244 



Physics of the Soil. 



Besides doing the work better the coulter diminished the 

 draft 20.86 per cent. 



A later series of observations was made on a clover sod 

 with the same sod plow provided with a wheel coulter, but 

 at a time when the soil was dryer than when the other 

 measurements were made. The results found were: 



In this set of trials the coulter has reduced the draft 

 25.34 per cent. 



305. Draft of Sod Compared With Stubble Plow. Another 

 set of trials were made at the time of (30i to compare the 

 stubble type of plow, Fig. 78, with that of Fig. 77, and the 

 results are given below: 



In this case the shape of the plow altered the draft 20.9 

 per cent., and the difference is probably a measure of the 

 difference in the amount of pulverizing done by the two 

 plows. 



