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

How to cite: Koestel, J., Fukumasu, J., and Nimblad-Svensson, D.: Influence of cropping and fertilization on soil macropore characteristics in a long-term field study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20510, https://doi.org/10.5194/egusphere-egu24-20510, 2024.

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

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

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

How to cite: Spinoso Sosa, S., Hafner, B., Adamczewski, R., and Zare, M.: Exploring the interplay of shoot to root hydraulic conductance in varying soil water contents, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17648, https://doi.org/10.5194/egusphere-egu24-17648, 2024.

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

How to cite: Mikha, M., Green, T., Untiedt, T., and Hergret, G.: Soil Structural Stability Influenced by Land Management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1343, https://doi.org/10.5194/egusphere-egu24-1343, 2024.

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

How to cite: Tang, Y. and Cai, S.: Study on methodology and efficiency of microbially induced carbonate precipitation on improvement of marine silty sand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2980, https://doi.org/10.5194/egusphere-egu24-2980, 2024.

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

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

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

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

How to cite: Szécsy, O., Rékási, M., Szabó, A., and Szűcs-Vásárhelyi, N.: Correlations between microbial activity and soil texture in Hungarian soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8747, https://doi.org/10.5194/egusphere-egu24-8747, 2024.

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

How to cite: Qi, S. and Wang, G.: Freeze-thaw processes regulate microbial controls on soil organic carbon decomposition in Qingzang alpine grasslands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9003, https://doi.org/10.5194/egusphere-egu24-9003, 2024.

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

How to cite: Jin, Y., Yan, J., Knight, B., and Zheng, W.: Effects of Plant Growth-Promoting Rhizobacteria (PGPR) on Saltwater Evaporation: A Case Study Using Bacillus Subtilis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14526, https://doi.org/10.5194/egusphere-egu24-14526, 2024.

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

How to cite: Lin, L.:  Effects of paleosol on collapsibility of loess sites under immersion test conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-209, https://doi.org/10.5194/egusphere-egu24-209, 2024.

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

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

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

How to cite: Berli, M., Shillito, R. M., Or, D., Giovando, J. J., Pak, J., Pradhan, N., Vermeeren, R. A., Floyd, I. E., and McKenna, S.: Fire effects on soil structure and hydraulic conductivity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12707, https://doi.org/10.5194/egusphere-egu24-12707, 2024.

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

How to cite: Wu, H., Maestrali, M., Lucas, M., Raynaud, X., Nunan, N., and Schweizer, S.: Meta-analysis of soil pore size distribution and its relationship with various soil properties and land management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21045, https://doi.org/10.5194/egusphere-egu24-21045, 2024.

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

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

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

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

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

How to cite: Duddek, P., Ahmed, M. A., Javaux, M., Vanderborght, J., Lovric, G., King, A., and Carminati, A.: Root hairs facilitate root water uptake across soil textures – a numerical study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17397, https://doi.org/10.5194/egusphere-egu24-17397, 2024.