87 



June 15. From two to four waterings suffice for fruit trees in the vicinity 

 of Boulder, Colo. The last irrigation is given on or before September 5, 

 so that the new wood may have a chance to mature before heavy freezes 

 occur. In the Bitter Root Valley, Montana, young trees are irrigated 

 earlier and oftener than mature trees. Trees in bearing are, as a rule, 

 irrigated about July 15, August 10, and August 20, of each year." 



R. W. Fischer, Horticulturist for the Montana Agricultural College, 

 states the following: ^ 



"As a general rule, young trees need not be irrigated more than once or 

 twice during a season. Old bearing trees will require from two to four 

 irrigations. Young trees are irrigated about June 15th and possibly July 

 15th. Old trees are irrigated about June 15, July 1, July 20, and August 

 15th. In connection it may be added that the mean annual rainfall is about 

 12 to 15 inches, about half of which comes in the months of May, June, 

 July and August." 



3. Fall and AVinter Irrigation. 



Experience shows that irrigation too late in the summer keeps the tree 

 in growing condition and the immature growth is easily damaged by the 

 early frost in the fall. This is one of the causes of winter killing of trees. 

 On the other hand when irrigation is stopped too early in the summer and 

 the soil is not retentive, there is insufficient water to meet the demands of 

 soil evaporation and of tree transpiration during the fall and winter, and 

 the soil becomes too dry for the trees, which are consequently damaged or 

 killed. In many orchards the practice is not to irrigate after the beginning 

 of August. In some cases, especially on porous non-retentive soils, it 

 would be well to irrigate in the fall or mid-winter after the leaves have 

 fallen and when there is no danger of starting a second growth. The 

 proper time for this last irrigation would be in late October or in November 

 and only sufficient water should be added to moisten the soil. 



4. Running Water in the Furrows. 



The stream of water or heads used in orchard irrigation depend on the 

 manner of delivering and the depth applied on the land. Some canal com- 

 panies deliver a continuous flow in proportion to the area irrigated, others 

 deliver the water in turns or rotation and each irrigator receives a larger 

 head than by continuous flow for a portion of the time. The second method 

 is preferable. It les'sens the losses of evaporation and seepage, eliminates 

 the waste of a continuous flow when not in use, enables the irrigator to 

 apply the water in a short length of time, and encourages proper applica 

 tion of water. 



The heads delivered to the irrigator for orchard irrigation by furrows 

 may range from a few miners' inches to 100 or more miners' inches. For 

 small orchards heads of from y 2 a cubic foot per second to 1 cubic foot per 

 second or 20 to 40 miners' inches are desirable. The table below gives the 

 time necessary to irrigate 4 inches deep, different size orchards with differ- 

 ent sizes of streams: 



