114 DRY FARMING 



off weeds below the surface and the narrow bladed types 

 (Figs. 39B, 39D) to loosen up hard ground or to dig 

 out the creeping roots of such plants as quack grass. 



A type of cultivator developed for stirring the soil 

 and cutting weeds between rows of plants like potatoes 

 and corn and known as an intertillage cultivator, differs 

 from the others in form of carriage but not in function 

 nor in mode of action. (Fig. 39 C). 



86. Disc Harrows. — The disc harrow (Fig. 40 A. & B.) 

 is used chiefly to loosen up the surface of soddy ground 

 like breaking, or to cultivate the surface of stubble fields 

 to conserve moisture or kill weeds, or to form a seed bed 

 on stubble or plowed land. In view of its peculiar 

 structure it ridges the land if "lapping half" is not 

 practised or a double disc used. The alfalfa renovator 

 (Fig. 40D) is especially designed (1) to dig the fibrous 

 rooted grasses out of alfalfa and (2) to loosen up the 

 surface of alfalfa fields without too serious injury to 

 the plant roots. 



On account of its rolling action the disc harrow can 

 be used under many conditions. In the West its chief 

 function has been working down the virgin prairie sod. 

 The standard disc harrow has either full round discs or 

 cutaway blades usually 16 inches in diameter, sixteen in 

 number and spaced six inches apart. This is the four- 

 horse size. The sixteen-inch discs rotate at greater speed 

 than the larger ones and thus pulverize the ground more ; 

 they have less bearing surface on their edges and there- 

 fore more penetration. 



Single disc harrows should have one lever for each 

 gang. When 'lapping over", i.e., allowing the disc to 

 extend half way over the work of the previous round, is 

 practised the ground is left level and not ridged. The 



