164 HARNESSING THE EARTHWORM 



Only a cursory examination of the data is needed to show 

 the higher fertility status of the casts. What is the explanation ? 

 Is it due to substances brought up from the subsoil, or can it 

 be attributed to direct action of the worms on the soil material? 

 To answer these questions, it is necessary to examine the habits 

 of earthworms. They make their tunnels, in part, by pushing 

 the earth away on all sides, but mostly by swallowing it and 

 depositing the excrement at the surface. In dry or cold weather 

 they retire to considerable depth 4 to 6 and even 8 feet. In 

 favorable weather they are active in the top 6 or 8 inches of soil. 

 Their food consists of plant and animal remains on the surface 

 and in the upper layers of the soil; and apparently some nutri- 

 ment is obtained from the soil itself. In the light of these facts 

 it is interesting to speculate as to what would happen in an in- 

 verted profile, i.e., with the A and C horizons reversed. The 

 fact that worm casts are less acid (or less alkaline in alkaline 

 soils) than the soil even where the worms are confined to the 

 surface soil (6, 9), shows that the change in reaction is not de- 

 pendent upon the transporting of less acid (or less alkaline) 

 subsoil to the surface. Burrowing in the subsoil is done only to 

 provide living quarters during unfavorable weather. It would 

 appear, therefore, that the amount of subsoil carried to the sur- 

 face is relatively small. If the subsoil is calcareous, the amount 

 of such material brought to the surface might, over a long period 

 of time, be sufficient to increase the calcium (and perhaps mag- 

 nesium) content of the surface soil. Likewise, if the subsoil con- 

 tained a higher concentration of any other material, it might 

 influence the composition of the surface soil. 



The main benefit, chemically (and biologically), of earth- 

 worm activity is the digestion of plant material and its intimate 

 mixing with mineral soil. The concentration of the principal 

 plant-food elements (except K) in the plant is considerably 

 higher than it is in the soil. For example, in southern New Eng- 

 land, forest tree leaves contain in the neighborhood of 0.5 to 

 2.5 per cent N, 0.1 to 0.5 per cent P, 0.6 to 2.0 per cent K, and 



