Norwegian agriculture is challenged by increased production demand and climate change while being faced with tight restrictions to its environmental impact. Due to climate change, an increase in extreme weather events is expected. High intensity rainfall events lead to flooding and water-logged conditions, which have negative impacts on yield and operational conditions related to tillage and transport (trafficability of the soil). Two thirds of Norway's agricultural area is drained to prevent water logging, but at times these drained soils have problems with too high water content, leading to delayed tillage in spring time resulting in lower yields. About 10% of the cultivated land is considered poorly drained.

Saturation and infiltration excess overland flow leads to sheet erosion. Erosion rates often follow a seasonal pattern with the highest soil losses during late autumn and early spring. For most of the total soil loss only a few runoff events are responsible each year. Soil loss from agricultural areas in Norway is not only harmful because of the loss of nutrient rich topsoil, but also because of off-site effects, especially in freshwater systems.

Poorly drained soils are prone to deterioration of its structure. In areas where overland flow concentrates, this may lead to the development of gullies. Ephemeral gullies make up a considerable part of the sediment losses from agricultural areas. In addition, they are shortcuts for sediment transport, forming a connection between the hillslope and the surface water system.

Seasonal saturation excess because of snow melt and rain also leads to high flow rates in Norway’s stream and river network. Flooding problems at the intersection between streams and roads occur even in first order streams.

While many soil conservation and water retention measures complement each other, they sometimes affect each other adversely. Intensification of tile drainage, for example, may reduce sheet and gully erosion risk levels, but will have an adverse effect on peak flow rates and flood risk. Other measures, like buffer zones, serve both purposes. But when, how and under which circumstances water retention and soil conservation measures function remains a complex question.

Understanding the spatio-temporal dynamics of water in the vadose and groundwater zones therefore is a key component of integrated agro-ecological management strategy at low (farm) and high (regional) levels. While the mechanics of overland water movement and infiltration are generally well understood, there are many significant challenges for system understanding at larger spatial scales, especially under increasingly non-normal weather conditions.

NIBIO endeavors to reconcile measurements and observations with agrohydrological system understanding. Complexity and scale (time and space) are the main challenges in this endeavor. In this presentation we will present how NIBIO uses geophysics for understanding agrohydrological threats and solutions, with focus on drainage, erosion and buffer zones.

How to cite: Bloem, E., Barneveld, R., Krzeminska, D., and Stolte, J.: Geophysics for managing Norwegian agrohydrological threats, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16030, https://doi.org/10.5194/egusphere-egu23-16030, 2023.

Near surface geophysical electromagnetic techniques are proven tools to support ecosystem services such as agriculture, soil remediation, nutrient management, and heritage conservation. Key influencing geophysical properties are electrical conductivity (σ, or resistivity (ρ)), dielectric permittivity (𝜀) or magnetic susceptibility (μ), that are targeted to model soil properties and state variables such as texture, bulk density, cation exchange capacity (CEC) or water content. To translate geophysical properties into quantitative information on the targeted soil properties, relationships between these have to be considered in appropriate models. These so-called pedophysical models can then be integrated into interpretation schemes (e.g., after inversion, or through incorporating this into forward modelling procedures). This modelling step, translating geophysical properties into soil properties (and vice versa), thus constitutes a key aspect of near surface exploration.

While hundreds of pedophysical models exist to perform this task, these often depend on many properties and parameters defined within a specific range e.g., electromagnetic frequency, texture, and salinity; impeding applications to cases where information about the studied soil is scarce. Therefore, selecting an appropriate pedophysical model for a given scenario is often a very complex task.

To facilitate solutions for pedophysical modelling we present pedophysics, an open source python package for soil geophysical characterization. The package implements up-to-date models from the literature and, based on the user’s needs, automatically provides an optimal solution given a set of input parameters and the targeted output.

First, a virtual soil is defined by inputting any of its available properties. This soil can be defined in discrete states to simulate the evolution of its properties over time. Secondly, a module (predict) is called to predict the target property of interest. Following this workflow, for example, a soil with a given texture and changing water content could be defined to obtain its 𝜀 or σ at a predefined frequency, or, inversely, its water content could be predicted based on changing σ.

However, as soil properties required as input parameters for pedophysical models are often unknown, it can, in such cases, be impossible to obtain a viable prediction outcome. The pedophysics package accounts for such limitations by implementing pedotransfer functions, that allow obtaining the missing properties from the available ones. For example, if CEC is unknown, it is determined based on soil texture and a location.

In summary, the package synthesizes specific pedophysical modeling knowledge. Time-varying properties can be calculated in a straightforward way, and, through the integration of pedotransfer functions, target properties can be predicted with a minimum of information about the studied soil. Thus, by translating known properties to targeted ones, pedophysics is contributing to improve interpretability of near surface modeling schemes; enhancing soil electromagnetic geophysical exploration techniques in ecosystem services applications.  

How to cite: Mendoza Veirana, G., de Smedt, P., Verhegge, J., and Cornelis, W.: Pedophysics: a python package for soil geophysics., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-297, https://doi.org/10.5194/egusphere-egu23-297, 2023.

The cultivation of date palms (Phoenix dactylifera) is widespread in hyper-arid regions and relies on high-frequency irrigation to achieve satisfactory yields. Adequate irrigation management is of great importance, and requires understanding of the dynamics of sap flow and water storage within the date palm stem. Traditionally, sap flow estimates are obtained using heat dissipation probes. This method provides point estimates that may not represent the spatial distribution of sap flow within the date palm stem. The aim of this study is to investigate whether electrical resistivity tomography (ERT) measurements on date palm stems can be used to obtain information on the spatial distribution of sap flow in order to obtain improved estimates of transpiration. In a first step, laboratory experiments were used to improve understanding of the electrical and hydraulic properties of date palm stems. A laboratory set-up was developed that induced flow in a date palm stem segment using vacuum pressure while making time-lapse ERT measurements. It was found that such ERT monitoring allows to visualize changes in radial flow variability due to different flow conditions. In addition, the electrical conductivity of the outflow was considerably higher than that of the introduced solution, which suggest the presence of stored salt in the stem segment. The relationship between bulk electrical conductivity and water content of date palm stem segments was investigated on smaller samples using multi-step-outflow experiments combined with bulk electrical conductivity measurements. The results showed that the water redistribution in the sample was slow after the initial desaturation, which suggests that the water is tightly bound as in a clay soil. The observed relationship between bulk electrical conductivity and saturation could be described with models established for porous media. In a second step, field experiments were performed that combined ERT and sap flow measurements on both juvenile date palm trees growing in lysimeters and mature date palm trees. For this, a custom-made measurement system was used to acquire high-speed ERT measurements with a temporal resolution of several minutes. The high-resolution monitoring of both the juvenile and mature date palms showed a high spatial variability in electrical conductivity within both the juvenile and mature date palm stems. This has obvious implications for the installation of sap flow sensors, where low-conductivity areas likely indicating regions without flow should be avoided. ERT monitoring also revealed diurnal changes in the spatial distribution of the electrical conductivity that are associated with the tree response to irrigation. An induced drought period for the juvenile date palm in the lysimeter also resulted in a noticeable decrease in the mean electrical conductivity on the second day after irrigation was stopped, suggesting that ERT may also provide an early indicator of water stress.

How to cite: Bukhary, T., Huisman, J. A., Wang, H., Zimmermann, E., and Lazarovitch, N.: Electrical resistivity tomography and sap flow measurements on date palm stems to support irrigation management, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13024, https://doi.org/10.5194/egusphere-egu23-13024, 2023.

Characterization of agricultural soils using geophysical techniques makes it possible to study the heterogeneity of a soil and the preferential pathways of water flows without causing disturbances to soil and plants. Increased knowledge of soil heterogeneity allows the most optimal management of the water resource in terms of crop, yield and sustainability. In this study, time lapse monitoring, using electrical resistivity tomography (ERT), is proposed as a reliable and non-invasive technique to quantify the movement of water flows during the irrigation process.

ERT surveys were conducted in melon cultivated land in southern Tuscany (Italy). Four survey campaigns were carried out between June and August 2022, in which ERT data were collected by taking measurements, before, during, and after the irrigation phase. The investigation was conducted with a 3-D grid in which the 72 electrodes were spaced 0.3 m apart and arranged in three parallel lines, 0.3 m apart and 6.9 m long, for a total of 24 electrodes in each line. The plants were located above a ridge having a height of 20 cm with respect to the ground level and the electrodes were positioned to incorporate 5 melon plants in the configuration. A dipole-dipole configuration was adopted for the acquisition of electrical resistivity data. Commercial ViewLab 3D software was used to process the geoelectrical data.

The interpretation of the ERT results provided information on the spatial and temporal distribution of water flows in the soil and in the root zone of melons during the irrigation phases. The investigation made it possible to identify the preferential ways of infiltration of the irrigation water, the points where the water is absorbed by the roots, and the points where the water instead follows a preferential way distributing itself entirely below the area of root growth. During the investigations, the irrigation time underwent changes dictated by the climatic conditions, therefore the irrigation time and frequency were increased. This manifested itself in the ERT sections with an increase in the conductivity below the roots, i.e., at a depth of about 35 - 40 cm with respect to the ground level. This phenomenon can be explained by the fact that over time the water has developed a greater preferential path, completely bypassed the root system and collected below it, in the zone delimiting the worked soil with the unworked soil.

In the present case study, the ERT technique proved to be a valid survey and monitoring method for mapping the preferential paths of water flows in agricultural land. The ERT sections made it possible to study the distribution of water along the soil profile, highlighting the presence of preferential paths that produce an accumulation of water below the root zone and therefore in an area that is not very usable for cultivation. This technique can therefore be used in this context to study a better irrigation system and an optimal management of the water resource, avoiding preferential paths of the flows which lead to a lower availability of water for the plant.

How to cite: Innocenti, A., Pazzi, V., Napoli, M., Fanti, R., and Orlandini, S.: Electrical Resistivity Tomography (ERT) to assess the drip irrigation water in a field cultivated with melon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7128, https://doi.org/10.5194/egusphere-egu23-7128, 2023.

France is one of the largest producer of wine in the world. Thus, viticulture is a major activity area, particularly in south-west of France where vineyards occupy as much as 42% of the agricultural surface. Vineyards worldwide are being subjected to stress brought about by changes in average temperatures, precipitation, seasonal timing that drives phenology, as well as extreme weather events (van Leeuwen, 2004). Specifically, the Bordeaux vineyards are submitted to strong climate change impact, due to the increase in the duration of heat waves (i.e., increase in evaporative demand), and the decrease in summer precipitations (i.e., decrease in water availability in the soils; Soubeyroux et al., 2020). These stressors contribute to Grape yield and quality.

Our approach consists of identifying the factors that control water availability in vineyard soils in order to adapt cultivation practices.

For this purpose, we have instrumented a vineyard plot (~1 ha) in Medoc. This observatory allows the monitoring of water fluxes within the soil-vine-atmosphere continuum on two rows of vines located in areas with contrasting soil types: one is located in a sandy area, while the other is located in a clayey area. The observatory combines:

• Soil water status monitoring with
• Spectral Induced Polarization (SIP) measurement campaigns carried out along the two selected rows of vines and repeated at a bi-monthly rhythm,
• two permanent multi-level soil water content probes
• Vines water status monitoring using sap flow sensors, together with water potential measurement campaigns repeated on a monthly basis

• Ground water level continuous measurement sensors
• Meteorological parameters monitoring

Our observations show that during the drought of the summer 2022, the vines in the sandy row suffer of greater water stress than the vines in the clay row, and that the soil in the sandy row dries out more quickly and to a greater depth than the soil in the clay row. This highlights the impact of soil type on soil water availability. Our early results suggest that in the case of a prolonged drought period, the vines located on clay plots would thus suffer less from water stress than in the case of plots with more draining soil.

Références:

Soubeyroux, JM, Bernus, S, Corre, L, Gouget, V, Kerdoncuff, M, Somot, S, Tocquer, F, 2020. Le nouveau jeu de simulations climatiques régionalisées sur la France pour le service DRIAS, XXXIIIeme colloque de l’Assoc Internat de Climatologie, pp 637-642.

Van Leeuwen, Cornelis, Philippe Friant, Xavier Choné, Olivier Tregoat, Stephanos Koundouras, and Denis Dubourdieu. 2004. Influence of Climate, Soil, and Cultivar on Terroir. American Journal of Enology and Viticulture 55(3):207–17. doi: 10.5344/ajev.2004.55.3.207.

How to cite: Chaffaut, Q., Schmutz, M., and Cavailhes, J.: Impact of drought on the water status of vines in a Bordeaux vineyard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8126, https://doi.org/10.5194/egusphere-egu23-8126, 2023.

Pristine peatlands are precious for their Carbon (C) storage ability and the vast range of ecosystem services they provide. Globally, peatlands were heavily altered over the years especially by draining the water table for meeting energy and agricultural needs. Draining the peat results in its enhanced microbial decomposition, increased dissolved C leaching and increased susceptibility to peat fires, thus turning peatlands into C-source ecosystems. Currently, the carbon dioxide (CO₂) released from degraded peatlands amounts to approximately 5% of global anthropogenic emissions. Climate change concerns have sparked an interest to reduce these emissions and different initiatives are put forward for the protection, proper management, and restoration of the peatlands. Denmark has its own national goal of reducing CO₂ emissions by 70% by 2030; of which agriculture is expected to be a significant contributor. Comprehensive characterization of peat inventory providing status on the C stocks, water table depths and emissions is required for improved land use planning as almost 4.8 million tonnes of CO₂ per annum is released from cultivated organic lands (~ 170,000 ha in total). To achieve this, measurements of peat depth (PD) for volume characterization are invaluable. The conventional mapping approach of PD using peat probes is laborious, time-consuming, and provides only localized and discrete measurements. In addition, these manual probing measurements are also prone to errors as occasionally the probes are obstructed by stones, wood and human artefacts causing underestimation and other times they might easily penetrate the soil underlying the actual peat causing overestimation. In Denmark, we are comparing and contrasting the suitability of different electromagnetic sensors, precisely, working on electromagnetic induction (EMI), ground penetrating radar (GPR), and gamma-ray radiometric (GR) principles to accurately characterize the Danish peatlands. We are testing the sensors on both ground-based and air-borne configurations to improve the feasibility, increase accessibility and save costs. A novel drone-based transient EMI sensor is being designed in this direction. So far the results suggest that the EMI and GR techniques are promising to demarcate the peatland boundaries and estimate the PDs up to a certain extent; depending on the gradient in transition between the mineral and organic soils. Ground penetrating radar provided unequivocal results in high-resistive ombrotrophic peat while failing in low-resistive minerotrophic peat due to low signal penetration. In the drone-borne configuration, GR proved superior due to its ease of use and less to no success was achieved using a GPR. Moving forward, we plan on fusing the multisensor datasets using machine learning to improve the prediction accuracy of PDs, find a means for mapping water table depths and perform advanced modelling for comprehending the effects of different management scenarios on CO₂ emissions.

How to cite: Koganti, T., Vigah Adetsu, D., Larsen, M., Skovgaard Mohr, K., Beucher, A., and H. Greve, M.: Sensor-based mapping of Danish peatlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2251, https://doi.org/10.5194/egusphere-egu23-2251, 2023.

Polders are areas reclaimed on the sea thanks to hydraulic structures like dikes. To prevent flooding, these low-lying areas are constantly drained by a network of ditches that release excess water in the sea (e.g. at low tide). The use of subsurface drainage pipes connected to existing drainage ditches further enabled the drainage of the lands and made them suitable for agriculture. While the groundwater remains saline water from its seaborn nature, with years and precipitation, a fresh water lens, lighter than the deeper saline water, developed near the soil surface, on top of the saline water. This fresh water lens is essential for most conventional crops that would suffer from saline conditions. The thickness of freshwater lenses varies throughout the year as a function of the recharge from rainfall and evapotranspiration.

However, intensive rainfall events and prolonged summer droughts are becoming more frequent with Climate Change and lead to decreasing freshwater lens thickness, endangering crop yield. Controlled drainage systems that enable to regulate the water level in the subsurface drains has the potential to mitigate this issue by imposing a temporary higher water level, hence increasing recharge of the freshwater lens. 

To better understand the dynamics of the fresh/saline water interface throughout the year, we equipped two fields with multilevel piezometers with both head and salinity sensors replicated three times in each field. Along each multilevel piezometer we also installed 1D resistivity sticks with 16 electrodes to obtain a vertical electrical resistivity profile. In addition, electromagnetic induction surveys enabled us to expand the local observations to the entire area (4 ha in total).

The datasets collected in the two fields in the conventional scenario (i.e. without controlled drainage) during the first year, showcase the usual dynamics of the interface, its lateral as well as vertical variability. The use of geoelectrical techniques enable us to distinguish fresh and saline water boundaries and its variability per soil layers. The electromagnetic induction surveys reveal old paleochannels that influence the dynamics of the freshwater lens at the field-scale. Moreover, the dataset also demonstrates how different crops (grass and flax) lead to different ground water and salinization dynamics. In this work, we present our first year of collected field data and related interpretation before the installation of the controlled drainage system.

How to cite: Blanchy, G., Mehmandoostkotlar, A., Everaert, B., Huits, D., Garré, S., Hermans, T., and Nguyen, F.: Geophysical monitoring of the fresh-saline groundwater interface in Belgian polders, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7736, https://doi.org/10.5194/egusphere-egu23-7736, 2023.

Farms in Western Australia (WA) are highly variable in soil texture and water retention capacity; therefore, spatial information of soil moisture status in the field is important for crop management. In practice, farmers often rely on point sensors to determine soil moisture in their fields for crop planning. The limitation of point measurements to account for spatial variability highlights the need to develop methods to assess soil moisture across variable broadacre fields. This information could be used for more effective site-specific crop management practices. In this study, we used a mobile nonintrusive electromagnetic induction (EMI) sensor to map soil apparent electrical conductivity (ECa) and to predict soil moisture levels across the field at three depths (0 – 0.5, 0.5 – 0.8 and 0.8 – 1.6m). The predicted soil moisture was compared with the point measurements of soil moisture sensors and soil samples. The inverted electrical conductivity (EC) from EMI surveys was converted into soil moisture using calibrations between electrical resistivity tomography (ERT) to volumetric moisture, which were developed for the different soil textural classes of the field, with R² of 0.97 to 0.99. The soil moisture variability of the field was also compared with the spatial distribution of 2019 barley yield production. No significant difference was found between the EMI estimated soil moisture values and the point moisture measurements, as well as moisture extracted from soil samples for 0 – 0.5m and 0.5 – 0.8 m depths with Pearson R values of 0.62 and 0.73 respectively. Barley yield was not correlated with mapped soil moisture or soil texture, which may be due to relatively high initial moisture levels following two years of fallow rotation. This study successfully demonstrated spatial soil moisture estimation using EMI sensor in a field with horizontally and vertically variable soil texture.

How to cite: Shaukat, H., Flower, K., and Leopold, M.: Comparing quasi-3D soil moisture derived from electromagnetic induction with 1D moisture sensors and correlation to barley yield in variable duplex soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4650, https://doi.org/10.5194/egusphere-egu23-4650, 2023.

Water transfer through the unsaturated zone, in terms of upward or downward water fluxes, is a critical term for estimation of the water budget. As fluid flow modifies diffusive heat transfer through advective processes, since the early 90s several studies have attempted to deduce vertical water flow from soil temperature series. Likewise, if information on the water content profiles is known, bulk thermal properties can be inferred from thermal time series at different depths.

In this study we compare two field sites in the Paris Basin Area, with two different types of soil and vegetation. We present our preliminary results from two approaches aiming at retrieving inferring soil bulk thermal parameters, namely heat capacity and conductivity, as well as vertical water flow.

On the one hand, thermal measurements until a depth of 1.8 m have been carried out in a managed crop field. Using frequency decomposition of the thermal series, the upward and downward flows are determined. The water fluxes are compared with high-frequency EM time-lapse maps in an attempt to spatialize the variations.

On the other hand, the thermal properties of a wetland area are inferred from soil thermal time series inversion using the thermo-hydrodynamic code suite Ginette, and are compared with spatial distribution of vegetation derived from remote sensing imagery.

The two approaches are compared and discussed with their respective caveats and abilities.

How to cite: Pascal, S., Titouan, H., Agnès, R., Pascal, M., Emmanuel, L., and Hermann, Z.: Determination of upward/downward soil water fluxes using soil thermal profile series : two field case studies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17083, https://doi.org/10.5194/egusphere-egu23-17083, 2023.

To address the non-invasive way of studying soil structure and its dynamics at different scales, several geophysical techniques can complement traditional characterization methodologies. In this context, the most widespread methods for soil investigations rely on the different electrical properties of earth materials which change with the content and salinity of the incorporated fluids. Although the use of seismic methods in soil science studies is not as common as for geotechnical and reservoir characterization, seismic wave fields contain information about the mechanical properties of the subsurface and may offer insights about soil compaction that other geophysical methods cannot provide.

In this work, we evaluate the ability of seismic techniques to assess the differences between small and strong degrees of compaction in soils, relating and validating them with traditional direct measurements. The experiment was conducted at the Experimental Farm “L. Toniolo” of the University of Padova in Legnaro (northeastern Italy), under controlled conditions. The acquisition scheme was designed to resolve small-scale seismic velocity contrasts. Three different levels of induced compaction were investigated with indirect (i.e. geophysics) and direct (i.e. bulk density, texture, volumetric water content) measures.

Preliminary results of refraction and surface waves seismic analysis clearly agree with traditional direct measurements. We demonstrate that this approach is not only sensitive to the compaction phenomenon, but it allows to observe both its lateral and in-depth variability. This study opens up interesting future scenarios for geophysics to highlight the different mechanical responses caused both by soil plastic deformation and soil water distribution due to increasing compaction.

How to cite: Carrera, A., Pavoni, M., Barone, I., Boaga, J., Dal Ferro, N., Cassiani, G., and Morari, F.: On the use of seismic geophysical methods to characterize different soil compaction levels, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12699, https://doi.org/10.5194/egusphere-egu23-12699, 2023.