CULTP/ATION. 203 



there deposit much mineral matter obtained from 

 the sub-soil, and thus render it riclier. 



The retention of atmospheric manures is more 

 fully insured by the better exposure of the clayey 

 portions of the soil. 



Tlie sub-soil often contains matters which are defi- 

 cient in the surface-soil. By the use of the sub-soil 

 plow, they are rendered available. 



Sub-soiling is similar to under-draining in continu- 

 ing the tillering of grasses. 



"When the sub-soil is a thin layer of clay on a sandy 

 bed (as in many parts of the country), the sub-soil 

 plow, by passing through it, opens a passage for water, 

 and often affords a sufficient drainage. 



If plants will grow better on a soil six inches deep 

 than on one of three inches, there is no reason why 

 they should not be benefited in proportion, by disturb- 

 ing the soil to the whole depth to which roots will 

 travel — even td a depth of two feet. The minute 

 rootlets of corn and most other plants will, if allow- 

 ed by cultivation, occupy the soil to a greater depth 

 than this, having a fibre in nearly every cubic inch of 

 the soil for the whole distance. There are very few 

 cultivated plants whose roots would not travel to a 

 depth of thirty inches or more. Even the onion sends 

 its roots to the depth of eighteen inches when the soil 

 is well cultivated. 



The object of loosening the soil is to admit roota 

 to a sufficient depth to hold the plant in its position, 

 — to obtain the nutriment necessary to its growth, — • 

 to receive moisture from the lower portions of the 



