212 POWER AND THE PLOW 



dent of velocity, with this exception, that greatly increased 

 velocity slightly increases the force required to lift and turn 

 the furrow slice, owing to the distance the dirt is thrown. 



The rolling coulter is said by Prof. F. H. King to reduce 

 the draft in sod ground from 20.86 to 25.34 per cent. Gould 

 declared in favor of the coulter because of its saving in draft, 

 but Sanborn claimed a loss of 10 to 15 per cent, due to the 

 tendency of the coulter attached to the beam to raise the plow 

 out of the ground. Practically, the coulter is regarded as 

 essential for the majority of conditions, and in the absence 

 of recent tests it may be assumed that the thin edge of the 

 coulter saves power in cutting the furrow wall as compared 

 with the rather blunt shin of the plow bottom. 



From the variation in the shape of plows designed for dif- 

 ferent conditions we are led to expect great difference in draft 

 in the same soil. In the English experiments already quoted 

 there was a difference of 46 per cent, between the plows having 

 the lightest and the heaviest draft under the same conditions; 

 53 per cent, was the maximum difference in tests in 1850 by 

 the New York Agricultural Society. Sanborn found varia- 

 tions in sulky plows ranging from 5.9 to 7.5 Ibs. per square 

 inch of cross section, and in another experiment from 5.15 

 to 6.28 Ibs. in walking plows, all furrows being of the same size. 

 King reports a comparison of the draft of sod and stubble 

 plows in clover sod, two years old, as wet as could be worked. 

 The furrows were approximately 5.5 x 14.4 inches. The sod 

 plow had a draft of 4.45 Ibs. per inch and the stubble plow 

 5.38 Ibs. The difference, .93 lb., is mainly due to the work of 

 pulverization, which is added by the stubble plow to that of 

 cutting, lifting, and turning. At the Winnipeg motor contest 

 in July, 1909, one make of engine gang plows averaged about 

 2.5 Ibs. per inch lighter in draft than the other, all conditions 

 being equal. Not only the shape but the weight and adjust- 

 ment of different plows must be taken into consideration, how- 

 ever. 



