LaMotte STH Outfit - Manual (Page 13)

13
Calcium
Calcium defi ciency is seldom a direct limiting factor in plant growth,
because the lack of adequate calcium in a soil causes other growth
limiting defi ciencies to occur fi rst. Calcium is the dominant cation in
a soil’s base or cation exchange complex; it prevents excessive soil
acidity and stimulates benefi cial biological activity. Low calcium levels
may cause high soil acidity, diminishing the availability of some
nutrients (like nitrogen) and permitting toxic levels of other minerals
(like aluminum) to develop in the soil solution. In general, calcium
plays an essential role in maintaining the chemical equilibrium of the
soil solution.
This test measures the amount of calcium present in the base exchange
complex. Calcium test results confi rm and supplement soil acidity readings.
Sandy soils normally contain less calcium than clay or organic soils.
Sandy soils should give readings of approximately 500 ppm, clay soils
1000 ppm, and organic soils such as peats or forest loams 5000 ppm
calcium. Lower levels in clay or organic soils indicate that the active
calcium has been replaced by hydrogen or other ions, as in highly alkaline
or highly acid soils.
PROCEDURE
1. Use a transfer pipet (0364) to transfer fi ve drops of the general soil
extract to a fl at-bottomed glass turbidity vial (0242).
2. Add one drop of *Calcium Test Solution (5108PS). Swirl gently to
mix.
3. Match the milky turbidity of the test sample against the turbidity
standards on the Replaceable Calcium Chart (1303). 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 replaceable calcium.
4. If the test sample turbidity corresponds to or exceeds the lightest
standard (2800 ppm), repeat the test on a diluted sample. Transfer
one drop of the general extract to a clean turbidity vial and add four
drops of demineralized water. Then follow Steps 2 and 3 as above.
Multiply the test result by 5 to obtain parts per million replaceable
calcium.