Formation of the Soils (SS of Dade, Florida)

Soil forms through processes that act on deposited or accumulated geologic material. The kind of soil that forms depends on five major factors—the type of parent material; the climate under which the soil material has existed since accumulation; the plant and animal life in and on the soil; the relief, or lay of the land; and the length of time that the forces of soil formation have acted on the soil material.

The five soil-forming factors are interdependent. Each modifies the effect of the others. Any one of the five factors can have more influence than the others on the formation of a soil and can account for most of its properties. For example, if the parent material is quartz sand, the soil generally has weakly expressed horizons. The effect of the parent material is significantly modified in some areas by the effects of climate, relief, and plants and animals in and on the soil. As a soil forms, it is influenced by one or more of the five factors. A modification or variation in any of the factors results in a different kind of soil.

Parent Material

The soils in this survey area formed in different kinds of parent material. The soils on the Atlantic Coastal Ridge formed in sandy marine sediments. Examples are Canaveral, Dade, Margate, and Opalocka soils.

Some of the soils formed in varying amounts of recently accumulated organic material. Examples are Dania, Lauderhill, and Pahokee soils, which are in low, wet areas (6, 16).

Some of the soils formed in accumulations of marl (calcium carbonate). The marl formed through precipitation of periphyton from fresh water. Biscayne, Pennsuco, and Perrine soils formed in recent accumulations of marl.

The soils in the survey area are underlain by the Miami Oolite Formation, a hard, porous limestone formed from small spherules of calcium carbonate. This formation crops out in many areas.

Climate

This survey area has a humid, subtropical climate. Extreme temperatures are moderated by the Atlantic Ocean and Biscayne Bay. These bodies of water increase the humidity of the area. The average rainfall is about 58 inches per year. The climate aids in the rapid decomposition of organic matter and hastens chemical reactions in the soils. Few differences among the soils within the survey area are caused by local variations in climate.

Plants and Animals

Plants and animals provide the parent material for the organic soils and organic horizons. Periphyton in the form of blue green algae precipitates calcium carbonate from fresh water and forms the parent material of the soils that consist of marl.

Human activities have altered the soils in many areas, creating new soils. Rock-plowing or scarifying in preparation for cultivation completely alters the natural soils and changes the soil classification. Krome and Chekika soils formed through human activities.

Relief

Relief has affected the formation of soils in this survey area mainly through its influence on soil-water relationships. Other factors of soil formation generally associated with relief, such as erosion and temperature, are of minor importance.

Some of the differences among the soils in the survey area are directly related to relief. The survey area is a nearly level plain that has an elevation of 0 to 20 feet. The shallow, mineral soils on flatwoods in the Everglades have a water table within the underlying limestone. Unless a drainage system has been installed, the soils in the swamps and marshes in the Everglades are covered with water for long periods. In many areas they have a high content of organic matter.

Time

Time is an important factor of soil formation. The physical and chemical changes brought about by climate, living organisms, and relief occur slowly. The length of time needed to convert raw geological material into a soil varies, depending on the nature of the geological material and the interaction of the other soil-forming factors. Some of the basic minerals in soils weather fairly rapidly. Others are chemically inert and show little evidence of change over long periods. The translocation of fine particles, which results in the formation of various horizons within the soil, always takes a relatively long time. In terms of geological time, relatively little time has elapsed since the material in which the soils in the survey area formed was laid down or emerged from the sea.

In this survey area the dominant kinds of geological material vary considerably in their resistance to weathering. The sandy material is almost pure quartz and is highly resistant to weathering. The limestone and marl are much less resistant. The finer textured silt and clay are products of the earlier weathering of these materials.

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