70 SOILS 



soils, especially in the East, this line marks the 

 depth of plowing. The depth at which the vege- 

 tation that gives the surface soil its black colour 

 and looser texture has been buried is about nine 

 inches. Many soils, especially those made by wind 

 or built by water, and peat and muck soils, show 

 very little if any difference in colour or texture be- 

 tween the first nine inches of soil and that below. 



In nearly all cases the subsoil contains less 

 available plant food than the soil above because it 

 is not affected as much by weathering, being pro- 

 tected, and because it is less affected by acids re- 

 sulting from the decay of vegetation, since it con- 

 tains less humus. We might call the subsoil 

 rotting rock, and the soil rotted subsoil. This 

 is a providential arrangement. If the plant food 

 in all the soil, down to bed-rock, were as easy to lose 

 as that in the first nine inches of soil our fields would 

 become unproductive much sooner than they do 

 now. The subsoil is a store of plant Tood that is 

 held in reserve. We should look upon the rocks, 

 stones, pebbles and subsoil of our fields as so much po- 

 tential plant food. It is being doled out to us from 

 year to year as fast as it can be used to advantage. 



As the surface soil slowly wears away and is 

 carried off in crops, the subsoil gradually becomes 

 surface soil. The roots of deep-feeding plants, 

 as clover and alfalfa, bring up plant food that they 

 secure below the roots of ordinary crops. When 

 these crops are cut, and the stubble and roots 

 plowed under, a part of the plant food that the sub- 

 soil has contributed to their growth is returned to 

 the surface soil, enriching it. Earthworms bring 

 to the surface subsoil that has never seen the light 

 of day and this adds richness. A plowing some- 

 what deeper than usual may mix an inch or more of 



