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ments by ridges. The highest compartment is flooded to the top of the ridge, which is then opened on the lower side. The water thus passes into the next compartment, and this procedure is continued until all the compartments are irrigated. If the land is properly prepared and irrigated before the wheat is sown, two subsequent irrigations will make a good crop. When the soil is thus used as a storage reservoir, in parts of Kansas and California no irrigation is needed between planting and harvesting.

Alkali-Arid region soils are usually rich in mineral ingredients. This is because such soils originated in the de

THE FURROW METHOD OF IRRIGATING

composition of rocks in regions where the rainfall is too scanty to wash out the soluble elements as in humid regions. The soluble salts are naturally distributed throughout the soil, and are not harmful until the application of irrigation water. They are then leached out of the higher grounds and concentrated in the lower lands. Evaporation tends to bring them to the surface. Many irrigation waters also contain much salt in solution, which results in a further deposition of salt. The result of these factors is often ruinous to vegetation. Many thousands of acres have been thus rendered unfit for cultivation in the United States, and the agricultural industries of 59 villages in India were wholly or partly destroyed by the rise of alkali previous to 1864. Water containing over 1,000 parts of salt in a million has been used without injury. Most of the artesian wells of Dakota have a salt content much higher than this, and the effects of irrigating three or four years with this water rendered wheat lands of the Red river valley almost wholly unsuited to raise current crops. The most effective method of removing alkali from land is by underdrainage and flooding. The Cost of Irrigation in the United States as shown by the eleventh and twelfth census is as follows:

[graphic]

Average values per acre

1889 1899 Irrigated land . . . . . . . . . . . . . . . . . . . . . . $83.28 $42.53 Water right . . . . . . . . . . . . . . . . . . . . . . . . 26.00 Annual cost . . . . . . . . . . . . . . . . . . - - - - - - 1.07 0.38 First cost of water rights .......... 8.15 7.80

A rise in values would be expected, instead of a fall, as good lands with water supply were scarce in 1899, and those lands were first irrigated which required least labor and capital. It has been estimated that a perpetual water right in a grain country is worth from $25 to $50 per acre. The cost of irrigation from many of the original ditches was as low as $2 to $5 per acre.”

The Semi-Arid Region of the United States.—There are men still living who knew the Mississippi valley as a wilderness. For several generations a popular American slogan has been “westward the course of empire takes its way,’’ and the rapidity with which the fertile lands of the great river valleys were brought under cultivation has been almost incredible. As this huge wave of immigration swept across the prairie to the great plains, it encountered the subhumid belt as a buffer between the humid and the arid regions. Gradually the settlements proceeded westward from the abundantly watered Mississippi and lower Missouri valleys, and pushed into the well defined subhumid slope which rises progressively toward the Rockies. These virgin lands, bordering upon the greatest wheat raising region of the world, and fully as fertile, since they were not washed by frequent rains, were a continual temptation to carry the “empire” yet farther west. The “Great American Desert” disappeared from the maps. During a series of years in which the rainfall was more adequate than usual, the agricultural areas leaped forward to the west from county to county. The first general advance was in 1883. Within five years, western Kansas and Nebraska and eastern Colorado were largely settled. To the east of the arid region is a strip of territory embracing portions of Kansas, Nebraska, the Dakotas and northwestern Texas, which has been designated as the “rain belt.” Its name resulted from the theory that the humid region was gradually extending itself toward the west as a consequence of the breaking of the prairie sod, the laying of railroad and telegraph, and the advent of civilization. There was supposed to be a progressive movement of the “rain belt.” as civilization advanced. While thorough cultivation undoubtedly makes a material modification in the effects of a given degree of aridity, it has been declared that the probability of a perceptible change in climate does not merit serious discussion.

1 Mon. U. S. Geol. Sur., 25:546-547. * Indus. Com., 10:xxxii.

The theory received a serious setback from the periodical exodus which occurred when succeeding years brought a rainfall at or below the normal. There were years when the average rainfall (10 to 20 inches) decreased by almost half; there were months without a cloud; there were days in the southwest when the winds were so dry and hot that green corn was turned into dry and rattling stalks. When crops shriveled and died on millions of acres, men lost hope and means, and they were forced to abandon the homes that represented the earnings of a lifetime. Whole counties were nearly depopulated. These vicissitudes caused the tide of migration to ebb and flow, and continually wore out its resources. The desert had been removed from the maps. The supplications of the devout and the dynamite of the “rainmaker,” a suggestion of the Indian medicine men who had held sway on the plains less than a century before, had vainly implored the heavens for the rain which alone was wanting for the production of profitable crops. Yet the blunt fact remained, and still remains, that many millions of acres were dead, vacant, and profitless simply because of their aridity. This land has little value now, for in many places a whole section does not yield enough to keep a fleetfooted sheep from starving.

South of Yellowstone park in the Wind river mountains of Wyoming rises Mount Union in majestic grandeur. Three streams take their course from this peak—the Missouri, the Columbia and the Colorado. Embraccd in the branching arms of these streams is the industrial future of a region greater in extent than any European nation save Russia. Could this vast district be reclaimed for settlement, it would be a task second to none in the realm of social economics, for here millions of people could find homes. Within this region is contained practically all that remains of the public domain. The only element lacking to make the land valuable is moisture. New influences are at work to remedy this, the bitter failures of 20 years ago have been largely forgotten, and a second wave of settlement is sweeping over the plains. Rather slowly and unwillingly public attention became fixed upon irrigation. While the water supply is sufficient to irrigate only a small fraction of the arid domain, approximately three-fourths of a billion acres, several million acres are already under irrigation, and there is a good prospect that many more millions will be irrigated in the future. At present this area forms potentially the best part of our national heritage. Although most of the land would be typical for raising wheat, and the completion of the irrigation works which the government now has under way will add millions of bushels to the annual production of wheat, the better adaptability of other crops to intensive cultivation under irrigation will doubtless soon render it unprofitable to irrigate wheat extensively. The introduction of irrigation will make possible the growing of diversified crops in some sections where wheat alone can now be profitably raised. Where the supply of water is insufficient for irrigation, the only remedy is the development of drought resistant crops for dry farming. One of the greatest of these is durum wheat. If there is water enough to irrigate but one acre of ground on the dry farm, this will make a green oasis with shade and foliage for the farmer's home, a pleasant contrast to the monotony of the gray and dusty summer plains with their shimmering waves of heat.

CHAPTER VIII.
IFERTILIZERS

Fertilizing consists in the physical application to the soil of elements which are immediately or mediately available for plant food, or which aid in changing from unavailable to available forms of plant food any elements already existing in the soil. It is meant, of course, to exclude water, the contribution of which is irrigation, but any elements held in suspension or solution by irrigation waters, and falling under the conditions of the definition, are fertilizers.

Historical—The Homeric Greeks were familiar with the use of manure as a fertilizer. Cato mentions irrigation, frequent tillage and manuring as means of fertilizing the soil. To these Virgil adds ashes. The ancient Peruvians were skillful in the application of manure, a practice that has existed in parts of Russia from time immemorial. The earliest records on agriculture show that the value of fertilizing had already been taught by experience. The degree to which intensive cultivation had developed, the natural fertility of the soil, and the incidental occurrence of materials that could be used as fertilizers have always been, in general, the factors determining the extent of the practice.

NATURAL FERTILITY.

Soil Composition and its Relation to Plant Life.—From a physical point of view the soil of the field may be analyzed as follows: (1) The soil proper, consisting of various sizes and arrangements of grains made up of insoluble or imperfectly soluble minerals; (2) humus, more or less decomposed organic matter derived from the decay of former animal and plant life; (3) the soil moisture, covering the soil grains, and containing in solution a varying amount of the soluble soil constituents; (4) the soil atmosphere, differing from air in composition to some extent, and usually saturated with water vapor; and (5) soil ferments, or bacteria, which so permeate the soil that it

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