LaMotte MORGAN SOIL pH TEST KIT ST-M - Manual (Page 2)

PRO CE DURE
1.
Fill one of the large depressions in a spot plate (0159) with sample
soil. Do not pack the soil down.
2. Place spot plate on a level surface. Add *Duplex Indicator (2221)
drop by drop until the soil is thoroughly saturated. Do not overfill. If
sample is flooded, some indicators will not react completely with soil,
producing a false reading. Wait 3 minutes.
3. Tilt the spot plate so that indicator flows down channel and collects
in smaller depression. If necessary, use the pointed plastic rod to start
the flow.
4. Match color in small depression plate to a color standard on the
Duplex Color Chart (1313).
5. Use result from Step 4 to choose a narrow range indicator for more
precise pH measurements. Use chart below to determine the proper
narrow range. Choose the indicator with the midpoint closest to
sample pH.
6. Using a second portion of soil and the narrow range indicator, repeat
Steps 1-5 in a clean depression. Consult Chapter Four of the LaMotte
Soil Handbook
(1504) for interpretation of the narrow range pH test
result.
Indicator Range
Midpoint
Value
Bromcresol Green (2207) 3.8 – 5.4 4.6
Chlorophenol Red (2209) 5.2 – 6.8 6.0
Bromthymol Blue (2210) 6.0 – 7.6 6.8
Phenol Red (2211) 6.8 – 8.4 7.6