On-the-go resistivity sensors employment to support soil survey for precision viticulture

There is an increasing need in agriculture to adopt site-specific management (precision farming) because of economic and environmental pressures. Geophysical on-the-go sensors, such as the ARP (Automatic Resistivity Profiling) system, can effectively support soil survey by optimizing sampling density according to the spatial variability of apparent electrical resistivity (ER).
The aim of this work was to test the sensitivity of the ARP methodology in supporting soil survey for precision viticulture. In particular, an optimization procedure for coupled geoelectrical and soil surveys is illustrated.
The research was carried out in a vineyard located in Tuscany (central Italy) affected by low yield due to soil salinity; the investigation was simultaneously conducted by soil survey and resistivity measurements. The ARP method consists in the electric current injection into the ground and in the continuous measure of the resulting potential, simultaneously providing three georeferenced values of ER related to 50, 100 and 170 cm depths for each point.
Forty-nine soil samples were taken at 10-30 cm depth and analyzed for moisture, particle size distribution and electrical conductivity. The best correlation (R2 = 0.609; P <0.01) was obtained between clay content and ER referred to the 0-50 cm depth (ER50).
The evaluation of the density reduction effect for both ARP and soil survey was expressed in terms of ER50 and clay predictability. Doubling the ARP swaths width (12 m) the ER50 accuracy was substantially in agreement with that obtained for the highest ARP survey density (22 swaths 6 m spaced); the further width doubling (24 m) provided a moderate accuracy. With regard to clay content prediction k accuracy values ranged between 0.87 and 0.49 for the 22 swaths/25 soil samples and 10 swaths/12 soil samples combination, respectively.