146 DRY LAND FARMING . 



row. Clearly these are cultivators and they will be so 

 considered. They are all used for digging up the soil 

 and to some extent for pulverizing it, while a harrow 

 simply pulverizes, with the additional function of cover- 

 ing the seed. A true harrow has spike teeth and they 

 are dragged through the soil by a cutting and sliding 

 rather than a revolving friction. The disc is more com- 

 monly used for loosening up the surface soil, hence it is 

 a cultivator rather than a harrow. It consists of a series 

 of wheels from 12 to 20 inches in diameter, which are 

 attached to an axle and revolve with the same when in 

 use. Those most in favor are in two sections. The 

 wheels have a sharp cutting edge, are to some extent 

 concave on the outer side, and they are generally used 

 at more of less of an angle to enable them to stir the 

 soil effectively. In each of the sections the discs face 

 outwards and this leaves a deep depression in the center 

 between the two sections. In order to leave the land 

 level and to do thorough work, what is termed double 

 discing is usually practised. Double discing means draw- 

 ing the disc over the land in one direction and lapping 

 the implement to half its width on the disced land on the 

 next trip. 



The value of the disc consists: (1) In stirring the 

 surface soil more effectively and to a greater depth than 

 this can be done by the ordinary harrow, and at a much 

 less expenditure of power than would be involved in 

 overturning the soil with the gang-plow. The friction 

 in the revolving wheels is much less than the same 

 would be in the dragging plowshare. (2) In loosening 

 surfaces too much impacted to be readily loosened with 

 the ordinary harrow. (3) In making a deeper seed bed 

 on overturned sod -lands than can be made by the harrow 

 alone. (4) In destroying weeds that are too firmly rooted 

 to be destroyed by the harrow. (5) In covering seed, and 

 in cultivating crops at least to a limited extent. 



