Effect of Irrigation with Reclaimed Wastewater on Soil Properties and Olive Oil Quality

Abstract

A number of Mediterranean countries have experienced severe imbalances of water supply and demand. Due to water scarcity, Jordan has very limited fresh water resources and the demand on water is ever increasing. Reclaimed wastewater is considered one of the alternative sources of irrigation water in these countries. A two consecutive year monitoring study was conducted in 2002 and 2003 to evaluate the effect of reclaimed wastewater (from Al-Samra Treatment Plant (STP)) on soil chemical properties, leaf mineral composition and olive oil quality. A reference olive orchard irrigated with fresh water of comparable age located near the STP was chosen for this comparative study using the local olive cultivar ‘Nabali Baladi’ in both locations. Soil, water, olive leaves, fruits and olive oil samples were analyzed according to standard methods. Irrigation with reclaimed wastewater significantly increases K and P concentrations in the soil of the STP olive orchard as compared to the reference orchard; while irrigation water indicated no significant differences in pH values between the two sources of irrigation water. Water salinity and Na+ were much higher in reclaimed wastewater as compared to fresh water. However, Cl-, SO42- and heavy metal concentration remain within the standard limits in both water sources except for Mo which exceeds the standard limit. Olive leaf tissue showed higher N, P and K concentrations from orchard irrigated with reclaimed wastewater. However, Fe and Mn concentrations were higher in olive leaves from the reference orchard. Results also showed no trend of increasing heavy metal concentrations in the leaves of olive trees in both orchards. Percent of olive oil content, expressed as dry matter, was significantly higher in fruits from the STP orchard as compared to the reference orchard. Olive oil quality parameters indicated no significant differences in moisture content, specific gravity, refractive index, free acidity and iodine value extracted from olive fruits at both locations. Trace elements (Fe, Cu) and heavy metals (Pb, Cd) in olive oil were below the detectable level for both olive orchards. This indicated that there was no residual effect of RWW irrigation on the concentrations of trace elements and heavy metals in olive leaves during the study period.