180 IRRIGATION PRACTICE 



McClatchie observed that, as a result of heavy win- 

 ter irrigations, the tree roots grew while there was no 

 visible growth above the ground. The strengthened roots 

 then made possible rather rapid growth above ground at 

 a later period. Roots were found plentifully to a depth 

 of 16 feet and one was followed to a depth of 20 feet. 

 Available moisture was observed to a depth of 20 to 25 

 feet. The major use of water by the trees was in the 

 spring and early summer. In the later summer the trees 

 were somewhat sluggish so far as the use of water was 

 concerned. As a result of his investigations, McClatchie 

 advised the use of winter irrigation, and not to exceed 

 one summer irrigation, for the successful production of 

 fruit in that section of Arizona. 



It must not be believed, however, that under fall and 

 winter irrigation plants are given less moisture than when 

 the water is added in summer. More likely the liberal 

 use of water in fall and winter, when few farmers use it, 

 means that really more water is thus used for the produc- 

 tion of dry matter. In the experiment above cited, it was 

 found that approximately 48 inches of water were received 

 throughout the season. This was used by the orchard 

 proper, by the cover-crop for the maintenance of soil 

 fertility, and by evaporation. Whether in winter or sum- 

 mer, water should be used sparingly. 



Winter and fall irrigations are two excellent methods 

 whereby the waters which now largely go to waste may 

 be so conserved as to increase the duty of the summer 

 flow. In time, as more reservoirs are built arid all the 

 fall and winter waters are held back in these reservoirs, 

 fall and winter irrigation will not be so important; but 

 even under these future ideal conditions, it may be found 

 desirable to irrigate the soil in the fall, so that, in the 



