182 CULTIVATION. 



of that air renders available the minerals of the soil ; 

 and its carbonic acid, being absorbed by the water in 

 the soil, gives it the power of dissolving and supply- 

 ing to roots more earthy matter than would be dis- 

 solved by purer water. 



All of these actions the soil must be capable of 

 performing, before it can be in its highest state of 

 fertility. There are comparatively few soils now in 

 this condition, but there are also few which could 

 not be profitably rendered so, by a judicious appli- 

 cation of the various modes of cultivation. 



The three great objects to be accomplished are : 



1. To adopt such a system of drainage as will 

 cause as much as possible of the water of rains to 

 pass through the soil, instead of evaporating from the 

 surface. 



2. To pulverize the soil to a considerable depth. 



3. To darken its color, and to render it capable of 

 absorbing atmospheric fertilizers. 



The means used to secure these effects are under- 

 draining^ sub-soil and surface-plowing, digging, ap- 

 plying muck, etc. 



CHAPTEE II. 



UNDER-DRAINING. 



ALL soils which are cultivated should be thorough- 

 ly underdrained, either naturally or artificially. 



