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Between the chernozems and gray-brown podzolic soils in the United States lies a zone of prairie soils (or brunizem soils). Rainfall is 25 to 40 in (60 to 100 cm) and diminishes greatly across this belt. This soil group is similar to the chernozems in general profile and appearance, but differs in that it lacks the excess calcium carbonate of the chernozems. The prairie soil is, therefore, a transitional type between the major soil divisions: pedocal and pedalfer.

Of special interest in the United States has been the origin of natural tall-grass prairies of the upper Mississippi Valley and the Great Plains states. Here forest were lacking over vast expanses at the time of the coming of white men. Although many explanations have been offered for the existence of the prairies:, including the possibility of deforestation by burning, it seems likely that a major contributing factor has been that the prairie soils become almost completely dry between summer rains down to a depth of a foot or so (0.3 m) as a result of the dryness and heat of summer air masses. Although the prairie grasses can survive these conditions, deciduous forests, which border the prairies on the east, cannot.

Prairie soils are extremely productive, combining the fertility of the chernozems with somewhat moister climate. Perhaps the outstanding crop associated with the prairie-soil belt is corn. The corn belt is practically identical with the prairie-soil belt, although the corn belt actually extends eastward into the gray-brown forest soils of Indiana and Ohio. Corn requires not only high temperatures during the growing season but ample moisture as well. This last requirement is met by periods of summer thunderstorms inter spread with hot, dry periods.

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