680 SOILS: PROPERTIES AND MANAGEMENT 



droughts. While compacting the soil, this implement 

 leaves a mulch. 



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Fig. 72. — Types of packers and pulverisers : (1), solid or barrel roller; 

 (2) , corrugated roller ; (3) , crusher and subsurface packer ; (4) , 

 bar roller. 



585. Clod crushers. — The aim of these clod crushers 

 is to break up lumps. As to mode of action, there are 

 several forms. The corrugated and the bar roller and 

 the clod crusher concentrate their weight at a few points, 

 and are open enough so that the fine earth is forced up 

 between the bearing surfaces. They are very effective 

 in reducing lumpy soil to comparatively fine tilth. They 

 have very little leveling effect further than the breaking- 

 down of lumps. 



The planker, drag, or float, variously so-called, con- 

 sists essentially of a broad, heavy weight without teeth, 

 which is dragged over the soil. The lumps are rolled 

 under its edge and ground together in a manner which 

 very effectively reduces their size. At the same time 

 the soil is leveled, smoothed, and, to a degree, compacted. 

 This implement may well be used in the place of the roller 



