LaMotte STH Outfit - Manual (Page 14)

14
Sulfate
Sulfur is essential to the formation of protein and affects various aspects
of plant metabolism. Sulfur-defi cient plants are pale green in color with
thin, reedy stems. Negatively charged sulfate ions are easily leached. The
major sources of soil sulfate are fertilizer containing sulfate compounds
and atmospheric sulfur dioxide carried into the soil by precipitation.
PROCEDURE
1. Use a transfer pipet (0364) to transfer fi ve drops of the general soil
extract to a fl at-bottomed turbidity vial (0242).
2. Add one drop of *Sulfate Test Solution (5171). Swirl gently to mix.
3. Compare the turbidity of the sample to the turbidity standards of the
Sulfate Chart (1314). Lay the chart fl at under natural light and hold
the turbidity vial one-half inch above the black strip in the middle of
the chart. View the black strip down through the turbid sample and
compare the resulting shade of gray with the six standard shades. The
test result is read in parts per million sulfate.
Aluminum
All soils contain signifi cant amounts of aluminum in inorganic colloidal
material and in the form of undecomposed minerals. In neutral, slightly
alkaline, or slightly acid soils, this aluminum is in inert combinations
that do not affect plant growth. In more acidic soils, aluminum can
form soluble salts toxic to plant growth. A high test result indicates an
undesirable acid soil. Plants which normally thrive on acid soils may fail
on a soil with a high active aluminum test reading. A medium test result
is generally tolerable - especially for grasses, corn, oats, potatoes, and
tobacco. A low or negative aluminum test result is preferable.
PROCEDURE
1. Use a transfer pipet (0364) to transfer two drops of the general soil
extract to one of the larger depressions on a spot plate (0159).
2. Add two drops of *Universal Extracting Solution (5173).
3. Add one drop of *Aluminum Test Solution (5101).
4. Stir with a clean stirring rod (0519). Allow to stand for one minute.
5. Match the resulting color with the Active Aluminum Color Chart
(1301). The test result is expressed in relative values of active
aluminum from very low to very high. For approximate corresponding
values in parts per million or pounds per acre, see page 19.