PLANT NUTRIENTS AND THEIR ABSORPTION 121 



injury is also accentuated by the lack of care, such as improper tillage, the insuffi- 

 cient use of manure or other fertilizers, and withholding irrigation, thereby allow- 

 ing the soil to become too dry. If the soil be allowed to dry out excessively, the 

 concentration of alkali in the soil moisture may become harmful, while a more 

 abundant supplj^ of water would so dilute the salts present as to reduce the 

 concentration to a point where normal growth could take place. 



" In certain localities the dissolved salts are predominantly chlorides, in others 

 sulphates and in still others bicarbonates. A few wells have been found to contain 

 large amounts of nitrates." 



Alkali in the soil may also have a marked effect on root distribution. 



"It is especially interesting that the roots of the lemon trees have not pene- 

 trated deeply in this soil, more than 95 per cent, of them being within 18 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. 



"Local areas occur in a Valencia orange grove near Garden Grove in Orange 

 Count}'' where many of the trees have been severely injured by alkali brought up 

 as a result of a temporarily high water table in the winter and spring of 1916. 

 The water table receded within a few months but the alkali salts remained in the 

 soil. A considerable number of trees have recently died, and all of them in cer- 

 tain areas became excessively chlorotic, following the rise of the alkali." 



When irrigation is practiced, the composition of the irrigation water is an 

 important factor. Kelly and Thomas found from their investigations, "a 

 remarkably close relationship between the composition of the irrigation water, 

 on the one hand, and the accumulation of alkali salts and the condition of the 

 orange and the lemon trees, on the other. In every case we have studied, where 

 saline irrigation water has been applied for a series of years, alkaline salts have 

 accumulated in the soil and the citrus trees have been injured in consequence. 

 The rates at which salts have actually accumulated vary, however, in different 

 soils, depending on (1) the composition of the water, (2) the amounts appUed, 

 and (3) the freedom with which it penetrated into the subsoil. "^"^ 



The injurious effects of high concentrations produced by excessive 

 amounts of alkaH or other salts in the soil are due largely to the inability 

 of plants to absorb water by osmosis from a solution having a higher 

 osmotic concentration than that of the plant itself. Hence, the harmful 

 effects of alkali are partly those of starvation and drought. The con- 

 centration of the soil solution requires attention only under conditions 

 where the salt content of the soil is naturally high, as in salt marshes and 

 in regions near salt water generally, or where the moisture supply is 

 restricted, as in arid or semiarid regions. However summer drought 

 may produce temporarily excessive concentrations in any soil and so 

 bring about injury. 



Remedial Measures. — When a soil once becomes impregnated with 

 alkali about the only effective treatment is flooding the land with irriga- 

 tion water to dissolve out the excessive amounts which are then either 

 forced down to a depth where they will do no harm or carried away in 

 the drainage water. Provision for thorough drainage is very important 



