110 SOILS: PROPERTIES AND MANAGEMENT 



designated as being in a puddled condition. This con- 

 dition is detrimental to plant growth, for it not only 

 impedes root development and extension, but also pre- 

 vents the circulation of air and water, a function necessary 

 for proper soil sanitation. In the second condition an 

 increase in pore space must occur, as each large grain 

 presents considerable internal air space. If the granules 

 as well as their component particles were arranged in 

 columnar order, the pore space would reach the high 

 percentage of 72.58. Under natural conditions, then, 

 the pore space might range from zero plus to about 72 

 per cent. 



However, not only are the particles of a normal soil 

 not of the same size, but they are far from round. A 

 soil, as already demonstrated, ordinarily presents varying 

 amounts of particles, ranging in size from stone and 

 coarse gravel to the very finest clay. These particles 

 may also differ in shape, varying from almost perfect 

 spheres to flakes, chips, and fragments of every con- 

 ceivable form. Therefore the laws that apply to the 

 ideal condition will hold only in a general way in a normal 

 soil. It is evident, first, that the more compact the 

 soil, the less is the pore space ; secondly, that it is possible 

 to so manipulate a soil as to work the small particles in 

 between the larger ones and create an impervious or 

 puddled condition; and, thirdly, that by the forming 

 of granules the pore space of a soil may be increased to 

 a high percentage. 



From the standpoint of size and arrangement of particles 

 there are really two classes of soils, those of single grain 

 structure and those that are granular. In the former 

 each particle functions separately. In order to do this 

 the particles must be large. This condition is found in 



