IN REPLY TO POWELL: THE DUTY OF WATER IN 



ARIZONA. 



BY W. A. HANCOCK. 



MAJOR J. W. POWELL, in his paper in THE 

 IRRIGATION AGE, for February, has evidently 

 aimed to sustain his assertions before the Irrigation 

 Congress at Los Angeles, and in so doing has fallen 

 into some very grave errors. In the interest of Ari- 

 zona in particular, and the Arid West in general, I 

 propose to give him and his paper a little attention. 



AMOUNT OF WATER REQUIRED. 



Under the head of " The Amount of Water Re- 

 quired" he says: "Grass growing in turf will tran- 

 spire in one day a weight of water as great or greater 

 than the weight of the dried grass, 1 ' and he enumer- 

 ates a number of vegetables, cereals and perennial 

 vines and trees, that will likewise " exhale every day 

 a weight of water equaling the weight of the dried 

 growth of the year." Further on he says, " Thus a 

 ton of hay requires 100 tons of water for its growth, 

 and an acre of grass that will make two tons of hay 

 will require 200 tons of water.' 1 " An acre inch of 

 water weighs 226,600 pounds, or about 11 }<% short 

 tons." 



The truth is that an acre inch of water contains 

 3,630 cubic feet and at 62.3 pounds per cubic foot, it 

 weighs 226,149 pounds, or 451 pounds It^sthan Major 

 Powell states, but it is 11.3 tons instead of 11% tons, 

 and hence the acre of grass will transpire only 1.77 

 acre inches of water, instead of 18 acre inches, as 

 Major Powell claims. If the crop of grass tran- 

 spired 18 acre inches during its growth, it would 

 transpire 2,034 tons instead of 200 tons, or 1,000 times 

 the weight of the dried crop instead of 100 times. 



Major Powell makes the absolute duty of water 

 what the crop will transpire during its growth. As a 

 result, after eliminating his errors, the absolute duty 

 for the crop of two tons would be 1.77 acre inches: 

 Add to this his allowance for evaporation and waste, 

 6 acre inches, and the practical duty is 7.77 acre 

 inches, instead of 24 acre inches as he claims. 



Remember, I do not claim this to be the practical 

 duty of water, but I say that it results from his theory, 

 after eliminating his errors. To follow his theory a 

 little farther, he says the absolute duty of water is 

 what the crops transpire, and that in applying this 

 water under economic conditions the loss by evapo- 

 ration and waste would be 6 acre inches, which must 

 be added to the absolute duty to make up the practi- 

 cal duty; and I will assume that this rule will apply 

 as well after eliminating his mistakes about the abso- 

 lute duty, so that the practical duty should be the 



transpiration of the crops, 1.77 acre inches plus the 6 

 acre inches, for evaporation and waste, or 7.77 acre 

 inches, and all water applied over and above this 

 would be an injurious duty under his rule. Now, let 

 us consider a practical test of the question, in central 

 Arizona. 



AS APPLIED TO ALFALFA. 



The principal plant relied upon for hay is alfalfa. 

 By the 1st of March we give it an irrigation of 4 

 acre inches, 452}^ tons f water per acre. In 50 

 days we cut it, and realize \% tons P er acre. By the 

 1st of May, it is again irrigated with 5 acre inches 

 of water. 565 1 ^ tons per acre. In 45 days we again 

 cut 1*4 tons per acre. This process we repeat 3 

 times more, cutting the last crop about the 5th of 

 November. The total amount of water applied is 

 24 acre inches. If we deduct 6 acre inches for evap- 

 oration, we have 18 acre inches, Major Powell's 

 mistaken duty for one crop of 2 tons, and we have 

 cut 5 crops, making 1% tons per acre. The weight 

 of 24 acre inches is 2,713% tons per acre. If the 

 transpiration is 100 times the weight of the dried 

 crop, and this is the absolute duty of the water, 

 then it, is 750 tons per acre, or 6.66 acre inches, and 

 the evaporation and waste is 1,963% tons of water per 

 acre, or 17.34 acre inches. 



Take the result of one cutting that is produced in 

 45 days with 5 acre inches of water, and the trans- 

 piration would be 150 tons per acre, or 133 acre 

 inches, and the evaporation and waste 414J^ tons per 

 acre, or 3.67 acre inches of water. For another illus- 

 tration of the practical result, I will take a crop of 

 wheat or barley: It may be sown from October 1st 

 to February 15th following, and will be cut from May 

 10th to July 1st, but its growth is principally in Feb- 

 ruary, March and April say 90 days. It is ordi- 

 narily irrigated 3 times, applying altogether 14 acre 

 inches, or 1,583 tons per acre. 



The dried crop, grain and straw, will weigh 2 tons 

 per acre. The transpiration being 100 times the 

 weight of the dried crop will be 200 tons per acre, or 

 1.77 acre inches, and the evaporation and waste must 

 be 1,383 tons per acre, or 12.23 acre inches. 



Now, one more illustration of the practical test on 

 this subject: After our wheat and barley are re- 

 moved, from the 20th of June to the 10th of August 

 we can plant corn on a large proportion of our soils 

 with a certainty of producing a profitable crop, if we 

 are diligent and have the water to apply. To pro. 



351 



