LaMotte POTASSIUM MODULE AM-31 - Manual (Page 3)

PRO CE DURE
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 filter 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 filtrate tube (0749) and filter suspension through
the filter 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 (5161). 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 filtered extract and
retest. Add the soil sample filtrate 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 final 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.