Trees play a key role in subsurface water dynamics through stemflow and throughfall, affecting runoff and soil infiltration. However, a comprehensive understanding of their role in hydraulic responses across spatial scales requires integrated approaches and further research. In this study, we investigated the effects of rainfall partitioning on subsurface water dynamics across multiple spatial scales on a forested hillslope (30 degrees slope) in the Re della Pietra catchment of Central Italy. Four hierarchical spatial scales were considered to capture subsurface water dynamics: the point scale (via single-ring infiltration tests at three depths), the single-tree scale (through artificial stemflow events), the plot scale (covering a 100 m2 area, assessed either by an artificial throughfall event alone or in conjunction with multiple artificial stemflow events), and the hillslope scale (through piezometers data). Geophysical surveys were also conducted at the plot and single-tree spatial scales using both Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) to improve interpretation of hydrological functioning. Our results showed that the soil exhibits dual-permeability behavior, with throughfall promoting infiltration primarily into the matrix, while stemflow enhances fast-flow infiltration. Infiltrometer tests indicated lower infiltrability between tree stems (mean Ks values ranging from 177.8 to 237.4 mm h-1, depending on depth), consistent with the artificial throughfall events. In contrast, at tree bases, artificial stemflow produced rapid infiltration through macropores and fractures, reaching a mean steady-state rate of 1031.9 mm h-1. Numerical model inversions yielded consistent hydraulic parameters, and dual-permeability modeling showed that, at the plot scale, the stemflow-driven fast-flow region had higher Ks than the matrix (1047.4 vs. 217.5 mm h-1). Geophysical surveys confirmed these dynamics: ERT detected vertical wetting beneath stems, while GPR revealed lateral subsurface flow at depth. Piezometer data further identified fast-flow pathways at the hillslope scale, where rapid water table rises could be explained by flow connectivity between vertical and deeper lateral pathways. By combining controlled infiltration experiments, hydrological modeling, and geophysics, this study explicitly links point-, tree-, and plot-scale infiltration processes with hillslope-scale responses. These findings clearly demonstrate how stemflow-driven fast-flow pathways connect with lateral subsurface domains, thereby providing new insight into the mechanisms controlling rapid groundwater fluctuations on forested hillslopes.

Purpose. Accurate characterization of water infiltration into the vadose zone requires estimating key soil hydrodynamic properties, including the macroscopic capillary length (λc) and saturated hydraulic conductivity (Ks). These parameters quantify the contributions of capillarity and gravity (λc) and gravity-driven flow (Ks) during infiltration. Both λc and Ks can be estimated in the field using a simple Beerkan infiltration test, which requires minimal equipment, limited water, and no specialized operators. Their calculation, however, depends on “integral” shape parameters that vary strongly with soil type. In this study, we present new formulations based on integrating the hydraulic conductivity function expressed in terms of pressure head. These formulations allow accurate estimation of shape parameters even under dry soil conditions, providing an alternative to previous methods that rely on diffusivity or conductivity expressed as a function of water content.Method. We applied the new formulations to calculate soil-dependent shape parameters for the twelve USDA textural classes. Their performance in estimating λc and Ks was evaluated using synthetic cumulative infiltration curves generated with HYDRUS-2D/3D and compared with results obtained using default literature values. For practical applications, we propose two approaches to select appropriate shape parameters: (i) based on soil samples to determine textural class, and (ii) using texture-dependent parameter maps for site-specific selection. Both approaches were tested using a dataset of 167 Beerkan infiltration experiments across seven sites in Burundi, Ghana, Italy, and Senegal.Results. The sample-based approach provides higher accuracy in estimating λc and Ks, whereas the map-based approach eliminates the need for laboratory analysis and still outperforms default literature values, making it suitable for large-scale studies. To support the map-based method, we provide parameter maps at 250 m resolution for six countries (Burundi, Cameroon, Ghana, Italy, Kenya, and Senegal), alongside complementary soil property maps from the SoilGrids database (clay, sand, silt content, dry bulk density, and USDA soil texture classes), all freely accessible. Additionally, we propose a simplified method for estimating λc using a new empirical relationship that requires only the Mualem–van Genuchten shape parameter n, which can be derived from SoilGrids texture data using pedotransfer functions such as Rosetta3. Complementary maps of all Mualem–van Genuchten parameters are also provided.Conclusions. This work improves and simplifies the field estimation of key soil hydrodynamic properties by providing shape parameters for all USDA texture classes and accessible maps for parameter extraction. The approach facilitates the hydraulic characterization of large areas and extensive datasets, supporting both local and regional-scale infiltration studies.Data availabilitySoil property and parameter maps at 250 m resolution for Burundi, Cameroon, Ghana, Italy, Kenya, and Senegal are available in the open-access digital repository Zenodo at https://doi.org/10.5281/zenodo.17397791FundingThis work was supported through the project GALILEO ― Strengthening rural livelihoods and resilience to climate change in Africa: innovative agroforestry integrating people, trees, crops and livestock (project number: 101181623), funded by the European Union.

Accurate prediction of soil water movement in complex environments requires detailed knowledge of the spatial and temporal variability of soil hydraulic properties, in particular hydraulic conductivity. The study presents the results of a field campaign documenting topsoil hydraulic properties in an oak-wood grassland (WG) in a Mediterranean ecosystem in Sardinia (Italy), a vulnerable ecosystem endangered by climatic and land-use changes. Emphasis is provided to the impact of the trees on soil hydraulic properties, through the assessment at the field complemented by a detailed investigation at the individual-tree spatial scale. Particle size distribution, organic matter, and dry bulk density were sampled, and infiltration was evaluated through Beerkan tests using single-ring automated infiltrometers. The data was processed with a recently proposed fractional wettability infiltration model to derive saturated hydraulic conductivity (Ks). Results revealed a complex spatial pattern of soil hydraulic properties strongly influenced by the tree presence. Mean Ks under canopy (U) was 376.6 mm h- 1, approximately 2.3 times higher than in adjacent open areas (O). Detailed measurements below and around an individual oak showed similar mean Ks values but also highlighted a spatial gradient in the Ks distribution, with the highest and more variable Ks values near the trunk and a progressive decline outward. Notably, the outermost under-canopy positions showed Ks values comparable to those detected in the first meters of the adjacent open area, suggesting that tree influence may extend beyond the canopy projection. The results suggest that the sampling strategies of the hydraulic soil properties should account for the fine-scale tree-induced heterogeneity for obtaining representative estimations. Incorporating this fine-scale variability into hydrological models can improve simulations of soil-water processes and enhance predictions of how land-use changes, for example induced by land abandonment, affect hydrological dynamics in tree-dominated Mediterranean ecosystems.

The ‘2018 Marganai Forest Soil Erosion Experiment Database’ is a comprehensive collection of measures taken during scientific experiment trials designed to investigate the effects of forest canopy coverage on soil erosion under intense artificial rainfall, four years after coppicing. The investigation involved the establishment of eight paired plots with and without forest canopy coverage, subjected to artificial rainfall simulation aimed to measure the amount of sediment transported by runoff. The work represents a valuable resource for researchers interested in understanding the complex implications of forest management practices on soil erosion. The paper, produced using Quarto in a Gitlab-based RStudio project, is an example of ‘reproducible research’ documenting that the database provides detailed information on the experimental setup as well as on the range of different measurements that have been collected. The database, produced using NFS-DataDocumentationProcedure, is stored in an SQLite file, extensively exploiting the relational properties of the engine, enhancing data accessibility, interoperability and reusability.

Incident gross precipitation is divided by tree canopies into three main parts: i) intercepted rainfall, which evaporates directly from the canopies, ii) throughfall, which reaches the soil surface after passing through the canopies, and iii) stemflow, which is concentrated from the canopies to the stems. Stemflow tends to infiltrate preferentially around the base of the stem, and once belowground, is channeled by tree roots.The objective of this research was to investigate the contribution of stemflow and throughflow to subsurface water dynamics in a hillslope forested with beech trees. The experimental activities were carried out in a 10 x 10 m plot located in the Lecciona catchment of the Appennine Mountains, Central Italy. Stemflow was collected from seven beech trees located within the plot. Stemflow and throughfall were sequentially and then simultaneously induced using controlled water applications. Time-lapse ground-penetrating radar (GPR) surveys were conducted under each line of trees. Overland flow and subsurface runoff were collected with V-shaped gutters positioned at the bottom of the trees and at the downhill plot edge.Stemflow infiltration rates were calculated by a mass balance, i.e., subtracting the collected overland flow from the injected volume and then dividing by the stem basal area and the time of steady infiltration. Mean values for each tree and for the entire plot, the latter considering the throughfall experiments, were approximately 1000 mm/h. The GPR data enabled the detection of active preferential flow paths, assessment of hillslope connectivity, and estimation of flow velocities. GPR gave relevant information in the flow pathways in the soils, the effects of root systems and its combination with matrix flow.This experiment represents a straightforward, replicable, and non-invasive method for characterizing the role of trees in water runoff and infiltration at the hillslope spatial scale, and more broadly, in understanding how forested hillslope respond to rainstorms.

Abstract Infiltration regulates the movement and storage of water at the soil–atmosphere interface and is, therefore, a key component of many related physical and biogeochemical processes. Numerous studies have examined infiltration over the past two centuries. These efforts have resulted in the development of numerous models that capture the effects of specific soil properties and initial and boundary conditions. This proliferation of models has advanced our collective ability to understand infiltration processes but has also made it challenging for researchers to select appropriate approaches for analyzing experimental infiltration data or for conducting basic research on soil parameters like saturated hydraulic conductivity or sorptivity. Here, we aimed to reduce this uncertainty by developing a comprehensive literature review of published infiltration models, including their underlying philosophies and evolution over the years. Through this effort, we compiled and examined 138 unique infiltration models. We grouped models into two major categories, empirical and conceptual, noting that boundaries between those two categories are at times debatable. After classifying and providing a full historical retrospective of these models, we examined specific model parameters and how their usage has changed with time. We also reviewed different methods applied to estimate infiltration parameters, as well as the challenges that arise when using such methods. Finally, we proposed a framework for identifying suitable models depending on field conditions, experimental plan, and data availability.

Protection forests play a critical role in mitigating surface landslides and controlling hydrological processes, yet their identification and assessment remain a challenge in forest and land management. This study, conducted as part of the PRIN-PNRR MILETO project, introduces in Italy a novel procedure for identifying protection forests using a deterministic statistical approach tailored to surface landslides in Italy. The SlideForMAP software forms the core of this methodology, integrating key inputs on soil and vegetation characteristics to assess landslide susceptibility. By explicitly incorporating the role of vegetation, the software offers a refined analysis of areas prone to landslides. Computationally efficient, the method supports the evaluation of extensive regions, facilitating applications at a regional scale. In southern Italy the MILETO project has implemented this methodology to map and evaluate protection forests though case studies. These areas, often characterized by steep terrain and varying climatic conditions, are particularly prone to hydrogeological hazards like landslides. The project focuses on linking hydrological and soil stability models with vegetation dynamics, a key determinant in mitigating landslide risk.These outputs provide actionable insights for forest and land managers. The hazard maps enable planners to pinpoint locations where protection forests mitigate landslide risks most effectively, while heat maps highlight areas for intervention to enhance forest functionality. This systematic approach bridges the gap between theoretical modeling and practical forest management, supporting sustainable landscape practices and disaster risk reduction approaches. By focusing on direct protection forest detection, this case study in southern Italy contributes to integrating environmental modelling and geospatial data to create a robust framework for safeguarding vulnerable regions.

Adapting cities to climate and global changes requires tremendous progress in managing the water cycle in cities. So far, the water pathways are disconnected from the natural water cycle in urban areas. Runoff water is collected and routed to sewer systems. Best management practices were then developed to restore the natural water cycle by promoting water infiltration into specific urban drainage systems. These are often called “SUDS” for Sustainable Urban Drainage Systems and infiltrate the runoff water collected over urban catchments. However, SUDS may lose their capability to infiltrate water as the soil clogs and becomes less permeable. For these devices, soil hydraulic conductivity must be monitored over time. Water infiltration techniques have been developed to characterize the soil hydraulic properties. The Beerkan method was pioneered by Braud et al. in 2005 and then used by many soil scientists (Angulo-Jaramillo et al., 2016). Several algorithms were developed to treat the data and estimate the soil hydraulic properties. In 2006, Lassabatere et al. (2006) initiated the BEST method to identify the saturated hydraulic conductivity and the whole set of unsaturated hydraulic parameters from Beerkan runs combined with field data (bulk density and particle size distribution). Since then, the method has been improved and adapted to many types of soils and configurations (see Angulo-Jaramillo et al., 2019, for a review). The Beerkan run is easy to perform. It requires one operator to prepare known volumes of water, infiltrate them into a ring inserted in the soil, and score the infiltration times. The cumulative infiltration, which assigns the cumulative infiltrated volume to the infiltration time, is the raw data that is used in most hydraulic characterization algorithms. However, its ease of use requires human resources (one operator) and may be time-consuming, particularly for fine soils that infiltrate very slowly. Di Prima et al. (2016) recently designed an automated infiltrometer that replaces the operator. The device automatically supplies the water before desaturation of the soil surface and records the infiltrated volume as a function of time. This device has been deployed for several studies, allowing the hydraulic characterization of several types of soils under several field conditions. However, so far, no studies have focused on comparing the automated infiltration, referred to as “Automated Beerkan,” and the manual version of the Beerkan runs. In this study, we performed the two types of runs at the same places in order to avoid uncontrolled variations due to spatial variability in urban soils. We present the cumulative infiltrations obtained at the same point with the automated Beerkan and the original Beerkan (manual version). The cumulative infiltrations were inverted using the BEST methods, and the obtained hydraulic parameters were compared. Di Prima, S., et al.,2016. Geoderma 262, 20–34. https://doi.org/10.1016/j.geoderma.2015.08.006 Angulo-Jaramillo, R., et al., 2016. Springer, Switzerland. https://doi.org/10.1007/978-3-319-31788-5 Angulo-Jaramillo, R., et al., 2019. Journal of Hydrology 576, 239–261. https://doi.org/10.1016/j.jhydrol.2019.06.007 Braud, I., et al. 2005. European Journal of Soil Science 56, 361–374. https://doi.org/10.1111/j.1365-2389.2004.00660.x Lassabatere, L., et al., 2006. Soil Science Society of America Journal 70, 521–532. https://doi.org/10.2136/sssaj2005.002

The heterogeneous distribution of water-repellent materials at the soil surface causes a phenomenon known as fractional wettability. This condition frequently triggers destabilization of the wetting front during water infiltration, resulting in the formation of fingered bypass flow. However, few analytical tools exist to understand and model this behavior. Moreover, existing infiltration models fail to fit certain infiltration curves that exist in experimental data. For these reasons, we introduce a novel infiltration model to simulate water infiltration under fractional wettable conditions. We conceptualize the soil surface as a composite of two distinct portions: a water-repellent fraction, where hydrophobic effects impede water infiltration, and a wettable fraction, where capillarity and gravity are the dominant forces controlling the process. The new model was validated using a dataset comprising infiltration data from 60 field measurements. Additionally, validation was performed using 660 analytically generated infiltration curves from six synthetic soils with varying textures. This innovative approach enabled us to account for the combined influence of these two fractions and to enhance the interpretation of infiltration curves with mixed shapes, which other common methods are unable to reproduce.

Urban areas are increasingly under pressure due to rapid expansion and extreme rainfall events driven by climate change. Rather than relying solely on pipes to regulate stormwater, new management systems promote direct infiltration of water and pollutants into the soil. Soils fulfill multiple functions, including water infiltration and pollutant filtration. Urban soils, however, are often highly heterogeneous; the presence of macropores can accelerate water flow while reducing pollutant retention. Yet, infiltration and filtration are typically assessed using surface measurements and soil-destructive methods, which fail to capture the complexity of water and pollutant transport pathways in the subsurface. In this study, we present a prototype of a large-ring infiltrometer coupled with a ground-penetrating radar (GPR) to simultaneously monitor water and nanotracers movement in the subsurface. This provides a more comprehensive characterization of both infiltration and filtration functions. Superparamagnetic iron oxide nanoparticles (SPIONs) were chosen as nanotracers due to their nontoxicity, small size, and advantageous electromagnetic properties. Although distinguishing between subsurface zones imbibed with water and those containing SPIONs was challenging, GPR imaging revealed distinct spatial patterns and temporal dynamics even under identical infiltration conditions. Comparative analyses with water and solute transport models further elucidated the underlying subsurface processes. Typologies of infiltration and filtration patterns, linked to soil heterogeneity, are presented. Our results emphasize the need for a more comprehensive characterization of infiltration and filtration functions to improve flood risk assessment and evaluations of groundwater pollution threats.

Nowadays, there is a particular need to estimate soil water content accurately over space and time scales in various applications. For example, precision agriculture, as well as the fields of geology, ecology, and hydrology, necessitate rapid, onsite water content measurements. The time domain reflectometry (TDR) technique is a geophysical method that allows, in a time-varying electric field, the determination of dielectric permittivity and electrical conductivity for a wide class of porous materials. Measuring the volumetric water content in soils is the most frequent application of TDR in soil science and soil hydrology. TDR has grown in popularity over the last 40 years because it is a practical and non-destructive technique that provides laboratory and field-scale measurements. However, a significant limitation of this technique is the relatively high cost of TDR devices, despite the availability of a range of commercial systems with varying prices. This paper aimed to design and implement a low-cost, compact TDR device tailored for classical hydrological applications. A series of laboratory experiments were carried out on soils of different textures to calibrate and validate the proposed measuring system. The results show that the device can be used to obtain predictions for monitoring soil water status with acceptable accuracy (R2 = 0.95).

The comprehension of hydrological processes inherent in the water cycle and its constituents is of paramount significance when formulating adaptation strategies to address climate and global changes. The Sahel region serves a crucial role as a buffer zone between the arid desert and the more verdant and precipitation-laden areas of Senegal. The savanna region comprises a dynamic amalgamation of woody perennials intermixed with agricultural crops and pastures. The sustained vitality of this ecosystem hinges upon sustainable agriculture, mandating the judicious utilization of water resources. The formulation of strategies geared towards optimizing water resource management necessitates a comprehensive understanding of hydrological processes. This includes the investigation of water infiltration at the soil surface, the dynamics of water redistribution within the soil profile, and the mechanisms governing groundwater recharge. These scientific insights will help to develop effective strategies for the sustainable utilization of water resources within the Sahel region. The intended investigation seeks to characterize the hydraulic properties of sandy soils that extensively prevail within the savanna ecosystem.The utilization of water infiltration experiments coupled with corresponding modeling presents a robust framework for non-intrusive on-site hydraulic soil characterization. These methodologies have been widely employed across diverse contexts (Angulo-Jaramillo et al., 2019, for a review). To achieve this objective, the Beerkan method, initially proposed by Braud et al. (2005), involving the controlled infiltration of known water volumes into a designated ring, has been identified as a pertinent approach. Recently, Di Prima et al. (2016) have introduced an automated infiltrometer as a substitute for the manual Beerkan method, thereby streamlining and enhancing the procedural aspects of hydraulic soil characterization.The study pursues a dual objective: (i) to characterize the hydraulic properties of sandy soil and delineate their spatial variability, both horizontally and vertically across the soil profile; and (ii) to assess the influence of the chosen water infiltration setup (Manual versus Automated Beerkan) on the obtained results. The investigation involved the excavation of three pits arranged as steps, providing access to five distinct horizons that spanned from the soil surface to a perched aquifer positioned at 2.5/3 m depth. Both Manual and Automated Beerkan experiments were conducted at the soil surface and for each horizon. Cumulative infiltrations were subjected to analysis using the BEST methods for precise determination of hydraulic parameters. Furthermore, bulk density and particle size distributions were determined for each Beerkan run by coring the soil at the conclusion of the experiment.The examination of infiltration rates and hydraulic parameter profiles across the soil profiles, along with the comparative analysis of values derived from manual versus automated Beerkan runs, furnished pertinent insights to address the study's dual objectives.ReferencesAngulo-Jaramillo, R., et al., 2019. Journal of Hydrology. 576, 239–261. https://doi.org/10.1016/j.jhydrol.2019.06.007Braud, I., et al., 2005. European Journal of Soil Science 56, 361–374. https://doi.org/10.1111/j.1365-2389.2004.00660.xDi Prima, S., et al.,2016. Geoderma 262, 20–34. https://doi.org/10.1016/j.geoderma.2015.08.

Time-lapse ground-penetrating radar (GPR) surveys, combined with automated infiltration experiments, provide a non-invasive approach for investigating the distribution of infiltrated water within the soil medium and creating three-dimensional images of the wetting bulb. This study developed and validated an experimental protocol aimed at quantifying and visualizing water distribution fluxes in layered soils under both unsaturated and saturated conditions. The 3D images of the wetting bulb significantly enhanced the interpretation of infiltration data, enabling a detailed analysis of water movement through the layered system. We used the infiltrometer data and the Beerkan Estimation of Soil Transfer parameters (BEST) method to determine soil capacitive indicators and evaluate the physical quality of the upper soil layer. The field survey involved conducting time-lapse GPR surveys alongside infiltration experiments between GPR repetitions. These experiments included both tension and ponding tests, designed to sequentially activate the soil matrix and the full pore network. The results showed that the soil under study exhibited significant soil aeration and macroporosity (represented by AC and pMAC), while indicators related to microporosity (such as PAWC and RFC) were notably low. The RFC value of 0.55 m3 m−3 indicated the soil’s limited capacity to retain water relative to its total pore volume. The PAWC value of 0.10 m3 m−3 indicated a scarcity of micropores ranging from 0.2 to 30 μm in diameter, which typically hold water accessible to plant roots within the total porosity. The saturated soil hydraulic conductivity, Ks, values ranged from 192.2 to 1031.0 mm h−1, with a mean of 424.4 mm h−1, which was 7.9 times higher than the corresponding unsaturated hydraulic conductivity measured at a pressure head of h = −30 mm (K−30). The results indicated that the upper soil layer supports root proliferation and effectively drains excess water to the underlying limestone layer. However, this layer has limited capacity to store and supply water to plant roots and acts as a restrictive barrier, promoting non-uniform downward water movement, as revealed by the 3D GPR images. The observed difference in hydraulic conductivity between the two layers suggests that surface ponding and overland flow are generated through a saturation excess mechanism. Water percolating through the soil can accumulate above the limestone layer, creating a shallow perched water table. During extreme rainfall events, this water table may rise, leading to the complete saturation of the soil profile.

We have constructed a new, simplified constant-head infiltrometer automated with a self-contained water level datalogger (HOBO U20L-01) repurposed to measure changes in gas pressure inside an inverted bottle reservoir. Our field tests of six of these infiltrometers confirmed that recorded changes in gas pressure were strongly correlated with changes in water level in the infiltrometer reservoir (R2 = 0.9998). Further, by using the derived experimental calibration function, we were able to obtain accurate near-steady-state infiltration rates. This infiltrometer is cheaper and lighter than current commercially available infiltrometers. It can be easily assembled with materials readily available in most hardware stores, and its user-friendly datalogger does not require any programming knowledge. This infiltrometer is compatible with various ponding infiltration methods, and its generic design allows for modifications with locally available materials to meet diverse research needs. Currently available infiltrometers are often bulky and can be costly and complex to build. Our infiltrometer is lightweight, relatively low cost, and easy to assemble. A calibration equation was used to derive infiltration rates from pressure data. Tests at three sites confirmed the accuracy of our infiltrometer for different soil types and vegetation covers.

Modeling agricultural systems, from the point of view of saving and optimizing water, is a challenging task, because it may require multiple soil physical and hydraulic measurements to investigate the entire crop cycle. The Beerkan method was proposed as a quick and easy approach to estimate the saturated soil hydraulic conductivity, Ks. In this study, a new complete three-dimensional model for Beerkan experiments recently proposed was used. It consists of thirteen different calculation approaches that differ in estimating the macroscopic capillary length, initial (θi) and saturated (θs) soil water contents, use transient or steady-state infiltration data, and different fitting methods to transient data. A steady-state version of the simplified method based on a Beerkan infiltration run (SSBI) was used as the benchmark. Measurements were carried out on five sampling dates during a single growing season (from November to June) in a long-term experiment in which two soil management systems were compared, i.e., minimum tillage (MT) and no tillage (NT). The objectives of this work were (i) to test the proposed new model and calculation approaches under real field conditions, (ii) investigate the impact of MT and NT on soil properties, and (iii) obtain information on the seasonal variability of Ks and other main soil physical properties (θi, soil bulk density, ρb, and water retention curve) under MT and NT. The results showed that the model always overestimated Ks compared to SSBI. Indeed, the estimated Ks differed by a factor of 11 when the most data demanding (A1) approach was considered by a factor of 4–8, depending on the transient or steady-state phase use, when A3 was considered and by a practically negligible factor of 1.0–1.9 with A4. A relatively higher seasonal variability was detected for θi at the MT than NT system. Under both MT and NT, ρb did not change between November and April but increased significantly until the end of the season. The selected calculation approaches provided substantially coherent information on Ks seasonal evolution. Regardless of the approach, the results showed a temporal stability of Ks at least from early April to June under NT; conversely, the MT system was, overall, more affected by temporal changes with a relative stability at the beginning and middle of the season. These findings suggest that a common sampling time for determining Ks could be set at early spring. Soil management affected the soil properties, because the NT system was significantly wetter and more compact than MT on four out of five dates. However, only NT showed a significantly increasing correlation between Ks and the modal pore diameter, suggesting the presence of a relatively smaller and better interconnected pore network in the no-tilled soil. This study confirms the need to test infiltration models under real field conditions to evaluate their pros and cons. The Beerkan method was effective for intensive soil sampling and accurate field investigations on the temporal variability of Ks.

The addition of natural or synthetic zeolites induces changes in a soil’s chemical, physical, and biological characteristics. Zeolites possess intricate internal frameworks that allow them to modify soil structure and texture, thereby impacting soil hydrological properties. This potential offers opportunities to control soil and groundwater pollution as well as optimize irrigation management practices. In this study, three sandy-loam soils and a silty-loam soil were collected and mixed with different amounts of synthetic zeolite derived from coal fly ash. Repacked soil samples were combined with four levels of zeolite ranging from 1% to 10% by weight and were then hydraulically characterized. This included measuring soil water retention curves (SWRCs) of soil-zeolite mixtures. The data revealed, in accordance with recent research findings, that zeolite influences the hydraulic behavior of soils. In general, we observed that, as the percentage of zeolite increases in the soil, the SWRCs are shifted upwards. This effect is fundamental for explaining the observed changes in the whole set of investigated soil hydraulic properties. The observed changes are also fundamental to evaluate selected soil physical quality (SPQ) indices of agronomic interest, which are investigated in depth in the present research. A specific focus was on the impact of zeolite on modifying the soil’s capacity to retain water, hence on the energy required by plants to acquire a unit mass of soil water (referred to as integral energy, EI). Finally, the ANOVA test, linear regression, and multivariate analysis were performed on the entire dataset to support, from a statistical standpoint, the observed correlations between SPQ indices and zeolite amounts. These findings underscored the significance of soil texture in selecting the appropriate soil type for zeolite amendment, confirming that coarse-textured soils are more suitable for zeolite treatment compared to fine-textured soils.

<p>In the Sahel region, agroforestry is a land-use system widely adopted as a more sustainable agricultural production system. In this type of system, woody perennials that are grown in association with agricultural crops and pastures, constitute spatially disconnected zones where microclimate and soil’s infiltrability, physical, chemical, and biological conditions are assumed locally improved. Particularly the stemflow concentrates a part of the intercepted rainfall from the canopies to the stems. Hence stemflow can induce preferential infiltration around the stem base and promote groundwater recharge.</p> <p>In the West African Sahel, <em>Faidherbia albida</em> (Delile) A.Chev. is commonly adopted as multi-purpose woody perennial in agroforestry systems. It is a deciduous tree with an inverse phenology as it loses the leaves during the rainy season. Although, the absence of leaves during the rainy season is expected to decrease the interception and to consequently decrease stemflow, evidence of stemflow at the base of <em>F. albida</em> trees were reported in the literature when the stems were partially covered with green leaves (Chinen, 2007).</p> <p>In this study, we carried out timelapse ground penetrating radar (GPR) surveys in conjunction with a simulated stemflow event to investigate stemflow-induced infiltration by an <em>F. albida</em> tree trunk and root system. We established a survey grid (2.1 m × 2.1 m) around an <em>F. albida</em>, consisting of twelve horizontal and ten vertical parallel survey lines with 0.3 m intervals between them. Two stemflow pulses, each of 20 L, were poured on the tree trunk using a PVC pipe with a 1-mm-diameter hole every 50 mm. The pipe was connected to a plastic funnel and positioned around the tree trunk at 0.4 m from the soil surface. One grid GPR survey was carried out before the stemflow simulation experiment. A total of 40 L of water was used during the experiment. A second survey was carried out after the injection of the first 20 L, while the last survey was carried out after the second stemflow pulse. We collected a total of 66 (3 GPR surveys × 22 survey lines) radargrams using a GSSI (Geophysical Survey System Inc., Salem, NH) SIR 3000 system with a 900-MHz antenna. We therefore obtained for each survey line a pre-wetting and two post-wetting radargrams. Next, we created other forty-four matrixes based on absolute differences between pre- and post-wetting amplitude values. Higher differenced values occurred because of amplitude changes and time shifts related to wave propagation.</p> <p>The analysis of the differentiated radargrams provided evidence of deep infiltration along the tap roots. The wetted zone extended mainly in-depth providing evidence of the potential role played by the <em>F. albida</em> trees in groundwater recharge processes due to their deep rooting, preferably reaching the groundwater table. Put all together, this study shows a first signal of the importance of accounting for stemflow infiltration in the water balance of agroforestry systems with <em>F. albida</em> trees.</p> <p><strong>References</strong></p> <p>Chinen, T., 2007. An observation of surface runoff and erosion caused by acacia albida stemflow in dry savanna, in the south-western republic of Niger 10.</p>

The hydrological response of sloping catchments is strongly conditioned by the connectivity of subsurface preferential flows. The objective of this paper is to investigate the role played by stemflow infiltration in subsurface water flow dynamics, focusing on a forested hillslope located in an Aleppo pine Mediterranean forest (Pinus halepensis, Mill.) located at Sierra Calderona, Valencia province, Spain. We combined stemflow artificial experiments with the ground-penetrating radar (GPR) as a non-invasive technique to investigate stemflowinduced preferential flow paths activated by different trees and the related hydrological connectivity at the hillslope scale. Our observations allowed us to identify different dynamics associated with the initiation of stemflow and then lateral preferential flow, including the activation of connected preferential flow paths that received stemflow water from different trees. These observations provided empirical evidence of the role of stemflow in the formation of lateral preferential flow networks. Our measurements also provided estimations for flow velocities, which provided new insight on the magnitude of stem-induced lateral preferential flow paths. The applied protocol offers a simple, repeatable and non-invasive way to conceptualize hillslope responses to rainstorms.

The addition of natural or synthetic zeolites alters a soil's chemical, physical and biological properties. Due to the existence of a complex internal structure, zeolites have the potential to modify soil structure and texture with a direct impact on soil hydrological properties, introducing the possibility of controlling soil and groundwater pollution as well as irrigation management practices.In the present study, a series of laboratory tests were conducted on soil samples mixed with zeolite to investigate the possible changes in hydraulic and solute transport properties and related parameters. To determine the above properties, four soils of different textures were selected and two distinct groups of experiments were conducted on disturbed (i.e., repacked) soil samples by adding known amounts of zeolite (i.e., 1, 2, 5 and 10%; w/w). Solute transport properties were determined on one group of soil samples using the so-called Kachanoski approach to monitor miscible flow experiments. Soil hydraulic properties were determined on the second group of soil samples by measuring soil water retention curves (SWRCs) and saturated hydraulic conductivity (K-s). In general, we observed significant changes in the measured properties with zeolite percentages of 5% and 10%. However, some changes were also evident at 1% and 2% of zeolite addition. These observed differences may be mainly ascribed to changes in the soil's pore size distribution due to the addition of a finer fraction (i.e., zeolite) to soils. This fraction reduces macropores (that are occluded in proportion to their amount) and thus enhances the formation of meso- and micropore regions.