316 DRY-FARMING 
Subsurface packing 
The subsurface packer invented by Campbell is 
shown in Figure 88. The wheels of this machine, 
eighteen inches in diameter, with rims one inch thick 
at the inner part, beveled two and a half inches to a 
sharp outer edge, are placed on a shaft, five inches 
Fia. 83. Subsurface packer. 
apart. In practice about five hundred pounds of 
weight are added. 
This machine, according to Campbell, crowds a 
one-inch wedge into every five inches of soil with a 
lateral and a downward pressure and thus packs 
firmly the soil near the bottom of the plow-furrow. 
Subsurface packing aims to establish full capillary 
connection between the plowed upper soil and the 
undisturbed lower soil-layer; to bring the moist soil 
