144 



PREPARATION OP LANDS. 



nary plough, making the whole depth to which the land is 

 stirred, from eighteen to twenty-four inches. 



454. The benefits of subsoil ploughing are very similar 

 to those of deep ploughing. Recent investigations show 

 that nitrogen and other fertilizing substances exist deep 

 below the surface. Subsoil ploughing enables the roots of 

 plants to reach them by loosening the soil to a greater 

 depth. 



455. A very excellent 

 implement known as 

 he Michigan, or double 

 mould-board plough, 

 (Fig. 19,) is designed to 



Fig. 19. 



obviate the necessity of 

 the subsoil plough, to 

 some extent. The smaller mould-board cuts off a thin 

 surface and turns it into the last furrow, where it is 

 completely covered with a finely pulverized soil by the 

 principal mould-board. 



Fig. 20. 



456. An implement designed to supersede the use of 

 the plough in many soils, is known as the digger, (Fig. 20.) 



