SOIL DEFICIENCIES 263 



Whenever the water table rises, in land under irrigation in arid 

 sections, to within four or five feet of the surface, it is a sign of 

 danger. Such a rise means that the water in the soil is in such a 

 distance of the surface that the salts will be constantly moving 

 from the reservoir in the soil water, and accumulating in the soil. 

 Injury will result if such an action continues. The remedy is 

 drainage. 



The bulk of the alkali salts in an arid region will be usually 

 found some distance from the surface of the soil, when the water 

 table is many feet below the surface. The depth at which this 

 accumulation occurs depends to some extent upon the depth to 

 which the rainfall penetrates. For example, Thomas H. Means 

 found that the alkali salts in coarse sands of a certain district 

 were largely four to eight feet from the surface, while in sandy 

 loam, in which the rain can not penetrate so deeply, the alkali 

 occurs at a depth of three or four feet. The rain dissolves the 

 alkali and carries it down into the soil. On evaporation, some 

 of the alkali returns to the surface, but the bulk of the evapora- 

 tion must take place below the surface, for otherwise the alkali 

 which is washed down would be brought up again. 



Surface accumulations of alkali salts take place where the 

 ground-water is sufficiently near the surface to cause the bulk of 

 the evaporation of water to take place at or near the surface. 

 Dissolved material from the soil, and that brought in by the 

 ground-water, will be brought to the surface. Hence basin-like 

 depressions surrounded by sloping land usually contain alkali. 



Effect of Alkali on Plants. Alkali 1 usually causes injury at 

 the base of the trunk, or the root crown of the plant. The bark 

 of green herbaceous stems is usually turned to a brownish color 

 for half an inch or more, and is soft and easily peeled off. The 

 rough bark of trees is turned nearly black, and the green layer 

 turns brown. The plant either dies, or becomes unprofitable to 

 the grower. 



The amount of alkali which various plants will stand depends 

 upon a number of conditions, among which are the age of the 

 1 California Bulletin 128, p. 5. 



