Spinach biomass yield and physiological response to interactive salinity and water stress

Critical shortages of fresh water throughout arid regions are forcing growers to decide among the following options, applying insufficient fresh water, causing water stress, applying saline water causing salt stress or applying some combination minimizing saline water application, causing combined water and salt stress. A comprehensive approach to manage drought and salinity is to evaluate the impact of water stress and salt stress individually and then examine their interactions on plant production. To analyze salinity and water stress responses and their interaction together on spinach growth, an experiment was conducted from April 1 to May 21, 2013, using 6 different irrigation waters at electrical conductivity (EC): 0.85, 4, 7, 9, 12, 15dSm−1. Soil moisture was recorded by sensors and stress treatments had the following soil water matric pressure control (−45kPa), −200 to −300kPa, and −400 to −500kPa. We evaluated three replicates per treatment for yield, vegetative parameters, ion composition, and physiological parameters. The results showed that the spinach yield response to salt and water stress was very different. Spinach yield initially increased with salinity and subsequently decreased only when the irrigation water was EC 9dSm−1and above (osmotic pressure of −310kPa). In contrast, yield decreased at the first water stress level (−230kPa) relative to control. The additional presence of salinity stress decreased the relative yield response due to water stress. Similarly under water stress the relative yield response to increasing salinity was reduced. Although no model provided good prediction of stress response, the best predictive model (relative error) was one that considered the response to multiple stresses as the product of the response to the individual stresses.