116 SOILS: PROPERTIES AND MANAGEMENT 



amount of internal space. Each individual space is 

 larger under such conditions, and this accounts for the 

 ready movement of water and air through such soils. 

 A clay soil, while containing a very large amount of pore 

 space, has the disadvantage of very minute individual 

 pores. The large amount of space occurs because of 

 the lightness of the particles and the tendency toward 

 granulation. The small size of the individual spaces 

 is a direct function of size of particle, or texture. 



A very simple formula may be used for a determination 

 of the percentage of pore space in any soil, provided the 

 absolute and the apparent specific gravities are known : 



TAp. Sp. Gr ^ 1001 

 Percentage or pore space = 100 77 



LAb. bp. Gr. 1 J 



Thus a soil having an apparent specific gravity of 1.60 

 and an absolute specific gravity of 2.60 has 38.5 per cent 

 of pore space ; while in a soil in which the above figures 

 are 1.10 and 2.50, respectively, the percentage of pore 

 space is 56. The following figures, taken from King, 1 

 illustrate the relation that texture holds to total pore 

 space in soils : - PERCENTAGE OF 



PORE SPACE 



Sandy soil 32.49 



Loam 34.49 



Heavy loam 44.15 



Loamy clay soil 45.32 



Clayey loam 47.10 



Clay 48.00 



Very fine clay 52.94 



1 King, F. H. Physics of Agriculture, p. 124. Published 

 by the author, Madison, Wisconsin. 1910. 



