Soil salinity assessment using directed soil sampling from a geophysical survey with electromagnetic technology: a case study

Spatial characterization of soil salinity is required for establishing salt control measurements in irrigated agriculture. For that, cost-effective, specific, rapid, and reliable methodologies for determining soil salinity in-situ and processing those data are required. This paper shows the usefulness of an integrated methodology involving a hand-held electromagnetic sensor (Geonics EM38), and the ESAP (Electrical conductivity or salinity, Sampling, Assessment and Prediction) software package to assess, predict and map soil salinity at field scale. The salinity of a 1.74 ha plot of a surface-irrigated field of Navarre, northern Spain, was analyzed by reading the bulk soil electrical conductivity (ECa) with the EM38 sensor at 180 locations. At 20 of those sites, soil core samples were taken at 0.3 m intervals to a depth of 0.9 m, and electrical conductivity of the saturation extract (ECe), saturation percentage (SP) and water content (WC) were measured. Salinity was the dominant factor influencing the EM38 readings. The multiple linear regression (MLR) calibration model predicted ECe from EM38 readings with RI ranging from 0.38 to 0.90 for the multiple-depth profile. The ESAP software also provided field range average estimates of soil salinity. Eighty-one percent of the field had ECe values above 4 dS m(-1). The obtained salinity map was helpful to display the spatial patterns of soil salinity and identify sources/causes of salt loading.