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Fluid Journal : Fluid Journal 2002-2004
Spring 2004 Fluid Journal 2 Tree nutrition Potassium. In 2000 to 2002, a range of leaf K concentrations was observed in both the 'Fuji' and 'Spartan' orchards. Annual leaf K concentration less than or equal to 1.3 percent (and thus close to the deficiency threshold of 1.0 to 1.2% for apple) was observed for check treatments at some time during the study in five 'Fuji' orchards (examples in Table 1), and three 'Spartan' orchards (data not shown). Midsummer leaf K concentration was decreased by heavy crop loads. Variations in annual leaf K concentrations partially relate to variations in crop load, which may explain the low leaf K concentrations for the check treatment observed for only a single year in orchard 10 (data not shown). Orchard 1, by contrast, was consistently low in leaf K concentration when not receiving K Mag fertilizer. In one Spartan orchard K concentrations were deficient without K Mag fertiliza- tion in 2002, even after three annual applications of 112 lbs/A of K as K Mag. K Mag fertilizer applications signifi- cantly increased leaf K concentration in direct proportion to the amount applied in four orchards in 2000 and this effect increased to 8 of 14 orchards in 2001. K Mag fertilizer applications significantly increased leaf K concentration in 7 of 11 orchards in 2002, including the four orchards with lowest leaf K concentra- tions. This implies that broadcast K Mag fertilization is generally effective at improving tree K nutrition. Magnesium. In contrast to leaf potassium concentrations, K Mag fertilization did not increase leaf Mg concentration (sample data for 'Fuji', Table 2). Only in orchard 1 in 2002 did application of K Mag decrease leaf Mg concentration. It therefore appears difficult to increase leaf Mg concentration in apple when co- applying K. However, it has been well documented that application of K fertilizer not containing Mg at rates between 112 to 225 lbs/A of K, as in this study, usually decreases apple leaf Mg concentration. This generally was not observed after application of K Mag since leaf Mg was not decreased upon application of up to 225 lbs/A of K as K Mag. Thus, K Mag fertilization at least maintains leaf Mg concentration when K fertilizer is being applied. Fruit quality Fruit quality parameters at harvest were significantly affected by K Mag fertilization in some orchards for both 2000 and 2001 harvests (data not shown). Results from the 2002 harvest are typical and indicate statistically significant results in 5 of the 10 orchards where detailed fruit quality measure- ments were made in 2002. Fruit param- eters of prime importance for growers include percent red color, fruit size, and absence of major fruit disorders, since these have a direct effect on grower returns. In 2002, the most important fruit quality effects were measured in orchards 1 and 7, which also had the lowest leaf K concentrations when unfertilized (Table 3). Both orchards had increased fruit size, implying a yield response to K Mag fertilization. It was noteworthy that all orchards that showed fruit responses to K Mag fertilization had leaf K values < 1.4 percent. The only exception to this pattern was one orchard that had a leaf K concentration of 1.29 percent when not receiving K Mag fertilizer yet fruit that did not respond to fertilization. This orchard was also characterized by a high variation in vegetative growth and crop load within the experimental block. Increases in red coloration and acidity of fruit have previously been associated with improved K nutrition of apple trees. K Mag fertilization failed to improve red color in orchard 7 containing 'Spartan,' which is a naturally highly colored cultivar averaging 95 percent red in this orchard. Higher fruit acidity (orchards 7 and 9) can be associated with improved fruit tartness and consumer acceptabil- ity. No incidence of fruit disorders at harvest was increased by K Mag fertilization (data not shown). In one 'Fuji' orchard, incidence of watercore disorder was decreased by K Mag fertilization. Dr. Gerry Neilsen and Dr. Denise Neilsen are both research scientists at the Pacific Agri-Food Research Centre in Summerland, British Columbia. Table 3. Statistically significant fruit quality effects with K Mag fertilzation in experimental orchards, 2002 harvest. Check 81 261 184 9.9 8.2 7.1 0.72 112KMag 89 263 201 10.3 8.9 7.3 0.68 225KMag 88 22 217 10.7 9.2 7.6 0.47 Orchard 1 1 7 7 9 10 11 Red Fruit Fruit Titra-table Titra-table Titra-table Watercore color (%) wt (g) wt (g) acidity acidity acidity (fraction) (mg 100ml-1) (mg 100ml-1) (mg 100ml-1) Treatment (lbs/A)
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