Water consumption, irrigation efficiency and nutritional value of Atriplex lentiformis grown on reverse osmosis brine in a desert irrigation district

Arid regions in southwestern U.S. are faced with increased water shortages with the possibility of compromised water quality. The use of impaired water resources, including saline water, for agriculture is a possibility. The halophyte forage shrub Atriplex lentiformis (quailbush) was irrigated over three growing seasons with brine (2.6–3.2 g L−1 total dissolved solids) from a reverse-osmosis water treatment plant in an agricultural district in Marana, Arizona, in the Sonoran Desert, U.S. The goal was to determine if a halophyte crop could be grown productively on saline irrigation water in a way that maximized yield yet minimized excess deep percolation of salt past the root zone. Our hypotheses for this project were: (1) A. lentiformis could consume water at or above the potential evapotranspiration rate (ETo) measured at an on-site meteorological stations; (2) need for a leaching fraction could be minimized due to the high salt tolerance of the crop; and (3) water could be presented on a constant schedule typical of the delivery from a desalination plant, with excess water presented in winter utilized in summer via the deep rooting systems of A. lentiformis. Three irrigation treatments were tested based on the potential evapotranspiration rate (ETo): (1) plots irrigated at ETo adjusted daily via an on-site micrometeorology station; (2) plots irrigated at 1.5 ETo adjusted daily; (3) plots irrigated at a constant rate throughout the year based on the mean of annual ETo. The plants produced 15–22 tons ha−1 year−1 of biomass and could be irrigated at the rate of ETo, ca. 2 m year−1 at this location. Drainage volumes ranged from no drainage in Treatment 1 to 12–14% of applied water in Treatments 2 and 3. It is concluded that irrigation of halophyte forage crops provide a viable strategy for extending water supplies and disposing of saline water in arid-zone irrigation districts.