to do.  Indeed, the profit in storing and pumping water rests largely upon the economical application of water to crops.  This necessitates the statement of one of the first principles of scientific irrigation practices, namely, that the yield of a crop under irrigation is not proportional to the amount of water applied in the form of irrigation water.  In other words, the water stored in the soil by the natural precipitation and the water that falls during the spring and summer can either mature a small crop or bring a crop near maturity.  A small amount of water added in the form of irrigation water at the right time will usually complete the work and produce a well-matured crop of large yield.  Irrigation should only be supplemented to the natural precipitation.  As more irrigation water is added, the increase in yield becomes smaller in proportion to the amount of water employed.  This is clearly shown by the following table, which is taken from some of the irrigation experiments carried on at the Utah Station:—­

Effect of Varying Irrigations on Crop Yields Per Acre

Depth of Water Wheat Corn Alfalfa Potatoes Sugar Beets Applied (Inches) (Bushels) (Bushels) (Pounds) (Bushels) (Tons) 5.0 40 194 25 7.5 41 65 10.0 41 80 213 26 15.0 46 78 253 27 25.0 49 77 10,056 258 35.0 55 9,142 291 26 50 60 84 13,061

The soil was a typical arid soil of great depth and had been so cultivated as to contain a large quantity of the natural precipitation.  The first five inches of water added to the precipitation already stored in the soil produced forty bushels of wheat.  Doubling this amount of irrigation water produced only forty-one bushels of wheat.  Even with an irrigation of fifty inches, or ten times that which produced forty bushels, only sixty bushels of wheat, or an increase of one half, were produced.  A similar variation may be observed in the case of the other crops.  The first lesson to be drawn from this important principle of irrigation is that if the soil be so treated as to contain at planting time the largest proportion of the natural precipitation,—­that is, if the ordinary methods of dry-farming be employed,—­crops will be produced with a very small amount of irrigation water.  Secondly, it follows that it would be a great deal better for the farmer who raises wheat, for instance, to cover ten acres of land with water to a depth of five inches than to cover one acre to a depth of fifty inches, for in the former case four hundred bushels and in the second sixty bushels of wheat would be produced.  The farmer who desires to utilize in the most economical manner the small amount of water at his disposal must prepare the land