Most areas identified as dust bowls were put into agriculture in periods of relatively high rainfall, and failed badly when climate shifted to slightly less rainfall. The original plant live of these areas had very deep root structures and allowed water to penetrate meters into the soil. With a change to mainly annuals the root structures had to be rebuilt each year, and in particular the early part of the year the roots were not deep enough to sustain crops through a drought. These annual grasses, our grain crops, failed to maintain the condition of the soil in several ways. The humus level progressively declined, and with it the ability of the soil to hold water, the ability of clay particles to be bound to humus, and thus prevent solid barriers to water penetration from forming was lost over several years.
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