Complementary irrigation with saline water and soil organic amendments modified soil salinity, leaf Na⁺, productivity and oil phenols of olive trees (cv. Chemlali) grown under semiarid conditions

Compost, olive mill wastewater and legume cover crops combined with complementary irrigation by saline water were tested under field conditions during 2016 and 2017 cropping seasons ('Off' and 'On' years respectively), in an organic mature olive grove cv Chemlali, grown at a density of 100 trees. ha(-1). The experiment was conducted with four agronomic practices (TC-no amendment; TP-olive trees amended with compost, TM-olive trees amended with olive mill wastewater and TL-olive trees intercropped with legumes) factorially combined with two irrigation treatments (NI: non-irrigated olive trees and IR: olive trees irrigated with saline water of 4 g.l(-1)). The complementary irrigation by a limited quantity of saline water (4 m(3).tree(-1) per season) applied during the fruit growth (May-September) increased significantly the soil water content (SWC) mainly in the plot amended with compost. In both irrigated and rain-fed plots, the soil electrical conductivity (SEC) increased significantly during the dry season mainly in the control and the plot amended with olive mill wastewater (OMWW). Under rain-fed conditions, leaf sodium contents decreased by about 30 and 50%, respectively in olive trees amended by compost and those intercropped with legumes. Complementary irrigation with saline water increased leaf sodium levels in all plots, mainly in trees amended with OMWW, by about 40% compared to those of OMWW plot grown under rain-fed conditions. The level of leaf nitrogen increased by the application of both soil organic amendments and irrigation, while leaf phosphorus level was only affected by irrigation salinity, except for trees intercropped with legumes. Shoot growth, oil yield and fruit pomological characteristics were significantly improved either by the soil organic amendments or by the complementary irrigation. Nevertheless, phenol contents in fruits and in olive oil were significantly affected by compost and irrigation with saline water. Intercropping olive trees with legumes enhanced phenol contents in fruits and olive oil.