pore network modeling and compared the results with measured water retention characteristics. There were fundamental differences in macropore structure and connectivity between vertical peat layers. Macropore connectivity was higher and the flow routes through the peat matrix were less tortuous in the near-surface peat than in the deeper layers. Furthermore, the number and volume of macropores, the average width of pore throats, and the structural anisotropy of peat decreased with depth. Therefore, gas exchange with the atmosphere may be slowed down because of narrower and more tortuous air-filled diffusion channels as the distance between the peat layer and the soil-atmospheric interface increases.
The network analysis also suggests that local and global network connectivity metrics, such as the network average clustering coefficient and closeness centrality, might be proxies for gas diffusion capability in air-filled pore networks. However, the applicability of the metrics was restricted to the topmost peat layer with high porosity. The spatial extent and larger-scale connectivity of the network and the spatial distribution of the pores within the network may be reflected in different network metrics in contrasting ways.
The hysteresis of peat water content was found to affect the evolution of the interconnected air-filled pore volume in unsaturated peat. Therefore, the volume available for the formation of anaerobic pockets may be smaller and methane production may be slower in wetting conditions than in drying conditions. This hysteretic behavior might be one of the reasons behind observed hotspots and episodic spikes of methane emissions, and therefore hysteresis should be included in biogeochemical models describing methane dynamics in peat.

How to cite: Kiuru, P., Palviainen, M., Grönholm, T., Raivonen, M., Kohl, L., Gauci, V., Urzainki, I., and Laurén, A. (.: Peat macropore networks and their conceptual implications for methane production and emission, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5285, https://doi.org/10.5194/egusphere-egu22-5285, 2022.

Organic matter is a hallmark of healthy soils and soil functions. It is critical in developing a stable structure and is a significant reserve of resources for soil life. Soil carbon flux is also an essential regulator of atmospheric GHG concentrations and climate. Therefore, the stability and persistence of soil organic matter are considered a critical soil resiliency metric. Although the acceleration of soil carbon loss via disturbances such as tillage is widely recognized, we lack a predictive modeling framework that relates the tillage intensity to mineralization rates. Here, we show a framework that combines a model of soil structure evolution and water-retention-curve-based microbial moisture sensitivity function.  

How to cite: Ghezzehei, T., Alvarez-Sagrero, J., and Perez-Rojas, Y.: Acceleration of Organic Matter Decomposition by Tillage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10889, https://doi.org/10.5194/egusphere-egu22-10889, 2022.

Understanding the compressive behavior of soils is essential for establishing management strategies to reduce the risk of soil compaction. Soil compressive properties such as precompression stress, compression index, and swelling index are used to estimate the stress-strain relationship of soil, i.e., the changes of soil volume as a function of applied stress. However, there is no consensus regarding the influence of basic soil physical properties and conditions, such as soil texture, organic carbon content, clay mineralogy, water content, and bulk density on soil compressive properties. Moreover, soil compressive behavior has been measured following non-standardized methods, for example regarding sample size, loading time, methods to obtain the compressive properties from the stress-strain curve, and stress components and packing state of the soil by which the soil compressive behavior can be expressed. These differences in methodology influence the obtained values of soil compressive properties, make comparisons difficult, and limit our understanding of the soil’s stress-strain relationship. We conducted a comprehensive literature study in search of quantifications of compressive properties of agricultural and forest soils, such as precompression stress, compression index, and swelling index, in peer-reviewed articles from the Web of Science and Scopus databases, which currently includes more than 200 articles. We systematically collected the compressive properties as well as information on the soil, soil conditions, methodologies, and other relevant information for each of the published studies. A large part of data originates from a limited number of laboratories in Brazil, Denmark, Germany, Iran, and Sweden, while other parts of the world are less or not represented. We find large variability in soil mechanical properties, that is associated both with variability in soil texture and land use but also with methodological issues. Initial soil moisture was identified as a key driver of soil mechanical properties. Our database allows compiling, synthesizing, and analyzing the data in favor of a comprehensive establishment of relationships between basic soil physical attributes and compressive properties. At the same time, the database is used to identify knowledge gaps and future directions for studies. These findings help the potential development of pedotransfer functions to improve estimations of the soil response to compaction, and to provide a research agenda for a more unified approach for the study of soil compressive properties.

How to cite: Chagas Torres, L., ten Damme, L., Holzknecht, A., Dietrich, M., Nemes, A., and Keller, T.: Soil compressive behavior: a global assessment of research outputs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2573, https://doi.org/10.5194/egusphere-egu22-2573, 2022.

Soil compaction forms a major threat to the well-functioning of agricultural soils. By reducing the pore volume and continuity both crop growth and ecological services, like water infiltration and storage, can be negatively impacted. It is often most severe at the interface between topsoil and subsoil, just out of reach of regular tillage operations. At this depth a plough pan can be formed, restricting interaction between top- and subsoil for roots, and gas and water transport. In this study we looked at a combination of mechanical and biological remediation to alleviate this problem. The experiment was performed on a sandy loam field near Ghent, Belgium with a highly compacted plough pan, which almost completely restricted roots to reach the subsoil and was practically impermeable for gases. Subsoiling was performed once in three different maize-based cropping systems: forage maize in monoculture, a ley-arable crop rotation with two years of alfalfa and a maize-winter cereal rotation.

The mechanical remediation (subsoiling) clearly helped to break open the restricting plough pan. Rootablility and air permeability clearly increased, leading to a significant increase in maize yield. On a longer time scale, however, we observed that this loosened soil was very prone to recompaction. In the second year after the subsoiling the highly compacted plough pan returned. This same year also showed no difference between the subsoiled and untreated control in maize yield.

To see if deep rooting crops can help stabilize the loosened soil after subsoiling, this study included treatments with fodder radish and alfalfa as (cover) crops. These crops showed a high rooting density in the subsoil, especially where the tines of the subsoiler had passed. Although this did not seem to improve the overall physical soil quality, it did protect the soil from complete recompaction. The penetration resistance did not markedly increase after standard agricultural practice.

How to cite: Vanderhasselt, A., Steinwidder, L., D'Hose, T., and Cornelis, W.: Remediation of subsoil compaction by subsoiling and deep rooting crops, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5244, https://doi.org/10.5194/egusphere-egu22-5244, 2022.

Lightweight agricultural robots are expected to be widely used in the future and will use the same tracks for many operations within a season (i.e. repeated wheeling) and perhaps across seasons. The objectives of this study were to characterize the effects of repeated wheeling and wheel load from the traffic of a lightweight autonomous field robot on soil structural properties and the potential risk of soil compaction.

The experiment was conducted on sandy loam soil at water content close to field capacity. The field had not been tilled for approx. a year and stubbles were remaining from the previous crop. The robot used for the experiment was the AGROINTELLI ROBOTTI 150D. In total, three wheeling scenarios with one, five and ten passes were conducted both with the robot alone (3.3 Mg, inflation pressures 60-80 kPa) and at its maximum load with an implement (3.8 Mg, inflation pressures 70-90 kPa). For each treatment, rut depth and apparent cohesion were measured in the field and soil cores were taken at 10 cm depth for measuring air permeability (k_a) and effective air-filled porosity (ε_pyc) in the laboratory.

The results show that both wheel load and repeated wheeling had a significant effect on rut depth and apparent cohesion. Rut depth seemed to increase linearly with the number of wheel passes. However, apparent cohesion decreased after one pass, then increased linearly with the consecutive passes. Thus, a single pass weakened the soil structure and made it more sensitive to compaction for the following passes. Both k_a and ε_pyc, decreased significantly with repeated wheeling but not with wheel load. The average value of k_a at the tenth wheel pass was 7 µm², being five times lower than the first pass for both loads. The values of ε_pyc for the fifth and tenth passes were similar for both loads (approx. 0.15 cm³∙cm^-3). This was not the case for the value of the first pass, which was higher for the robot alone compared to loaded (0.21 and 0.17 cm³∙cm^-3 respectively), although not significantly. 

Repeated wheeling from lightweight autonomous field robots can cause significant compaction even for a soil that has not been tilled recently. Even though soil properties were not critical for crop growth, the compacted wheel tracks may serve as hotspot areas e.g. water erosion. Thus, attention should be drawn towards avoiding traffic and limiting the number of wheel passes.

How to cite: Calleja Huerta, A., Lamandé, M., Green, O., and Munkholm, L. J.: Effects of load and repeated wheeling from lightweight autonomous field robots on soil structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3581, https://doi.org/10.5194/egusphere-egu22-3581, 2022.