THE IRRIGATION AGE. 



151 



ECONOMICAL USE OF IRRIGATION WATER 



Extensive Tests in Idaho That Indicate the Most Profitable Quantities and the Best Distribution of Water for Ordinary 



Crops Under Average Conditions 



Under condi- 

 tions such a s 

 prevail in Idaho 

 on a normal proj- 

 ect with med- 

 ium clay loam, 

 irrigated land 

 should be sup- 

 plied with suffi- 

 cient water dur- 

 ing the season 

 to enable each 

 irrigated acre to 

 retain 2 feet, ac- 

 cording to a 

 recent investi- 

 gation of the U. 

 S. Department 

 of Agriculture. 

 This applies, it 

 is said, to at 

 least 75 per cent 

 of the irrigation 

 projects in 



Idaho and probably to as large a per cent of the 

 projects in other States. In order that the land 

 may retain the needed 2 feet of water per acre, the 

 former should receive about 2% feet on medium 

 clay and sandy loam soils. Where the soil is porous 

 or has a porous subsoil lying closer to the surface 

 than 6 feet, more than this quantity of water should 

 be delivered to the consumer, the exact quantity 

 depending, of course, upon the porosity of the soil. 

 Where an Idaho project is devoted one-half to 

 grain and the other half to alfalfa or other crops, 

 the total volume of water should be distributed 

 something as follows: 18.7 per cent during May, 

 28 per cent during June, 32.8 per cent during July, 

 17.2 per cent during August, and 2 per cent during 

 the first half of 

 September. After 

 this time the 

 only demand for 

 water is for live 

 stock and do- 

 mestic purposes. 

 These conclu- 

 sions, which are 

 based upon co- 

 operative exper- 

 iments conduct- 

 ed by the U. S. 

 Department of 

 Agriculture and 

 the State Land 

 Board of Idaho, 

 are reported in 

 a new profes- 

 sional paper, No. 

 339, of the U. S. 

 Department of 



Cipoletti Weir With Measuring Rod 



Agriculture, en- 

 titled "Experi- 

 ments on the 

 Economic Use 

 o f Irrigation 

 Water in Idaho," 

 by Don H. Bark. 

 During the 

 course of this in- 

 vestigation the 

 water was meas- 

 ured upon 529 

 individual tracts, 

 covering a total 

 area of slightly 

 over 3,600 acres. 

 The land was 

 used for staple 

 crops, alfalfa, 

 clover pasture, 

 spring and win- 

 ter grains, pota- 

 t o e s and or- 

 chards. 



Experiments show that the yield of grain on 

 the heavier soils such as clay, clay loam, sandy 

 loam, and fine sand, will normally increase with the 

 supply of water until an amount varying between 

 1.4 and 1.8 acre feet has been applied. After this 

 the application of more water will decrease the yield 

 of grain, and, in many cases, the yield of straw as 

 well. Alfalfa requires larger quantities of water, 

 and the experiments did not reach a point at which 

 an increased supply began to lessen the yield. If 

 the yield alone is considered, it is difficult, it is said, 

 to apply too much water to alfalfa, provided no 

 more is applied at one time than the soil will 

 promptly absorb. With both grain and alfalfa, 



, h o w e v e r, the 



amount of water 

 that it is profit- 

 a b 1 e, from a 

 business point of 

 view, to use de- 

 pends upon the 

 relative cost of 

 land and of 

 water and other 

 local economic 

 conditions. 



With pota- 

 toes, it is found 

 that there is a 

 strong tendency 

 for the yield to 

 increase with the 

 supply of water. 

 The rate of in- 

 crease, however, 

 grew smaller as 

 the quantity of 



