LaMotte STH Series - Manual (Page 14)

Calcium
Calcium deficiency is seldom a direct limiting factor in plant
growth, because the lack of adequate calcium in a soil causes other
growth limiting deficiencies to occur first. Calcium is the
dominant cation in a soil’s base or cation exchange complex; it
prevents excessive soil acidity and stimulates beneficial 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 confirm 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clay or organic soils indicate that the active calcium has been
replaced by hydrogen or other ions, as in highly alkaline or highly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.
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