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Fluid Journal : Fluid Journal 2002-2004
3 Fluid Journal Summer 2002 Most growers make split applications of K for potato production. While making these applications they should be aware of the critical tissue K concentrations required and the fundamental nutrient status of the potato plant. Potassium status can be defined as the ratio between the total plant K uptake divided by the tuber K uptake rate. When this ratio or balance is greater than 1.0, there is more K uptake than required for tuber growth. When the ratio is less than 1.0, uptake is less than that required for tuber growth. Mobile nutrients will be translocated out of the vegetative portions of the plant to the developing tubers. This approach can be used for mobile nutrients and especially applied as a K fertility factor for Russet Burbank potatoes or other varieties commonly produced in western agriculture. The problem with excessive K in the plant is that this excessive K can be translocated to the tubers, causing a decrease in dry matter because of increasing water content. Low K concentrations, on the other hand, decrease tuber dry matter via metabolic reduction in starch formation as well as reducing photosynthate needed for growth. Conclusions Soils. K fixation could be as high as 27 percent of the applied K at relatively low STKC. It is our recommendation that potato growers seriously consider a maintenance approach to K fertilization in an attempt to avoid high corrective rates required to overcome soil K deficiencies that might occur in-season. It is also recommended that higher rates of K should be split applied with at least 50 percent of the applied K being applied during the fall with the remainder at the time of planting (see Table 1). Of those higher concentrations, the bulk of the K fertilizer applied for potatoes in the spring should be as K2SO4. Maintenance levels for K application should especially be made for sandy coarse-textured soils that might have soil CECs of less than 10 meq/100 g of soil. Plant. Optimum tuber concentration for highest dry matter is 1.8 percent on a dry matter basis of 22 percent. At this concentration, 0.48 lb K2O/A is required to grow 100 lbs of fresh weight tubers. This relates to at least 3.4 lbs K2O/day for tuber growth during bulking. An additional concern is the efficiency of the K fertilizer applied. Our data indicate that K efficiency is between 30 and 40 percent. This could result in a crop availability of between 6 to 8 lbs of K2O/A/day to meet the demands of the tuber and the plant. Therefore, the goal of a K fertilization program for potatoes is to provide sufficient available K to achieve this concentration during the entire tuber bulking stage. Dr. Tindall is manager of agronomy at J. R. Simplot Company and Dr. Westermann is a USDA/ARS soil scientist.
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