438 THE SMALL GRAINS 



Common salt is often present in large quantities, and 

 is more harmful to crops than generally supposed. 

 When the quantity exceeds 5000 pounds to an acre-4-feet, 

 barley should be grown in preference to wheat (Lough- 

 ridge, 1901, p. 8). Removal of white alkali may be done 

 in two ways : (1) by tile under-drainage into a stream at a 

 lower level, or (2) by bringing it to the surface thjough 

 irrigation and evaporation, and then scraping it off and 

 carting it away. The second method is hardly practi- 

 cable on a large scale, though large quantities of salts 

 may be removed in that way. 



476. Control of the alkali may be effected in some meas- 

 ure, when it is not present in too great an excess, though 

 too great for the tolerance of crops, by driving it downward 

 by irrigation and keeping it there through mulching of 

 the surface soil or constant cultivation, thus preventing 

 evaporation. Rice is rarely injured by alkali, not because 

 of its tolerance, as often supposed, but because the alkali 

 is kept down by flood irrigation and not permitted to con- 

 centrate at the surface. Moreover, a well-managed rice 

 farm is well drained. 



The essential feature of perfect irrigation is drainage, 

 while the essential feature of perfect drainage of marshes 

 for cropping is provision for irrigation. 



