Il8 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



of each size can be calculated from the weights of the various 

 separations made in the physical analysis of the soil. 



Relation of Fineness to Fertility. The state of division of a 

 soil has some effect upon its fertility. If two portions of a rock 

 are prepared, one coarse, and the other finely ground, plants will 

 grow better on the latter. With the same material, the rapidity of 

 solution is in direct ratio to the extent of surface it exposes. The 

 finer the particles, the more abundantly will the plant be supplied 

 with the necessary nourishment. For example, a cube of rock I 

 foot square has 6 sides each 12 inches square, or 6 times 144 

 square inches of surface. Cut this cube into cubes of I inch 

 square, or 12 times 144 cubes, each of which has six sides, one 

 inch square, or the exposure is 6 times 144 square inches. It is 

 easily seen that as the division increases, the surface exposed to 

 the action of roots also increases. 



It must not be assumed, however, that finely pulverized sandy 

 soils would yield the same amount of plant food as clay soils. 

 While this might be true in exceptional cases, as a rule sandy 

 soils contain less plant food, as may be shown by a complete 

 chemical analysis of the soil. 



