TECHNICAL DISCUSSION 163 



either soil. The proportion of calcium that was in exchangeable 

 form was about the same in the casts as it was in the AI horizon 

 in the field soil, but in the forest soil the proportion in the casts 

 was distinctly higher than in the A horizons. The proportion 

 of magnesium that was exchangeable was definitely higher in 

 the casts in both soils. 



In all cases the pH of the casts was higher than in the 

 parent soil. Nitrate nitrogen was not determined on the forest 

 soils. Lime applied sometime in the past to the cultivated soil 

 had raised the pH, total calcium, and, with one exception, the 

 exchangeable calcium content of all horizons considerably above 

 the corresponding values found in the forest soils. 



DISCUSSION 



Soil in which earthworms are active is invariably in better 

 physical condition than is similar soil without earthworms. 

 Though it is the opinion of some that the worms are present be- 

 cause of the favorable soil conditions, there is sufficient evidence 

 (1, 3, 8, 10) to indicate that earthworms do very definitely im- 

 prove soil structure by increasing aggregate content and porosity, 

 thus facilitating aeration, water absorption, root penetration, and 

 drainage. Stockli (10) reported that casts contained no par- 

 ticles larger than 2 mm. in diameter and that in some cases par- 

 ticle size was reduced by means of a rubbing action inside the 

 digestive tract of the worm. Mechanical analyses of our samples 

 showed no essential differences in the texture of casts and topsoil. 



From the biological standpoint, casts have been found to 

 contain a much larger bacterial population than the unworked 

 soil (10). 



The data on chemical properties herein reported confirm 

 those published by Powers and Bollen (5) and by Puh (6), with 

 one notable difference in Puh's work. She found the casts to be 

 markedly higher in total calcium but not in exchangeable cal- 

 cium. No explanation for this difference was given. 



