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• DETERMINATION OF AVAILABLE POTASSIUM, CALCIUM, <br />MAGNESIUM, AND SODIUM IN SOILS <br />Montana State University - College of Agriculture <br />Stock Solutions: <br />Potassium - 1000ppm: Weigh ~.9066g of pure dry (1 hour in oven <br />at 105 C) KC1 into liter volumetric flask, <br />add distilled-deionized water to dissolve, <br />then bring to volume with distilled-deionized <br />water. <br />Sodium - 1000ppm: Weigh 2.5421g of pure dry (1 hour in oven <br />at 105°) NaCl into a liter volumetric <br />flask, add distilled-deionized water to <br />dissolve, then bring to volume with <br />distilled-deionized water. <br />Ammonium Acetate-1N: Weigh 154.16g of ammonium acetate (pH7) <br />into a 2 liter volumetric flask and dilute <br />to volume with distilled-deionized water.. <br />• Standard Solutions: <br />200ppm Potassium: Pipet 100m1 of 1000ppm K stock solution <br />into SOOm1 volumetric flask, then bring <br />to volume with 1N NH4OAC. (Ammonium <br />acetate extracting solution) <br />200ppm Sodium: Pipet 100m1 of 1000ppm Na stock solution <br />into SOOml volumetric flask, then bring <br />to volume with 1N NH4OAC. <br />PROCEDURE FOR ANALYZING SOILS SAbiPLES <br />1. Weigh 2.5g of soil into 250m1 erlenmeyer flask. <br />2. Add 50m1 of 1N ammonium acetate extracting solution. <br />3. Shake the soil on mechanical shaker for 30 minutes. <br />4. Centrifuge the extract until clear. <br />5. An aliquot of extract is diluted to volume, with the final <br />volume 18 SrC12.' <br />• 6. Analyze directly for Ca, Na, Mg, & K directly on Perkin-Elmer <br />Atomic Absorption Spectrophotometer. <br />1The dilution required will depend upon the type of soil analyzed. <br />It is important to match the $ SrC12 in both standards and samples. <br />6-64 <br />