LaMotte STH Series - Manual (Page 5)

Test Procedures
pH
pH is a measure of acidity or basicity. Soils can have a pH from 3.5
to 11.0, but plants grow well in the range of 5.0 to 8.5. In soils
with a low pH (acidic), some nutrients can reach toxic levels and
the activity of soil microbes is greatly reduced. Soils with a high
pH (alkaline) generally have a lower micro-nutrient availability
and some levels may be deficient.
Procedure:
1. Fill a test tube (0204) approximately one-third full of soil. Use
the Demineralizer Bottle (1155) to add demineralized water
to the tube, until it is one-half inch from the top. Cap and
shake until the soil is well dispersed.
2. Add 5 drops of Soil Flocculating Reagent (5643WT). Cap
and shake to mix. Allow contents to settle before proceeding
to Step 3.
3. Use a 1 mL pipet (0354) to transfer 1 mL of the clear solution
above the soil to one of the large depressions on a spot plate
(0159). Transfer a second 1 mL sample to the other large
depression on the spot plate.
4. To the first sample on the spot plate, add two drops of
*Duplex Indicator (2221). Compare the resulting color
reaction against the Duplex Color Chart (1313).
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