182 The Commercial Apple Industry 



water requirements. The Hood River Valley, with an 

 average rainfall of about 35 inches per annum, found 

 irrigation necessary, whenever cover-crops were grown. 



Time to irrigate orchards. 



In practice, the fruit-grower recognizes the need of 

 applying water by a slight change in the color and rigidity 

 of the foliage. It is unwise to wait until the trees begin 

 to show signs of wilting, since this delay may prove injur- 

 ious. It is equally unwise to pour on water just because 

 it is available. Over-irrigation should be guarded against. 



It is generally thought that the amount of free water in 

 the upper three or four feet of soil should range between 

 6 to 10 per cent. For the inexperienced, the following 

 simple test is suggested : Soil samples should be taken from 

 a depth of about 3 feet. Measure out 6 pounds and 4 

 ounces (100 ounces) of soil, expose this to a bright sun for 

 the greater part of a day, and then re-weigh. The number 

 of ounces lost will correspond to the percentage of free 

 water. If the loss is less than 6 ounces the soil probably 

 should be irrigated. More than 10 per cent loss will indi- 

 cate a super-abundance of water. 



Number of applications. 



In the Yakima and Wenatchee valleys, the first irriga- 

 tion is usually given about the first of May, depending 

 on the soil, the slope, and amount of winter rains. A south 

 slope requires water probably two or three weeks earlier 

 than heavy soil or a steep north slope. In Idaho, the 

 first application of water is usually about the first of June, 

 while in Hood River the water is turned on between June 

 first and fifteenth. 



