Water relations and gas exchange in olive trees under regulated deficit irrigation and partial rootzone drying

Abstract

It is widely believed that partial root drying (PRD) reduces water losses by transpiration without affecting yield. However, experimental work carried out to date does not always support this hypothesis. In many cases a PRD treatment has been compared to a full irrigated treatment, so doubt remains on whether the observed benefits correspond to the switching of irrigation or just to PRD being a deficit irrigation treatment. In addition, not always a PRD treatment has been found advantageous as compared to a companion regulated deficit irrigation (RDI) treatment. In this work we have compared the response of mature 'Manzanilla' olive trees to a PRD and an RDI treatment in which about 50% of the crop evapotranspiration (ET c ) was supplied daily by localised irrigation. We alternated irrigation in the PRD treatment every 2 weeks in 2003 and every 3 weeks in 2004. Measurements of stem water potential (Y stem ), stomatal conductance (g s ) and net CO 2 assimilation rate (A) were made in trees of both treatments, as well as in trees irrigated to 100% of ET c (Control trees) and in Rain-fed trees. Sap flow was also measured in different conductive organs of trees under both PRD and RDI treatments, to evaluate the influence of alternating irrigation on root water uptake and tree water consumption. We found small and random differences in Y stem , g s and A, which gave no evidence of PRD causing a positive effect on the olive tree performance, as compared to RDI. Stomatal conductance decreased in PRD trees as compared to Control trees, but a similar decrease in g s was also recorded in the RDI trees. Sap flow measurements, which reflected water use throughout the irrigation period, also showed no evidence of g s being more reduced in PRD than in RDI trees. Daily water consumption was also similar in the trees of the deficit irrigation treatments, for most days, throughout the irrigation period. Alternating irrigation in PRD trees did not cause a change in either water taken up by main roots at each side of the trees, or in the sap flow of both trunk locations and main branches of each side. Results from this work, and from previous work conducted in this orchard, suggest that transpiration is restricted in trees under deficit irrigation, in which roots are left in drying soil when water is applied by localised irrigation, and that there is no need to alternate irrigation for achieving this effect.

Water Productivity and Fruit Quality in Deficit Drip Irrigated Citrus Orchards

“…Similarly, experiments with RDI have been successful in citrus (Domingo et al 1996;González-Altozano and Castel, 1999;Goldhamer and Salinas, 2000). Similar results were reported for almond , apple (Ebel et al, 1995), apricot (Ruiz-Sánchez et al, 2000), pear (Mitchell et al, 1989), pistachio (Goldhamer and Beede, 2004), wine grape vines (Bravdo and Naor, 1996;McCarthy et al, 2002), and olive (Moriana et al, 2003;Fernández et al, 2006). Accordingly, Fereres and Soriano (2007) published a comprehensive review on the use of deficit irrigation techniques to reduce water use in agriculture.…”

Review. Deficit irrigation in fruit trees and vines in Spain

“…However, in some fruit species, PRD has given similar results to those obtained with RDI, with no clear advantage of the former when the volumes of water applied in both methods were the same (Egea et al, 2010). Roots left in drying soil under localized irrigation system might be responsible for the reduction on transpiration and there is no need to alternate irrigation for achieving this effect (Fernández et al, 2006).…”

Comparison of irrigation scheduling strategies for achieving water use efficiency in highbush blueberry

“…Although there are a handful of studies in which negative results have been reported after applying PRD (Gu et al 2004;O'Connell & Goodwin 2004Neuhaus et al 2007), there are a greater number of studies that demonstrate successful application of the technique to grapes (Dry et al 1996;Loveys et al 1998;Stoll et al 2000;Chalmers et al 2004) and many other horticultural crops including apple (Leib et al 2006), pear (Kang et al 2002), mango (Spreer et al 2009), olive (Fernandez et al 2006), tomato (Tahi et al 2007) and raspberry (Grant et al 2004).…”