Long-Term effect of irrigation with saline reclaimed water on adult Mandarin trees

The progressive increasing pressure on water resources to satisfy, among others, the global population food requirements, has fostered the utilization of other non-conventional water resources, such as reclaimed water (RW). Although RW has usually been viewed as a way of disposing of water (mainly due to its high salt concentration), it is of note that it might also bring agronomic benefits for crops (organic matter and essential nutrients). Most studies have evaluated the effects of using saline RW on the short-Term (three seasons or less), and hence there are no experimental results beyond this point. Consequently, in this work we evaluated the sustainability of using saline RW to irrigate adult Mandarin trees over six consecutive seasons (from 2008 to 2013). The experiment was carried out in a 0.5-ha orchard with 9-year-old Mandarin trees. Two irrigation treatments were performed: 1) fresh water (FW) with an electrical conductivity (EC) of 1.4 dS m-1; and 2) reclaimed water (RW) from a nearby wastewater treatment plant with an EC of 3.4 dS m-1. The effects of both treatments were evaluated in base of the soil water content, tree water status, phytotoxic elements in leaves, fruit yield and water productivity. Throughout the experiment, RW showed higher concentration of NO3-, PO43-, SO42-, Cl-, K, B and Na than FW. Both treatments maintained soil water content near field capacity (¿240 mm m-1) and reached similar stem water potential values (from -0.8 to -1 MPa), which indicated the good plant water status. Only B showed a significant increase in leaf concentration in RW treatment throughout the years. RW led to notable reductions of yield and water productivity from the third season.