52 HARNESSING THE EARTHWORM 



phorus and potassium as well as the minor elements are 

 intimately mixed and compounded with a high percentage of or- 

 ganic material, all in a finely divided state, which exposes many 

 surfaces to the bacterial action so important in the topsoil. The 

 earthworms "sweeten" the soil, as the castings are rich in cal- 

 cium carbonate that has been secreted from the blood of the 

 earthworm in the metabolic processes and is then excreted in 

 the castings. 



Of particular note is the highly important fact that earth- 

 worm castings are very rich in nitrogen and may contain three 

 times as much nitrogen as is found in the soil in which the worms 

 work. This point is brought out by Horace Edward Stock- 

 bridge (Ph.D., Florida Agricultural College) in his book Rocks 

 and Soils: Their Origin, Composition and Characteristics. In 

 discussing earthworm castings, he says : 



. . . The amount of organic matter thus directly or indirectly 

 added to the soil may be inferred from the fact that Darwin 

 estimates that the material annually brought to the surface by 

 worms is two-tenths of an inch per acre ; equivalent to an average 

 of 10.59 tons of each acre inhabited by worms. . . 



Darwin states the ammonia content of worm castings to 

 be 0.018 per cent, while the average ammonia present in com- 

 mon surface soils, as determined by Knop and Wolff, is only 

 0.00056 per cent. It therefore appears that the action of the 

 worms has increased the ammonia content of the soil acted upon 

 more than threefold (321 per cent). 



When given in the number of pounds per acre represented 

 by 0.018 per cent of 10.59 tons, the amount of dry material 

 which Darwin estimated annually passed through the earth- 

 worms of England per acre, the yearly accession of ammonia 

 per acre is equivalent to 381.24 pounds. Ammonia is but one, 

 and perhaps not the most important, of the constituents made 

 available in the topsoil by the life- functions of earthworms. 

 Quoting further from Dr. Stockbridge, "This, be it borne in 

 mind, is but a change wrought in one year and capable of yearly 



