Can Irrigation Remediation Measures Enhance Avocado Root Performance Following Long-term Irrigation with Treated Wastewater?

Long-term irrigation with treated wastewater (TWW) in clay soils reduces Avocado orchard performance. This may be due to negative impacts of TWW on the rhizosphere that interfere with root growth and resource acquisition. The objective of this study is to evaluate the effects of water quality and remediation measures on root growth and performance of avocado trees planted in clay soil following long-term irrigation with TWW. A field experiment was set up in Kibbutz Yas’ur, the Western Galilee, Israel in 2016, including two control treatments of irrigation with freshwater (FW) and TWW and three remediation treatments irrigated with TWW: low-frequency irrigation (LFI), TWW diluted with FW 1:1, and improved aeration with Tuff trenches 30 cm deep and 30 cm wide, about 30 cm away from the trunk on both sides of the tree rows and filled with volcanic tuff. Root growth was monitored periodically using the mini-rhizotron technique and ingrowth cores. Additional measurements included tree circumferences and yield, a range of soil parameters, sap flow, and leaf physiology parameters. Mini-rhizotron measurements showed that the new root formation, and root length are highest in LFI and TWW as compared to other treatments at depths of 0-51.5 and 51.5-94.5 cm, respectively. Total root volume and surface area are highest in TWW and LFI at depths of 30-73 and 73-116 cm, respectively. Total root length, root surface area, root volume and specific root length in ingrowth cores were highest in FW. Thus, our initial results suggest that irrigation remediation measures can enhance root performance by creating a favorable rhizosphere environment due to better salt leaching and improved aeration. The ongoing study that covers soil physico-chemical properties, tree performance and root growth will improve our understanding and direct future remediation measures to reduce deleterious effects of TWW irrigation