TILLAGE 679 



of implements have something of the same action on the 

 soil. That is to say, any implement that compacts the 

 soil does a certain amount of crushing ; and, conversely, 

 any implement that crushes the soil does some com- 

 pacting. 



584. Rollers (Fig. 72). — The type of the first group 

 is the solid, or barrel, roller, which by its weight tends to 

 force the particles of soil nearer together and to smooth 

 the surface. The smaller the diameter in proportion to its 

 weight, the greater is 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 

 under which 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. 



Another form of roller is the subsurface packer. One 

 type of this implement consists of a series of wheels with 

 narrow, V-shaped rims, which press into the soil and com- 

 pact it while leaving the surface loose. The wheels 

 are designed primarily to smooth the land after plowing, 

 and to bring the furrow slices close together and in good 

 contact with the subsoil, in order to conserve moisture 

 and promote decay of organic material that may be plowed 

 under. This packer has been developed chiefly in semi- 

 arid and arid sections of country where the conservation 

 of moisture is especially important, but it might well 

 have a much larger use for the same purpose in sections 

 of the country that are subject to late summer and fall 



