LaMotte STH Series - Manual (Page 11)

Phosphorous
The role of phosphorous in plant nutrition is discussed in the
LaMotte Soil Handbook. For interpretation of test results see the
LaMotte Soil Handbook and page 22 of this manual.
The Phosphorous test is extremely sensitive. Special precautions
should be taken to prevent contamination. In particular, exposure
of the test components to fertilizer dust must be scrupulously
avoided. The operator’s hands and clothing, the work surface, and
the testing area in general must be clean and free of fertilizer
residues.
LaMotte offers the Model NF Test Kit (Code 5090) for
Phosphorous in Alkaline Soils, to be used in place of the test
described below when the soils are predominantly alkaline (above
pH 7.0).
Procedure:
1. Use a transfer pipet (0364) to fill a “Phosphorous B” Tube
(0244) to the mark with the general soil extract.
2. Add 6 drops of *Phosphorous Reagent 2 (5156). Cap and
shake to mix.
3. Add one *Phosphorous Reagent 3 Tablet (5157). Cap and
shake until dissolved.
4. Immediately compare the color that develops in the test tube
against the Phosphorous Color Chart (1312). Hold the tube
about one inch in front of the white surface in the center of
the color chart. View the chart and sample under natural light
for optimum color comparison. The test result is read in
pounds per acre Available Phosphorous.
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