166 HARNESSING THE EARTHWORM 



forested areas and subjected to chemical and mechanical analyses. 



At the time of sampling, the field soil contained approxi- 

 mately three casts to the square foot, averaging 2 ounces each, 

 or 16,000 pounds to the acre. 



In the field soil, casts contained less exchangeable hydrogen 

 and a lower clay content than the 0-6 inch layer; but the casts 

 had higher pH values and were higher in total and nitrate 

 nitrogen, organic matter, total and exchangeable calcium, ex- 

 changeable potassium and magnesium, available phosphorus, base 

 capacity, base saturation, and moisture equivalent. Total mag- 

 nesium was about equal in all samples. 



Forest soil samples showed similar but even more striking 

 results. Forest soil casts were higher in nitrogen, organic carbon, 

 and exchangeable calcium, and had a higher moisture equivalent 

 than the casts from the field soil. 



These changes in composition as the result of earthworm 

 activity are due chiefly to the intimate mixing of plant and animal 

 remains with mineral soil in the digestive tract of the worm and 

 to the action of digestive secretions on the mixture. That earth- 

 worms are beneficial to the soil has been established beyond a 

 doubt. Conditions favorable to the worms, however, are at the 

 same time favorable to plant growth, and quantitative measure- 

 ments under field conditions of the part the worms play in crop 

 production have not as yet been obtained. 



REFERENCES 



(1) BLANCK, E., AND GIESCKE, F. 1924 [On the influence of earthworms 



on the physical and biological properties of the soil.] Ztschr. 

 Pflanzenernahr. Diingung. u. Bodenk. 3 (B) : 198-210. (Abstract 

 in Exp. Sta. Rec. 54:718. 1926.) 



(2) DARWIN, C. 1837 The formation of vegetable mould through the 



action of worms. Trans. Geol. Soc. (London) 5 :505. [Also in 

 book form : D. Appleton and Co., New York. 1882.] 



(3) HENSEN, V. 1882 Uber die Fruchtbarkeit des Erdbodens in ihrer 



Abhangigkeit von den Leistungen der in der Erdrinde lebenden 

 Wurmer. Landw. Jahrb. 11:661-698. 



