168 THE ROYAL SOCIETY OF CANADA 



If the object be not lost sight of in the process we may arrive at a 

 point where useful recommendations can be made which are of general 

 application and, for the rest, a simple working plan may be evolved. 



III. THE LAW OF MINIMUM. 



If we admit that fertilizers effect increases in growth we must 

 realize a limit to these effects, otherwise we could continue to infinity. 

 It is also reasonable to suppose that this limit is constant, under 

 constant conditions, and can be attained by any "complete" fertilizer 

 if rightly handled and applied in sufficient amounts to bring up to the 

 requirements each of the elements contained therein. This, of course, 

 may demand different methods of application — for instance NaNC>3 

 may require slightly different practice than (NH^SCU — but each 

 complete fertilizer, under its own- ideal condition, should effect a 

 common limit to increase in growth. 



If now several "complete" fertilizers are added in excess of re- 

 quirements we should expect the increase in crop production to be the 

 same in each case. If the increases are not the same it is perhaps bet- 

 ter to assume that the "working conditions" for the fertilizers were 

 not ideal rather than to assume that one fertilizer is inferior to another ; 

 but having once adopted our method of application, then we can choose 

 the fertilizer responding best to that method. 



The work in fertilizer experiments recorded in the literature would 

 indicate that too little regard has been had to the law of minimum as 

 studied by Liebig and Mitscherlich. A fertilizer is said to be applied in 

 minimum only when the smallest amount is used which is necessary 

 to produce the largest increase in growth. All comparisons should be 

 made in minimum. 



According to Liebig the increase is directly proportional to the 

 application of the element in minimum. Mitscherlich has modified 

 this by stating that the "increase in plant growth with unit increase 

 of the element in minimum is proportional to the decrement from 

 the maximum" (see diagram I). Applications, then, applied in ex- 

 cess effect no further increase and hence the line becomes straight. 



AN APPLICATION OF THE LAW OF MINIMUM. 



It is evident that, if we wish to compare the effectiveness of 

 fertilizers, singly or mixed, we must discover the minimum in each case 

 before drawing conclusions. This point is to be found by making 

 applications in several amounts and, judging by results, to obtain the 

 minimum. For each material or mixture we can plot a curve according 

 to Mitscherlich (see diagram II). 



