Technical Abstract: Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit quality attributes such as sweetness, aroma, and texture are directly related to potassium (K)-mediated processes. However, during fruit growth and maturation, soil K supply alone is often inadequate to satisfy K requirements. Previous studies have demonstrated that supplemental foliar K applications can overcome this apparent deficiency, however, the suitability of potential K salts as foliar sources is still uncertain. In this study, we evaluated the effects of six foliar K sources (potassium chloride - KCl, potassium nitrate – KNO(3), monopotassium phosphate – MKP, potassium sulfate – K(2)SO(4), potassium thiosulfate - KTS , and a glycine amino acid-complexed K- Potassium Metalosate, KM) on fruit quality parameters of field-grown muskmelon ‘Cruiser’. Experiments were conducted during the spring of 2005 and 2006 at 2 locations (Weslaco and Santa Ana) in south Texas. Weekly foliar K applications were established starting at fruit set and continuing to fruit maturity. Leaf, stem, petiole, and fruit tissues from plots receiving supplemental foliar K treatments generally had higher K concentrations than those from control plots but this effect was not consistent among the K sources and between locations. Even though pre-plant soil K concentrations were very high, supplemental foliar K treatments resulted in generally higher K concentrations in plant tissues, suggesting that plant K uptake from the soil solution was not sufficient to saturate tissue K accumulation. Fruit from plots receiving supplemental foliar K generally had higher soluble solids concentrations (SSC), sugars, and the human wellness compounds - ascorbic acid and Beta-carotene than control fruit. However, this trend was more evident only at Weslaco and there were generally no consistent trends among K sources except for KNO(3) which tended to result in less firm fruit. Fruit yields were not affected by supplemental foliar K applications. These results generally support our previous controlled environment findings that supplementing soil K supply with foliar K applications during fruit development and maturation can improve muskmelon fruit quality by increasing firmness, sugars, ascorbic acid, and Beta-carotene contents. The current data also provide additional evidence of differences among potential foliar K sources, with KNO(3) consistently emerging as a less desirable source of K during fruit development and maturation.