Foliar Potassium Fertilization Effects on Muskmelon Fruit Quality

The contribution of inorganic fertilizers to crop productivity is well-established. Adequate nutrient supply with proper placement, timing, and application methods often results in enhanced nutrient use efficiency. Less well-studied, however, is the influence of fertilizers on retail quality and the nutritional and functional quality properties of foods, especially fruits and vegetables which are good sources of essential compounds (phytonutrients) that have been linked with  promotion of good health and wellbeing. Sugar content, aroma, appearance, and texture are key quality traits that influence consumer preference for many fruits and vegetables. These quality traits are directly related to potassium (K)-mediated processes. However, due to cultural practices, crop properties, and environmental factors, soil-derived K alone is seldom adequate to ensure the basic consumer quality standards. Controlled environment and field studies have shown that supplemental foliar K applications can overcome this apparent deficiency. However, considerable variation exists with regards to timing of foliar K application as well as suitability of potential K salts for foliar fertilization.  Multiyear greenhouse and field studies on the effects of foliar K fertilization on fruit quality parameters of muskmelons [Cucumis melo L. (Reticulatus Group)] revealed significant differences in timing (pre- or post-fruit set), as well as K fertilizer source (potassium chloride, potassium nitrate - KNO₃, monopotassium phosphate, potassium sulfate, potassium thiosulfate, and a glycine amino acid-complexed K).  Fruit yields were generally not affected by supplemental foliar K feeding. Several quality parameters (including fruit firmness, soluble solids concentrations (SSC), sugar contents, ascorbic acid, and beta carotene contents) were improved by supplemental post-fruit set foliar K applications. Among K sources, KNO₃ tended to have the least positive effects when applied after fruit set. These observations suggest a reassessment of fertilizer management guidelines with increased emphasis on produce quality. Supplemental foliar K feeding is a practice that growers can easily incorporate into existing foliar pesticide treatments using existing equipment.