214 



POWER AND THE PLOW 



prairie sod. The draft of a 6 x 14 inch furrow would present 

 an extreme range of from 250 to 900 Ibs., with 400 to 500 Ibs. 

 as an average for old land in the Middle West. 



The amount of moisture in the soil affects the draft, as the 

 soil kernels are more easily sheared when wet. In two sets 

 of tests on clover sod, dry soil caused from 142 to 144 per cent, 

 increase in draft over moist soil. In corn stubble in Illinois, 

 the same soil when so dry as to be loosened in chunks averaged 

 4.93 Ibs. per square inch, as compared with 4.67 Ibs. when 

 too wet for good plowing, and the same when in ideal condition. 

 In this series 150 tests were made by Professor Ocock on each 

 soil condition; heace the average is remarkably accurate. 

 The deeper soil layers contain more moisture, which is probably 

 as important an item as the proportionate decrease in cutting 

 edge for deep furrows. Ocock's thesis experiments showed 

 a gradual decrease in draft with an increase in depth except 

 in one case, for which no explanation can be given. In dry 

 corn stubble thirty tests at a depth of five inches averaged 4 

 per cent, lighter than the same number at one inch deeper. 

 The accompanying table from this source shows the draft per 

 square inch in five tests of each of six different plow bottoms, 

 used on a single frame, in each of three different soil condi- 

 tions at five different depths. All tests were on the same field 

 in uniform soil, but at different dates. 



DRAFT OF PLOWS IN ILLINOIS CORN STUBBLE 



