THE PRINCIPLES OF TILLAGE 119 



sirable and where, owing to the stubble, harrows do not 

 work satisfactorily. 



The smooth roller is but little used in the West. Its 

 function is similar to that of the surface packer but it 

 is less desirable than the latter since it leaves the surface 

 too fine and with too little mulch and in a condition 

 favorable to blowing. The surface packer leaves a 

 granular mulch and a surface that is not so likely to 

 blow. 



89. Drills as Tillage Machines. — The chief function of a 

 seed drill is to place the seed in the soil where it will get 



Fig. 43. — Types of Drills. 



(a) Hoe drill with press attachment; (b) Shoe drill; (c) Single disc 

 drill; (d) Double disc drill. 



the moisture, heat and air conditions necessary for 

 growth. Its efficiency as a seeder, aside from its me- 

 chanical faults or virtues is determined by the depth it 

 will place the seed and the firmness of the soil about the 

 seed after the operation. There are four chief types of 



