148 NATURE AND PEOPEETIES OP SOILS 



tion immediately after plowing. When the moisture condi- 

 tions are optimum, the clods are more easily shattered and 

 the formation of a suitable seed-bed is speedily accomplished. 



The cultivators proper are well represented by the ordinary 

 corn cultivator whether equipped with shovels, knives or discs. 

 Under the leveler and harrow type may be placed the spike 

 and spring-tooth harrow, the various kinds of weeders, the 

 acme harrow and the disc harrow. The latter may be equip- 

 ped with solid, cut-away, or spading discs. The grain drill, 

 either of the press or disc type, is a representative of the 

 seeder cultivators, which considerably influence the structural 

 condition of the soil although such action is not their primary 

 purpose. (See Fig. 26.) 



Packing and crushing are ordinarily performed by the same 

 implement, since any tool that compacts does a certain amount 

 of crushing; and, conversely, any implement that crushes the 

 soil does some compacting. Such an implement as the culti- 

 packer cultivates, packs and promotes granulation in one 

 operation. The difficulty of establishing a rigid classification 

 is evident. 



Rollers may be of the solid or barrel type, the corrugated 

 type, or the bar type. The subsurface packer is also included 

 in this group. Rollers tend to force the soil particles nearer 

 together and smooth the surface. If at the same time they 

 establish a soil-mulch so much the better. The rolling of the 

 land after seeding is an attempt to stimulate the capillary 

 movement of the water and to hasten germination by bring- 

 ing the seed in closer contact with the soil. 



The planker, drag, or float is a common type of single 

 crusher. It is generally broad and heavy, without teeth and 

 is dragged over the soil. The lumps are rolled under its edges 

 and ground together in such a manner as effectively to reduce 

 their size. The soil is leveled and smoothed at the same time. 

 This implement may be used iastead of a roller in many cases. 

 (See Fig. 27.) 



