306 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



Corona in which it had been found that 2520 pounds per acre of 

 sodium chloride distributed through the soil to a depth of four feet, 

 caused an orange tree to become completely leafless, while another 

 tree nearby, where the soil was similar in other respects, but contained 

 only 720 pounds per acre of sodium chloride, w r as much less severely 

 injured. "Here it is apparently the excess of common salt to which 

 the difference is due." 



In 1901 Loughridge 3 called attention to the extreme sensitiveness 

 of the lemon tree. lie said: "The lemon seems to be the least tolerant 

 of all of the fruit trees, for it was stunted by 1440 pounds common 

 salt per acre, distributed through four feet depth, and was killed 

 bj" 1900 pounds combined with 1900 pounds carbonate of soda." 



In harmony with the conclusions of Loughridge and Hilgard, 

 recent investigations by the writers have shown that different varieties 

 and species of citrus trees are quite sensitive to alkali, especially so 

 in the case of the lemon, and that after a few years irrigation with 

 saline water, both lemon and orange trees may be severely injured. 

 Again, it has been found that the effects produced by a given supply 

 of impure irrigation water may, for a time at least, be extremely 

 variable even in different portions of the same grove. Part of this 

 variability, as shown below, is probably due to differences in the 

 depth to which the water penetrates, which in turn affects the rate at 

 which the salts accumulate in the root zone. 



Experience in various localities has shown that, under certain 

 conditions, continued irrigation with comparatively pure water also 

 tends to hasten the accumulation of injurious amounts of soluble salts. 

 Several hundred thousand acres located in different parts of Califor- 

 nia, which were free from injurious amounts of alkali previous to the 

 introduction of irrigation, have since become veritable alkali lands. 

 Seepage, together with a rising water table incident to over-irrigation, 

 have been the principal means by which the salts have been brought 

 up from below and deposited near the surface. Small areas of citrus 

 groves have already become heavily charged with alkali by this means. 



In the course of investigations on the nutrition of citrus trees, we 

 have devoted considerable study to certain phases of the alkali prob- 

 lem. Early in this work, it became evident that the existing state of 

 knowledge was inadequate. The symptoms of alkali injury have not 

 been recognized clearly. The relations of fertilizers to the problem, 

 and especially the effect of applying irrigation water containing alkali 

 salts, are inadequately understood and appreciated. 



s Tolerance of Alkali by Various Cultures. Calif. Agr. Exp. Sta. Bull. 133 

 (1!MU), pp. 14-Ki. 



