What Is Arid Soil?

Composition

• The composition of the soil depends on the material from which it eroded. Generally, soil falls into two categories: organic soils, which form largely from decomposing plants; and mineral soils, which form from eroding rocks. Arid soils fall into the latter category, containing little organic matter. This means that even when arid regions receive rain, it drains through the spaces between soil particles quickly. Since these regions often go long periods without heavy rainfall, large deposits of calcium carbonate, gypsum and sodium form underneath the surface of the soil.

Problems

• All soils gather salt deposits as they form, but in areas that receive consistent rainfall, the sodium leaches out of the soil. This does not occur in arid regions, and salt deposit tend to gather underneath the surface of the soil at the deepest point of water penetration. The salt deposits then bind with gypsum and calcium to form a concrete layer, inhospitable to plants. Not all soils in arid and semi-arid regions have this problem, however. In areas that receive heavy rains at times, the concrete-forming nutrients leach out of the soil.

Identification

• Much of the time you can see arid soils, although they may not look like you expect. Only a few are completely barren and sandy. Most arid regions, especially in the United States, have at least sparse vegetation mostly in the form of grasses and shrubs. The surface of arid soil tends to look lighter than richer soils, due to the lack of organic matter present. If you dig through the topsoil, you may find white salt deposits and hit the hard concrete subsoil.

Improvements

• Once you identify the problem, you can take steps to alleviate it. As a gardener, you actually have an advantage over large crop farmers, as you have a relatively small area to make hospitable for your plants. Mix 3 to 4 inches of an organic matter, such as compost or decomposed manure, into the top layers of your soil, down 6 to 8 inches. This will increase the arid soil's ability to hold water. Before planting, you'll also have to water the area to a depth of at least 8 inches to leach the salt, gypsum and calcium carbonate out of the soil. In many areas, arid soil is not actually infertile; it just lacks the proper amount of moisture to sustain plants.