494 NATURE AND PROPERTIES OF SOILS 



is reached, the return for each added increment of fertilizer 

 becomes less and less. It is evident, therefore, that with an 

 excessive application of any mixture, the returns to an in- 

 crement will at last become so small that the increased crop 

 fails entirely to pay for even the fertilizer, not to mention 



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Fig. 60. — In the upper diagram the heavy line indicates the increase 

 m the yield of maize due to graduated applications of floats. The 

 lower diagram shows how the cost of the fertilizer approaches and 

 finally exceeds the value of the crop as the applications increase 

 in size. 



such charges as cost of application, harvesting of increased 

 crop, storage, and the like. The application of moderate 

 amounts of fertilizer is to be urged for all soils until the maxi- 

 mum paying quantity that may be applied to any given crop 

 is ascertained by careful experimentation. Over-fertilization 

 probably accounts for the fact that such a large proportion of 



