252 



THE IRRIGATION AGE. 



duce the crop will require 15 acre inches, or 1,696 

 tons of water per acre. The crop when dried will 

 weigh 3 tons per acre. Again applying Mr. Powell's 

 rule that the growing crop will transpire 100 times 

 the weight of the dried crop, and the transpiration 

 will be 300 tons per acre, or 2.65 acre inches, and the 

 evaporation and waste 1,396 tons per acre, or 12.35 

 acre inches. I will say here, further, in regard to the 

 irrigation of alfalfa, some soils will take an irrigation 

 of 12 acre inches in February and March, after 

 which 3 crops, making 5 tons per acre, may be cut 

 without further irrigation. Following the same gen- 

 eral rule the transpiration would be 500 tons per acre, 

 or 4.42 acre inches, and the evaporation and waste 

 would be 856 tons, or 7.58 acre inches. A second ap- 

 plication of 6 acre inches of water, 678 tons per acre 

 will produce 2 tons more of hay, and the transpiration 

 would be 200 tons, or 1.77 acre inches, and the evap- 

 oration and waste will be 478 tons per acre, or 4.23 

 acre inches. 



NOT ABSOLUTELY CORRECT. 



I must remind the reader that I do not make these 

 statements of the duty of water as absolutely correct. 

 There are variables here in central Arizona that I do 

 not pretend to account for or explain. It follows 

 from Major Powell's theory that the absolute duty of 

 water is the amount which the crops produced will 

 transpire while growing, and that the general rule is, 

 that the transpiration will be 100 times the weight of 

 the dried crops. Then by this rule, for the one crop 

 of alfalfa produced with five acre inches of water, 

 the transpiration is 1.33 acre inches. For the five 

 crops in one season the transpiration is 6.66 acre 

 inches, and the evaporation 17.34 acre inches. For 

 the three crops produced by one irrigation of twelve 

 inches, the transpiration would be 4.42 acre inches, 

 and the evaporation and waste 7.58 acre inches. For 

 the crops of wheat or barley using the 14 acre 

 inches, the transpiration would be 1.77 acre inches, 

 and the evaporation and waste 12.23 acre inches. 

 For the crpp of corn using 15 acre inches, the tran- 

 spiration would be 2.65 acre inches, and the evapo- 

 ration and waste 12.35 acre inches. 



Further on, Major Powell repeats that the abso- 

 lute duty of water is 18 acre inches, the possible duty 

 20 inches, and the practical duty 24 acre inches, and 

 all water put upon the land in excess of this is an in- 

 jurious duty. 



He says again, by improved or scientific methods 

 of cultivation, the crops may be doubled or multi- 

 plied five-fold, but under these circumstances the 

 water must be increased proportionately, even to the 

 extent of 60 or 100 acre inches or more. 



How does this correspond with his repeated asser- 

 tion that anything over 24 acre inches is an injurious 



duty? His theory is that for a 2-ton crop the trans- 

 piration is 200 tons, or 1.77 acre inches. 



If the crop is multiplied five fold, it is a ten ton 

 crop, and the transpiration will be 1,000 tons, or 8.85 

 acre inches. He says nothing about any increase in 

 the evaporation and waste, and after deducting his 

 6 acre inches for evaporation and waste, he leaves us 

 with 85.15 acre inches to be disposed of in some way. 

 Is it not an injurious duty? A goodly amount of 

 water surely, to lose any account of, in this arid 

 region. Some of my neighbors would think they had 

 quite a reservoir if they had a pond containing ten 

 acres of that depth. 



SOURCES OF WATER SUPPLY. 



Under the head of " The Sources of Water Sup- 

 ply," Mr. Powell treats of the rainfall and the water 

 catch. He makes his assertions for the most part 

 without assigning any reason for them, and without 

 disclosing how he obtains his information, or arrives 

 at his conclusions. He estimates the run-off at differ- 

 ent depths of the rainfall, but gives us no idea of the 

 proportional area of each, upon which his final esti- 

 mate is made, except by his maps. He gives us no 

 scale except the zones to work by, and as he says, 

 they everywhere run into each other so that no such 

 test could be made, and so far as we can see, it is a 

 mere guess, perhaps as nearly correct as his 11}< 

 tons for the acre inch of water. 



He nowhere states what the mean average runoff, 

 and the mean average flyoff is, on the area claimed to 

 have 20 incrlfcs and less of rainfall. He arrives at 

 the amount in some unexplained way, perhaps as 

 little known to him, as the weight of the acre inch of 

 water, or the 18 acre inches absolute duty of water, 

 and then he slashes off 30 per cent, of it and blandly 

 says that " space does not permit a discussion of the 

 facts which lead to this conclusion." This minus 

 quantity is the possible catch from which he again 

 slashes another 30 per cent, and again " the reasons 

 for this conclusion cannot be entered into for want of 

 space.'' He tells us that he takes into account the 

 runoff from the high mountainous country where the 

 rainfall is consequently great, but he does not tell us 

 what per cent., if any, he adds to the practical catch 

 on that account. 



He calls our attention to the fact that there is 

 little or no runoff from the low level lands, but he 

 fails to state (perhaps because he does not know it) 

 that this low level land is the very land we will irri- 

 gate, and that the rainfall, of from 2 to 10 inches upon 

 it, is of nearly, if not quite, as much benefit to our 

 crops as it would be if it runoff, and was returned to 

 the same, or other land. If we get 10 inches of rain- 

 fall on our crops, and then add thereto the full prac- 

 tical duty of water, are we not putting on 10 inches 

 of injurious water? 



