Growth and Nutrition of Two Cultivars of Zinnia elegans Under Saline Conditions

Abstract

Zinnia elegans, because of its economic value and the hardiness of its wild relatives, was selected as a potential salt-tolerant cut flower crop to grow in greenhouse systems using recycled agricultural wastewater. Using recycled wastewater for irrigation of cut flowers provides an alternative to high-quality water. This is especially important in coastal and inland growing regions of California where competition for high-quality water is increasing between urban and agricultural users and provides economic and environmental benefits because groundwater contamination is reduced or even prevented. A completely randomized design was used to determine the effects of water ionic composition and salinity on the growth and leaf mineral composition of Zinnia elegans. Two cultivars (Benary's Giant Salmon Rose and Benary's Giant Golden Yellow) were grown under irrigation with two different water ionic compositions mimicking dilutions of sea water (SWD) and concentrations of Colorado River water (CRW) at increasing salinity levels with electrical conductivities of 2.5 (control), 4.0, 6.0, 8.0, and 10.0 dS·m−1 in greenhouse sand tanks in Riverside, CA. Leaf mineral concentrations were determined for calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), chlorine (Cl), total sulfur (S), and total phosphorus (P). At harvest, final plant measurements included time to flowering, stem length, stem diameter (recorded at the soil line), internode length (recorded at the middle of the stem), inflorescence diameter, ray length, plant shoot fresh weight, number of leaves per plant, and number of shoots per plant. For both cultivars, plant tissue concentrations of Mg, Cl, Na, and total S increased as salinity increased in the irrigation water. Conversely, plant tissue concentrations of Ca, K, and total P decreased as salinity increased in the irrigation water. Both cultivars demonstrated high selectivity for K over Na as salinity increased in CRW and SWD with ‘Golden Yellow’ demonstrating a higher selectivity than ‘Salmon Rose’. Additionally, measured growth parameters tended to decrease as salinity increased in both irrigation water types for both cultivars. Stem lengths of 79 cm and 51 cm were found for ‘Salmon Rose' growing in 10 dS·m−1 in concentrations of CRW and SWD, respectively. ‘Golden Yellow' produced stem lengths of 74 cm and 46 cm in 10 dS·m−1 in response to concentrations of CRW and SWD, respectively. Inflorescence diameters of both cultivars approximated 8.0 cm at the highest salinity for both water types. Although significant differences were found, the minimum of 46 cm indicates that marketable flowers can be produced using both water types at least as high as 10 dS·m−1.