Long-terms effects of irrigation with treated municipal wastewater on soil, yield and olive oil quality

In Tunisia, water scarcity is one of the major constraints for agricultural activities. The reuse of treated wastewater (TWW) in agriculture can be a sustainable solution to face water scarcity. The research was conducted for a period of ten years in an olive orchard planted on a sandy–silty soil and subjected to two different irrigation treatments: (a) well water (WW) and (b) treated wastewater (TWW). The main aim of the present study was to investigate the influence of irrigation with TWW on soil chemical properties, olive tree yield and on virgin olive oil (VOO) quality during an heavy crop year (“on year”) in “Chemlali” olive orchard. Soil samples were collected at the beginning of the study (before irrigation), after five and ten years for each treatment. pH, electrical conductivity (EC), organic matter, major elements, salts and heavy metals contents in soil were investigated. Standard quality parameters, chlorophyll, β-carotene, total phenols (TP), induction time and total tocopherols such as α-,β-,γ-,δ-tocopherol of VOOs were also investigated. Results showed that irrigation with TWW increased soil pH, EC, OM, major elements, salts and heavy metals contents. Data obtained indicated that standard quality indices (free acidity, K232, and K270) of VOO and oil content were not affected significantly by water quality. Instead, chlorophyll, total phenols, induction time and δ-tocopherol values decreased significantly after ten years of irrigation with TWW. However, both fruit water content, and the concentrations of β-carotene and tocopherols (α, β and γ) in VOO increased.