LaMotte CALCIUM & CHLORIDE SOIL TESTS MODULE A - Manual (Page 3)

6. Use the pipet with the screw cap (0392) to add one drop of
Calcium Test Solution (5108PS). Gently swirl to mix.
7. Hold test tube about one-half inch above the black background in
the center of the Calcium Color Chart (1303). Viewing down
through the tube, match sample turbidity to a turbidity standard.
Record as ppm Calcium.
IN TER PRE TA TION OF RE PLACE ABLE CAL CIUM TEST RE SULTS
A lack of calcium in the soil rarely limits plant growth, but it helps to
provide a favorable equilibrium between the various constituents in the
soil which affect fertility. If there is a deficiency in the replaceable
calcium in the soil, the base exchange capacity is incompletely satisfied,
resulting in acid soil. Valuable biological processes are dependent upon
the important stabilizing effect of calcium in the soil, and without its
beneficial effects the nitrification process would bring about a highly
injurious acid condition.
Well-limed soils, those that are not naturally in need of lime, contain an
abundance of replaceable calcium. Hence, this test can be used to
confirm and supplement the interpretation of soil acidity measurements.
The amounts of calcium that are extracted from soil by the leaching
solution provide a measure of the amount of calcium contained in the
base exchange complex. Soils low in humus and clay give higher values
than soils that have a high percentage of colliodal clay and organic
matter, unless the latter are strongly acid and, consequently, have most
of their calcium replaced by hydrogen-ions.
Normal sandy soils should give 500 ppm calcium; clay soils 1000 ppm;
and humus soils, such as peats and forest mold, 500 ppm. Lower results
indicate that much of the active calcium of the soil has been replaced
by hydrogen or other ions, as in acid or highly alkaline soils.