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 iuiple- 



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 disc on the other hanc| 



