The integration of the environmental concerns into agricultural policy is the key strategy for enhancing the sustainability of agro-ecosystems EEA Report This relationship is more evident if we consider the increasing frequency of the climate-related hazards and the role of the agriculture in the climate adaptation strategies see IPCC Report by Field et al. The arena where agricultural land use and environmental processes meet is the soil: the thin upper part of Earth Crust Earth Skin represents one of the more complex systems in which lithosphere, hydrosphere, and biosphere interact and are strongly linked.
The thickness of the zone beneath the Earth surface that is of interest for the agriculture science is within the range 0—2 m. There is a growing demand of near-surface observing technologies for studying a wide spectrum of phenomena in the soil having implications on agriculture and environment, from the analysis of time-dependent change of water content to the detection of pollutants and from the analysis of soil salinization and fertility to the study of soil—root plant interactions Allred et al ; Vereecken et al.
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Geophysics addressed these challenging themes with novel observing technologies based on completely innovative sensors i. To date, geophysics provides a set of robust, cost-effective, and completely noninvasive or minimally invasive technologies for near-surface investigations able to estimate the physical properties of the shallow layers of soil and subsoil. Such technologies are used in a range of applications, from archaeology to hydrology or precision agriculture, and allow to acquire information that can be directly used for the description and monitoring of relevant features or can guide strategies for sampling Rossi et al.
Research on geophysical applications in agriculture and the environment has been conducted in Basilicata in the past decade, and this chapter provides an introduction to the techniques and an overview of selected results obtained within this context.
The geophysical exploration methods or geophysical surveying measurements within geographically restricted areas are used to determine the distributions of physical properties at depths that reflect the local subsurface geology. There is a broad division of geophysical surveying methods into those that make use of natural fields of the Earth and those that require the input into the ground of artificially generated energy.
The natural field methods utilize the gravitational, magnetic, electrical, and electromagnetic fields of the Earth, searching for local perturbations that may be caused by concealed subsurface features. Artificial source methods involve the generation of local electrical or electromagnetic fields that may be used like natural fields or, in the most important single group of geophysical surveying methods, the generation of seismic waves whose propagation velocities and transmission paths through the subsurface are mapped to provide information on the distribution of geological boundaries at depth.
Generally, natural field methods can provide information on Earth properties at greater depths and are logistically more simple to carry out than artificial source methods. The basic physical principles are quite simple: an energizing source, generally located on the surface, sends a primary signal i. The analysis of the geophysical signals measured by means of the receiving system allows us to reconstruct the spatial pattern of the physical properties of the subsoil i.
In absence of an artificially generated signal, the geophysical methods are identified as passive and the sensors can only detect the fluctuations of the natural geophysical field magnetic, electric, gravimetric. The investigation depth and the spatial resolution of the geophysical methods are strictly connected to the frequency of the energizing signal and to the electrodic distance between the transmitting and receiving sensors Steeples Density and elastic moduli, which determine the propagation velocity of seismic waves.
Subsidiary methods in brackets. Source: Kearey et al. Geophysical imaging techniques offer high spatiotemporal resolution combined with a noninvasive character and are a very attractive tool for soil characterization without disturbance Michot et al. Among the numerous techniques, electrical and electromagnetic methods are most often used, and we will describe some of them, with emphasis on methods which have been used in case studies from research teams in Basilicata.
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Self-Potential and Magnetometry are passive methods based on measurements of electrical and magnetic natural fields carried at the earth surface. They are the oldest geophysical methods and have been first applied using purely qualitative approaches. Nowadays, thanks to novel algorithms for tomographic data inversion, these old methods are becoming modern tools for innovative application in hydrogeophysics and environmental sciences Chianese and Lapenna ; Soueid Ahmed et al.
The SP method is a very promising tool for studying the water—plant root interactions, while the Mag method is suitable for mapping the presence of heavy metal in soil. Electrical conductivity ECa or its inverse resistivity ER is one of the most utilized variable to indirectly assess soil spatial variability in agricultural fields Corwin and Plant The techniques commonly used to measure the ECa variation within the root zone at field scale are essentially two: Electrical resistivity ER and Electromagnetic induction EMI.
EMI methods use dual coil systems in which a transmitter coil is used to generate a primary electromagnetic field. When this electromagnetic field travels through the soil, eddy currents are generated as a function of soil conductivity, and this produces a secondary magnetic field which is detected by the receiving coil together with the primary magnetic field.
Electrical conductivity is then calculated as a function of the difference between the primary and the secondary magnetic fields.
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The first applications in agriculture were on soil water Edlefsen and Anderson and salinity Rhoades and Ingvalson , but a major diffusion of the technique in the s is linked to the development of precision agriculture, based on optimization of agricultural management within a field. Technologically, this was also made possible by the growing availability of GPS which allowed the use in dynamic mode.
Characterizing electrical conductivity in the soil profile, though, is not simple, given the nonlinear relation between EC and depth with few exceptions. This requires complex processing of data Corwin and Lesch Furthermore, calibration is not easy; it is time consuming and needs to be repeated in case of lengthy measurements, since readings are affected by air temperature Dabas and Tabbagh Also, metals interfere with magnetic fields, and metallic objects in measurement areas may totally prevent a campaign. The ERT methods are able to describe the resistivity pattern at different levels of depth in subsoil, while the ARP is an optimal tool for the fast resistivity surveying of large areas.
The working principle of the ERT is the injection of a known DC electric current into the subsurface through an array of transmitting electrodes and in the subsequent measurement of the voltage difference with an array of receiving potential electrodes.
In this way, ERT is able to provide information about the spatial distribution of the electrical resistivity i. Some common collinear electrode configurations for resistivity studies. A—B: current electrodes; M—N: potential electrodes; a: electrode spacing; k: geometric factor; n: ratio of the distance between the A—M electrodes and the A—B dipole spacing. Details about array configurations and their sensitivity functions are reported in Loke Modern georesistivimeters have multielectrode systems able to acquire a large number of data by automatically switching quadrupoles for each array, which is composed of a consistent number of electrodes properly fitted on the ground.
All possible quadrupole spacings along the line are used for measurements, from the lowest—corresponding to adjacent electrodes—to maximum spacing, determined by the total array length. Representation of a 2D section of soil resistivity obtained after data inversion with numerical modeling. The continuous or automatic profiling of resistivity is an extremely fast and cost-effective tool for mapping the horizontal spatial variability of the apparent resistivity in large areas.
The spatial information collected by the ARP system is used for positioning measurements but also for computing a DEM Digital Elevation Model providing topographic attributes such as slope and position that facilitate the interpretation of resistivity variation and the definition of management zones Rossi et al.
Electrodes are metal discs. The ground-penetrating radar GPR is an active electromagnetic technique and nondestructive for physical detection, which utilizes similar principles to the reflection seismic method. Schematic representation of the GPR working principle a manual data acquisition system; b raw-data radargram. In recent years, research efforts have been done for implementing advanced data processing based on addressing GPR data processing as an inverse electromagnetic scattering problem.
This gives better results in determining target location and geometric features Soldovieri et al.
The EM and ERT methods have been largely applied in agriculture and environmental studies, from monitoring of saltwater intrusion in coastal areas to the diffusion of pollutants in groundwater; the time-dependent change of soil water content; the surveying of plant root biomass Amato et al. The ARP is increasingly used in precision farming viticulture giving contributes for improving the management strategies aimed to improve and enhance the quality of the crop production Rossi et al.
The GPR method can be applied to a wide range of agriculture and environmental problems such as the detection of pollutant leakage in groundwater, the mapping of the root—plant geometry, and the rapid mapping of soil water content. Recently, novel applications in precision farming have been carried out using advanced system of semi-automatic vehicles for GPR data acquisition Hubbard et al. Data were real time referenced by DGPS. Data were collected on 2. A total number of 59, measurements were taken.
The radargram corresponding to the ERT profile shows a higher attenuation of the signal in the right side, and this can be associated to increased soil water. Conversely, the left side of the radargram shows a continuous series of reflectors and can be related to the presence of discontinuities like stones or compacted soil.
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Bottom right : bar plot of V 1 solid gray bar and V 2 solid black bar resistivity average values and relative standard error bars of the three geophysical taxa D, C, I. This range of values can be attributed to different soil features Samouelian et al. The main electromagnetic anomalies are marked by capital letters while the black arrows indicate the travertine bank. The high potential of geophysical survey in agriculture has been now recognized; over the last decade geophysical sensors based on the nondestructive measurement of soil electrical conductivity or its inverse resistivity have been extensively used in precision agriculture, alone or coupled with terrain information, to help delineating uniform management zones Peralta et al.
Using such techniques, we are able to visualize soil features related to their electrical behavior; as current flux in soil is mostly electrolytic, resistivity is very sensitive to the two components that are mainly involved in charge transfer: the degree of pore water saturation and salinity Lesch and the specific surfaces associated to the presence of clay particles Tabbagh et al.
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Resistivity is even sensitive to the microstructure of clays, based on lab measurements of worldwide collected clay samples; a first database of clays resistivity was compiled by Giao and coauthors Giao et al. A soil conductivity survey conducted across different soils showed strong and consistent correlations with clay Sudduth et al. This sensitivity is very useful in agricultural soil mapping, since many relevant properties are heavily influenced by and covariate with clay content, such as: water holding capacity, organic matter content, soil structure, temperature, and cation exchange capacity.
For the opposite reason resistivity readings can also be used to localize resistive features, that act as barriers to current flux, such as gravel lenses Tetegan et al. This extraordinary sensitivity of the technique to the presence of insulating materials constituted the base for the use of the technique for imaging woody plant root system Amato et al. Plant roots are the key component of plant survivorship and ecology but at the same time are considered the most elusive aspect of belowground studies; this is mainly related to the lack of methodologies to study root systems at the appropriate spatiotemporal scale without interfering with their growth and development Amato Quantitative research on the use of resistivity tomography for mapping root system spatial variability has shown that lignified coarse plant roots exhibit a strong electrical response, that rooted soil resistivity can increase several hundred Ohm meter Amato et al.
First research on herbaceous roots Amato et al. In some cases, soil texture can dominate the resistivity pattern overshadowing soil structure and water-related properties Banton et al. For a given texture, though, soil structural state variation, by altering the proportions between water and air filled porosity, can exert a strong effect on resistivity; this is at the base of the successful use of high resolution resistivity tomography for mapping soil alterations induced by tillage Besson et al.
Basso and coauthors found that resistivity mapping allowed to discern between tilled, freshly tilled, and untilled soils better than penetrometry.
vasibirthsub.cf Time lapsed resistivity tomography was later used to evaluate soil structural recovery after compaction Besson et al. Satriani et al. Repeated resistivity measures were also used to infer within-field spatiotemporal organization of soil water, discounting this way the effect of soil texture Besson et al.
Soil acidity and high cation exchange capacity contributed to high concentrations of Al KCl in the soil, whereas high base saturation and total C had the opposite effect. Across a pH H2O range of 3.
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Brown Soils and Podzols are likely more susceptible to Al toxicity, with the highest mean concentrations of Al KCl measured across all depth zones. Additional keywords: base saturation, cation exchange capacity, pH, soil order, total carbon, total nitrogen. Soil, land care and environmental research. Shopping Cart: empty. Search our journals.
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