THE PRINCIPLES OF TILLAGE 



113 



Soil Looseners. 



Among the soil looseners — and these include inter- 

 tilling machines — are those having discs, cutting blades 

 or stirring points. Those having revolving discs are 

 known as disc harrows, while most of those having stir- 

 ring points are called drag harrows. Those having 

 cutting blades may have spring teeth, "duck" feet, or 

 long slanting knives and are generally spoken of as 



Fig. 39. — Types of Cultivators, 

 (a) Wide-bladed or duck-foot cultivator; (b) Spring-tooth cultivator; 

 (c) Narrow-bladed two-row intertillage cultivator; (d) Alfalfa renovator 



at work. 



cultivators. But all are soil looseners and their chief 

 functions are to control weed growth and to loosen 

 the surface soil in order to kill weeds or make a soil 

 mulch or admit air. 



85. Cultivators. — The cultivators have cutting points 

 of various widths and designs. The wide bladed or 

 ''duck footed" types (Fig. 39 A) are chiefly used to cut 



