CORN TILLAGE 163 



depth is attained. The earlier in the season the land 

 is plowed, the greater is the increase in depth that can 

 properly be made. Hence, fall plowing or early winter 

 plowing may be deeper, sometimes an inch deeper, than 

 plowing done in February or March. Usually the yield is 

 decreased by bringing to the surface, especially near 

 the time of planting, any very large amount of clay from 

 the subsoil. But while this may reduce the first crop, 

 the increased depth is apt to increase the yields of sub- 

 sequent crops. 



155. Subsoiling. A method of suddenly increasing 

 the depth of plowing consists in running a special subsoil 



FIG. 78. A SUBSOIL PLOW, 



plow in the bottom of every furrow made by an ordinary 

 turn-plow. This may double the depth of soil stirred. 

 As a rule, subsoiling is best done in November or Decem- 

 ber, or before the beginning of the rainy season of winter. 

 After the winter rains begin, the subsoil of most fields 

 is usually too moist for the advantageous use of a sub- 

 soil plow. If subsoiling is done when the subsoil is too 

 wet (and this may be the case while the surface soil is 



