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Show 1364 CONSUMPTIVE USE OF WATER IN IRRIGATION "Detailed experiments have been made by Widtsoe at Logan, Utah, under climatic and irrigation conditions similar to those existing on the North Side tract, to determine the amount of water required to produce a pound of dried crop. The amount of water so required varies with the different factors including kind of crops, degree of fertility, amount of water applied, amount of soil moisture at beginning of season, etc. Detailed results are published in Bulletin 285 of the U. S. Department of Agriculture and Bulletin 116 of the Utah. Experiment Station. For the conditions existing on the North Side Tract during 1917, these experiments indicate that approximately 1 300 lb. of water would be required to produce a pound of dried crop. This includes the transpiration requirements of the plants and evaporation losses from the fields. The average yield of the hay and pasture crops during 1917 was 4i tons per acre. As the hay when cured in the stack contains about 15% moisture, this is equivalent to about 7 600 lb. of dry matter per acre for the hay and pasture crops. The average yield of wheat was determined as approximately 25 bushels per acre and the straw as 1$ times the weight of the grain making a total production of 3 800 lb. of crop per acre for wheat. As the wheat and straw contain about 10% moisture, this is equivalent to 3 400 lb. of dry matter per acre, which is taken as the average yield for crops aside from hay and pasture. The low average grain yields were due to the large acreage on which grain was planted late in the spring as a nurse crop for alfalfa. "The average yield over the entire tract for all crops was then approximately 5 600 lb. of dry matter per acre. At an average water cost of 1 300 lb. of water per pound of dry matter this would require for its production 2.65 acre-ft. of water per acre. This quantity includes the water withdrawn from the moisture stored in the soil and precipitation during the growing season." The water requirement, 2.65 acre-ft. per acre, is equivalent to the consumptive use as herein defined. It must be noted, however, that percentages of moisture in the hay and in the grain are estimates only, that the probable error in measuring the crop yields is unknown, that the percentage of wheat and straw likewise is estimated, and that in the light of these conditions the close agreement of the determinations of the consumptive use by the several methods should not be considered as conclusive evidence of the dependability of the method. Valley Consumptive Use In the early years of irrigation of any valley, the valley consumptive use is relatively large because the deep percolation losses, Dv, go to moisten dry soil to great depths and build up the water-table, and are, therefore, temporarily non-recoverable. Moreover, the non-cropped area is relatively large during the early years of irrigation, and losses therefrom are larger than in later years. Sevier Valley, Utah.-The Sevier Valley, in Utah, is typical of the older irrigated valleys in which deep percolation losses have become very small, since nearly all these losses shortly reach the high water-table which slopes toward the stream channels (or is quickly built up and thus made to slope toward the channels) so that there are very small, if any, non-recoverable losses from percolation. Likewise, the non-cropped area is small, and hence its losses are practically negligible. In this valley it is very probable that the consumptive use is almost equal to valley consumptive use; hence, from Equation (7), U - Hv - Rv. The inflow to, and the outflow from, the Sevier Valley for the 7-year period, 1914 to 1920, has been measured by the Utah State Engineer's Office |
