Growth and nutrition of two cultivars of zinnia elegans under saline conditions

Authors: CARTER, CHRISTY - Tennessee Technological University; Grieve, Catherine

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2010
Publication Date: 7/1/2010
Citation: Carter, C.T., Grieve, C.M. 2010. Growth and nutrition of two cultivars of zinnia elegans under saline conditions. HortScience. 45(7):1058-1063.

Interpretive Summary: Uncertainties concerning the allocation and dependability of good quality water have led to increased interest in the use alternative, non-potable waters for irrigated agriculture. Treated urban effluents, runoff from greenhouse operations, agricultural drainage waters, or naturally-occurring low quality waters are abundant in many arid or semiarid areas. All of these available waters are salty. Reuse of these waters for production of floricultural crops, therefore, requires an understanding of how plants response to the stress imposed by salts in the irrigation waters. Such an understanding will allow growers to match specific crops to available water qualities, and further, to institute management practices to sustain quality of the flowering stems. This report describes the response of zinnia, a commercially valuable cut flower, to irrigation with waters prepared to simulate saline wastewaters found in two areas of southern California: (1) the inland Coachella and Imperial Valleys where saline run-off waters are available, and (2) the coastal areas where seawater intrusion is a problem. Two zinnia varieties, Salmon Rose and Golden Yellow, were grown in greenhouse sand tanks. Five salinity levels of each water composition were imposed with electrical conductivities (EC) of 2, 4, 6, 8, and 10 dS/m. Neither variety showed visible signs or injury associated with salinity. Flower quality was rated on stem length and weight, stem and flower diameter. Marketable flowering stems were produced in all treatments. The results of this study clearly demonstrate that zinnias may be produced under irrigation with waters as saline as 10 dS/m without reduction of commercial acceptability. Growers, extension specialists, research scientists, landscape professionals and home gardeners will find this information valuable in managing salinity in recycled irrigation waters.

Technical Abstract: Zinnia elegans, because of its economic value and the hardiness of its wild relatives, was selected for its potential as a 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, 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 (EC) of 2.5 (control), 4.0, 6.0, 8.0, and 10.0 dS•m-1 in greenhouse sand tanks in Riverside, California. Leaf mineral concentrations were determined for Ca, Mg, Na, K, Cl, total-S, and total-P. At harvest, final plant measurements included time to flowering, stem length, stem diameter, internode length, flower diameter, ray length, plant weight, number of leaves, and number of shoots. For each measurement, a two-way ANOVA was performed on replicates of tank means based on 15 individuals per cultivar per tank. If differences were found, a Tukey’s post-hoc procedure was used to determine differences between individual means. For both cultivars, Mg, Cl, Na, and total-S showed general increases in concentration in plant tissues as salinity increased in the irrigation water. Conversely, Ca, K, and total-P decreased in concentration in plant tissues as salinity increased in the irrigation water. Additionally, 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 approximated 8.0 cm at the highest salinity for both water types in both cultivars. Even though significant statistical differences were found and different water compositions influenced stem length, 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.