Using geophysical monitoring methods (ERT and EMI) to delineate homogeneous management zones within agricultural fields

The improvement in crop yield, both in quantity and quality, depends on the adoption of appropriate management strategies for the agronomic and irrigation practices. In precision agriculture (PA), an accurate and high-resolution description of the spatial variability at the field scale of the environmental factors which affect the crop yield allows to optimize the management of the agricultural practices, by applying different amounts of agricultural inputs (i.e. water and nutrients) as a function of the spatial variability of those factors within the fields. Therefore, the use of monitoring methods with high spatial resolution is fundamental, not only to improve crop yield, but also for a more efficient use of resources (i.e. soil and water) and thus to increase the environmental sustainability of agricultural production. The techniques of geophysical prospecting, including electrical resistivity tomography (ERT), electromagnetic induction (EMI) surveys, and ground penetrating radar (GPR) are proximal sensing procedures with high spatial resolution for quick and non-invasive monitoring of the soil variability at the field scale. In recent decades, the geophysical methods have been increasingly used as a tool for the characterization of the spatial variability of soil properties and their zoning. In PA the delineation of homogeneous management zones based on the soil electrical resistivity measured with the geophysical techniques has become a common practice. The objective of this work is to compare the reliability of two different EMI sensors – the Geonics EM-38 and the GSSI EM-P400 (relatively new and still not widely used in PA) – in delineating the homogeneous management zones. The data of soil electrical resistivity were collected in an experimental site of about 4 ha in one campaign, in autumn after the harvest, when the soil moisture condition is near the field capacity. The soil zoning was carried out through the Management Zone Analyst software (by USDA). ERT data were simultaneously collected along two perpendicular transects, following the main directions of soil variability. The ERT sections were used to compare the response functions of the two different EMI sensors. The depths of exploration of EM-P400 seem to be greater than those of EM-38 nevertheless the zonation maps derived from the two EMI sensors are comparable.