EFFECT OF CONTINUOUS CROPPING. 133 



land by means of manure and the legumes. It will be observed 

 that where this latter system is practiced tfie nitrogen in the 

 soil is actually increased, whereas the phosphoric acid and potash 

 are reduced to a very small extent. 



The startling effect of continuous crop farming is shown by 

 an experiment covering 30 years at the Illinois Experiment Sta- 

 tion: 



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

 creased 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 fertilization the yield on a 

 portion of the same field has been increased 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, 

 followed by corn again. Stable manure with commercial fertil- 

 izers was applied to the clover ground to be plowed under for 

 corn. The difference in the yields obtained between 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 of the land de- 

 termined by the net income, it would be found that the well 

 farmed acres would be worth an enormous price as compared 

 with a gift of the land that produced the smaller yield." 



Henry says that "with sharp competition confronting every 

 one who cultivates the soil, the careful saving of farm manures 

 and their judicious application are vital factors in farming oper- 

 ations, and as essential to continued success as plowing the land 

 or planting the cr.op. * * * When one must choose between com- 

 mercial fertilizers and barn-yard manures, it is reasonable to 

 estimate that the latter have a value of at least two-thirds the 

 former, based on their nitrogen, phosphoric acid and potash con- 

 tents." These manures benefit the soil because the vegetable 

 matter they contain acts as a mulch and forms humus, but so far 



