THE SOIL PARTICLE 



97 



be expected to go on in the soil that would not take place in 

 the laboratory beaker. The relation of this absorption to bac- 

 terial activity also cannot be overlooked. 



The minerals of the soil are all very resistant to solution; 

 if they were not, they would long ago have been leached away. 

 Such materials, while almost insoluble under ordinary cir- 

 cumstances, allow appreciable amounts of nutrients to appear 

 in the soil solution, because of the immense amount of surface 

 exposed, although the specific solubility remains the same. 



In order to present some idea of the internal surface of 

 ordinary soils, a few figures are given on the same soil classes 

 for which the number of particles have already been calcu- 

 lated : 



Table XX 



APPROXIMATE INTERNAL AREA OF SEVERAL AVERAGE SOIL 



CLASSES 1 



While these figures are as grossly inaccurate as those re- 

 garding the number of particles, they tend to emphasize the 

 tremendous internal surface possessed by even the coarser 

 soils. The data presented for an acre-foot of soil, while al- 

 most too large for adequate comprehension, are probably 

 much too low. It is not to be wondered at that the slowly 

 soluble minerals are able to supply sufficient nutrients to the 



1 When the approximate number of particles and their sizes in any 

 given weight of soil are known, the internal surface may be calculated 

 by the following formula: 



Surface = jt D 2 X number of particles. 



