32 



SOILS AND FERTILIZERS 



surface, but if the surface is covered with a layer of 

 fine earth, the subsoil water cannot readily pass 

 through such a medium, and evaporation is checked. 

 Hence shallow surface cultivation conserves the soil 

 moisture. 



The means by which surface cultivation is accom- 

 plished must, of necessity, vary with the nature of the 



With surface cultivation. 



Fig- 13- 



soil. If a harrow is used the pulverization should be 

 complete. If a disk is used the teeth should be set at 

 an angle, and not perpendicularly, so as to prevent, as 



Fig. 14. Without surface cultivation. 



suggested by King, 12 the formation of hard ridges 

 which hasten evaporation. When the disk is set at an 

 angle, a layer of soil is completely cut off, and the 

 capillary connection with the subsoil is broken. Sur- 

 face cultivation should be from two to three inches 



