LEVELERS AND HARROWS 483 



Disc implements are not adapted to stony soil, whereas 

 toothed forms are as effective here as on soil free from 

 stone, so long as the stones are not large enough to collect 

 in the implement. On the other hand, on land full of 

 coarse manure, sod, etc., the disc implement is the 

 more efficient. The spading harrow (cutaway disc) is 

 very little different from the disc harrow, except that 

 it takes hold of the soil more readily. A recent attempt 

 to accomplish a large amount of pulverization, and with 



Fig. 142. Riding cotton- and corn-planter. It also cultivates the soil. 



greater uniformity, is represented by the double-disc 

 implements. In these implements there are two sets 

 of discs, one set in front of and zig-zagged with the 

 other, and also adjusted to throw the soil in opposite 

 directions. 



Weeders are a modified form of the spring-toothed 

 harrow, adapted to shallow tillage of friable, easily 

 worked soil, where the aim is to kill weeds and create 

 a thin surface mulch. They are wide and are fitted with 

 handles, and therefore stand intermediate between 



