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Surface Electrical Resistivity Tomography: a non-invasive tool to assess the compaction in paddy soils
Get PDFS oil compaction has direct effects on soil physical properties (increase in soil strength, bulk
density, decrease in total porosity, soil aeration, water infiltration rate, and saturated hydraulic
conductivity) often reducing root penetration and plant growth, thereby causing a reduction of soil
productivity. However, the presence of compacted layers in rice paddy fields increases the
efficiency of the traditional flooding irrigation method. For this reason, the use of monitoring tools
to detect depth, thickness and lateral continuity of compacted soil layers in paddy fields is of
crucial importance for the assessment of their irrigation efficiency. Electrical Resistivity
Tomography (ERT) is a non-invasive geophysical method which allows to detect soil horizons with
different degrees of compaction. Particularly, arrays constituted of short electrodes spaced a few
centimeters can be used to investigate with high vertical resolution the soil profile.
In a sandy loam paddy field located in the Lomellina region (PV; RISTEC project, RDP-EU, Lombardy
Region), a surface ERT survey was conducted in February 2019 to verify the effectiveness of this
technique in assessing soil compaction. The ERT was carried out with Wenner arrays of 48
electrodes spaced 0.1 m along a 5 m transect, to investigate the soil profile up to about 1 m depth
in proximity of a soil profile trench dug for soil description and sampling. The results of the
traditional soil survey (accurate description of soil horizons, including the compacted layer) were
considered as reference data to evaluate the reliability of ERT results. During the ERT survey, soil
samples were collected at different depths and distances along the ERT transect: texture, bulk
density and porosity were successively measured in laboratory. Moreover, the volumetric soil
water content was measured with a probe (ML2 ThetaProbe, Delta-T Devices). Main results show
that the correlation between electrical resistivity (ER) and bulk density, soil porosity and volumetric
water content is well in line with those observed in recent studies. Data points in the scatter plots
are clustered based on the bulk density values; particularly, the cluster corresponding to high bulk
density values (i.e. compacted soil) includes the measurement points at the depth where the ERT
image shows a greater ER gradient. This depth also corresponds to the compacted layer observed
during the investigation of soil profile with traditional methods. These results confirm that
compacted layers can be effectively detected in ERT images by identifying depths characterized by
higher ER gradients in soils with a relatively homogeneous soil texture. Consequently, an integrated approach combining surface ERT and soil sampling with a hand auger at a few depths
to check the texture homogeneity and eventually collect a few soil samples for further analysis
(e.g., bulk density, volumetric water content, soil hydraulic conductivity) could be explored to
assess the presence and continuity of compacted layers in paddy soils, instead of intensive and
extremely invasive surveys
The LAUE project for broadband gamma-ray focusing lenses
Full text linkWe present the LAUE project devoted to develop an advanced technology for
building a high focal length Laue lens for soft gamma--ray astronomy (80-600
keV). The final goal is to develop a focusing optics that can improve the
current sensitivity in the above energy band by 2 orders of magnitude.Comment: 7 pages, 6 figures, presented at the SPIE conference on "Optics for
EUV, X-ray, and Gamma-ray Astronomy". To be published in the Proceedings of
SPIE, vol.8147, 201
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