Comparison of EM38 and Syscal Pro measurements for soil mapping in an agroforestry system

Abstract: This study aimed to assess and compare the performance of EM38 (Geonics Limited) and Syscal-Pro (Iris instruments) EMI tools in soil spatial heterogeneity mapping. Mainly, the two tools were evaluated for their ability to explain the spatial variability of the soil resistivity, which strongly correlates with the soil’s physical status properties. Moreover, the effect of two surface soil roughness caused by two different tillage modalities has been studied.

The experimental plot (30 m width x 100 m length) consisted of an agroforestry system located in San Piero a Grado (Pisa, Italy, (, 43°41’07” N, 10°20’32” E).  Two 100-meters length deep open drains were located on the edges.  The soil texture is loam, with clay content values from 7.64% to 15.14% and sand content ranging from 22.36% to 49.37%. The intercropping system consisted of wheat (Triticum aestivum L) and pea (Pisum Sativum L) in the inner part of the field, and two rows of poplar (Populus x euramericana Dode Guiner) on the edges experimental plot.

Data were acquired before seed-bed preparation by pulling the two tools over the soil. For the Syscal-pro, 13 cylindrical stainless-steel electrodes were pulled by a tractor, allowing soil resistivity data acquisition according to the reciprocal Wenner-Schlumberger array (Telford, 1976). A total of five transects with 5 m spacing were spanned to the inner field zone, whereas four additional transects allowed to detail the resistivity gradients closed the two deep open drains.

Regarding the EM38 tool, a preliminary laboratory activity allowed the development of a specific data acquisition (DAQ) system for continuous monitoring of the resistivity data recording and spatializing. This DAQ system is based on a CR1000 Data logger (Campbell Scientific, United States), which allows collecting the speed and position of the EM-38 device by carrying it on a specifically designed sled system.

Two Garmin’s GPS (model 79S/SC for Syscal Pro and model GPS16X-HVS for the EM38) enabled georeferencing the collected data.

Preliminary results have shown a range of electrical conductivity values between 30 mS/m and 45 mS/m, spatially distributed according to the pattern obtained by Syscal-Pro. Further investigation is required to better understand the relationship between EM38 and Syscal-Pro measurements, after which the vertical domain explored has been standardised between the two methods.

Keywords: Agroforestry system, EM38, Syscal, soil bulk resistivity, soil bulk conductivity, spatial variability.