148 THE APPLE 



the floor of each check. The water is admitted through the check 

 box which was used for the alfalfa, and conducted into a short head 

 ditch, from which it is distributed to the furrows. The chief ob- 

 jection to this method is that the checks are too small for orchard 

 tracts in furrow irrigation. 



Time to irrigate. The best orchardists believe that frequent 

 examinations of the stem, branches, foliage, and fruit are not suffi- 

 cient to determine the true condition of the trees. The roots and 

 soil should also be examined. The advice of such men to the 

 inexperienced is : Find out the position of the greater part of the 

 feeding roots, ascertain the nature of the soil around them, and 

 make frequent tests of the moisture of the soil. In a citrus orchard 

 of sandy loam, samples are taken at depths of about 3 feet and the 

 moisture content determined by exposing the samples to a bright 

 sun for the greater part of a day. It is considered that 6 per cent, 

 by weight, of free water is sufficient to keep the trees in a vigorous 

 condition. 



Dr. Loughridge 1 found an average of 3.5 per cent in the upper 

 2 feet and an average of 6.16 per cent below this level in an 

 orchard that had not been irrigated since October of the preced- 

 ing year. It had received, however, a winter rainfall of about 

 16 inches. On examination it was found that most of the roots 

 lay between the first and fourth foot. These trees in June seemed 

 to be merely holding their own. When irrigated July 7, they began 

 to make new growth. A few days after the water was applied the 

 percentage of free water in the upper 4 feet of soil rose to 9.64 per 

 cent. The results of these tests seem to indicate that the percentage, 

 by weight, of free moisture in orchard loams should be between 

 5 and 10 per cent. 



Many fruit growers do not turn on the irrigation stream until 

 the trees begin to show such signs of suffering as a slight change 

 in color or a slight curling of the leaves. In waiting for these 

 signals of distress both trees and fruit are liable to be injured. 

 On the other hand, the man who pours on a large quantity of 

 water whenever he can spare it, or when his turn comes, is apt 

 to cause more damage to the trees by an overdose of water. 



1 R. II. Loughridge, assistant professor of agricultural geology and chemistry 

 in the University of California, in experiments at Riverside, California. 



