BULLETIN 318 THE EFFECTS OF ALKALI ox CITRUS TREES 319 



it accumulate there as a result of other agencies. The net effects will 

 be similar, provided the concentration and proportions of the soluble 

 constituents in contact with the roots be the same. 



Several groves have been studied where alkali salts either occurred 

 originally or have been brought up recently by capillarity, due to a 

 high water table. The results have revealed some information addi- 

 tional to that set forth above, which seems to be of sufficient interest 

 to warrant brief discussion. 



A twenty-year-old lemon grove located near San Diego, that has 

 been irrigated with reasonably pure water the greater portion of the 

 time, has been studied. During the past few years, the trees have 

 become less thrifty than formerly. Many of the older leaves have 

 become yellow or brown in irregularly shaped areas around their 

 margins and have fallen excessively at certain times. Some of the 

 leaves are variegated and show the usual symptoms of mottle leaf. 

 The yields and quality of the fruit have also depreciated. 



Soil samples to a depth of four feet have been analyzed, and the 

 results are recorded in table 12. The data show that this soil contains 

 considerable amounts of soluble salts of which sodium is the predom- 

 inant basic constituent. In this ease, however, a considerable portion 

 of the sodium, especially in the third and fourth feet, must occur in 

 combination other than the chloride, since the chlorine content is 

 insufficient to combine with all of the sodium present. The data indi- 

 cate that considerable amounts of both sodium sulfato and sodium 

 bicarbonate occur in the subsoil layers. The water table is many feet 

 below the surface and it is probable that a large portion of the salts 

 accumulated in the subsoil previous to modern agriculture, although 

 the irrigation water may have tended to increase the amounts present. 



It is especially interesting that the roots of the lemon trees have 

 not penetrated deeply in this soil, more than 95 per cent of them 

 being within eighteen inches of the surface. There is probably some 

 connection between this fact and the higher concentration of alkali 

 salts found in the third and fourth feet, 



The above discussion should not be interpreted to mean that a 

 definite degree of injury to a given variety of citrus trees can always 

 be predicted with certainty from a single soil analysis. On the con- 

 trary, other factors are evidently involved in the problem that have 

 not yet been fully evaluated. The following discussion is of interest 

 in this connection. 



Local areas occ-ur in a Valencia orange grove near Garden Grove 

 in Orange County where many of the trees have been severely injured 

 by alkali brought up as a result of a temporarily high water table in 



