Salt Tolerance Of Spinach As Related To Seasonal Climate.

Salt tolerance compilations are utilized to provide recommendations to growers affected by saline soils or waters. Differences among individual experiments are often large leading to uncertainty regarding suitability of specific crops under characterized salinity conditions. In addition to differences in possible varietal differences and experimental design (water composition) and initiation of imposition of saline treatments) climatatic and seasonal differences may also be important. We conducted three sets of experiments with spinach (Spinacia oleracea L., cv. Racoon) under saline water irrigation at different seasonal periods (December 2012- March 2013 and April- May 2013 and  late April- mid June 2013)) in sand tanks in U.S. Salinity Laboratory, Riverside. Our objective was to evaluate seasonal differences in plant salinity stress response as well as effect of water composition. Initial experiment were carried out using 6 different irrigation waters, two water types and three salinity levels (either sulfate dominated or chloride dominated) at EC: 4, 7, 9, dSm^-1. The second and third sets of experiments were conducted with 6 different irrigation waters (mixed salts) at EC: 0, 4, 7, 9, 12, 15 dSm^-1.  We evaluated the saline water irrigation on spinach yield and growth parameters together with photosynthesis, stomatal conductance, transpiration, and chlorophyll content under seasonal climate differences.

The result obtained from three different experiments shows that mild salinity levels improved plant growth and gas exchange parameters (except transpiration rate) and severe irrigation water salinity levels caused yield loss and decreased all gas exchange and vegetative parameters. Irrigation water salinity up to 9 dSm^-1 did not cause any yield loss in the first set of experiments, indicating that this cultivar is considerably more salt tolerant than spinach varieties reported in the literature.  The experiments under warmer conditions with higher ET₀ values caused higher yield loss at comparable salinity levels as compared to the early season experiments when ET₀ was lower. These results indicate that seasonal differences are important and thus must be considered when reporting and evaluating salt tolerance data.