Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2006
Publication Date: 1/22/2007
Citation: Lester, G.E. Jifon, J.L. 2007. Foliar applied potassium: Effects on cantaloupe quality. Acta Horticulturae. 731:115-120. Interpretive Summary: Supplementing soil K with foliar K applications during muskmelon fruit development and maturation improved fruit quality by increasing firmness, sugar content, ascorbic acid, and beta-carotene levels. Differences between the two K sources (an organic form glycine-complexed K or an inorganic form KC1) were minimal and use of a surfactant tended to have a positive effect on the supplemental foliar K applications. These quality improvements were obtained by implementing a simple management tool (foliar applied K using generally available K compounds plus a surfactant) that growers the world over can adopt.
Technical Abstract: Cantaloupe [Cucumis melo L. (Reticulatus Group)] fruit quality (ascorbic acid, beta-carotene, total free sugars, and soluble solids concentration (SSC) are directly related to plant potassium (K) concentration during fruit growth and maturation. During fruiting, soil fertilization alone is often inadequate due to poor root uptake and competitive uptake inhibition from calcium and magnesium. Foliar applications of glycine-complexed K during cantaloupe fruit development has been shown to improve fruit quality, however, the influence of organic-complexed K vs. an inorganic salt form has not been determined. In this study, the effects of two K sources; glycine-complexed K vs. KC1 (with or without a surfactant), were studied following application of the K sources during the fruit growth and maturation period of glasshouse grown orange-flesh cantaloupe ‘Cruiser’. Plants were fertilized throughout the study with soil-applied N-P-K fertilizer. Flowers were hand pollinated and only one fruit per plant was allowed to develop. Starting at 3 to 5 d after fruit set, and up to 3 to 5 d prior to fruit maturity (i.e. full slip), entire plants were sprayed weekly, including the fruit, with a glycine-complexed potassium (Potassium Metalosate, 24% K diluted to 4.0 mL L-1) or KC1, (24% K diluted to 4.0 mL L-1) with or without a surfactant. Fruit from plants receiving supplemental foliar K were firmer, both externally and internally, than those from non-treated control plants. This increase in firmness is related to a more positive pressure potential in fruit from plants receiving supplemental K vs. control. In general, all K treated fruit had significantly higher SSC, total sugars, total ascorbic acid, and beta-carotene contents than control fruit. Autumn vs. spring grown fruit, regardless of treatment, had higher SSC, total sugars, total ascorbic acid, and beta-carotene contents. There were no consistent differences among the K sources (with or without surfactant) on these fruit quality parameters, however, addition of a surfactant tended to increase SSC and beta-carotene in some instances.