236 



THE PRINCIPLES OF SOIL MANAGEMENT 



in semi-aricl and arid regions, is the excessive accumu- 

 lation of soluble salts "alkali salts" in the soil. 

 They may become so concentrated as to injure crops or 

 prevent their growth. (See page 307.) In the original 

 condition of such soils they are usually distributed in 

 relatively small amounts through a deep section of soil. 

 But by excessive irrigation, which produces seepage and 

 a general rise in the water-table, aided by those careless 



tillage methods which 

 permit free evaporation 

 at the surface, these 

 soluble salts become con- 

 centrated in the root 

 zone, and at the surface 

 as an alkali crust. It 

 has frequently happened 

 that land not originally 

 in a seriously "alka- 

 line" condition has be- 

 come so by careless 

 management. It is obvious that to avoid this injury 

 there must be (a) conservative irrigation, and (6) the 

 most thorough tillage methods which shall avoid surface 

 evaporation. Where an excess of akali salts exists, 

 they are most successfully removed by means of a deep 

 thorough drainage system, coupled with heavy irrigation 

 which shall wash out of the soil the excess of salts. 



It is a safe and wise rule to cultivate the soil as soon 

 after applying water as its moisture condition will per- 

 mit without injury, and this should be kept up at fre- 

 quent intervals until an effective dust mulch has been 



Fig. 75. Middle breaker plow. Some- 

 times used in constructing irrigation and 

 drainage ditches. 



