Calcareous Conditions

Calcareous Surface Soils and Subsoils

Calcareous or high lime soils occur in two kinds of situations in Iowa. One situation occurs where erosion has been so rapid that calcareous parent material is exposed at the surface. These soils are likely to be more limited by drought conditions and erosion hazards than by the calcareousness, but the calcareous condition is an additional disadvantage.
The other situation where calcareous soils occur is caused by wetness. North-central Iowa has many depressed areas or “potholes” that contain calcareous materials or have calcareous materials distributed as rims or bands around the depressed area. Some floodplains also have calcareous soils. Water evaporating from the wet soils leaves behind enough calcium carbonate to cause the calcareous condition. Snail shells also contribute calcium carbonate to many of these soils because snails like the wet environment.

Calcareous conditions raise the soil pH above neutral and can limit the availability of phosphorus and iron. Higher rate of phosphorus fertilizer may be needed for some crops like corn and alfalfa. These same crops are likely to need extra potassium fertilizer because of wetness. Soybeans growing on calcareous soils often suffer from iron deficiency. Calcareous conditions can also influence the type and amount of herbicide used for weed control.

Calcareous soils can be identified in two ways: by color and by an acid test. Calcium carbonate is white or grayish white and can cause the soil to be lighter colored. Positive identification, however, is made by the acid test. A few drops of dilute hydrochloric acid will cause a calcareous soil to effervesce (emit bubbles of carbon dioxide). A 1 N or 1 M solution of hydrochloric acid in a dropper bottle is suitable for this test.