PULVERIZERS AND PACKERS 487 



compact the soil, (b) Those whose primary purpose 

 is to pulverize the soil by crushing the lumps. Both 

 sets of implements have something of the same action 

 on the soil. That is to say, any implement which com- 

 pacts the soil does a certain amount of crushing; and, 

 conversely, any implement which crushes the soil does 

 some compacting. 



344. Rollers. The type of the first group is the solid 

 or barrel roller, which by its weight aims to force the 

 particles of soil nearer together and to level the surface. 



Fig. 147. The bar roller and pulverizer. 



The smaller the diameter in proportion to its weight, 

 the greater the effectiveness of the roller. Its draft is 

 correspondingly greater. As a crusher, the roller is 

 relatively inefficient on hard, lumpy soil, because of its 

 large bearing surface. Lumps are pushed into the soft 

 earth rather than crushed. 



It should be mentioned that there is one condition 

 where the roller is effective in loosening up the soil 

 structure. This is on fine soil on which a crust has 

 developed as a result of light rainfall. Here the roller 

 may break up the crust and restore a fairly effective 

 soil mulch. 



