Is a Systematic Two-Dimensional EMI Soil Survey Always Relevant for Vineyard Production Management? A Test on Two Pedologically Contrasting Mediterranean Vineyards

Abstract

Thanks to recent technological developments, apparent soil electrical conductivity (EC_a) can now be mapped over large areas, providing new data for precision agriculture. However, in Mediterranean vineyards, rooting depth can be greater than usual and the volume of soil that needs to be explored is greater. This study examined two vineyard blocks in southern France and looked at the ability of an EC_a map, derived from a commercial mobile EMI system, to predict water-related vineyard variability [defined by variation in a normalised difference vegetation index (NDVI) map of the canopy]. To validate the EC_a–canopy relationship, electrical resistivity tomography (ERT) profiles and soil observations (42 soil cores sampled to 4 m depth) were made over seven representative transects across the two blocks. In one of the blocks, the EC_a map and the NDVI map were correlated, whereas only weak correlations were found for the other block. The examination of ERT data and soil observations in the first block showed a clear relation between soil electrical properties and soil properties known to influence vine water supply (e.g. bedrock depth) and a good discrimination of ERT measures at the measurement depth explored by EM38. In contrast, the second block showed lower ERT measurements and they were not directly related to any soil property that could cause variations in plant water. The contrasting responses between the two blocks demonstrate, as a prerequisite to EC_a survey, the importance of prior and local knowledge of soil patterns.