FOR BETTER CROPS IN THE SOUTH 



25 



of the series. With more organic 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. 

 Phosphorus is also commonly found to be one of the most deficient 

 plant foods in long cultivated 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, it is one of the strong evidences of insufficient phos- 

 phorus. 



The results obtained 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 producing 

 very profitable crops even for land of that valuation. 



Crop Yields in Soil Experiments 

 Typical Corn Belt Prairie Soil near Bloomington, Illinois 



Plant Food Applied 



Corn 

 Bushels 



1904 



Oats 



Bushels 



1905 

 Wheat 

 Bushels 



None 



Nitrogen ... 

 Phosphorus. 

 Potassium _ . 



60 

 60 

 73 

 56 



61 

 70 

 73 

 63 



29 

 31 

 39 

 33 



Nitrogen, phosphorus 



Nitrogen, potassium 



Phosphorus, potassium 



Nitrogen, phosphorus, potassium 



78 

 59 

 75 



81 



85 

 66 

 70 

 91 



51 

 30 

 38 

 52 



Gain for phosphorus when added to ni- 

 trogen . _ 



18 



15 



20 



It will be seen that the addition of nitrogen or potassium, 

 separately or together, produces little benefit and sometimes 

 the effect is a decrease in yield, although nitrogen did appre- 

 ciably increase the yield of oats in 1904. After phosphorus has 

 been applied, then nitrogen can be utilized with marked benefit. 



