Secondary treated wastewater as a valuable and safe source for drip irrigating tree crops

Wastewater represents a support source for irrigation and mineral nutrients supply in agricultural systems, offering agronomical and environmental advantages. This work investigates the effect of STW (secondary treated wastewater) irrigation on apple and nectarine crops. Physiological, nutritional status and contaminants accumulation in vegetative and reproductive organs were assessed based on the different physiological traits of the two species. Trees were grown, for two consecutive seasons, in pots and drip irrigated with: Tap water (TW), Tap water plus an addition of mineral fertilizer (TW+MF) and Secondary treated wastewater (STW). Furthermore a laboratory trial was carried out to asses two E.coli strains internalization on young GF 677 micropropagated plants. Regarding the pots trial, apple and nectarine tree physiological, vegetative and fruit growth/quality parameters were in most of the cases promoted by STW, compared to TW trees, although TW+MF trees showed the highest values. This response is related to the different amount of nutrients supplied to the trees. Although STW provided a “fertigation-like” effect, results suggest that it did not completely fulfil tree nutrient demand. Treatments affected mainly leaf rather than fruit mineral concentration, with concentrations mostly in the optimal range for all treatments, except the TW, which showed nutritional deficiencies. STW irrigation improved nectarine fruit growth rate and influenced positively apple fruit quality parameters. Heavy metal concentration was unaffected by STW-irrigation with concentrations in fruit tissues within international limits imposed for human consumption in both species. No E.coli and few total coliforms were detected in the vegetative and reproductive tissue of both species. As for the laboratory trial, E.coli strains was able to enter roots but without any translocation in the areal part of the plant, not representing a hazard for human health. The overall results indicate STW as a convenient and safe source for drip irrigating tree crops.