240 



Physics of the Soil. 



mentally different shapes depending upon the character of 

 the work which they are expected to do. 



If the chief object of the plow is to cut a clean furrow 

 slice and turn it over so as to completely cover whatever 

 may be upon the surface a shape represented in Fig. 77 is 

 used. 



FIG. 77. Typo of sod plow, wliicb pulverizes but little. 



If on the other hand the primary object of the plow is to 

 thoroughly pulverize the soil, making it deep and mellow, 

 a form represented in Fig. 78 must be used. Then accord- 

 ing as one or the other of these two chief objects vary in 

 importance shapes of plows will be chosen which are in 

 termediate between these two extremes. 



I. Kind and Condition of Soil and Shape of Plow, It 

 must be clear from the mechanical action of the plow that 

 its form should be adapted to the soil. If the soil has a 

 tendency to be too open and porous, and is naturally coarse 

 grained, like the sandy soils, it should be plowed with a 

 steep mold board, a little over wet and as deep as other con- 

 ditions will permit, so as to break down the granulation 

 and secure the closer texture. 



If the soil is generally too close in texture, is heavy and 

 soggy, it needs the less steep mold board used when the soil 

 is a little dry so as to shear into thicker layers and form 

 granules of larger size. 



If plowing must be done when the soil is a little too wet 



