Submitted to: Plant and Soil
Publication Type: Review article
Publication Acceptance Date: 10/19/2009
Publication Date: 9/13/2010
Citation: Lester, G.E., Jifon, J.L., Makus, D.J. 2010. Impact of potassium nutrition on postharvest fruit quality: Melon (Cucumis melo L.) case study. Plant and Soil. 335(1):117-131. Interpretive Summary: Supplementing soil K supply with foliar K applications during fruit development improves fruit quality by increasing firmness, sugar content, ascorbic acid and beta-carotene levels. Among the K salts, KNO(3) has little or no beneficial effects on fruit quality when applied during fruit maturation, perhaps due to a dilution effect resulting from N stimulation of vegetative growth at the expense of roots and fruits. Perhaps foliar fertilization KNO(3) would be more beneficial during the vegetative growth stages when N is most needed for development of leaves with high photosynthetic capacity. These fruit quality improvements summarized in this review were obtained by implementing a simple management tool that growers can easily adopt. Future research is needed to validate these findings in typical commercial field trials (differing in K concentrations), under different production environments (temperate vs. tropical) and productions systems (conventional vs. organic), and also to evaluate the effect of K source (amino acid complexed K versus potassium chloride and others) on marketable quality and health-bioactive attributes of various fruits.
Technical Abstract: Among the many plant minerals, potassium (K) stands out as a cation having the strongest influence on quality attributes which determines fruit marketability, consumer preference, and the concentration of critically important human-health associated phytonutrients. However, many plant, soil, and environmental factors often limit adequate uptake of K from the soil in sufficient concentrations to satisfy fruit K requirements during development to optimize the aforementioned quality attributes. The objective of this review is to summarize 1) published fruit studies comparing K sources, applied via the soil or foliage and their affect on phytonutrient concentrations; and 2) using Cucumis melo L (muskmelon) fruit, produced with optimal soil K fertility, as a case study, comparing K sources, seasonal effects (spring vs. autumn), and the number of K applications during fruit development on maturity, yield, marketability, firmness, sugars, relative sweetness, and fruit concentrations of K, soluble solids, ascorbic acid, and beta-carotene. Fruit studies revealed that specific K fertilizer sources in combination with specific application regimes reliably produced harvested fruit with improved quality attributes. Potassium fertilizer sources in order of effectiveness (Gly amino-complexed K = K(2)SO(4) = KCl > KNO(3) < no K) when applied wet (foliar or hydroponic) vs. dry (soil) were superior in improving fruit marketability, along with many human-health nutrients. The muskmelon case study demonstrated that two K sources: amino acid complexed K and K(2)SO(4) plus a surfactant, applied weekly as a foliar spray during fruit development, from both autumn and spring-grown plants, had the greatest impact on improving fruit firmness, sugars, marketability, as well as the concentrations of human-health bioactive compounds K, ascorbic acid, and beta-carotene. Among several foliar applied K salts studied so far, KNO(3), a fertilizer best used during vegetative growth, consistently resulted in no benefit to fruit quality; with results similar to that of control treatments, indicating this source of K not be used for foliar K supplementation during fruiting because of its N component.