552 SOILS: PROPERTIES AND MANAGEMENT 



(1) What are the right proportions of nitrogen, phos- 

 phorus, and potash to apply under given conditions ? 



(2) What would be the effect if any one of these should 

 not be present in such a quantity as to make it equal in 

 function to the others? The first query cannot be dis- 

 posed of until the question of fertilizer mixtures has been 

 considered. The second, however, is not affected by so 

 many factors, and is more clearly a question of the func- 

 tion of the elements concerned. 



Any element that exists in relatively small amounts as 

 compared with the other important constituents natu- 

 rally becomes the controlling factor in crop development. 

 Any reduction or increase in this element will cause a 

 corresponding reduction or increase in the crop yield. 

 This element, then, is said to be " in the minimum." 

 In fertilizer practice, ideal conditions would exist if no 

 constituent functioned as a decided minimum and the 

 entire influence of each single element were fully utilized. 

 In other words, the fertilizer would be balanced as to its 

 relationship to normal plant growth. That such a con- 

 dition is more or less ideal and theoretical is obvious, 

 from the fact that the various fertilizer carriers undergo 

 more or less radical changes after being applied to the 

 soil. The composition of the soil itself is also a disturb- 

 ing factor. Nevertheless, the nearer an approach can be 

 made to such conditions, the greater will be the economy 

 of fertilizer practice. 



Numerous persons have investigated the question as 

 to what effect an increase of an element in the minimum 

 may have on crop yield, and various ideas have been 

 advanced thereon. The idea of a definite law governing 

 the increase of plant growth according as the element 

 in the minimum is increased, was first suggested by 



