THE PRINCIPLES OF TILLAGE 



115 



gang working on the once disked ground finds a dif- 

 ferent resistance from the one working on the un- 

 disked ground, hence does not "balance". By setting 

 the gang on the loose soil at a different angle the imple- 



Fig. 40. Types of Disc Harrow. 



(a) Full bladed disc; (b) Double disc; (c) Spade harrow; (d) Spiked 

 disc or alfalfa renovator. 



ment may be made to pull straight and thus do better 

 work. In hillside work the machine has a tendency to 

 crowd downhill. This can be overcome when levers are 

 provided for adjusting each gang separately. 



The full bladed and cutaway discs are the two most 

 common types-. The former does better work although 

 excellent results have been obtained from a double disc 

 with full blades on the front and cutaway blades on the 

 rear. 



In recent years a disc attachment for seeders has been 

 largely used. The "single disc" drill (Fig. 43C) is a 

 disc harrow which cultivates the soil to some extent as 

 well as sows the seed. The double <lisc on the other hand 



