150 FARM MECHANICS 



most to receive the beneficial action of the air, rain and 

 sunshine. 



The moldboard of a plow must be smooth in order to 

 properly shed the earth freely to make an easy turn- 

 over. The shape of the shear and the forward part of 

 the moldboard is primarily that of a wedge, but the roll 

 or upper curve of the moldboard changes according to 

 soil texture and the width and depth of furrow to be 

 turned. Moldboards also differ in size and shape, ac- 

 cording to the kind of furrow to be turned. Sometimes 

 in certain soils a narrow solid furrow with, a comb 

 on the upper edge is preferable. In other soils a . 

 cracked or broken furrow slice works the best. When 

 working our lighter soils a wide furrow turned flat over 

 on top of a jointer furrow breaks the ground into frag- 

 ments with wide cracks or openings reaching several 

 inches down. Between these extremes there are many 

 modifications made for the particular type or texture 

 of the soil to be plowed. We can observe the effect that a 

 rough, or badly scratched, or poorly shaped moldboard 

 has on any kind of soil, especially when passing from 

 gravelly soils to clay. In soil that contains the right 

 amount of moisture, when a plow scours all the time, 

 the top of the furrow slice always has a glazed or shiny 

 appearance. This shows that the soil is slipping off 

 the moldboard easily. In places where the plow does 

 not scour the ground is pushed to one side and packed 

 or puddled on the underside instead of being lifted 

 and turned as it should be. A field plowed with a de- 

 fective moldboard will be full of these places. Such 

 ground cannot have the life to bring about a satis- 

 factory bacteria condition necessary to promote the 

 rapid plant growth that proper plowing gives it. 



Cultivated sandy soils are becoming more acid year 



