PRINCIPLES OF PLANTING AND CULTIVATION 29 



the subsoil plow. In general, plowing should be done with a plow 

 which has a quick turn to the moldboard, and which cuts a deep, 

 rather narrow furrow, so that the soil as it is turned over is thrown 

 with considerable velocity and in such a manner that the particles 

 grind forcibly upon one another. This is a very important part of 

 the mechanical preparation of the soil. 



Harrowing. After plowing, the ground should never be allowed 

 to lie exposed to the sun and wind more than a few hours. The 

 harrow should follow the plow as quickly as possible. It is a good 



FIG. 4. Disk harrow 



rule in cultivating the soil never to *plow more during any one 

 day than can be harrowed before night. Formerly, harrowing and 

 compacting the soil were practically one and the same operation, 

 but in recent years harrows have been constructed on quite different 

 principles. The advent of the disk harrow, as shown in figure 4, 

 which not only loosens and lifts the soil but pulverizes it, marks 

 one of the great advance steps in soil cultivation. This implement, 

 however, does not compact the soil. The acme harrow, shown in 

 figure 5, which is another important pulverizing implement, com- 

 pacts the soil to a slight extent, but its action is more that of the 



