PAPERS ON BIOLOGY AND AGRICULTURE 241 



larly desirable for furnishing on a large scale a part 

 at least of the available nitrogen needed in producing 

 farm crops. One of the most outstanding of these le- 

 gumes at the present time is sweet clover (Mellilotus 

 Alba). There are many interesting and valuable factb 

 regarding the influence of sweet clover as a soil enriching 

 crop under the various soil and climatic conditions found 

 in Illinois. In 1905 the Illinois Experiment Station be- 

 gan the use of sweet clover for soil improvement on the 

 Odin Experiment Field (Marion county). The object 

 of this experiment as stated in the field records was "to 

 test the value of sweet clover as a leguminous green 

 manure crop." Starting with this test the Experiment 

 Station has made practical use of sweet clover for soil 

 improvement purposes in many parts of the state. Sweet 

 clover has been very successful under field conditions 

 as a means of securing available nitrogen for the produc- 

 tion of general farm crops. 



Some very valuable facts have been brought out by 

 the Illinois Experiment Station regarding the available 

 nitrogen created in the soil when sweet clover is plowed 

 under as a green manure crop. (111. Bui. 233.) The fol- 

 lowing table gives some results obtained on the Minonk 

 Experiment Field (Woodford county) during the season 

 of 1919. The land on this field is typical of the common 

 prairie corn belt soil. In this test a spring growth of 

 sweet clover was plowed under late in April and the 

 land planted to corn. The figures represent pounds per 

 acre of available nitrogen found in the surface soil at 

 various dates on treated and untreated land. 



Soil treatment April 26 May 30 July 1 Aug. 12 



Sweet clover turned under 38.7 76.8 67.2 143.6 



No soil treatment 10.1 8.1 11.8 11.8 



Limestone and rock phosphate had been applied to the 

 land where the sweet clover was turned under. Lime- 

 stone is usually essential to the successful growing of 

 sweet clover on average corn belt land. The above re- 

 sults show that as compared with the untreated land the 

 decomposition of the green sweet clover when plowed 

 under does greatly increase the supply of available nitro- 

 gen. It requires about iy 2 pounds of nitrogen to pro- 



