LaMotte STH Series - Manual (Page 13)

Magnesium
Magnesium is a constituent of chlorophyll, and chlorosis can
result from magnesium deficiency. Like calcium, magnesium
cations play a role in base or cation exchange. Magnesium is
subject to more leaching than calcium. Soils giving a low test
reading should receive dolomitic lime or fertilizer which contain
considerable magnesia. Soils giving high magnesium tests and low
calcium tests should receive gypsum or high calcic lime, in order
to restore the calcium-magnesium balance.
Procedure:
1. Use a transfer pipet (0364) to transfer ten drops of the general
soil extract to one of the larger depressions on a spot plate
(0159).
2. Add one drop of *Magnesium Test Solution 1 (5140). Stir
with a clean rod (0519). A pale yellow color will develop.
3. Add *Magnesium and Manganese Test Solution 2 (5145PS)
one drop at a time with stirring, until the pale yellow color
changes to one of the darker shades indicated on the
Magnesium Color Chart (1306). About two drops are usually
required. Under some conditions, a precipitate will form
shortly after *Manganese-Magnesium Test Solution #2 has
been added. This will not effect the test reading. The test
result is expressed in relative values of Magnesium from very
low to very high. For approximate corresponding value in
parts per million or pounds per acre, see page 22.
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