202 SOILS AND FERTILIZERS 



izer, especially where clover is grown with difficulty. 

 MISCELLANEOUS FERTILIZERS 



256. Salt is frequently used as an indirect fertilizer. 

 Sodium and chlorine, the two elements of which it is 

 composed, are not absolutely necessary for normal 

 plant growth. When salt is applied to the soil and 

 the sodium undergoes fixation, potassium may be 

 liberated. An early experiment of Wolff illustrates 

 this point : a buckwheat plot fertilized with salt pro- 

 duced a crop with more potash and less sodium than 

 a similar unfertilized plot. 



Salt may be used to check the rank growth of straw 

 during a rainy season, and thus prevent loss of the 

 crop by lodging. It should not be used in excessive 

 amounts, as it is destructive to vegetation ; 200 pounds 

 per acre is a fair application. Salt also improves the 

 physical condition of the soil by increasing the surface- 

 tension of the soil water. Salt should not be used on 

 a tobacco or potato crop, because it injures the quality 

 of the product. 



257. Magnesium Salts. — Magnesium is present in 

 the ash of all plants, and is an essential element of 

 plant growth. Usually soils are so well stocked with 

 this element that it is not necessary to apply it in 

 fertilizers. Some of the magnesium salts, as the 

 chloride, are injurious to vegetation, but when associa- 

 ted with lime as carbonate, magnesia imparts fertility. 

 In many of the Stassfurt salts magnesium is present. 



