LaMotte STH Outfit - Manual (Page 7)

7
6. Add two drops of the chosen narrow range indicator to the second
sample on the spot plate. Compare the resulting color reaction against
the appropriate color chart to obtain a precise soil pH reading.
Interpretation of pH Reading:
If the pH is
Then the soil is
Below 5.5 Strongly Acid
5.5-6.0 Moderately Acid
6.1-7.0 Slightly Acid
Above 7.0 Alkaline
Extraction
The following extraction procedure uses *Universal Extracting Solution
(5173PS) to produce a single soil extract which is used in each of the
following tests: nitrate nitrogen, ammonia nitrogen, nitrite nitrogen,
phosphorus, potassium, calcium, magnesium, sulfate, aluminum, iron, and
manganese. The pH, chloride, humus, and plant tissue tests use extraction
procedures described in the individual instructions for those tests.
The Extraction Tubes (0704) are marked at 7 and 14 mL. The instructions
below assume that a number of tests will be performed with the general
soil extract. Therefore 14 mL of extracting solution and eight level
measures of the soil sample are called for in Steps 1 & 2. If only a single
test is to be performed (e.g., nitrate nitrogen), fi ll the extraction tube to
the 7 mL line (Step 1) and add only four level measures of the soil
sample (Step 2).
PROCEDURE
1. Fill an Extraction Tube (0704) to the 14 mL line with *Universal
Extracting Solution (5173PS).
2. Use the 0.5 g spoon (0698) to add eight level measures of the soil
sample. Cap and shake for one minute.
Note: When adding samples with high concentrations of carbonates
to the *Universal Extracting Solution (5173), swirl tube to mix for
30 seconds before capping to allow gases to escape.
3. Use a piece of fi lter paper (0465) and a plastic funnel (0459) to fi lter
the soil suspension into a second extraction tube (0704). (Fold the
fi lter paper in half and then in half again to form a cone which is
fi tted into the funnel.) The fi ltrate in the second extraction tube is
the general soil extract for use in the 11 individual test procedures
listed previously.