FARM MACHINERY 205 



them up. Yet the disk plow cannot be used in extremely 

 hard ground, such as might be found in a road, as it could 

 not be kept in the ground. The other soil condition to which 

 the disk plow is well adapted is where the soil is so sticky 

 that the moldboard plow fails to scour well, as in heavy 

 clay or gumbo soils. The black, waxy soil found in Texas 

 and other parts of the South is such a soil. The disk plow 

 with its scraper to clean the disk will turn a furrow regardless 

 of the scouring properties of the soil. Where the moldboard 



Fig. 115. A modern disk sans plow at work. 



plow will do good work, it is to be preferred to the disk plow. 

 As generally constructed, the latter is a very clumsy imple- 

 ment and very heavy, the weight being necessary to keep 

 the plow in the ground. Claims for its lightness of draft 

 cannot be substantiated by tests when compared with mold- 

 board plows under favorable moisture conditions. Often 

 the disk plow is given credit for doing more work than it 

 actually performs, in that the bottom of the furrow is not 

 flat and measurements are often made of the deepest point. 

 The diameter of the disk proper varies from 20 to 30 

 inches in different plows. A 24-inch disk will do the most 

 satisfactory work under usual conditions. It pulverizes the 



