Walworth, James L.
Abstract or Description:
Iron deficiency is a frequent problem for many ornamental plants growing in the low desert areas of Arizona. The underlying cause for this disorder is the high pH levels of our soils. Calcium carbonate (CaCO3) deposits are a common feature of high pH desert soils. Calcium carbonate accumulates in desert soils because precipitation is not sufficient to wash or leach these naturally occurring materials out of the soil. Calcium carbonate may be visible as light colored concretions (lumps) which range in size from less than one inch to several inches across or as a solid layer, ranging from a few inches to several feet in thickness, although calcium carbonate is often present even when it is cannot be seen. If these deposits form solid layers they are known as caliche. When calcium carbonate dissolves in water, it raises pH to 8.0 to 8.5, and this is the pH range of most desert soils. In this high pH environment, iron solubility is greatly reduced. In desert soils there is usually plenty of iron; it just is not soluble enough to provide adequate nutrition to susceptible plants. Over-watering plants growing in calcareous soils can induce or worsen iron deficiency. Additionally, cold winter soils may induce iron defi ciency, which often disappears when soils warm in the spring.
Revised 1/2013. Originally published: 2006.
College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ)
Soil, Water & Enviromental Science
University of Arizona Cooperative Extension Publication AZ1415