Growth and Salinity Tolerance of Zinnia Elegans When Irrigated with Wastewater From Two Distinct Growing Regions In California

Using recycled greenhouse effluents to irrigate salt-tolerant floral crops provides an economic and environmental benefit for growers.  Producers are able to reduce their direct use of high quality water for certain crops and simultaneously reduce or prevent groundwater contamination.  We selected Zinnia elegans as a potential salt-tolerant crop for use in a recycled greenhouse system based on the known hardiness of its wild relatives and because of its economic value to the floriculture industry.  Using a completely randomized design of three replicates with ten plants each, we exposed two Zinnia cultivars (Benary’s Giant Golden Yellow and Benary’s Giant Salmon Rose) to increasing irrigation water salinities with electrical conductivities (EC) of 2.0 (control), 4.0, 6.0, 8.0, and 10.0 dS m^-1, and two ionic water compositions that simulated dilutions of sea water (typical of well-waters or degraded waters in coastal growing regions) and concentrations of Colorado River water (typical of tailwaters present in the inland valley areas of Southern California).  We determined Na⁺, Cl^-, Mg²⁺, Ca²⁺, K⁺, total-P, and total-S concentrations in leaves.  Stem length, stem diameter, inflorescence diameter, ray length, plant weight, number of leaves, and time to flower were measured at harvest.  Ion and morphological data for each cultivar were analyzed with a two-way fixed-effects GLM ANOVA and a Tukey’s post-hoc procedure was used to determine differences between individual means.  Both cultivars showed similar trends with respect to ion accumulation in leaves as concentrations of Mg²⁺, Na⁺, Cl^- and total-S tended to increase and Ca²⁺, K⁺, and total-P tended to decrease as salinity of the irrigation water increased.  Significant two-way interactions were found for Mg²⁺ (P < 0.001), K⁺ (P < 0.0001), Cl^- (P < 0.01), total-P (P < 0.05), and total-S (P < 0.01) for “Salmon Rose”.  Significant two-way interactions were found for Mg²⁺ (P < 0.0001), K⁺ (P < 0.0001), Cl^- (P < 0.01), and total-S (P < 0.001) for “Golden Yellow”.  Morphological features of both cultivars decreased as salinity increased in the irrigation solutions for both water types.  A minimum stem length (45 cm) and inflorescence diameter (approximating 8 cm) were found at the highest salinity, indicating that marketable flowers can be produced with saline irrigation waters at least as high as 10 dS m^-1.