No. 4.] 



SOIL FERTILITY 



127 



acid and 124 pounds of potash; but if we adopt German 

 averages as a basis of calculation, the quantities would be 

 18 pounds of phosphoric acid and 78 pounds of potash. 

 It would not be strange if the practitioner, supposing that 

 he must adapt his fertilizer to the composition of his crop, 

 becomes confused in the midst of such discrepancies. All 

 this goes to show that the mathematical method of discussing 

 fertility, even if it was rational in all other respects, must 

 lie regarded as subject to great inaccuracies, when applied 

 to a particular season or looalit3^ 



The fact is, that season, environment and methods of ma- 

 nuring the soil materially affect the composition of the plant. 

 A striking illustration of this may be found in the figures 

 obtained on the station farm in an experiment to test 

 methods of maintaining soil fertility. In 1897 and 1898 

 careful determinations were made of the average composition 

 of the entire corn plant, covering a crop on 12 acres in each 

 case. The percentages of nitrogen, phosphoric acid and 

 potash in the dry matter of the crop of these two seasons 

 were as follows : — 



The growth of 1897 contained in a unit of dry matter 20 

 per cent more potash than the croj) of 1898, while the dry 

 matter of the crop of 1898 had a })hosphoric acid content 55 

 per cent greater than the cro]) of 1897. In the light of 

 these figures, the adaptation of fertilizers to the composition 

 of crops, as shown by average percentages, seems to be a 

 precarious undertaking. 



In ord(T to com})ass the factors which relate to soil fer- 

 tility as we understand it to-day, we must step outside of 



