SOILS AND FERTILIZERS 



79 



crumbles it. It may be used where the soil is too hard 



or too sticky for 



the successful use 



of the moldboard 



type. 



The subsoil plow 

 is intended to fol- 

 low after the regu- 



i i j FIG. IQ. Subsoil Plow. 



lar plow and to 



loosen the subsoil in the bottom of the furrow. The 



subsoil may con- 

 tain a large amount 

 of plant food, but 

 it is usually not 

 immediately avail- 

 able for the plant. 

 If it were thrown 

 on top, it might 

 require some time 

 before the air and 

 the sun could act 

 on it and make 

 available its food 

 material. The 

 subsoil plow 

 loosens the soil 

 and aerates it 

 without checking 

 plant growth by 

 throwing the soil 

 on top. 



There are some deep tillage machines on the mar- 

 ket now in response to a demand of deeper tillage. 



FIG. 20. Deep Tillage Machine. 



