"rain belt." Its name resulted from the theory that region was gradually extending itself toward the consequence of the breaking of the prairie sod, the railroad and telegraph, and the advent of civilizati was supposed to be a progressive movement of the "" as civilization advanced. While thorough cultivation edly makes a material modification in the effects of a gree of aridity, it has been declared that the proba perceptible change in climate does not merit serious The theory received a serious setback from the exodus which occurred when succeeding years brough at or below the normal. There were years when t rainfall (10 to 20 inches) decreased by almost 1 were months without a cloud; there were days in the when the winds were so dry and hot that green corn into dry and rattling stalks. When crops shriveled a millions of acres, men lost hope and means, and forced to abandon the homes that represented the ea lifetime. Whole counties were nearly depopula vicissitudes caused the tide of migration to ebb an continually wore out its resources. The desert ha moved from the maps. The supplications of the the dynamite of the "rainmaker," a suggestion of medicine men who had held sway on the plains century before, had vainly implored the heavens f which alone was wanting for the production of prof Yet the blunt fact remained, and still remains, tha lions of acres were dead, vacant, and profitless sim of their aridity. This land has little value now, f places a whole section does not yield enough to k footed sheep from starving. Ne people could find homes. Within this region is contained tically all that remains of the public domain. The onl ment lacking to make the land valuable is moisture. fluences are at work to remedy this, the bitter failures years ago have been largely forgotten, and a second wa settlement is sweeping over the plains. Rather slowly an willingly public attention became fixed upon irrigation. the water supply is sufficient to irrigate only a small fra of the arid domain, approximately three-fourths of a b acres, several million acres are already under irrigation there is a good prospect that many more millions will be gated in the future. At present this area forms potential best part of our national heritage. Although most of the would be typical for raising wheat, and the completion irrigation works which the government now has under waj add millions of bushels to the annual production of whea better adaptability of other crops to intensive cultivation irrigation will doubtless soon render it unprofitable to ir wheat extensively. The introduction of irrigation will possible the growing of diversified crops in some sections wheat alone can now be profitably raised. Where the supp water is insufficient for irrigation, the only remedy is the opment of drought resistant crops for dry farming. One greatest of these is durum wheat. If there is water enou irrigate but one acre of ground on the dry farm, this will a green oasis with shade and foliage for the farmer's ho pleasant contrast to the monotony of the gray and dusty mer plains with their shimmering waves of heat. It is meant, of course, to exclude water, the contr which is irrigation, but any elements held in suspens lution by irrigation waters, and falling under the con the definition, are fertilizers. Historical-The Homeric Greeks were familiar wit of manure as a fertilizer. Cato mentions irrigation tillage and manuring as means of fertilizing the soil. Virgil adds ashes. The ancient Peruvians were skill application of manure, a practice that has existed in Russia from time immemorial. The earliest records culture show that the value of fertilizing had alr taught by experience. The degree to which intensive ( had developed, the natural fertility of the soil, and th tal occurrence of materials that could be used as have always been, in general, the factors determining of the practice. NATURAL FERTILITY. Soil Composition and its Relation to Plant Life. physical point of view the soil of the field may be a follows: (1) The soil proper, consisting of various arrangements of grains made up of insoluble or in soluble minerals; (2) humus, more or less decompos matter derived from the decay of former animal and (3) the soil moisture, covering the soil grains, and in solution a varying amount of the soluble soil co (4) the soil atmosphere, differing from air in comp some extent, and usually saturated with water vapor soil ferments, or bacteria, which so permeate the s the plant indirectly through their influence upon the c sition of the soil. At the beginning of the nineteenth century Sir Hum Davy said that the substances which constitute the soil certain compounds of the earths, silica, lime, alumina, mag and of the oxides of iron and magnesium; animal and vege matters in a decomposing state, and saline, acid or alkaline binations."'1 He also fully understood that the soil furnished nourish for the plants, and that different plants flourish best in diff soils. While he described the soil elements, often with prising accuracy, and was the most expert chemist of his he did not adequately appreciate the plant foods contain the soil, and his conception of the functions of the ele which he described was often extremely vague. For exa he held that the silica which plants contain imparts to their rigidity. He recognized in a general way, however, phosphoric acid, potash and lime enter into the compositi plants, and he successfully combated many unscientific no The derivation of soils from rocks was also known in his Mineral or artificial manures were first studied systemat by Liebig, whose views found their way into the United S before the middle of the century. The publication of his in 1840 marked a new era in agricultural chemistry. B his time it was very generally held that organic substances the chief food of plants. This has been called the h theory. It was rejected by Liebig, who went to the opp extreme and held that organic matter has no part in plant Practical knowledge of the use of manures, wood ashes, sl terhouse refuse, gypsum, lime and plaster as fertilizers widely diffused and acted upon before the time of Liebig 1 Yearbook U: S. Dept. Agr., 1899, p. 203. early date, and then it was only another step to supply artificially the needed water. Irrigation was a condition that was indispensable to the settlement of large portions of western America, Australia and South Africa. In meeting these problems during the nineteenth century, the Anglo-Saxon race had its first experience with extensive irrigation. Throughout all the centuries of previous history, the art of irrigation was quite exclusively the possession of Indian, Latin and Mongolian races. It was used extensively by the ancient Chinese, Egyptians, Persians and by the people of India. The Homeric Greeks used small canals in irrigating. In Italy, it was probably as old as the Etruscans. The Romans borrowed the system from the east, and brought it to their country and southern France. The ancient Peruvians also practiced it, and in Spain it dates back to the Iberian life existing under the Roman conquerors. Modern Irrigation in Foreign Countries.-Irrigation is more or less extensively practiced by all of the great nations of the globe, even in subhumid and humid regions. As a rule, however, the wheat crop is not extensively irrigated, for irrigation is more profitable with other crops. The total area watered runs into millions of acres in most of the European nations. Wheat is frequently irrigated in the Po valley. In Mexico, Argentina and Australia, wheat is irrigated to some extent. Both streams and wells furnish the water. Extensive systems have been planned for Australia, and over 1,000,000 acres could be irrigated in New South Wales alone. Argentina contains large areas which are irreclaimable except by irrigation. The lower valley of the Nile with its delta comprises another great irrigation system, 6,000,000 acres being under cultivation. Egypt is so arid that dry farming is impossible. In 1902 British enterprise completed a dam across the Nile at Assuan. It is built of granite, and is 70 feet high, 23 feet wide at the top, 82 feet wide at the bottom, and 14 miles long. It is the largest irrigation dam in existence, and the reservoir has a storage capacity of over thirty billion cubic feet. The largest increase in irrigated area in recent years has been made in British India, where about 30,000,000 acres have been reclaimed or made secure for cultivation by constructing new supply works. It has been estimated that 80,000,000 acres more can be reclaimed in India. In 1892 over $150,000,000 had been |