Thus many circumstances combine to produce large crops with only a moderate amount of labor. In the United States the average value of the crops on an acre of irrigated land is from 25 to 65 per cent greater than in the country as a whole.
Chief Crops in Irrigated Regions.—(I) Hay.—The most valuable irrigated crop in the United States is alfalfa. It occupies 30 per cent of the irrigated land, and often yields from three to five crops each year. Other kinds of hay crops occupy another 30 per cent of the irrigated land. This is not surprising in view of the fact that in the United States as a whole hay is more important than any crop except corn.
(2) Fruit.—The next most valuable irrigated crop in the United States is grapes and orchard fruits such as prunes, cherries, peaches, and apples. Subtropical fruits such as the orange and lemon stand next in importance. In other subtropical countries where fewer animals are kept and less hay is needed the importance of fruits is even greater. For instance, the chief money crop of Greece is little seedless grapes which are sold in our stores under the name of dried currants. Without them the Greeks would not know what to do for ready money.
(3) Rice.—Although relatively little rice is raised in the United States, it is the most important of irrigated crops in the world as a whole. The crop in this country grows in the semi-monsoon regions along the Gulf and South Atlantic Coasts. Rice is the only great crop the cultivation of which is limited to irrigated regions. It cannot grow properly unless its roots are bathed for months in slowly moving water. Monsoon countries practice irrigation chiefly for the rice crop, although other crops need it in the early spring before the rains arrive.
Irrigation Supports Dense Populations.—Irrigation adds enor mously to the density of population. For instance, in the Ebro and Tagus Valleys of Spain much of the land produces twelve times as much as it would without irrigation and therefore supports a corresponding number of people. Utah has an area of 85,000 square miles, but most of the 400,000 people live in the 1500 square miles that are irrigated. There the population is more than 200 for every
square mile, while elsewhere it is less than one. In Arizona it is estimated that one person is added to the population for every two acres brought under irrigation, or over 300 per square mile. In the Libyan oasis west of Egypt, which would be uninhabited without irrigation, there are 500 people for each square mile. Egypt is still more remarkable. Its cultivated area, including the long, nar row flood plain and the triangular delta, amounts to about 11,000 square miles, and contains 11,000,000 people, or 1000 per square mile. It is one-fifth as large as Iowa, but supports five times as many inhabitants, or twenty-five times as many per square mile.
The effect of irrigation on the density of population is well illus trated by comparing Mesopotamia and Egypt. Both regions have rivers capable of use for irrigation, and both were densely populated before the time of Christ. Then the people degenerated and were troubled by fierce invasions. Accordingly in Mesopotamia the dams and canals were neglected, and were ruined by disastrous floods of the Tigris and Euphrates. Hence for centuries the formerly fertile plains have had almost no population. Now that•the Great War has put this region under the protection of England new irrigation works are being built, and in a few generations the population may be as dense as that of Egypt.
How Irrigation Prevents Famine.—One of the most important advantages of irrigation is that it prevents famine. Thus it saves millions of lives, especially in densely populated areas like India and China. In India the British government has not only carried out great irrigation schemes to reclaim deserts, but has spent millions of dollars to irrigate land that needs water only in occasional years of special drought. One such project cost $1,500,000. Its ordinary receipts from the sale of water are not enough by over $60,000 per year to pay interest and running expenses, but in a single dry year, 1896-7, when the crops would have failed without it, this one project enabled the farmers to raise crops worth $750,000 and saved thousands of lives.