314 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



the different groves from which these samples were taken are located 

 considerable distances apart. It may be mentioned in passing, that 

 more or less mottle leaf occurs in many of the groves in this locality 

 that have been irrigated with comparatively pure water. In such 

 cases, the cause of the mottle leaf inheres in the soil itself. Consider- 

 ably more mottle leaf occurs in grove E than in groves M or S. It 

 is interesting to note that the soil of the former differs considerably 

 from that of the two latter. Further discussion on this point will be 

 submitted elsewhere. 



In addition, the vertical distribution of salts varies in different 

 groves under the same saline irrigation supply. (Compare the data 

 from groves and C, tables 4 and 6.) It is not possible at present to 

 explain these variations. Differences in the amounts of water applied, 

 in cultural operations and in the degree of compactness of the subsoil, 

 are probably among the most important factors. 



While large portions of these groves have been severely injured, 

 it is interesting to note that the effects have not been uniform over 

 the entire area that has been irrigated with saline water. In some 

 places, little or no effects were evident in 1918, and again in 1919 

 the degree of injury was still much less pronounced in certain places 

 than in others. It is important, however, that some of the trees which 

 were healthy in 1917 have since begun to show definite signs of injury. 

 Soil samples have been drawn from among the severely injured trees of 

 the grove (B) and from an area of the same grove where the trees 

 have been only slightly injured. Analyses of these samples are 

 submitted in table 7. 



The results show that the subsoil below the second foot of the 

 severely injured area contains considerably more salts than in the less 

 injured portion. Especially is this true of the chlorine and sodium, 

 the two constituents that seem to be most responsible for the injury 

 in these groves. These variations are probably due to inherent differ- 

 ences in the physical nature of the subsoil which are such as to modify 

 the rates of penetration and accumulation of salts. At any rate, it is 

 interesting that the more severe injury has taken place where the 

 greater amounts of salts have accumulated. As already pointed out, 

 the least affected portions of this grove have now begun to show definite 

 injury. Tt is highly probable that the injury will become severe over 

 the entire orchard if the use of the present irrigation supply be not 

 discontinued. 



As bearing further on the variability of Ihe effects of saline irriga- 

 tion water, studies have been made on the chemical reactions that take 

 place when salts are added to soils. It has been found that alkali salts 



