Irrigation with RO concentrate and brackish groundwater impacts pecan tree growth and physiology

Abstract

Water scarcity has become a salient problem in southern New Mexico. A combination of drought and a decrease in surface water for irrigation encouraged to search for other sources of water. Desalination of brackish groundwater (BGW) using reverse osmosis (RO) results in a highly salty water or RO concentrate. In this study, impacts of using BGW and RO concentrate for irrigating pecan trees inside a greenhouse were evaluated. The objective was to determine if pecan trees are suitable for irrigation with BGW and RO concentrate, and evaluate the possible effects on pecan growth and physiological parameters. For each of two growing seasons (2017 and 2018), three irrigation treatments of 0.8, 4.0 (BGW), and 8.0 ds/m (RO) were applied every 14 days for 8 months. Four-year-old pecan trees were planted in pots filled with sandy-loam soil. Response variables included plant height and diameter, as well as physiological data including photosynthetic rate, chlorophyll content, transpiration rate, stomatal conductance, stem water potential, and leaf ions concentrations. Net pecan growth was 2.75 cm less in RO concentrate irrigated pots than control by the end of the second season. Plants irrigated with RO had the lowest chlorophyll content (30.75) and the lowest stem water potential (-17.22 bar). Na+ and Cl− concentrations reached 0.056 and 0.027 meq/l in the leaf samples in RO irrigated pecans. All trees survived the first season but only 75 % of the pecan trees irrigated with BGW and 50 % of those irrigated with RO survived the two seasons of the experiment. This suggested that continuous long-term irrigation with BGW and RO concentrate is not suitable in arid areas and new irrigation scheduling protocols are needed for safe reuse of BGW and RO concentrate.