THE ABSORPTION OF MINERAL ELEMENTS 



87 



proportionally to the difference between the yield actually obtained 

 and the maximum yield, consequently, the increase gradually 

 diminishes with its approach to the maximum yield. This de- 

 pendence of the yield on increasing amounts of fertilizers Mitscher- 

 lich terms not the law of minimum, but the law of action of growth 

 factors. 



When several factors are acting simultaneously, that is, when 

 a number of them are increasing at the same time, Mitscherlich 

 has noted also significant deviations from the law of the minimum. 

 He found that the increase in one of the nutrient elements slightly 



100 



50 



4 



100.0 

 93.75 

 87.5 



- 75.0 



50.0 



Fir,. 37.- 



-The influence of the simultaneous change of factors X and Z on the 

 yield y, according to Mitscherlich. 



augments the effect of the other nutrient substances. Thus in the 

 case of nitrogen deficiency, a potash fertilizer may increase the 

 yield, though, according to the law of minimum, this should not 

 be the case. The simultaneous action of two factors is graphically 

 represented in Fig. 37. 



The formula proposed by Mitscherlich has met with many 

 objections and has been amended by other investigators. Conse- 

 quently, it must be regarded only as a general scheme, one requir- 

 ing further analysis. Russel, for instance, has observed that 

 when very small quantities of mineral substances are added to the 

 soil, their action is considerably weaker than it should be accord- 

 ing to Mitscherlich's law. He explained this as a direct conse- 

 quence of soil adsorption. Hence the greatest effect is obtained 

 neither from too small nor too large, but from average doses of 

 fertilizers. In this connection, especially sharp criticisms have 



