428 SOILS. 



common salt, as in the marshes bordering the sea, or salt lakes, 

 that injury arises from the direct effects of the salty soil-water 

 upon the feeding roots themselves. In a few cases the grad- 

 ual rise of salt water from below in consequence of defective 

 drainage, has seriously injured, arid even destroyed, old orange 

 orchards. The natural occupancy of the ground by certain 

 native plants may be held to indicate that the soil is too 

 heavily charged with saline ingredients to permit healthy root 

 growth or nutrition until the excess of salts is removed. (See 

 below, chapters 23 and 26). 



The fact that in cultivated land the injury is usually found 

 to occur near the surface of the soil, concurrently with the 

 well-known fact that the maximum accumulation of salts at 

 the surface is always found near the end of the dry season, 

 indicates clearly that this accumulation is due to evaporation 

 at the surface. The latter is often found covered with a 

 crust consisting of earth cemented by the crystallized salts, 

 and later in the season with a layer of whitish dust resulting 

 from the drying-out of the crust first formed. It is this dust 

 which becomes so annoying to the inhabitants and travelers in 

 alkali regions, when high winds prevail, irritating the eyes and 

 nostrils and parching the lips. 



Effects of Irrigation. One of the most annoying and dis- 

 couraging features of the cultivation of lands in alkali regions 

 is that, although in their natural condition they may show 

 but little alkali on their surface, and that mostly in limited 

 spots, these spots are found to enlarge rapidly as irrigation is 

 practiced. Yet since alkali salts are the symptoms and result 

 of insufficient rainfall, irrigation is a necessary condition of 

 agriculture wherever they prevail. Under irrigation, neigh- 

 boring spots will oftentimes merge together into one large one, 

 and at times the entire area, once highly productive and perhaps 

 covered with valuable plantations of trees or vines, will become 

 incapable of supporting useful growth. This annoying 

 phenomenon is popularly known as " the rise of the alkali " in 

 the western United States, but is equally well known in India 

 and other irrigation regions. 



The soil being impregnated with a solution of the alkali 

 salts, and acting like a wick, the salts naturally remain behind 

 on the surface as the water evaporates, the process only stop- 





