LaMotte POTASSIUM MODULE FOR SOIL MACRONUTRIENTS KIT - Manual (Page 2)

PROCEDURE
1. Fill a test tube (0755) to line 7 with *Universal Extracting Solution (5173).
2. Use the 0.5 g spoon (0698) to add four level measures of soil. Cap tube and shake
for one minute.
NOTE: When adding samples with high concentrations of carbonates to
*Universal Extracting Solution (5173), swirl tube to mix for 30 seconds before
capping to allow gases to escape.
3. Fold a piece of fi lter paper (0465) in half. Fold in half again. Gently push corners
together to form a cone. Place cone in funnel (0459).
4. Place funnel in clean fi ltrate tube (0749) and fi lter suspension through the fi lter
paper. The clear solution is the extract used in the test.
5. Fill a clean test tube (0755) to line 3 with soil extract.
6. Add one *Potassium Reagent B Tablet (5161A). Cap and shake until tablet
disintegrates.
7. Add *Potassium Reagent C (5162) to line 7. Allow it to run slowly down the side
of the tube. Cap and mix gently. A precipitate will form if potassium is present.
8. Place a Potash Tube “B” (0246) on the Potash Reading Plate (1107) directly over
the black line.
NOTE: Face a window or some other source of daylight.
9. Use a pipet (0364) to add the treated test sample slowly to Tube “B” allowing it to
run down the sides of the tube while observing the black line through the solution.
Continue until the line just disappears.
10. The height of the column of test sample is measured against the potassium scale
on the tube. Record as pounds per acre potassium.
NOTE: For extremely high readings, dilute the fi ltered extract and retest. Add
the soil sample fi ltrate to line 3 of a clean test tube (0755). Dilute to line 6 with
*Universal Extracting Solution (5173). Test following the procedure beginning
with Step 5. Multiply fi nal reading by 2.
PRECAUTION: Large amounts of ammonium salts will produce a precipitate similar
to that obtained with potassium. If fertilizer containing ammonium salts has recently
been added to the soil, or if the soil pH is low (pH 4.0-5.0), a test should be made for
ammonium compounds. Equivalent quantities of ammonium salts will produce about
one-fourth as much precipitate as obtained from potassium salts.
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