Long-Term Physiological and Agronomic Responses of Citrus Irrigated With Saline Reclaimed Water

Abstract As a result of problems arising from water scarcity in many semiarid and arid regions, the use of reclaimed water (RW) for irrigation has gained importance during the last two decades due to the progressive implementation of the European Waste Water Directive (91/271/EEC) together with environmental concerns about the volume of treated sewage water in wastewater treatment plants. In this sense, RW has a great potential to become a valuable irrigation water source because it is free of charge and contains high amounts of organic matter and many nutrients essential for plant growth, which might reduce fertilizer application rates. However, the use of RW may have risks for agriculture since it often has a concentration of salts from domestic and industrial activities higher than that found in natural water resources. This salinity is especially a problem for citrus, as this species is sensitive to salt. High levels of chloride and boron can cause phytotoxic effects on citrus growth and reduce productivity, contributing to the yellowing and defoliation of trees. In the literature there are few studies addressing the effects of treated wastewater on citrus yield and quality, most of them either used RW with low electrical conductivity (EC) (below harmful thresholds for citrus trees) or reported the effect of reusing saline RW in the short term (experiments from several weeks up to about three seasons). This chapter will summarize the main results obtained by different authors on this topic. As a case study, we will show the effects of saline RW (EC ∼3 dS m −1 ) on plant physiology, yield, and water productivity in a commercial orchard of mandarin and grapefruit located in the region of Murcia, Spain.