Page:Popular Science Monthly Volume 48.djvu/681

Rh of Kentucky, the black prairies and "bluff"-lands of the Mississippi Valley, and hundreds of local examples. The common and beneficial practice of "marling" noncalcareous lands illustrates the same axiom. It logically follows that, inasmuch as actual examination shows practically all arid soils to be calcareous, "arid countries are rich countries" whenever irrigated; and the actual and concordant experience of mankind corroborates the conclusion.

In other words, the ancient civilizations have, consciously or unconsciously, chosen countries having naturally rich and durable soils, capable of supporting for a long time a denser population than the forested regions, without resort to artificial fertilization beyond irrigation. This seems to be the simple and rational explanation of their marked preference for arid countries; and unquestionably Egypt owes its perennially undiminished productiveness at least as much to its arid climate as to the alluvial deposits brought down by the Nile, as is shown in the oases of the Libyan Desert, as well as in India and China.

But if these things are true, then the steppes and alkali lands deserve the most earnest attention, both of agriculturists and of students of natural economy; for in them lie possibilities for the abundant sustenance and prosperity of the human race that have thus far been almost left out of account. While it is true that irrigation water may not be practically available for the whole of the arid regions of the globe, so much remains to be done in the study of the most economical use of water, of appropriate crops and methods of culture, that even an approximate estimate of actual possibilities in this direction can not yet be made. At all events, it is of the highest interest to study the problem of the reclamation of these intrinsically rich lands in all its phases.

Foremost in this problem is the question of the manner of dealing with the "alkali" salts, which, as experience proves, exist not only on the spots where they naturally show on the surface, for as soon as irrigation is practiced they appear at numerous points where no symptoms of alkali were noted before. Sometimes, indeed, the entire area of large farms may in the course of years become thus afflicted, so that orchards and vineyards that have been in bearing for a number of years become stunted, and in spots even perish.

Examination of the manner in which such injury comes about shows that it is rarely due to direct action of the salts on the roots. Almost always the injured part is at or near the root-crown, or base of stem or trunk; proving that it is the result of accumulation of the salts at the surface (so often obvious to the eyes), in consequence of evaporation.