Effects of irrigation with treated wastewater on olive tree growth, yield and leaf mineral elements at short term

In arid regions, such as Tunisia, the reuse of treated wastewater (TWW) in agriculture can be a sustainable solution for water scarcity. A two-year field experiment was conducted in order to investigate the short-term effects of TWW on olive growth, yield and concentration of total nitrogen (Nt), potassium (K), phosphorous (P), and heavy metals (i.e. Zn, Mn, Pb and Cd) in olive leaves. Olive trees were subjected to the following irrigation treatments: (i) trees irrigated with well water (WW) and (ii) trees irrigated with treated wastewater (TWW). For both treatments, the TWW and WW were applied at a rate of 4.5 m3 day−1 tree−1 (5000 m3 ha−1 year−1). After two years, non-significant injuries caused by salts and/or heavy metals were observed on shoot growth of trees irrigated with TWW. The application of TWW significantly increased concentration of Nt, P and K in the leaves, whereas heavy metals (Zn and Mn) showed a significant increase only after the second year of irrigation.

Research highlights▶ Our data showed that irrigation with TWW caused a limited vegetative growth retardation but a highly significant increase of the yield in both years. TWW worked as fertirrigation supplying N, P and K in large amounts. Finally, the application of TWW caused an increase of Mn and Zn in soil and leaves but within the usual range detected in plants.