672 SOILS : PROPERTIES AND MANAGEMENT 



are several types of colters. Blade colters are attached 

 to the beam or to the share in such a manner as to cut 

 the furrow slice free from the land side. They should 

 be adjusted in such a position as to cut the soil after it 

 has been raised and put in a stretched condition, at which 

 time the roots are most easily severed. This position is a 

 little back of the point of the share. A knife edge attached 

 to the share is commonly called a fin colter. A jointer 

 is a miniature moldboard attached to the beam for cutting 

 and turning under the upper edge of the furrow slice, 

 so that a neat, clean turn is effected without the exposure 

 of a ragged edge of grass which may continue growth. 

 This is used chiefly on sod land. A drag chain is an ordi- 

 nary heavy log chain, one end of which is attached to 

 the central part of the beam and the other to the end of 

 the double tree on the furrow side, and with enough slack 

 so that it drags down the vegetation on the furrow slice 

 just ahead of the turning point. It is used primarily in 

 turning under heavy growths of weeds or green-manure 

 crops. 



578. Subsoil plow. There is a third type of plow, 

 the so-called subsoil plow. The purpose of this imple- 

 ment is to break up and loosen the subsoil without mix- 

 ing the material with the soil. It consists essentially of a 

 small, molelike point on a long shin. This implement is 

 drawn through the bottom of the furrow, and shatters 

 and loosens the subsoil to a depth of 18 inches or 2 feet. 

 It is often useful on soils having a dense, hard subsoil. 

 Its use requires the exercise of judgment, as the process 

 may prove very injurious if done out of season. As a 

 general rule, it is best to use the subsoil plow in the fall, 

 when the subsoil is fairly dry and may in a measure be 

 recompacted by the winter rain. Spring subsoiling is 



