Farm Machinery 



449 



Subsoil plows. What are known as subsoil plows (Fig. 

 198) are employed to follow in the furrow made by a regular 

 plow for the purpose of loosening the soil below the plow depth. 



FIG. 198. Subsoil plow. 



They do not turn a furrow. In regions where hard-pan is 

 found just below plow depth, subsoil plows are very efficient 

 for increasing the depth of soil available for the roots. 



FIG. 199. Disc harrow. 



223. Harrows. For the purpose of following the plow and 



breaking up the clods and smoothing the surface soil, harrows 



are used. Disc, spring-tooth, spike-tooth, and blade harrows 



or Acme, are the common types. In choosing a harrow one 



2o 



