Saturday, 15 July 2006

A New Approach of Soil Structure Characterization in Field Conditions Based on Soil Electrical Resistivity Measurements.

Guy Richard1, Arlene Besson2, Philippe Cosenza3, and Isabelle Cousin1. (1) INRA, Unite de Science du Sol d'Orleans, Domaine de Limere, Olivet, 45166, France, (2) geocarta, 16 rue du sentier, Paris, 75002, France, (3) UMR 7619 SISYPHE, case courrier 123, UPMC 4 place jussieu, Paris, 75252, France

Soil structure of agricultural fields is generally heterogeneous because the mechanical stresses applied to the soil during tillage and traffic do not affect the whole soil volume. Soil structure is usually characterized physically by destructive methods such as bulk density, penetration resistance or from the visual morphological description of a soil profile. Our research is aimed at analysing the possibilities of a non destructive method based on electrical resistivity measurement to describe the structure of a cultivated soil. Experiments have been conducted on a Haplic Luvisol developed on loess material. A laboratory investigation has first been carried out in order to study the resistivity changes induced by compaction (1.1 to 1.7 and water content changes (0.10 to 0.24 g.g-1). Electrical resistivity depended significantly on the physical state of the soil (from 20 up to 120 Ohm.m). Resistivity decreased with the increase of density. The lower the water content the more important the resistivity decreased. Comparison with petrophysical data leads to better identify the impact of compaction on the water saturation degree of the microporosity and that of the macroporosity. Electrical resistivity also increased with the ionic strength but this effect was masked by the bulk density. The soil electrical resistivity was then measured in the field with 2D Wenner configuration using an inter-electrode spacing of 0.015 m along a 3.20 m transect. Comparisons between inverted electrical resistivity maps and visual morphological descriptions showed the ability of electrical resistivity to detect wheels tracks. Interpretation of electrical surveying in a heterogeneous field after ploughing was more difficult and probably needs 3D investigation.

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