220 Bulletin 88 



spiles are much used in the Northwest ; in Arizona, however, spiles 

 should be of some other material than wood, which cannot long; 

 withstand the alternate wetting and drying in this climate. Gal- 

 vanized iron, or clay, or cement tile would be preferable. The 

 division of water from cement pipe lines can be made with ease 

 and accuracy, an important argument for their use. 



Frequency of irrigation is a related subject. The smaller the 

 application at each irrigation, the more often the field must be irri- 

 gated. Investigations along this line have not been conclusive 

 except for the peculiar set of conditions under which the tests were 

 made. Many a test has been terminated by the untimely death of 

 the young plants when the irrigations were too infrequent. Sandy 

 soils or other soils that are shallow and underdrained by gravel 

 need frequent applications, while a deep, rich loam, with its large 

 capillary storage capacity, will require much fewer applications. 

 Heavy clay soils, in some places, require frequent irrigations 

 because it is impossible to make them take much water at an 

 application, either because of their physical condition or because 

 they are shallow and are underlain by hardpan that is nearly 

 impervious. 



There is much diversity in Arizona in methods of laying out 

 fields and irrigating. Farmers in the Yuma Valley prefer to grade 

 the lands level from end to end. Elsewhere in southern Arizona, 

 the general cvistom is to run water down the slope parallel to the 

 steeper side of the field, the lands varying from 30 to 100 feet in 

 ' width, and the lengths of runs depending on the slope, soil, crop 

 and the available head of water. In northeastern Arizona the cor- 

 rugation method is used without borders and the water is run 

 down the steepest slopes. In Yavapai County the Colorado system 

 of flooding from field laterals is used for alfalfa and grain. 



Most Arizona soils take water readily. Uniformity of distribu- 

 tion is possible, but requires thought and skill on the part of the 

 irrigator. The use of the proper unit head in each land or in 

 each furrow will prevent waste of water in the upper or lower end 

 of the field and will give an even appearance to the field of grain 

 or other crop. 



WILFUL OR CARELESS WASTE 



This loss includes allowing excess water from the lower end of 

 a field to run onto unused land or, as sometimes happens, into the 

 highways. It is due sometimes to the absence of a good tail border, 

 sometimes to gopher holes, sometimes to a sleepy or forgetful 



