181 Eleventh Annual Report. 



These representative, partial analyses show certain facts 

 bearing upon irrigation: 



The three great rivers of the Territory are seen to be of 

 quite variable character for irrigating purposes, containing in the 

 instances mentioned, from 50 to 200 parts of soluble salts in 100,000, 

 in round numbers. The quantity of soluble salts is influenced by 

 the stage of water and by seepage from irrigated districts. The 

 nature of these salts is influenced by the same causes. The 

 Colorado river is less saline the year around than either the Salt 

 or the Gila. In summer, when its waters rise under the influence 

 of the melting snows in Colorado and Utah, the total soluble sol- 

 ids were observed to average as low as 25 parts in 100,000 for 

 months at a time. 



Flood waters in all cases not only carry less salts but more 

 silt, including nitrogenous fertilizing materials. Barring the in- 

 convenience of excessively muddy water, therefore, flood waters 

 are in every way preferable for irrigating purposes. 



In winter the Colorado water, and in summer the Salt and 

 Gila waters, averaging low and therefore leaching and flowing more 

 slowly through the country drained, carry larger amounts of sol- 

 uble salts and less silt. During the exceedingly dry summer of 

 1900, the solubles in Salt river rose to 156.6 parts, a concentra- 

 tion which in some soils and with tender plants would possibly 

 cause injury if long continued. 



At the foot of irrigated districts both on the upper Gila and 

 in the Buckeye district the soluble salts increase in quantity, largely 

 through the effects of seepage water from irrigated districts above. 

 In its slow passage through the soil, for instance, as shown in the 

 table, the soluble content of the Buckeye supply has increased 

 27, 69 and 127 percent over that of the Salt and Gila rivers 

 above, from which it is derived. This increase of soluble solids 

 is a fact which, together with such matters as the original alkalinity 

 of the soil, the natural drainage, and the crops to be raised, should 

 be duly considered by prospective settlers in a given locality. 



199.2 parts to the 100.000 of wateris equal to 5423 pounds of 

 salts per acre for one acre foot of water. For four acre feet, the 

 amount used per year in mixed farming in some parts of southern 

 Arizona, the total would be 21692 pounds of salts added to the soil 

 in one vear. 



