wheat is greatest when the crop follows either corn or potatoes. After these crops, placed in the order that they merit for preparing the soil for wheat, come summer fallow, millet, vetch, peas, wheat and oats. The more dry and unfavorable the season, the more important it was to introduce a cultivated crop into the rotation. The best rotations included a perennial grass, for which purpose brome grass is well adapted to North Dakota. The rotations vary greatly in different states, and soil, climate, and economic causes must determine which rotations are most advantageous for any locality. Summer fallowing is widely practiced on the Pacific coast, largely because there is practically no rotation feasible.

Crop Rotations in Foreign Countries.-In Canada, summer fallowing is rapidly becoming general throughout the territories, where the profitable corn crops of the United States cannot be grown on account of the latitude. The system of agriculture most prevalent in Russia is the three-field system, which is universally practiced in the center of the Russian wheat belt. The usual sequence of crops is winter rye, spring wheat and fallow. The arable land is divided into three corresponding parts. At a given time each part is in a different stage of the system. Other crops are being introduced, and this is lessening the area of fallow land. Among the private land owners this signifies progress in agricultural methods. Among the peasants it frequently signifies a harmful overworking of the land, the penalty of which is the drastic retribution of greatly reduced yields. Another system, still more primitive than the three-field one, is also found in Russia, especially in the steppes of the southeast, where the greatest extension of the wheat area is taking place. By this system the land is tilled until it becomes exhausted. It is then allowed to lie fallow in order to recover its fertility. This may require 10, 15, or even 30 years. In Archangel, Olonetz, Vologda, Viatka and Perm, the forest must be cleared to prepare the new land for cultivation, but in the southeastern provinces of Orenburg and Astrakhan, in New Russia, Kherson and northern Caucasia, all that is required is to plow the land. As population grows, this wasteful method of farming is being replaced by the three-field system. Impoverishment of the land by continuous wheat cropping

has been the custom in Argentina. Sixty per cent of the wheat is raised under the renting system. The colonist owns nothing which grim necessity does not compel him to own, and he practices his ruinous methods of farming until the land is completely exhausted. Then he fastens the bullocks and horses to the carts, packed with his many children and his few miserable pots, boxes, beds and implements, and travels until he finds new fields. Mixed farming as known in the United States is little understood or practiced in Argentina, and the farmer is generally either a wheat grower or a maize grower. There is complaint of the methods of farming in all parts of the Republic, however, and a practice of rotating crops is already beginning, by alternating wheat and maize, or by planting the land with alfalfa after three or four years of wheat cropping.'

For the best crops of wheat in Egypt, it is sown every fifth year, the rotation being (1) cotton; (2) "birsen" (clover) or "full" (beans); (3) wheat; (4) dura (maize); (5) "birsen." A commercial success has been made of growing wheat and alfalfa together on the dry uplands of North Africa. In Algeria two rows of wheat are sown 4 inches apart. A space of 40 inches is left between the double rows, and in this space the alfalfa is sown. Wheat is sown only every other year. This is of interest, as alfalfa is now the greatest American fodder crop, especially in the arid southwest where durum wheat is being more extensively grown.

Experiments with Mixed Crops have been made, chiefly in Canada and North Dakota. Results seem to be in favor of unmixed grain, although wheat and flax have an advantage under certain conditions, as when wheat is apt to lodge, or when there is a superabundance of moisture. In the latter case flax has increased the yield of wheat as much as 6.5 bushels per acre, in addition to giving 1.2 bushels of flax per acre.

IRRIGATION.

Historical. Irrigation is of prehistoric origin. Water, as was shown in a former chapter, is one of the greatest essentials of all plant growth, and it is also one of the most variable quantities involved. Since the effects of these variations upon vegetation appear quickly, they must have been noticed at an

1 U. S. Dept. Agr., Bu. of Statistics, Bul. 27 (1904), pp. 41-42.

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

invested, and yielded a large profit, though it was often obtained indirectly. India has the largest reservoir in the world. It covers an area of 21 square miles, and it was constructed for irrigating in Rajputana. It is known as the great tank of Dhebar.

Irrigation in the United States.-In America, the town-building Pueblo Indian tribes practiced irrigation perhaps a thousand or more years ago. Their ditches and canals can still be traced in the little valleys near the mesas of southwestern Colorado and adjacent portions of Utah, Arizona and New Mexico, where the cliff dwellings are found, as well as across the border valleys through which are scattered numerous ruins of community dwellings. Their knowledge of engineering is evident, and remarkable. Careful levels have been run over several miles of their canals. The grade was found to be fairly uniform and suited to a canal of such dimensions, as well as in accord with present day knowledge of hydraulics, safe velocities and coefficients of friction. While these well defined remains of ancient irrigation works have long outlived the civilization to which they belonged, there are cases where they have been utilized in modern works. The ditches at Las Cruces, New Mexico, have been used uninterruptedly for over 300 years. Some 70 years before the settlement of Jamestown, the Spaniards irrigated on the Rio Grande. Adventurous mission fathers pushed on to California, carrying the art of irrigation with them.

The beginnings of irrigation by English-speaking people in this country were in the Salt Lake valley of Utah, in July, 1847. The Mormon pioneers, driven out from Illinois and Missouri, stopped from necessity on the shores of the Great Salt Lake. They diverted the waters of the little canyon streams upon the present site of Salt Lake City, so that they might raise a crop from the very last of their stock of potatoes and save the band from starvation. At about the same time water for irrigation was drawn from the ditches used for placer mining by the gold miners of California. After the stoppage of hydraulic mining by the passage of anti-débris laws, the ditches were either abandoned or used exclusively for irrigation. Many were enlarged and are still used.

The Extent of Wheat Irrigation in 1899 is shown in the table below:1

While considerable wheat is irrigated in some states, practically all that is grown in them, yet the average per cent of irrigated wheat in all the irrigating states is relatively small, only 14 per cent. Excluding California and Washington, where much wheat is raised and little irrigated, this rises to 36.5 per cent; 17.7 per cent of the wheat produced is irrigated, compared to 14.1 per cent of the acreage. On this basis which, however, takes no account of differences in soil, rainfall and climate, the yield in these states would be increased over 25 per cent if all the wheat were irrigated.

The Problems of Irrigation in our country are, and have been. along two general lines: Agricultural and engineering; and legal and social. Of these two lines, the latter has presented the greatest difficulties. Litigation and controversy have been a menace and a source of loss to many communities because no institutions existed for adequately defining, limiting and protecting water rights. The claims of navigation came into conflict with those of irrigation. When streams flowed through more than one state, interstate difficulties arose. Some of these are the basis of a suit by the state of Kansas against the state of Colorado.

Work at the solution of either class of problems has been immensely handicapped by a most lamentable lack of knowledge

1 12th U. S. Census, 6:825-870.