Physiological responses of almond trees under regulated deficit irrigation using saline and desalinated reclaimed water

Regulated deficit irrigation (RDI) strategy using reclaimed water (RW) is becoming a common procedure in some Mediterranean regions. Full and regulated deficit irrigation were combined with desalinated (EC 1 dS m) and saline (EC 3 dS m) reclaimed water to irrigate young potted almond trees over a 3-year period. The full irrigation treatments received 130% of the crop evapotranspiration (ET) and the RDI treatments received 80% of ET during the kernel filling. Trunk diameter decreased in both RDI treatments at the end of the experimental period, although this response was more marked in the trees irrigated with saline RW. There were negative relationships between shoot growth and leaf Na and Cl contents in the saline treated trees, in which the accumulation of salts in leaves was associated with osmotic adjustment, which was responsible for maintaining midday leaf turgor. Plant water status, measured by the leaf and water potential, decreased in almond exposed to water deficit or irrigated with saline RW, indicating a slight dehydration in these plants due to the difficulty in water uptake from the substrate. Trees subjected to both deficit irrigation treatments showed lower stomatal conductance values than full irrigated treatments during the RDI period. However, at the end of experimental period, the lowest P values were found in plants irrigated with saline RW, especially in trees irrigated with saline RW combined with RDI strategy, verifying the relevance of duration of exposure to the stress. Saline and desalinated RW can be successfully used for irrigating almond trees, which might be of great economic and competitive significance for agriculture, but further research focused on a longer term should be carried out since detrimental effects might appear. Deficit irrigation combined with saline RW in P. dulcis is not recommended since it intensifies the negative effects of water and salt stress applied individually.

This work was supported by the EU and WATER JPI for funding, in the frame of the collaborative international Consortium DESERT, financed under the ERA-NET WaterWorks 2014 Cofunded Call. This ERA-NET is an integral part of the 2015 Joint Activities developed by the Water Challenges for a Changing World Joint Programme Initiative (Water JPI), and “Fondo di Sviluppo e Coesione” 2007e2013 e APQ Ricerca Regione Puglia “Programma regionale a sostegno della specializzazione intelligente e della sostenibilita sociale ed ambientale e FutureInResearch”. SA acknowledges the financial support for the Spanish Ministry of Science, Innovation and Universities within the José Castillejo Program (CAS19/00396). CRT acknowledges the financial support for a postdoctoral training and development fellowship (20363/PD/17) of Consejería de Empleo, Universidades y Empresa (CARM), through the Fundación Séneca – Agencia de Ciencia y Tecnología de la Región de Murcia and for a contract Juan de la Cierva-Incorporación (JC2019-040871-I) of the Spanish Research Agency of the Ministry of Science and Innovation.