240 ILLINOIS STATE ACADEMY OF SCIENCE 



understood. The old Roman farmers (111. Bui. 179, p. 

 472) knew that beans possessed the power of enriching 

 the land, and these early farmers followed the practice of 

 plowing under lupines as a means of adding nitrogen and 

 enriching their cultivated lands. There are many early 

 writings which indicate that legume plants were consid- 

 ered valuable for soil enrichment, but it was not until 

 after 1886 that Hellriegel first announced the discovery 

 that bacteria living in symbiotic relationship with legum- 

 inous plants have the power to fix free atmospheric nitro- 

 gen. From the time of Hellriegel 's discovery down to the 

 present day there has been much experimental work done 

 looking toward the utilization of legumes as a means of 

 furnishing a supply of combined nitrogen sufficient to 

 meet the requirements of crops in general farm practice. 



After the fact was thoroughly established that le- 

 gumes do have the power to fix free atmospheric nitro- 

 gen, there have been efforts made to determine the ap- 

 proximate amount fixed by these plants. The amount 

 of nitrogen fixed is influenced by different soil conditions 

 and other factors. It is apparent that when legumes 

 properly inoculated are grown in a soil rich in available 

 nitrogen they will utilize the supply in the soil rather 

 than make use of the free atmospheric nitrogen. On the 

 other hand, if legumes properly inoculated are grown in 

 a sandy soil or other soil low in nitrogen they will at 

 once fix comparatively large amounts of free nitrogen in 

 order to make proper growth. 



Some experimental work conducted by the late Dr. 

 Hopkins ( 111. Bui. 76) shows a comparison of inoculated 

 and uninoculated alfalfa when grown on common corn 

 belt prairie land. The results of this test show that the 

 alfalfa when properly inoculated fixed about 40 lbs. more 

 nitrogen per acre than did the uninoculated alfalfa. The 

 amount of nitrogen fixed as indicated by this experiment 

 might vary with different soil conditions ; however, this 

 test serves to show the possibilities of the utilization of 

 free atmospheric nitrogen by legumes under field condi- 

 tions. 



There are many legume plants which adapt themselves 

 to general farm practice, and some of these are particu- 



