THE EARTHWORM IN SCIENTIFIC LITERATURE 49 



(B.S.[A], M.S., Ph.D., Forest Ecologist, Branch of Research, 

 Forest Service, U. S. Dept. of Agriculture; one time Soil Tech- 

 nologist, Bureau of Chemistry and Soils, University of Wiscon- 

 sin) : 



Subsoils contain plant food elements. It is important to bear 

 in mind that subsoils also contain the important elements. In 

 general, the surface soil contains more rUrogen than the sub- 

 soil, owing to the presence of more organic matter. Some deep, 

 black soils may have as high percentage of nitrogen in the sub- 

 soil (to a limited depth) as is contained in the surface stratum. 



The percentage of phosphorus in the surface layer is com- 

 monly greater than or equal to that contained in the subsoil. 

 There is often a close relationship between the phosphorus and 

 the amount of organic matter in mineral soils. This accounts for 

 the higher phosphorus content of the upper strata. . . On ex- 

 haustive cropping, the higher content of the surface soil is gradu- 

 ally reduced; until it equals at least the percentage contained in 

 f he subsoil. 



The potassium content is usually greater in the subsoils, 

 especially when they are fine-textured. More potassium is found 

 in subsoils of humid climates because of the presence of more 

 fine particles, which are not only richer in potassium than the 

 coarser surface particles, but which absorb much more of the 

 potassium leached down from the surface stratum. 



In arid and semi-arid soils, the phosphorus and potassium 

 content of the surface soil is very much the same as that of the 

 subsoil. 



From the foregoing quotation, it is readily appreciated what 

 a great change may be made in the surface soil by the transloca- 

 tion of the subsoil to the top layers through the action of earth- 

 worms, especially when they are present in large numbers. The 

 further importance of this soil movement from the depths to the 

 top will be more fully understood in the light of the chemical 

 changes the soil undergoes in its passage through the earthworm, 

 which render it immediately available for the growing of crops. 



Every farmer and student of the soil knows that he cannot 

 mix his topsoil with any great quantity of subsoil, without se- 



