FOR iJKTTKi! mors 



17 



increased the corn yields, althonj>-h with wheat, phosphorus has 

 given a marked increase and potassium some further )i:'<i.\i\, not- 

 witlislandinj];- the fact that these two best treated plot series 

 were naturally slit,'htly less productive than the other three 

 of the series. With more org-anic matter the effect of applied 

 potassium will probably disappear. 



Soils Deficient in Phosphorus — Phosphorus is the element 

 of plant food most likely to be deficient in the common gently 

 rolling prairie or upland timber soils of Central United States. 

 as in Illinois, Indiana, and Ohio. Phosphorus is also commonly 

 found to be one of the most deficient plant foods in long culti- 

 vated soils in eastern and southern United States. 



The total amount of phosphorus contained in the surface 

 seven inches of the commonest type of soil in the Illinois corn 

 belt is no more than would be required for fifty crops of corn of 

 100 bushels each, or for about seventy such crops if the grain 

 only were removed from the land. The next soil stratum is 

 poorer in phosphorus than the surface soil and even a rich sub- 

 soil is of little value when buried beneath a worn-out surface. 



The common so-called worn-out soil of southern Illinois con- 

 tains but little more than half as much phosphorus as the corn 

 belt soil. If clover failure is becoming more frequent than 

 formerly on Illinois soils it is one of the strong evidences of 

 insufficient phosphorus. 



The results obtained from the University of Illinois soil 

 experiment field near Bloomington, 111., on the typical slightly 

 rolling prairie land of the central Illinois corn belt will serve to 

 demonstrate that phosphorus is the element which limits crop 

 yields on soils of this character, notwithstanding the fact that 

 this soil is valued at not less than $150 an acre and is still pro- 

 ducing very profitable crops even for land of that valuation. 



Crop Yields ix Soil Experiments 

 Typical Corn Belt Prairie Soil near Bloomington, Illinois 



Plant Food Applied 



None 



Nitrogen _.. 

 Phosphorus 

 Potassium . 



Nitrogen, phosphorus 



Nitrogen, potassium 



Phosphorus, potassium 



Nitrogen, phosphorus, potassium 



Gain for phosphorus when added to ni- 

 trogen 



18 



15 



20 



