Caliche in the Home Yard
J.L. Walworth, Department of Soil, Water, and Environmental Science
J. Kelly, Pima County Cooperative Extension
Caliche is a common problem in southern Arizona soils. Caliche is layer
of soil in which the soil particles are cemented together by calcium
carbonate (CaCO3). These layers may form at or below the soil surface.
Caliche may appear as light colored concretions (lumps) which range
in size from less than 1 inch to several inches across. Caliche may
also appear as a solid layer, ranging from a few inches to several feet
in thickness. Caliche layers range from relatively loose to highly consolidated,
solid rock-like conglomerations.
Where does caliche
Caliche is the a natural formation in desert soils. Calcium is continually
added to the soil, mainly dissolved in rain water. This calcium combines
with carbon dioxide dissolved in soil water, forming insoluble calcium
carbonate deposits. Over time, calcium carbonate builds up and consolidates
into solid, sometimes massive deposits. Not all desert soils have caliche.
Caliche formation depends on numerous factors, including amount of rainfall,
water infiltration, and soil drainage.
What does caliche
do to Plants?
Physical problems associated with caliche can be reduced or eliminated by breaking apart and removing as much caliche as practical when making holes for planting. Holes should penetrate completely through the caliche layer to allow water to drain rapidly. The latest planting guidelines recommend a shallow hole rather than a large deep hole. A hole no deeper than the root ball and up to 3 to 5 times as wide will permit normal development and growth of the roots and tops of your plants. If it is not practical to dig the entire diameter of the hole through the caliche, then a smaller drainage hole can be made that pierces through the caliche and provides drainage. Do not place drain holes directly under the root ball as this will force excess water through the root system and may encourage root suffocation and disease. Drainage can easily be checked prior to filling with soil or planting by partially filling the hole with water. If the water level drops at least four inches in four hours, then drainage should be adequate.
If good drainage can not be attained by penetrating caliche, soil can
be added to increase the depth of soil available for rooting. Sufficient
soil should be added to provide two feet total depth over the entire
rooting zone (one and a half to four times the mature plant canopy.
Use soil that is similar in texture and set trees and shrubs several
inches above grade to allow for settling.
Solid chunks of caliche should be removed from the soil. Adding powdered
or prilled (pelleted) elemental sulfur at the following rates will increase
iron availability and may improve soil drainage: ½ ounce (14
grams) per cubic foot of soil in sandy soils, 1 ounce (28 grams) per
cubic foot of soil in silty soils, and 2 ounces (56 grams) per cubic
foot in clayey soils. Sulfur should be thoroughly mixed with the soil.
Addition of sulfur is not recommended for cacti, succulents, or other
desert plant species.
If lawns are to be established where caliche occurs, at least eight
inches of topsoil can be placed over the caliche to provide an adequate
medium for the grass.
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