Availability of Calcium in Calcareous Soils

Ten Arizona soils ranging in calcium carbonate content from 0 to 13% were collected and tested under greenhouse conditions for available calcium using soluble radiocalcium and radiostrontium salts for A value measurements. Neither the total amount of radioelement absorbed nor the percentage of radioelement in the plant derived from the added source was found to be related to the soil calcium soluble in water or 1:1 HCl, the calcium carbonate content or “active” calcium as measured by the Drouineau method. Further study showed that plants took up more soil calcium from acid soils of the humid Midwest than from some calcareous soils of Arizona. The amount of exchangeable calcium in soils was significantly correlated with the amount of available calcium in soils. Calcium carbonate was found to be very poorly available to plants regardless of its source.