THE IRRIGATION AGE 



305 



IRRIGATION EXPERIMENTS IN ARIZONA. 



Investigations Covering a Period of Four Years at the Experi- 

 ment Station Farm at Tucson. 



BY PROF. ALFRED J. M'CLATCHIE, 



Agriculturist and Horticulturist of the Arizona Agricultural Experiment 

 Station. 



(Continued.) 



ORCHARDS. 



Since it is important that trees be properly irri- 

 gated from the first, it will be well to begin the dis- 

 cussion of orchard irrigation with the setting of the 

 trees. During the first year all varieties of fruit trees, 

 whether . decidiious or citrus, need to he treated in 

 about the same manner. 



excellent check to the flow of the irrigating water, as 

 well as a benefit otherwise. When the winter irrigation 

 is finished the soil should be thoroughly cultivated to a 

 depth of eight to. twelve inches, and the surface be 

 permitted to remain dry until the time of the summer 

 rains. 



Where the soil is of the proper character the tree 

 roots penetrate to great depths, enabling them to 

 thrive though the surface stratum be quite dry. In 

 the station orchards their roots are abundant at a 

 depth of twelve to sixteen feet, and many of them 

 penetrate to a depth of more than twenty feet. This 

 characteristic makes it possible to store in the soil 

 during winter much, if not all, of the water needed to 

 produce a good crop. To one orchard at the station 

 farm all of the water used by the trees during the 



Hg. 4. Irrigating young strawberries through shallow furrows. 



Before the trees are set furrows are run near the 

 lines of the tree rows for the early irrigations. Usually 

 water is run through the furrows before the trees are 

 set, and as soon thereafter as practicable. The fur- 

 rows should be cultivated up within a month, and 

 fresh ones made for each subsequent irrigation. The 

 young orchard should be irrigated .only along the tree 

 rows, and the soil should be kept moist to a depth of 

 several feet. This will induce the trees to send their 

 roots down deeply, instead of out laterally near the 

 surface. Deep irrigation followed by deep cultivation 

 will prevent the growth of roots near the surface. 

 Since much depends upon the treatment of the orchard 

 during its early growth, it pays to give the trees special 

 attention the. first season. 



As the trees get older they will need less frequent 

 irrigation during the growing period, and more of the 

 water may be applied during winter. After they are 

 four or five years old, at least three-fourths of the 

 water needed may be applied to deciduous trees during 

 January. February and March. The remainder needed 

 may be applied when water is most abundant during 

 summer. The furrows do not need to be cultivated 

 up. after each winter irrigation ; but they should be re- 

 newed as often as once a month, if a green manuring 

 crop is not grown in the orchard. Such a crop is an 



past three seasons has been applied from December to 

 March, while the trees were dormant above the surface. 

 That they were not dormant beneath the surface was 

 shown by an examination made February 20, 1900, 

 revealing that, at a depth of ten to sixteen feet even, 

 young roots three to six inches longs had already 

 grown. 



As demonstrated by experiments reported on in 

 bulletin No. 37, a deciduous orchard may be kept in 

 excellent condition and will produce good crops of fruit 

 if irrigated during the winter only. In fact, the re- 

 sults from the winter-irrigated orchard were better 

 than from the same orchard irrigated during earlier 

 years through the summer, and better than from other 

 similar summer-irrigated orchards the same seasons. 



Aside from the difference in the results obtained, 

 and the amount of labor involved, it should bo taken 

 into consideration that the water available during the 

 winter has a much less value, upon account of its com- 

 parative abundance, than the water available during 

 the summer. ' Even if a greater amount were used by 

 the winter-irrigating plant it would still be the .cheaper 

 method. 



. Citrus orchards, upon account of being evergreen, 

 need somewhat different treatment than do deciduous, 

 orchards. In deep soils a large part of the water they 



