466 Report S.A.A. Advancement of Science. 



production of oats — and thus again the wasteful use of water is 

 emphasised. 



It is generally true with all the ordinary crops grown in the 

 Western States, that increasing the amount of water increases the 

 yield up to a certain point, after which an increase in the water 

 causes a decrease in the yield. Not all the crops are alike in this 

 respect, however. Some crops, because of their nature — leaf 

 surface, root system, etc. — find 10 inches of water about right for 

 the season's growth. Other plants, because of their different 

 natures, find 15 inches or 20, or 25 to 30 inches the best. Now, the 

 farmer in an irrigated district should know the water requirements 

 of the different plants that he grows as thoroughly as he knows the 

 soil of his farm, his water right, or any other matters upon which 

 his success as a farmer depends. Not all plants decrease in yield 

 after a certain amount of water has been applied. Potatoes appear 

 to be a crop, the yield of which increases continually if water is 

 applied, up to the limit of the practical application of water. 

 To illustrate : — in one set of experiments, 7I inches of water pro- 

 duced 160 bushels of potatoes; 15 inches 233 bushels; 30 inches 

 274 bushels; and 71 inches 315 bushels. This illustrates the 

 necessity for the farmer to thoroughly understand the nature of the 

 plants with which he is dealing. 



It may be noted, in reviewing the yields of wheat, oats, and 

 potatoes just considered, that the value of the first few inches of 

 water applied is much greater than that of the later applications. 

 For instance :— 5 inches of water produced about 33 bushels of wheat, 

 or about 6.6 bushels per inch; 15 inches of water produced about 40 

 bushels of wheat, or about 3.2 bushels per inch of water; while 20 

 inches of water also produced 40 bushels of wheat, or only two 

 bushels per inch. The value of the first 3 inches of water applied 

 to wheat, therefore, is more that three times as much as the value of the 

 last 5 inches, in a total depth of 20 inches. Similar results mav 

 be observed in the case of oats. Five inches of water produced 58 

 bushels, or 12 bushels per inch; while 20 inches of water produced 

 86 bushels of oats, which is less than 5 bushels per inch of water. 

 The difference is certainly very striking. Even in the case of 

 potatoes, the yield of which increased steadily with the increase of 

 irrigation water, the same fact holds. Seven and one-half inches 

 of water produced 160 bushels, or about 22 bushels per inch ; while 

 30 inches of water produced 274 bushels, which is only about nine 

 bushels per inch. Corn, alfalfa (lucerne), the various grasses, sugar 

 beets, vegetables and all other crops show similar results ; namely, 

 that the value of water is highest when it is used sparingly and 

 carefully ; that the value of water is lowest when it is applied 

 liberally and carelessly. With this generalisation in mind, note 

 how these results may be viewed in their relation to the increase of 

 the irrigated area. 



According to the investigations of the Department of Agri- 

 culture, under the direction of Dr. Mead and his associates, 30 



