242 ILLINOIS STATE ACADEMY OF SCIENCE 



duce one bushel of corn, and on August 12 there was suf- 

 ficient available nitrogen in the soil to produce about 95 

 bushels of corn. Comparing the untreated land with the 

 treated land it may be seen that the sweet clover con- 

 tained about Sy 2 to 12 times as much available nitrogen 

 as when no sweet clover was turned under. 



The farm lands in southern Illinois are very different 

 in composition and productiveness from those in the cen- 

 tral and northern parts of the state. On these lighter 

 soils of the south part of the state clovers cannot be 

 grown successfully without the judicious use of lime- 

 stone. When limestone and sweet clover as a green ma- 

 nure are used on these lands the supply of available 

 nitrogen is greatly increased. 



The following table gives results obtained on the New- 

 ton Experiment Field (Jasper county) during the season 

 of 1919. (Bui. 233.) The land on this field is typical of 

 the light prairie soils of southern Illinois. The figures 

 represent pounds per acre of available nitrogen in the 

 surface soil at various dates. 



Soil treatment May 12 June 18 July 4 Aug. 19 



Sweet clover turned under 18.6 36.8 30.6 78.2 



No soil treatment 14.0 22.6 9.2 25.9 



Limestone and rock phosphate were used in addition 

 to the sweet clover. The decomposition of the sweet 

 clover furnished available nitrogen far in excess of that 

 on the untreated land. On August 19, the available nitro 

 gen on the treated land was sufficient to produce 50 

 bushels of corn while on the untreated land there was 

 enough for about 16 bushels of corn. 



The data above cited show that legume crops when 

 worked into the soil do increase greatly the supply of 

 available nitrogen. This plan of soil management is 

 practical and fits into the scheme of general farm prac- 

 tice, and there is no question regarding its economy when 

 compared with the cost of commercial nitrogen as sold 

 on the market today. 



It has been demonstrated clearly that sweet clover as 

 a green manure crop may add large amounts of available 

 nitrogen to the soil ; now it is well to look at actual crop 

 yields and note the influence of this treatment. The 



