THEORY OF SOIL FERTILITY 191 



groups. One group is specifically benefited 

 by nitrogenous fertilization, the second by 

 phosphatic, and the third by potassic. That is, 

 in each class or group, one element more than 

 any other rules or dominates the growth of 

 that group, and hence each particular element 

 should be applied in excess to the class of 

 plants for which it is a dominant. In this sys- 

 tem it is asserted that nitrogen is the dominant 

 ingredient of wheat, rye, oats, barley, meadow 

 grass, and beet crops. Phosphoric acid is the 

 dominant fertilizer ingredient for turnips, 

 Swedes, Indian corn (maize), sorghum and 

 sugar cane; and potash is the dominant or 

 ruling element for peas, beans, clover, vetches, 

 flax and potatoes. It must not be understood 

 that this system advocates only single ele- 

 ments for the others are quite as important up 

 to a certain point, beyond which they do not 

 exercise a controlling influence in the manures 

 for the crops for the three classes. This spe- 

 cial or dominating element is used in greater 

 proportion than the others, and if soils are in 

 a high state of cultivation, or have been 

 manured with natural products, as stable 

 manure, they may be used singly to force a 

 maximum growth of the crop. * * * 



"Another system which has been urged, 

 notably by German scientists, is based upon 

 the fact that the mineral constituents, phos- 

 phoric acid and potash, form fixed compounds 



