52 THE POPULAR SCIENCE MONTHLY 



THE ILLINOIS SYSTEM OF PERMANENT FERTILITY 



By Peofessoe CYRIL G. HOPKINS 



UNIVBESITT OF ILLINOIS 



I HAVE been invited to write upon the Illinois system of permanent 

 fertility; but I wish to state in the beginning that, in complying 

 with this request, I am speaking in a representative capacity. Many 

 have contributed to the development of this system, including both able 

 investigators in other states and countries, my own colleagues in the 

 investigation of Illinois soils, and the truly scientific farmers of this 

 state, some of whom have kept their own farm practise so close up to the 

 work of the experiment stations as to exert great influence upon the 

 adoption of systems of permanent fertility. 



It is more than fifty years since Liebig wrote the following words: 



Agriculture is, of all industrial pursuits, the richest in facts, and the poorest 

 in their comprehension. Facts are like grains of sand which are moved by the 

 wind, but principles are the same grains cemented into rocks. 



An important part of the work performed in Illinois has consisted 

 in assembling the facts the world affords and cementing these into con- 

 crete forms which serve as a firm foundation upon which to build sys- 

 tems of permanent agriculture. 



The main problem of permanent fertility is simple. It consists, in a 

 word, in making sure that every essential element of plant food is con- 

 tinuously provided to meet the needs of maximum crops; and, of 

 course, any elements which are not so provided by nature must be pro- 

 vided by man. The whole subject has been greatly and unnecessarily 

 complicated, not only by erroneous theories commonly held by farmers 

 and something advocated by unscientific " scientists " holding official 

 positions, such as the theory that crop rotation will maintain the fertil- 

 ity of the soil, but also by the ruinous policy of most commercial fertil- 

 izer interests in urging and often persuading farmers to use small 

 amounts of high-priced so-called " complete " fertilizers which add to 

 the soil only a fraction of the plant food actually required by the crops 

 removed, with the inevitable result that the land itself is steadily im- 

 poverished. 



The more rational system makes use of abundant quantities of all 

 essentials, but at a cost low enough to be within reasonable reach. 

 Those materials which are naturally contained in the soil in inexhaust- 

 ible amounts are liberated from the soil and thus made available for 

 crop production; those contained in the air are likewise drawn upon as 

 needed; while those materials which must be purchased are bought and 



