A Test Method to Evaluate Salt Tolerance of Ornamentals

Abstract

Because salts in irrigation water decrease plant growth, we wanted to develop a quick and easy method for evaluating salt tolerance that could be used in the greenhouse. Using plastic containers with lids, sea salt, and rooted cuttings, we monitored changes in plant quality, growth, and leaf water potential as electrical conductivity (EC) and sodium (Na) levels increased. In the first of two experiments, we compared sea hibiscus (Hibiscus tilliaceus) leaf water potential and plant quality in solutions with an EC of 0, 2.1, 4.2, 6.1, or 8.2 dS·m−1 (0, 240, 420, 610, or 1010 mg·L−1 Na). After 14 days, sea hibiscus quality in solutions with an EC of 6.1 or 8.2 dS·m−1 was less than plants in solutions of 0, 2.1, or 4.2 dS·m−1. There was no difference in quality among plants in 0, 2.1, or 4.2 dS·m−1 solutions. To test this method, in Expt. 2, we compared coleus (Coleus ×hybridus), copperleaf (Acalypha wilkesiana), ficus (Ficus benjamina), jasmine (Jasminium multiflorum), and plumbago (Plumbago auriculata) plant quality and growth in solutions with an EC of 0, 1.3, 2.1, 4.2, 5.6, or 6.1 dS·m−1 (0, 170, 240, 420, 520, or 610 mg·L−1 Na). Coleus quality declined at an EC greater than 1.3 dS·m−1, whereas jasmine and plumbago quality declined at an EC greater than 2.1 dS·m−1 Copperleaf and ficus declined at an EC greater than 4.2 dS·m−1. Plant response did vary with low to medium salt-tolerant plants tolerating at an EC up to 1.3 and 170 mg·L−1 Na, whereas plants with a greater salt tolerance tolerated at EC and Na values up to 4.2 dS·m−1 and 420 mg·m−1 Na, respectively. The use of this method benefits growers by determining upper EC and Na limits when faced with poor-quality water resulting from saltwater intrusion or when using reclaimed wastewater with greater EC and Na levels.