82 THE PRINCIPLES OF SOIL MANAGEMENT 



Since normal field soils are mixtures in different 

 proportions of these groups, the number of particles 

 in unit weight of any class will be different from those 

 shown above, and will not reach the extreme upper 

 limits. 



The number of particles in one gram oLthe classes 

 of soil whose analyses are shown by the curves on page 

 78 is approximately as follows: 



Table XI. Approximate Number of Particles in One 



Gram op Soil 



Coarse sand 3,276,000,000 



Medium sand 3,956,000,000 



Sandy loam 6,485,000,000 



Fine sandy loam 4,902,000,000 



Silt loam 9,639,000,000 



Clay loam 16,371,000,000 



Clay 19,525,000,000 



30. Surface area of soil particles. The significance of 

 these large numbers of soil particles in any mass of soil 

 lies in their relation to the surface area of the particles. 

 These surfaces of the particles hold on to the moisture 

 the more, the greater their area. This large surface 

 also increases the rate of chemical solution, by which 

 the food constitutes contained in the mineral particles 

 become available for the plant's use. Another important 

 property of this immense surface area of soils is to retain 

 food materials in a semi-available form, as will be ex r 

 plained in discussing the absorptive power of soils. 

 (See page 299.) 



The surface area of a fine-textured soil is greater than 

 the first thought might indicate. This immense area 

 exposed by soils is shown by the following table, which 



