286 University of California Publications in Agricultural Sciences [Vol.3 



the first six inches to .012 per cent at a depth of three feet. He also 

 reports the nitrifying power of the soil as fairh' good and the 

 ammonifying power as high. The organic matter content is quite low, 

 much lower, in fact, than one would suppose from the healthy appear- 

 ance of the trees. 



Irrigation water is pumped from wells situated on the tract and the 

 irrigation practice follows closely that of southern California. Water 

 is applied in four shallow furrows to each middle about once a month. 

 This is followed in a few days by shallow cultivation in both direc- 

 tions. The amount of water applied is sufficient to wet the soil five 

 feet deep and throughout the whole area except for a small space 

 between the trees in each tree row. In June the temperature of the 

 water as used is about 75° F. Hilgard advanced the idea that June 

 drop might be caused l)y low temperature of the irrigation water. 

 While it is entirely po.ssible that cold water may influence drop, we 

 have found the drop to occur regularly where the water was not cold. 



A practical horticulturist after examining the trees and digging into 

 the soil would hardly CDnelude that the trees were suffering for w-ater. 

 Moreover, Portier states" that in sandy loam soils 6 per cent by weight 

 of free water is sufficient to keep citrus trees in a vigorous condition. 

 In the Riverside-Redlands di.striets the average moisture content of 

 the .soils in citrus orchards runs from 4 to 9 per cent, depending on the 

 soil type. In spite of this it is possible, of course, that the average 

 moisture content of the Edison soil is below the optimum. 



The management of the orchard consists of clean shallow cultivation 

 throughout the year with a fairly deep plowing in I\rarch. No cover 

 croi).s have as yet been grown. Light applications of manure and com- 



; Irrigation of Orchards, TJ. S. Dept. Agr. Farmers' Bull. no. 404 (1910) p. 24. 



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