170 



THE IRRIGATION AGE. 



irrigating water consequently short. This being the 

 season of greatest growth, it is important that crops be 

 supplied with plenty of water. In order to provide for 

 this demand on the part of the crop, the application of 

 large amounts during the winter and early spring is 

 practiced by most farmers. This method is especially 

 useful in the case of orchards and alfalfa, and can 

 be resorted to for soaking soil intended to be used for 

 spring crops. Thus, water is commonly applied at the 

 station farm, and upon other farms of the region, not 

 when most needed by the crop, but when it is available. 

 This is a condition that naturally exists where flood 

 waters are not stored in catchment basins along the 

 river. The beneficial results coming from such a reser- 

 voir can be most nearly obtained by using the soil itself 

 as a storage reservoir. It is hoped that the experiments 

 reported upon in this bulletin, and others in progress, 

 will help farmers to realize the possibilities along this 

 line. Next to storage reservoirs for impounding flood 

 waters, the greatest need of the region is a better under- 



side. The adobe soil is moistened more slowly than the 

 loam, and retains' its moisture longer. Both become 

 quite hard, if permitted to dry without cultivation at 

 the proper stage of desiccation, the adobe soil cracking 

 as it dries. The period during drying when the adobe 

 soil may be cultivated is especially short. In the case 

 of either soil it is very important that a cultivation be 

 given at just the right time, in order to maintain a 

 proper physical condition of the soil. Water does not 

 percolate rapidly through the adobe or the loam 

 stratum ; but when it once reaches the gravel, it passes 

 downward rapidly until the clay is reached. Hence 

 only deep-rooted crops, such as alfalfa and fruit trees, 

 are much benefited by water that passes beyond the 

 stratum of loam. Determinations of the maximum 

 water capacity of the soil of the loam stratum show 

 that the amount of water required to saturate it is ap- 

 proximately two and one half feet. Determinations of 

 moisture content made from samples taken a few days 

 subsequent to irrigation, when superfluous water ap- 





TYTICAL ARTESIAN WELLS AND RESERVOIR NEAR ST. DAVIDS, ARIZONA. PHOTOGRAPHED BY W. W. SKINNER, UNIVERSITY 



OF ARIZONA AGRICULTURAL EXPERIMENT STATION. 



standing of the best way or ways of obtaining the great- 

 est return from the water available for irrigation. 

 While steps are being taken to procure storage facilities 

 in southern Arizona, all can practice economy in the 

 use of water, and thoughtfully make the best of the 

 existing conditions. 



SOIL OF THE STATION FARM. 



The soil of most of the station farm is a clayey, 

 gravelly loam underlaid with a stratum of gravel. The 

 loam is five to six feet deep, and the gravel stratum 

 about eight feet thick, beneath which lies a stratum of 

 fine clay about twenty feet deep. The loam of a portion 

 of the farm is overlaid with a fine adobo, the super- 

 imposed stratum varying in depth from a few inches at 

 one side of the section to six to eight feet at the other 



plied had had time to settle away, showed that the soil 

 a? it lay above the gravel had the power to hold about 

 one and one-fifth feet of water. Hence the latter 

 amount is about what would be necessary to apply to- 

 this soil, if thoroughly dry, to. put it into good condition 

 for the growth of any of the crops reported upon, ex- 

 cept the orchard fruits. Moisture determinations made 

 when the soil was so far dried cut that most crops would 

 suffer for water showed the presence of a little over 

 one-half foot of water in the lo'am stratum of five and 

 one-half feet. Thus the amount of water that might be 

 economically applied at any irrigation would be theo- 

 retically the difference between 1.2 feet and .5 feet, or 

 about .7 feet. This agrees very closely with the amount 

 that experience has shown to be necessary to apply at 



