The determination of small amounts of exchangeable potassium in soils, employing the sodium cobaltinitrite procedure
1941
This investigation was undertaken for the purpose of developing, if possible, a procedure for measuring the small amounts of replaceable potassium found in many soils, e.g., in Alabama about 15% of the soils contain less than 40 pounds per acre of replaceable potassium. Displacement of the potassium is achieved by leaching the soil with ammonium acetate. The displaced potassium, after being freed of ammonia and organic matter, is taken up in 0.16 normal acetic acid and precipitated as potassium sodium cobaltinitrite. Complete precipitation is obtained by rapidly adding the solution containing the potassium to an equal volume of 20% sodium cobaltinitrite containing an additional 4% of sodium as the acetate. Mixing of the solutions is done at room temperature and precipitation is allowed to go to completion at about 3 degrees C. The amount of potassium present is finally determined by dissolving the washed precipitate in water and titrating with permanganate. The method is sensitive to a concentration of potassium as low as 0.005% (0.1 mgm per 20 cc).
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