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Title: Growth and ion distribution is affected by irrigation with saline water in selected landscape species grown in two consecutive growing seasons: Spring - Summer and Fall – Winter

Author
item VALDEZ-AGUILAR, LUIS - National Council Of Science And Technology (CONACYT)
item Grieve, Catherine
item RAZAK-MAHAR, ABDUL - Shah Abdul Latif University
item MCGRIFFEN, MILTON - University Of California
item MERHAUT, DONALD - University Of California

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2011
Publication Date: 4/1/2011
Citation: Valdez-Aguilar, L.A., Grieve, C.M., Razak-Mahar, A., Mcgriffen, M.E., Merhaut, D.J. 2011. Growth and ion distribution is affected by irrigation with saline water in selected landscape species grown in two consecutive growing seasons: Spring - Summer and Fall – Winter. HortScience. 46(4):632-642.

Interpretive Summary: Competition between agricultural, industrial and domestic users for high-quality water resources has increased as the population grows. Irrigation of urban landscapes in western U. S. cities, for example, consumes up to 50% of the total municipal water used during the spring to fall season. One environmentally-sound approach to the conservation of our dwindling supplies of good quality water is the reuse of degraded, often saline, wastewaters. However, reclaimed waters generally contain soluble salts and ornamental plants irrigated with these waters often show salt-related reductions in plant height, number and size of branches, leaves and flowers. These shorter, smaller plants are perfectly acceptable for problem landscape sites, provided they remain attractive and that the leaves and flowers are undamaged (no yellowing or dead tissues). This report describes the response of five high-value landscape plants (boxwood, escallonia, juniper, hawthorn, and hibiscus) grown in the greenhouse and irrigated with saline waters. One experiment was conducted during the Spring-Summer season; electrical conductivities (EC) of the irrigation waters were 0.6, 2, 4, 6, and 8 dS/m. The second experiment was conducted over the Fall-Winter season with ECs of 0.6, 4, 6, 8, and 12 dS/m. Visual quality was monitored during the experiments and at final harvest fresh and dry weights of leaves, stems and roots were measured and plant tissues were prepared for mineral ion analysis. The species were ranked for salt tolerance based plant growth: hibiscus and juniper (highly tolerant), escallonia (moderately tolerant), hawthorn (moderately sensitive), boxwood (sensitive). Visual quality of the species followed the same pattern because the most salt tolerant plants sustained the least amount of injury due to irrigation with saline waters. The outcome of this greenhouse study will aid growers, extension specialists, landscape professionals, and gardeners in selecting ornamental species suitable for salt-affected sites.

Technical Abstract: Landscape irrigation is the second largest user of reclaimed water in industrialized countries; however its high concentration of soluble salts, especially Na+ and Cl-, may induce growth reduction and leaf necrosis or bronzing in ornamental species. The present study was conducted to determine the growth and quality responses and nutritional ion imbalances of selected landscape species during the container-production phase when subjected to irrigation with water of increasing NaCl+CaCl2 concentrations. Plants of boxwood (Buxus microphylla japonica), escallonia (Escallonia × exoniensis Fradesii), hawthorn (Raphiolepis indica × ‘Montic’), hibiscus (Hibiscus rosa-sinensis), and juniper (Juniperus C torulosa) were grown in a greenhouse in the Spring – Summer and in the Fall – Winter in separate experiments. Saline irrigation consisted of solutions with electrical conductivities (ECiw) of 0.6, 2, 4, 6, and 8 dS.m–1 in the Spring – Summer experiment and 0.6, 4, 6, 8, and 12 dS.m–1 in the Fall – Winter. Growth of the five species decreased when irrigated with saline waters. Leaf growth was highly sensitive to salinity and the average decrease in leaf dry weight was the criterion used to rank the tolerance of the species. In the Spring – Summer experiment the ranking was (higher tolerance to lower tolerance): juniper ~ boxwood > escallonia > hawthorn > hibiscus, whereas in Fall – Winter the ranking was: juniper~boxwood>hibiscus>escallonia>hawthorn. The species were ranked according to their visual attractiveness in the Spring – Summer experiment. The threshold ECiw at which visual attractiveness was affected gave the following ranking (higher to lower tolerance): hibiscus > juniper > escallonia > hawthorn > boxwood. Estimating the EC of drainage water from threshold ECiw, boxwood was classified as sensitive, hawthorn as moderately sensitive, escallonia as moderately tolerant, and hibiscus and juniper as highly tolerant. Tolerance of juniper was ascribed to Na+ and Cl- retention in the roots observed in both growing seasons and to the higher root biomass that allowed a higher accumulation of salts in this organ, preventing translocation to the leaves. Although boxwood exhibited acceptable tolerance in terms of growth, visual quality severely decreased; in contrast, growth of hibiscus was the most severely reduced but was rated as the most tolerant species in terms of visual quality. This opposite response may be due to an excellent capacity to compartmentalize salts in hibiscus whereas in boxwood this mechanism may be absent.