LaMotte SMART 2 Electronic Soil Lab - Manual (Page 78)

PROCEDURE
1. Press and hold ON button until colorimeter turns on.
2. Press ENTER to start.
3. Press ENTER to select TESTING MENU.
4. Select ALL TESTS (or another sequence containing 81 Potassium) from
TESTING MENU .
5. Scroll to and select 81 Potassium from menu.
6. Use the 1 mL pipet (0354) to add 2 ml of the soil extract to a clean tube
(0290) and dilute to the 10 mL line with deionized water.
7. Insert tube into chamber, close lid and select SCAN BLANK.
8. Remove tube from colorimeter. Add 4 drops of *Sodium Hydroxide, 1.0N
(4004WT). Cap and mix.
9. Use the 0.05 g spoon (0696) to add one measure of *Tetraphenylboron
Powder (6364). Cap and shake vigorously until all of the powder has
dissolved. Wait 5 minutes.
10. At end of 5 minute waiting period, mix tube again to suspend any settled
precipitate. Insert tube into chamber, close lid and select SCAN SAMPLE.
Multiply the result by 50 to determine the potassium concentration in
lb/acre.
11. Press OFF button to turn colorimeter off or press EXIT button to exit to a
previous menu or make another menu selection.
NOTES:
l For best possible results, a reagent blank should be determined to account
for any contribution to the test result by the reagent system. To determine
the reagent blank, follow the above test procedure to scan a distilled or
deionized water blank. Then follow the above procedure to perform the
test on a distilled or deionized water sample. This test result is the reagent
blank. Subtract the reagent blank from all subsequent test results of
unknown samples. It is necessary to determine the reagent blank only
when a new lot number of reagents are obtained.
l For the most accurate results, the sample and reagents should be at
25±4°C.
n
POTASSIUM CONCENTRATION CHART
POUNDS PER ACRE RANGE
0-44 lb/acre Very Low
50-76 lb/acre Low
82-143 lb/acre Medium
144-281 lb/acre High
Over 294 lb/acre Very High
78 SMART2 SOIL MANUAL 1.07