676 SOILS: PROPERTIES AND MANAGEMENT 



581. Leveler and harrow types of cultivator (Fig. 71). 



- In this group are the spike-tooth harrow, the smoothing 



harrow, the spring-tooth harrow, the disk harrow, the 



spading harrow, weeders, and the Acme and Meeker 



harrows. 



The spike-tooth harrow is essentially a leveling imple- 

 ment, adapted to very shallow cultivation of loose soils. 

 It is also something of a cleaner, in that it picks up surface 

 rubbish. The spring-tooth harrow works more deeply 

 than does the spike-tooth harrow, and can therefore be 

 used in many soils for which the latter is not adapted. 

 In working down cloddy soil it brings the lumps to the 

 surface, where they may be crushed. The disk harrow 

 depends for its primary advantage on 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 similar to that of the plow, surpassing 

 shovel cultivators in this respect. The disk harrow is 

 not adapted to stony soil, but the toothed forms are as 

 effective on such soil as on soil free from stones, as long 

 as the stones are not large enough to collect in the imple- 

 ment. On the other hand, on land full of coarse manure, 

 sod, and the like, the disk harrow is the more efficient. 

 The spading harrow (cutaway disk) is very little different 

 from the disk harrow, except that it takes hold of the soil 

 more readily. A recent attempt to bring about a high 

 degree of pulverization, and with greater uniformity, n 

 represented by the double-disk implements. In these 

 implements there are two sets of disks, one set in front 

 of and zigzagged with the other, and the two adjusted 

 so as to throw the soil in opposite directions. 



Weeders are a modified form of the spring-tooth har- 

 row, adapted to shallow tillage of friable, easily worked 



