260 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



washed out about as fast as they are formed and carried into 

 streams, and thence to the sea. 



In arid climates, since the rainfall is not sufficient to wash out 

 the soluble salts, they accumulate. As long as these salts are dis- 

 tributed uniformly through the mass of the soil, they cause no 



50000 



POUNDS OF SALT PER ACRE. 



10,000 15,000 0,000 25,000 



30,000 35,000 



Fig. 64. Salt content of sandy land and of gumbo soil, before and after 



irrigation. Irrigation causes the alkali to rise to near the 



surface of the gumbo soil. Bureau of Soils. 



injury, but the alkali may accumulate in the surface-foot of the 

 soil, or it may be carried away to accumulate in another field. 



When water comes in contact with the soil, it dissolves the 

 soluble constituents as far as it penetrates. If afterwards it 



