THE IRRIGATION AGE. 



169 



IRRIGATION EXPERIMENTS IN ARIZONA. 



Investigations Covering a Period of Four Years at the Experi- 

 ment Station Farm at Tucson. 



BY PROF. ALFRED J. k'CLATCHIE, 



Agriculturist and Horticulturist of the Arizona Agricultural Experiment 

 Station. 



During the past four years, especially during the 

 last half of that period, much attention has been given 

 at the station farm to irrigation from various stand- 

 points. One line of investigation has been the deter- 

 mination of the best method and the proper lime for 

 the irrigation of each crop grown in the 

 region. Another study has been the 

 amount of water needed by each crop, 

 and the best procedure for conserving the 

 water applied. The first crop studied 

 carefully along these lines was the sugar 

 beet. Next attention was turned to de- 

 ciduous orchards. Later potatoes, corn, 

 grains, melons, garden vegetables and 

 other crops were given consideration. 

 During the past season a beginning -was 

 made in studying the best method of irri- 

 gating Egyptian cotton, and the amount 

 of water needed for producing a crop. 

 Many data have been obtained that seem 

 worthy of publication at this time, that 

 they may become promptly available to 

 the farmers of the territory. Meanwhile 

 the investigations are being pursued with 

 increasing intensiveness. 



WATER SUPPLY. 



The station farm, where were made 

 the records that are the basis of this bulletin, is situated 

 near Phoenix, just below the Maricopa canal, in the 

 midst of typical Salt River valley farms. The sur- 

 rounding region is devoted to the production of alfalfa, 

 grain, orchard and small fruits and vegetables. The 

 station farm (as are other farms of the section) is 

 supplied with irrigating water from two canals (the 

 Maricopa and the Grand, which in this part of the 

 valley run about a half a mile apart) of the four main 

 ones supplying with water the portion of the valley 

 lying on the north side of the Salt River. The practice 

 being to turn water through two of the four canals for 

 four days and then through the other two for the suc- 

 ceeding four days, water can be obtained for irrigation 

 twice during each eight days by contracting for the 

 delivery of a portion through each of the two canals 

 mentioned above. 



The amount of water received from these canals 

 fluctuates very much during the year, varying with the 

 flow of the Salt River, from which they receive their 

 water. When the river is high enough to make it pos- 

 sible, water is delivered to farmers continuously, or 

 during four successive days with an intervening four 

 days when none is delivered. But as the river falls, the 

 "runs" are shortened more and more, until they may 

 have a duration of but a few hours. Under such cir- 

 cumstances water is available for irrigation from any 

 one canal upon but one day in eight, and small plants 

 are apt to suffer for water, if the weather be hot and 

 dry. By having water delivered through two canals, 

 a farmer can irrigate strawberries, garden vegetables, 

 and other shallow rooted crops every four days. This 

 possibility has been especially necessary during the past 



two summers while water has been so low. Without 

 water being available every four days, it has been prac- 

 tically impossible to maintain a field of strawberries, 

 for example, through the past three trying summers, 

 and in many cases a large percentage of the plants of a 

 field have been lost though watered every four days. 



The cause of the fluctuation of the river flow will 

 be indicated by the following table of the average pre- 

 cipitation at the six stations hi the water shed of the 

 Salt andits tributaries, according to the available records : 



Mmitliiy J an ' Feb ' Mar ' Apr ' May J une J uly Au &- Se P- Oct Nov. Dec. 



81 06t 03 



2.57 1 20 95 1.08 1.90 



WATER REGISTER. 



The variation in the supply of irrigating water from 

 month to month will be indicated by the following 

 table of the flow of the Salt River during the past 

 thirteen years, based upon the available records. 



TABLE I. MONTHLY FLOW OF SALT RIVER IN 1,000 ACRE FEET. 



It is a significant fact that although the rainfall is 

 heavier in the watershed of the Salt River during July 

 and August than during the winter, the flow of the 

 river is usually much greater during the latter season. 

 The parched condition of the watershed and the ra- 

 pidity of evaporation during the hot summer months 

 are undoubtedly responsible for the failure of most of 

 the rainfall of that season to reach the valley below. 

 During the months of December, January and February 

 an average of over three times as much water is avail- 

 able for irrigation as during the summer period of most 

 abundant rainfall. But it is naturally during the sum- 

 mer months that the most water is needed for irriga- 

 tion. The season of greatest need is from February to 

 July. During considerable of this period, especially 

 during May and June, the river, as will be seen by re- 

 ferring to Table I, is commonly low and the supply of 



