Long-term irrigation with reclaimed wastewater: Implications on nutrient management, soil chemistry and olive (Olea europaea L.) performance

Utilization of reclaimed wastewater (RWW) presents an alternative to irrigation of agricultural crops with fresh water (Fr), especially in dry areas characterized by water scarcity. While RWW often contains considerable amounts of valuable plant nutrients, it is also typically characterized by high salt content, which can impair agricultural yields and have environmental repercussions. The objective of this study was to determine the effect of long-term utilization of RWW and fertilization practice on soil properties and plant performance. We evaluated irrigation and nutrient management of olives with RWW versus Fr in a long-term field experiment. Two olive cultivars (Bamea and Leccino) were subjected to irrigation with RWW, either with standard or reduced fertilization, and irrigation with Fr with standard fertilization. During the eight years of the experiment, considerable amounts of N, P and K were delivered with the RWW. Trees irrigated with RWW receiving no additional fertilization were not negatively impacted, indicating sufficient nutrient allocation by the RWW. Fruit yield was higher in RWW treatments compared to the Fr, probably due to the presence of P. In the autumn of each year, soil salinity was higher in the reclaimed wastewater compared to the fresh water treatment, but this did not lead to increased leaf Na or Cl concentrations or to reduced tree productivity. From an agronomic point of view, the lack of response to salinity implies that irrigation of olive with reclaimed wastewater is sustainable as long as precipitation ensures sufficient seasonal leaching of salts. However, sodium absorption ratio of the soil solution slowly and steadily increased in the reclaimed wastewater treatments resulting in a high exchangeable sodium percentage (14%) reaching nearly double that of the fresh water treatment. The latter observations highlight the likelihood for adverse effects of long-term irrigation with reclaimed wastewater on the deterioration of soil physical and chemical properties.