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Fluid Journal : Fluid Journal 2008-2009
magnesium. In another study, the beneficial effects of supplemental foliar K application on fruit quality were greater when an organic form of K (Metalosate-K) was used compared to an inorganic source (e.g., KCl). Potassium chloride is the most widely used source of K; however, its relatively high salt index and its high point of deliquescence (POD) limit its use for foliar nutrition. A high POD increases the risk of crystallization following foliar sprays. The objective of this study was to evaluate the effectiveness of different K salts for foliar K fertilization on muskmelon fruit yield and quality. Supplementing Works Overview. Preplant soil tests at our study sites indicated moderate to very high potassium -1) levels, so no K was added to the soil. Phytotoxicity problems were not observed with any of the foliar K sources and concentrations used. The pH levels of spray solutions ranged from 6.5 to 7.7. Unbuffered solutions of most K sources tend to have alkaline pH levels that can cause leaf burns. All treatments were applied early in the morning (0500 to 0800 hr; >80% RH; <25o C; and <1 mph winds) to minimize the potential for leaf burn. Plant tissues from plots receiving supplemental foliar K treatments generally had higher K concentrations than those from control plots, suggesting that soil K supply alone was not sufficient to saturate tissue K accumulations (Table 1). However, differences in tissue K concentrations among the foliar K sources were not highly significant except for KNO3 treatments, which generally had the least beneficial effect on tissue K concentrations, perhaps a dilution effect resulting from NO3- enhanced vegetative growth. Soluble solids concentrations (SSC) differed significantly among the foliar K treatments in both years and were generally lower in 2007 than in 2006. With the exceptions of KCl and KNO3, all the other foliar K sources significantly increased fruit SSC levels compared to the control. Although SSC values were generally lower in 2007 than in 2006, the greatest relative benefit from supplemental foliar K was observed in 2007. Unseasonable weather conditions (cold fronts) during the 2007 growing season delayed vegetative development and, as a consequence, there was a substantial overlap between canopy development and fruit maturation. This is a probable reason for the marginal SSC values observed in 2007. Nevertheless, a positive and more pronounced response to foliar K treatments was recorded in 2007. In 2006 similar trends were also observed for total and component sugars (glucose, sucrose and fructose, data not shown) but variability in individual observations resulted in inconsistent trends among the K sources. In 2006, total ascorbic acid and beta- carotene concentrations were also generally increased as a result of supplemental foliar K applications. However, the trends were not consistent among K sources. Fruit firmness. While foliar K applications generally increased fruit firmness in both years, no significant differences were found among the K sources except for KNO3, which tended to result in less firm fruit compared to controls. Firmness measurements are a good indicator of fruit texture and shelf life. In a previous study, it was found that fruit firmness was closely correlated with fruit tissue pressure potential, with fruit from K-treated plants having significantly higher values than those of control plants. Fruit yields did not respond significantly to supplemental foliar K treatments in 2006, averaging 6,000 lbs/A based on a once-over harvest during peak maturity. In 2007, fruit yields averaged 20,100 lbs/A, based on several harvests over a two-week period, and were significantly affected by supplemental foliar K treatments (Table 1). Yields from KCL-treated plots were not significantly Treatment Leaf Petiole SSC Yield -1) -1) (%) cwt/acre 2006 2007 2006 2007 2006 2007 2006¶ 2007 Control 11.9cdZ 12.9b 48.2d 54.3b 9.2b 8.1b 57.8a 182.4b KCl 11.6d 14.1a 55.2bc 63.4a 10.0ab 9.3ab 59.5a 202.5a KNO3 10.7d 13.1b 47.6d 54.9ab 9.7ab 8.7b 54.4a 172.0b MKP 13.2bc 15.9a 51.6cd 59.4ab 10.6a 10.1a 64.1a 212.0a K2SO4 14.7a 14.9a 50.2cd 58.7ab 10.5a 9.7a 62.3a 206.8a KTS 13.9ab 16.8a 64.2a 73.9a 10.7a 10.4a 66.8a 229.6a KM 14.7a 15.4a 57.8b 66.5a 10.3a 9.8a 60.6a 208.8a Z Means with the same letter, within a column and location are not significantly different at Duncan's MRT 95% probability level (n=6-16). ¶ 2006 yields are based on a once-over harvest during peak maturity. Table 1. The effects of foliar potassium (K) sources (potassium chloride -- KCl, potassium nitrate - KNO3 , PeaK or Monopotassium phosphate -- MKP, potassium sulfate - K2SO4 , potassium thiosulfate - KTS, and Potassium Metalosate - KM) on tissue K concentrations, soluble solids concentrations (SSC) and yields of field-grown muskmelon ('Cruiser') fruit in south Texas. Weekly foliar K applications were made between fruit set and fruit maturity during the spring growing season in 2006 and 2007.
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