METHODS OF PLOWING 121 



enters into many chemical and physical combina- 

 tions that have an important influence on soil fer- 

 tility. Deep plowing brings to the surface sub- 

 soil that has not lost so much of its plant food as 

 the surface soil, not having been weathered so com- 

 pletely. After one or two seasons this rich, raw 

 soil becomes weathered sufficiently and is then 

 utilised by crops. Furthermore, the mere fining 

 of the soil by plowing increases its fertility by pre- 

 senting a large surface for the roots to feed upon. 

 The work of the nitrogen-fixing germs and of other 

 useful agencies that make for fertility is wonder- 

 fully hastened by the warmth and aeration induced 

 by plowing. It is chiefly the depth to which the 

 plow stirs soil that gives it preeminence among 

 tillage tools. 



Plowing to Deepen the Soil Reservoir. Plowing 

 may be made the means of increasing the water- 

 holding capacity of a soil. Soils of a close texture, 

 as the clays and clay loams, may be made to hold 

 more water by deep plowing, because rain will sink 

 into the loosened soil better. But sandy soils should 

 not be plowed deeply; they are too leachy at best. 

 Light soils through which water passes too readily 

 may be made somewhat more retentive by plowing 

 them at the same depth every year. The tramping 

 of the horses and the weight of the plow tend to com- 

 pact the soil at the bottom of the furrow, making 

 a kind of artificial hard-pan, or "plow bed, "which 

 checks the downward passage of water somewhat. 

 The depth at which this hard-pan should be formed 

 is six to eight inches, depending upon the rooting 

 habits of the crop grown. On the other hand, in 

 plowing heavy soils the aim should be to prevent 

 the formation of the hard-pan by varying the depth 

 from year to year. The benefit of deep plowing 



