670 SOILS: PROPERTIES AND MANAGEMENT 



two in width to one in depth. The greater the depth, the 

 less in proportion may be the width of the furrow dice. 



On clay soil in particular, there is also a relation be- 

 tween depth and condition. A wet soil should be plowed 

 more shallow, other things being equal, than a dry soil, 

 because the puddling action is less. On a dry soil the 

 depth should be increased, in order to increase the pul- 

 verization. Combining these principles, then, it may be 

 said that if a clay soil must be plowed when too wet, it 

 should be plowed with a sod plow and to as shallow a 

 depth as is permissible. But on an over-dry soil the 

 opposite conditions should be fulfilled — that is, the use 

 of a steep moldboard and to an increased depth. Like- 

 wise, on sandy soil, where the aim is generally to compact 

 the structure, this may be furthered by deep plowing 

 with a steep moldboard when the land is over-wet. 



575. Plow sole. — In connection with this phase of 

 the subject it is important to consider what is often called 

 the " plow sole," — that is, the soil at the bottom of the 

 furrow, which bears the weight of the plow and the tram- 

 pling of the team, and which under a uniform depth of 

 plowing does not become loosened. In clay soil, espe- 

 cially, it gradually becomes more compact, developing 

 in time something of a hardpan character, which is detri- 

 mental to the circulation of air and moisture and inter- 

 feres with the penetration of plant roots. Consequently, 

 occasional deep plowing, or even subsoiling, is recom- 

 mended to break up this unfavorable soil structure. 

 There is less tendency for the disk plow than for the mold- 

 board plow to form the " sole." 



576. Hillside plow. — The hillside plow is a modified 

 form of the moldboard plow. It has a double curvature 

 to the moldboard, so that it is essentially two plows in 



