Calcitic Lime

Calcium is one of the most important minerals in the soil. According to William Albrecht, it is the most important. In fact, it is the most needed element by weight and volume.

It is largely responsible for the availability of nutrients in plants, and it gives plant cells the ability to communicate. It is very influential on microbial activity, and also contributes immensely to the soil environment. While nitrogen, phosphorus, and potassium get a lot of attention, more and more focus is being put on calcium, particularly in organic horticulture.

Calcium should be applied when a soil test indicates a calcium deficiency, not simply to raise the pH (pH does not measure calcium levels). Since the most common soil tests are inherently inaccurate, the calcium number should be ignored and instead, the base saturation test should be consulted. Here, the percentage of exchange sites occupied by calcium would ideally be 60-68% (closer to 60% for sandy soil).

Even better, a Reams test (aka Lamotte test) more accurately tells us how much calcium is available to plants. Ideally, this would be 2000-8000lbs/acre (1000-4000 ppm and mg/kg), and at least 4000lbs/acre for turf. Further, the ratio of calcium:magnesium would ideally be 10:1 in general, and 7:1 for grasses and sandy soils.