| THE ILLINOIS SYSTEM OF PERMANENT FERTILITY |
By Professor CYRIL G. HOPKINS
UNIVERSITY 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:
An important part of the work performed in Illinois has consisted in assembling the facts the world affords and cementing these into concrete forms which serve as a firm foundation upon which to build systems 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 continuously provided to meet the needs of maximum crops; and, of course, any elements which are not so provided by nature must be provided 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 fertility of the soil, but also by the ruinous policy of most commercial fertilizer 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 impoverished.
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 inexhaustible 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
