Mapping impaired olive tree development using electromagnetic induction surveys

Background and aims: Future success of olive cropping in the Mediterranean depends critically on improving yield, reducing production costs, and preventing infestation by soil-borne pathogens. In order to put forward adequate soil management practices accurate knowledge of the spatial distribution of soil properties is required. The aims of this study were to delimit areas with constrained tree development in an olive orchard using electromagnetic induction (EMI), and to identify the causal relationships between apparent electrical conductivity (ECa) and soil properties. Methods: The experimental field was exhaustively sampled for different soil properties and ECa was measured in 2011 and 2012 under dry and wetter soil conditions, respectively. Results: The spatial ECa distribution matched the observed canopy coverage pattern well. Three zones were delimited according to ECa values from 0 to 27.5, from 27.5 to 57.5, and greater than 57.5 mS m−1. All ECa signals, regardless of soil-water status, exhibited a common dominant ECa pattern. The area with the lowest ECa values (0–27.5 mS m−1) showed optimal tree growth (45 % canopy coverage) and presented significantly lower average clay contents than the other two areas. Intermediate ECa values (27.5–57.5 mS m−1) identified accurately the area with deficient tree development and tree die-off (12 % canopy coverage), and corresponded with an area along the drainage pathway where profile-averaged soil-water, clay, stone and organic matter content were highest. Conclusions: EMI surveys detected subtle differences in soil properties and provided useful information to delimit areas with constrained tree development. The approach can be used as a screening technique before installing tree plantations.