YIELD PER ACRE. =========+===========+===========+=========+============= Number of| Weight of | Weight of | Total | Water used. Bushels. | Grain. | Straw. | Weight. | Acre-inches. | Tons. | Tons. | Tons. | ---------+-----------+-----------+---------+------------- 15 | .45 | .675 | 1.125 | 4.498 20 | .60 | .90 | 1.500 | 5.998 25 | .75 | 1.125 | 1.875 | 7.497 30 | .90 | 1.350 | 2.250 | 8.997 35 | 1.05 | 1.575 | 2.625 | 10.495 40 | 1.20 | 1.800 | 3.000 | 12.000 ---------+-----------+-----------+---------+------------- S. Fortier has made several series of tests to determine the actual yield of grain crops under field conditions when supplied with different amounts of water. Two of these were made at the Montana experiment station in 1902 and 1903, (see reports of these years), in large tanks placed in a field, level with the ground. The results of the last year’s experiments are shown graphically in the figure below, from which it will be seen that the yield increased quite regularly with the amount of water supplied, up to the depth of 36 inches of water. [Illustration: FIG. 37.—Experiments on Cereal production with various amounts of water (Fortier, Report Mont. Expt. Sta., 1903).] It should be noted that in this case (and as usual) not only the quantity but the quality of the grain was greatly improved as the water-supply increased, it becoming larger and more uniform in size. Of similar experiments made in the San Joaquin Valley, California, in 1904, Fortier says:[68] “In experimenting with barley last winter the natural rainfall, which amounted to 4½ inches during the period of growth, produced at the rate of nine bushels per acre, while the application of sixteen inches of water increased the yield to twenty-two bushels per acre. In the same case; of wheat, the rainfall, alone, produced straw, but no grain; four inches of additional irrigation water produced a yield at the rate of ten bushels, and sixteen inches of water increased the yield to thirty-eight bushels per acre.” [68] “Water and Forest,” January, 1905. “The Use of Water,” by S. Fortier. It is thus obvious that, other things being equal and with conditions sufficiently favorable for the growth of crops, the rule as formulated above is verified in practice. Whitney (Bulletin 22, Bureau of Soils, U.S. Dept. Agr.), has carried this rule so far as to claim that in all soils, the moisture supply is the _only_ important factor, and that so long as this is provided for, soil fertility continues indefinitely without replacement of ingredients withdrawn. The latter conclusion is so thoroughly disproved by experience as well as experiment that it hardly requires discussion here.