EDAPHIC OR SOIL FACTORS: PHYSICAL 



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natural mature soil and dried, the volume of the measuring cylinder 

 (1,000 cc.) minus the volume of the dried, solid soil particles gives 

 directly the hollow space or pore volume of the soil in thousandths. 

 Ramann (1911, p. 308), who examined the pore volume of a diluvial 

 sand dune near Eberswalde, determined at different depths the follow- 

 ing pore volumes: 



Centimeters Parts per 1,000 



to 10 506 



20 to 30 459 



40 to 50 404 



60 to 70 382 



80 to 90 373 



The pore volume decreases from top to bottom, rapidly at first then 

 more slowly. The densest packing of soil is found under water (pore 

 volume 200 to 300 parts per 1,000). In contrast to this, peat and 

 moor soils are very loosely packed (pore volume 840 to 850 per 1,000). 



More recent investigations by Burger (1922), using more delicate 

 methods, confirm the general results of Ramann, both agreeing quite 

 well on the investigations on the O2 and CO2 content of the soil. 



Table 27. — Pore Volume of the Soil of Two Seminatural Plant Commun- 

 ities, Parts per 1,000 

 (After Burger) 



In the dry meadow the topmost soil layer is rather densely packed, 

 whereas in undisturbed soil of the oak woods with its blanket of dead 

 leaves a loose upper layer favors the growth of rhizome geophytes. 

 The dense packing of the open meadow soil is due to dense root systems 

 and even more to the puddling effect of rainfall. After deforestation, 

 the pore volume of the soil decreases considerably. From the curves 

 plotted by Nitzsch (1925) for the elucidation of the relation between 

 water capacity and pore volume it follows that with increasing loose- 

 ness of the soil the water capacity is raised. Beyond a certain limit, 

 fixed by habitat conditions, it then decreases rapidly. 



Air Capacity. — Having determined the pore volume, including all 

 hollow spaces not occupied by solid soil particles (earth, stones, roots), 



