Importance and Distribution 19 



quiring different treatment and handling. The custom 

 of planting on higli ridges is for the purpose of facili- 

 tating drainage. A porous clay subsoil not only sup- 

 plies drainage without the leaching of plant-food but 

 it is an important factor in the production of well- 

 shaped tubers. A very deep sandy soil without a sub- 

 stantial foundation permits the loss of valuable fer- 

 tilizing elements by leaching and often produces long 

 ill-shaped potatoes that do not bring the highest prices 

 on discriminating markets. The surface soil should be 

 six or eight inches deep and the subsoil should provide 

 drainage without leaching. A stiff soil favors excessive 

 vine growth and the production of rough irregular po- 

 tatoes. Such soils also are usually cold and in the end 

 will prove unprofitable for commercial plantings. The 

 sweet potato is possible of profitable growth on a wider 

 range of soil than perhaps any other of the common 

 field crops. 



