320 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



the winter and spring of 1916. The water table receded within a few 

 months, but the alkali salts remained in the soil. A considerable num- 

 ber of the trees have recently died, and all of them in certain areas 

 became excessively chlorotic, following the rise of alkali. 



Soil samples have been drawn from an area where the orange trees 

 have died and also from among healthy trees near by, the analyses of 

 which are submitted in table 13. The results show that a high con- 

 centration of a number of salts occurs where the trees have died. 

 The amounts of chlorine, sulfate, sodium and calcium are all excessive, 

 extremely so in the case of sulfate. The concentration is undoubtedly 

 prohibitive to orange tree growth. 



On the other hand, the concentration of soluble sodium in the soil 

 where the trees still remain healthy is very much greater than was 

 found in some of the orange groves where severe injury has been pro- 

 duced by saline irrigation waters. In this case, however, the sodium 

 occurs largely as sulfate and bicarbonate, whereas the chloride pre- 

 dominated in the former case. On the whole, the results obtained in 

 this investigation indicate that sodium chloride is much more toxic 

 to citrus trees than sodium sulfate or sodium bicarbonate, which is in 

 agreement with the conclusions of Hilgard. 



An eight-year-old Navel orange grove near Bakersfield, portions 

 of which have been severely injured by alkali, has also been studied. 

 Analysis of soil samples (table 14) reveals a very high concentration 

 of salts where the trees have been severely injured. With the excep- 

 tion of the first foot of this soil, the concentration of chloride is not 

 excessive, but sodium sulfate occurs in large amounts. Unusually high 

 nitrate also occurs in the first foot. This soil is also supplied with 

 large amounts of soluble calcium, the main portion of which occurs 

 as the sulfate (gypsum). Extremely large amounts of gypsum occur 

 in the third, fourth and fifth feet. 



The analysis again shows a high soluble sodium content in the soil 

 where the orange trees are normal, but again the chlorine is low. In 

 the first three feet, the sodium is largely combined as bicarbonate. 

 In the second and third feet, considerable amounts of the normal 

 carbonate of sodium also occur. 



It will be noted that the fourth, fifth and sixth feet of this soil 

 contain extremely high concentrations of soluble salts, composed 

 mainly of calcium sulfate and sodium sulfate. The roots of the 

 healthy trees are largely confined to the upper two feet of this soil, 

 and so long as they remain there and the alkali does not rise, it is 

 possible that satisfactory growth will result. It is highly probable, 

 however, that the salts will tend to rise as a result of capillarity and 



