EXPERIMENT COVERING THIRTY YEARS. 43 



Every time that a crop is grown it robs the soil of a valu- 

 able portion of these elements. A ton of clover hay for 

 instance, takes from the soil $10.55 worth of fertilizer. 

 One hundred bushels of corn contains 148 pounds of nitro- 

 gen, 23 pounds of phosphorous and 71 pounds of potash, 

 worth at present market prices, 15, 12 and 6 cents per 

 pound, respectively, or $28.72. That much fertilizer is re- 

 moved with every 100-bushel corn crop. Other crops vary 

 in proportion. It is clear, therefore, that unless these ele- 

 ments are put back into the soil in some way, it will pro- 

 duce steadily declining crops and soon become exhausted 

 or mined out. How to put them back at the least expense 

 is our problem, and it is not alone for the benefit of future 

 generations; it has a vital bearing on our own crop yields. 



At the Illinois Experiment Station, an experiment cov- 

 ering 30 years shows the startling effect of continuous crop 

 farming: 



"At this station the yield on a typical prairie soil has 

 decreased under continuous corn raising from 70 bushels 

 to the acre to 27 bushels to the acre during this period, 

 while under a system of crop rotation and proper fertiliza- 

 tion the yield on a portion of the same field has been in- 

 creased during the same period to 96 bushels per acre. 

 These yields are not of a certain year, but averages of 

 three-year periods. The 96 bushels was obtained in a 

 three-year rotation in which corn was followed by oats in 

 which clover was sown. The next year clover alone, fol- 

 lowed by corn again. Stable manure with commercial 

 fertilizers was applied to the clover ground to be plowed 

 under for corn. The difference in the yields obtained be- 

 tween the rotation system where fertility was applied 

 and the straight corn cropping without fertility was 

 69 bushels per acre, or over two-and-a-half times that of 

 the system of continuous corn raising. A large proportion 

 of this difference in yield is clear profit, as the actual 

 expense of producing the 96 bushels to the acre was but 

 little more than in growing the 27. If the results of these 

 two yields were figured down to a nicety, and the value 



