24 THE WHEAT INDUSTRY 



by the ponderous, puffing, iron horse. The large 

 gang plows also predominate in the great unirri- 

 gated wheat districts of California, Oregon, Wash- 

 ington, and Idaho. Wherever irrigation is prac- 

 ticed the fields are smaller and so large plows have 

 not generally proved economical. 



The type of plow used varies somewhat with the 

 soil. It generally consists of a cutting edge 

 termed a lay or share and a moldboard. The 

 work is done by cutting under and turning over 

 the soil to whatever depth is desired, ordinarily 

 from four to eight inches. The moldboard type 

 of plow is used in regions of clay or sandy clay 

 soils and of fairly heavy rainfall. In regions 

 where the soil is more sandy and quite dry at 

 plowing time, another type called the disc plow 

 is extensively used. 



The disc plow cuts downward with a rolling 

 motion, pushes the soil to the side, and partly 

 turns it (Fig. 14). This machine has the advan- 

 tage of doing its work somewhat more easily than 

 the common moldboard plow but is not as well 

 adapted to all conditions. Its most extensive use 

 in the United States is in California and the states 

 of the Northwest, though it is used to some extent 

 in the Central states. 



The Time of Plowing. - - Autumn is the time 

 when the greater part of the plowing for wheat is 

 done. In winter wheat districts, this is of course 



