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Steppes support a short-grass vegetation cover suited to grazing of cattle and sheep, but inadequate for farming without irrigation or special dry-farming methods. Special attention is given by geographers and climatologists to the boundary between dry and humid climates, particularly because the limits of agriculture without irrigation are drawn by nature as a fluctuating line over a hazardous frontier zone. Here, productivity may in some years be high; in others, drought brings disastrous failures. Let us define a humid climate as one in which the precipitation on the average exceeds evaporation, so as to give permanently flowing streams and a generally moist soil; a dry climate as one in which evaporation on the average exceeds precipitation, so as to give ephemeral streams and a generally dry soil. This shift is explained by the temperatures, which are higher in the south and result in greater evaporation losses.
2. Main article
Middle-latitude steppes are characterized by short-grass prairie and by local occurrences of woodland and semi-desert shrubs. Middle-latitude steppes now constitute the great sheep and cattle ranges of the world. On the vast expanses of the High Plains, the American bison lived in great numbers until almost exterminated by hunters. Likewise, the short-grass veldt of South Africa supported much game at one time.. Steppe grasses do not form a complete good cover, and loose, bare soil is exposed between grass dumps. For this reason, overgrazing or a series of dry years often reduces the hold of grasses enough to permit destructive soil erosion and gullying from heavy local downpours.
3. References
Soils of the steppe lands are deficient in humus. They belong to the group of brown soils in less dry parts; Calcium carbonate is present in excess quantities and may form modules in the soil. Encrustations of calcium carbonate make a hard, whitish crust termed caliche in the southwestern United States. These calcium-rich soils are highly fertile in terms of bases favorable to grain crops, such as wheat, but unless irrigation is employed the advantage is lost. Traced toward humid-climate zones, which adjoin the steppes, the soils be-come darker brown in colour, denoting the increasing amounts of humus from heavier growth of grasses. Thus the grey or red desert and steppe soils grade into the rich, dark brown and black chestnut and chernozem soils of the prairies.
