482 



THE PRINCIPLES OF SOIL MANAGEMENT 



Cultivators are also adapted to till one or more rows 

 at a time. 



341. Leveler and harrow type of cultivator. In 

 this group come the spike-toothed harrow, smoothing 

 harrow,, the spring-toothed harrow, disc harrow, spading 

 harrow, weeders and the Acme harrow. 



The spike-toothed harrow is essentially a leveling 

 implement, adapted to very shallow cultivation of loose 

 soils. It is also something of a cleaner, in that it picks 



Fig. 141. Plow for loosening beets and other root crops. 

 Cultivates the soil deeply. 



up surface rubbish. The spring-toothed harrow works 

 more deeply than the spike-toothed harrow, and can there- 

 fore be used in many situations to which the latter is 

 not adapted. In working down cloddy soil it brings the 

 lumps to the surface, where they may be crushed. 

 The disc harrow depends for its primary advantage 

 upon the conversion of sliding friction into rolling 

 friction. Its draft is, therefore, less for the same amount 

 of work done. It has a vigorous pulverizing action simi- 

 lar to the plow, and more so than shovel-cultivators. 



