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Fluid Journal : Fluid Journal 2002-2004
1 Fluid Journal Summer 2002 Drs. Terry A. Tindall and Dale Westermann Fine-tuning Soil/Plant Needs Critical In Potato Production Western scientists probe into factors affecting potato crop needs for potassium. Summary: Potato growers should seriously consider a maintenance approach to potassium (K) fertilization in an attempt to avoid high corrective rates required to overcome K deficiencies that might occur in-season. Higher rates of K should be split applied with at least 50 percent of the K being applied during the fall with the remainder at the time of planting. Maintenance levels of K should especially be made for sandy, coarse- textured soils. The goal of a K fertilization program is to provide sufficient available K to the potato plant to achieve 6 to 8 lbs of K2O/A/day during the entire tuber bulking stage. The purpose of this study will be to focus on two primary factors that influence potato crop needs for potassium (K) in the Pacific Northwestern region of the United States. We will take a look at each aspect and draw some conclusions. Soils First of all, soil contributes greatly to K availability. In western agricultural soils, particularly Idaho, K has declined more than any other nutrient. Many soils that had soil test K concentrations of greater than 400 ppm in the mid-1960s are now in the range of 100 to 200 ppm. As recently as last year, soil test K levels have been observed in the 20 to 30 ppm range. Historically, many of these soils have had a tremendous crop requirement for K. That requirement has not diminished and cannot be maintained without additional K fertilizer being applied. Figure 1. Relationship between STKC and slow-release K from soil extracts. Figure 2. Relationship between STKC and K diffusion rate (DFFK) estimated by the Unocal® procedure. 400 720 1040 1360 1680 2000 0 100 200 300 400 500 STKC, ppm Slow Release K, ppm 175 0 0.5 1 1.5 2 2.5 70 80 90 100 110 120 130 140 150 STKC, ppm DFFK, ppmm/day To make accurate and reliable K recommendations, we need to determine the magnitude of selected K fractions and their interrelationships to each other and the standard soil test K concentrations. This is especially true as one compares current academic recommendations for K and those apparently higher K fertilization rates that are being reported by many growers. To help understand the relations between various soil fractions,
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