Electromagnetic induction: a support tool for the evaluation of soil CO2 emissions and soil organic carbon content in olive orchards under semi-arid conditions

Electromagnetic Induction (EMI), a non-invasive geophysical technique, can be a useful tool to study soil distribution of physical–chemical characters that strongly influence total soil respiration. Soil respiration emission flux (FCO2) was followed in an orchard (0.7 ha) with olive trees placed at irregular distances. FCO2 was measured in four different days at 6:00 and 15:00 h. Correlations between soil respiration and soil apparent electrical conductivity (ECa), measured by the EMI technique, were assessed. Statistically significant linear relationships were found between ECa, measured at 7 kHz, and FCO2 (R2 N 0.6). The strong relations found between daily FCO2 and ECa values allowed to spatialize soil respiration rate at field scale. The EMI technique combined with the statistical software called ESAP (Electrical conductivity Sampling, Assessment, and Prediction) seemed to be a very efficient tool to choose representative soil sites within the field onwhere to measure FCO2. The EMI/ESAP procedure was also compared with two soil sampling procedures, Joint Research Centre European Method (JRC-EU) and regular grid sampling, in order to estimate average soil organic carbon (SOC) value within the olive orchard. Results suggested that the above mentioned approach could be an interesting solution to reduce number of samplings and their cost reaching, in the meantime, reliable assessments of FCO2 and SOC at field scale