PAPERS ON BIOLOGY AND AGRICULTURE 243 



Experiment Station has followed the plan of locating soil 

 experiment fields at various points in the state, and thru 

 the operation of these fields by the University much re- 

 liable information is secured from year to year regard- 

 ing the permanent improvement of Illinois soils. Tn 

 the following tables some twelve experiment fields are 

 considered upon which sweet clover has been used as a 

 green manure crop during the past eight years. These 

 fields are distributed widely so that they represent in 

 general the predominating soil types of the state, and 

 are located in regions of varying climatic conditions. 



The following table gives corn yields obtained from 

 three experiment fields located in northern Illinois and 

 representing the Brown Silt Loam soil which is the pre- 

 dominating soil type of that region. 



CORN YIELDS 8 YEAR AVERAGE (1915-22) BUSHELS PER ACRE. 



The average of these three fields gives an eight year 

 average increase of 7.5 bushels of corn per acre for the 

 use of the lime-sweet clover treatment. This is a very 

 substantial increase on land which is maintaining an 

 average corn yield of almost 50 bushels per acre. 



The following table gives the corn yields obtained from 

 three experiment fields located in the central part of the 

 state and also representing the Brown Silt Loam soil 

 which is the common corn belt prairie farm land. 



CORN YIELDS 8 YEAR AVERAGE (1915-22) BUSHELS PER ACRE. 



Soil treatment Urbana Carthage Clayton Average 



Crop residues and lime- 

 stone—sweet clover. 68.7 51.6 52.2 57.5 



Crop residues only 57.5 43.2 43.3 48.0 



Gain for lime — sweet 



clover 11.2 8.4 8.9 9.5 



The average gain for the lime-sweet clover treatment 

 on these three fields on corn belt soil is 9.5 bushels of 

 corn per acre. This type of soil has often been referred 

 to as inexhaustible, and yet these experiments demon- 



