150 AGRONOMY 



Pulverizing the soil. The soil is pulverized and made fit 

 for crops by plowing, harrowing, spading, and raking. In ex- 

 tensive field operations the plow is used to break up the soil, 

 while the harrow, like a gigantic rake, is used to break up the 

 large clods and level the surface ; in the smaller areas, such 

 as the home garden, the same results are attained by the use 

 of the spade and the rake. The object of plowing or spading 



FIG. 107. Plowing 



is not only to loosen the soil, but to turn it over, thus bring- 

 ing new food supplies to the surface and fresh soil into cul- 

 tivation, while the topsoil, together with such fertilizers as 

 have been applied, is turned under to become fitted for a 

 succeeding crop. In humid regions the soil is stirred to a depth 

 of six or seven inches, but in arid regions the stirring may 

 extend much deeper without harm to the soil. When the soil 

 is underlaid by a stiff and heavy subsoil, the latter is often 

 loosened by siibsoiling or trenching. In subsoiling the subsoil 

 plow follows the surface plow in the same furrow but at a 

 greater depth. Trenching is restricted to small areas and is 



