Effect of Alternating Well Water with Treated Wastewater Irrigation on Soil and Koroneiki Olive Trees

The use of treated wastewater (TWW) in irrigation has a positive impact by bringing fertilizers and organics. However, increases in the soil’s sodium adsorption ratio (SAR) creates a barrier to long-term TWW irrigation. Alternating well water with wastewater irrigation is one practical solution that could be used to address the problem. This work aims to study the effect of alternating two years of well water with two years of treated wastewater irrigation on the soil characteristics of a Koroneiki olive tree mesocosm. Urban and agri-food wastewater treated using various technologies, such as lagooning, activated sludge, multi-soil-layering, and constructed wetlands, were used for irrigation. The results showed that an increase in salinity (SAR and ESP) in soil and olive tree leaves are the main negative effects of continuous irrigation with TWW on soil and tree performance. Several chemical and biochemical parameters, such as SAR and Na concentration, demonstrated that alternating well water with treated wastewater irrigation can reverse these negative effects. This recovery effect occurs in a relatively short period of time, implying that such a management practice is viable. However, long-term well water application reduces soil fertility due to the leaching of organics and exchangeable ions.