198 POWER AND THE PLOW 



Soils as well as woods, vary greatly in their tenacity. In 

 a light, sandy soil less abrupt curvature of the moldboard will 

 be required to fracture the furrow slice than in a stiff clay. The 

 friction of the furrow slice against curves in the plow con- 

 sumes more and more power as the curves are made more abrupt. 

 In the same soil the breaker moldboard runs with about 20 

 per cent, less draft than the stubble moldboard, hence the 

 power required to pulverize the soils adds at least one fourth 

 to the power required to cut and turn the furrow, and to over- 

 come the friction of the soil upon the plow. While the stubble 

 moldboard requires additional power on account of pulverizing, 

 the tenacity of the prairie sod is so great that, even at a much 

 shallower depth of plowing, with practically no pulverization, 

 the average sod-breaker takes from 40 to 60 per cent, more 

 power than a stubble plow of the same size working deeper in 

 old ground. 



