Supplemental foliar potassium applications with or without a surfactant can enhance netted muskmelon quality

Netted muskmelon [Cucumis melo L. (Reticulatus Group)] fruit quality (ascorbic acid, beta-carotene, total free sugars, and soluble solids concentration (SSC)) is directly related to plant potassium (K) concentration during fruit growth and maturation. During reproductive development, soil K 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 muskmelon 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. This glasshouse study investigated the effects of two K sources: a glycine-complexed K (potassium metalosate, KM) and potassium chloride (KCl) (both containing 800 mg K/L) with or without a non-ionic surfactant (Silwet L-77) on melon quality. Orange-flesh muskmelon 'Cruiser' was grown in a glasshouse and fertilized throughout the study with soil-applied N-P-K fertilizer. Starting at 3 to 5 d after fruit set, and up to 3 to 5 d before fruit maturity at full slip, entire plants were sprayed weekly, including the fruit, with KM or KCl with or without a surfactant. Fruit from plants receiving supplemental foliar K had significantly higher K concentrations in the edible middle mesocarp fruit tissue compared to control untreated fruit. Fruit from treated plants were also firmer, both externally and internally, than those from non-treated control plants. Increased fruit tissue firmness was accompanied by higher tissue pressure potentials of K treated plants vs. control. In general, K treated fruit had significantly higher SSC, total sugars, total ascorbic acid, and beta-carotene than control fruit. Fall-grown fruit generally had higher SSC, total sugars, total ascorbic acid and beta-carotene concentrations than spring-grown fruit regardless of K treatment. The effects of surfactant were not consistent but in general, addition of a surfactant tended to affect higher SSC and beta-carotene concentrations.