OKGAXIC CONSTITUENTS OF SOILS. 7 



was next proposed as a sign of quality, but researches into the amount of inorganic 

 matter abstracted by each crop have demonstrated that soils at a mixed character 

 contain abundant supplies of mineral food for numerous crops. 



Tliis was over 50 years ago, and the statements made are practically 

 as true to-day as they were then. There has been a marked advance 

 in agricultural practice, but until quite recently comparatively little 

 light has been shed upon the scientific principles which underlie 

 those practices. 



In all justice to Liebig, however, I must make another quotation 

 from his works to show that he himself recognized the insufficiency 

 of the views expressed by the above quotations. He says: 



But it has been observed that the crops are not always abundant in proportion 

 to the quantity of manure employed, even though it may have been of the most 

 powerful kind; that the produce of many plants, for example, diminishes in spite of 

 the apparent replacement by manures of the substances removed from the soil when 

 they are cultivated on the same field for several years in succession. 



From the above quotation it may be seen that Liebig recognized 

 that there are many cases which his theory of mineral requirement 

 failed to cover. Indeed, if he had followed the idea embodied in 

 the quotation to its final analysis he would have reached some 

 conclusions similar to those presented to you in the various papers 

 to-day. 



Even before, and especially since, the time of Liebig much material 

 has been accumulated and handled in a statistical manner. I 

 should here say that much valuable information has been thus 

 obtained, but it should be needless for me to add that even with all 

 these years of crop statistics at hand the difficult problems of the 

 causes of fertility or infertility of our agricultural lands have not 

 been thereby determined nor eliminated. The problem is not 

 solved, though much progress has been made through the applica- 

 tion of modern sciences. If the problem of soil fertility had been 

 solved by the application of such statistics, this symposium would 

 not have been held. The pessimistic views expressed by some I can 

 not share. Science is ever optimistic; the scientific investigator 

 must above all things be optimistic and have an abiding faith that 

 science will solve the intricate questions connected with his prob- 

 lem. The problem of soil fertility and infertility is broad enough 

 and big enough for many workers and methods of attack. We can 

 not all begin to unravel the tangled threads at the same point; there 

 are different viewpoints, and it is not improbable that some may 

 have a clearer vision than others to see the particular thread that 

 will undo the snarl. The solution of the problem can be reached only 

 through diligent experimentation, not by the statistics of even a 

 hundred years. 



