B. P. I.— 470. 



NOTES ON THE NUMBER AND DISTRIBUTION OF 



NATIVE LEGUMES IN NEBRASKA 



AND KANSAS. 



INTRODUCTION. 



Many hypotheses have been formed to account for the large stores of 

 nitrogen in virgin soils, but none of these have been entirely satisfac- 

 tory. It seems to be a well-established fact that small quantities of 

 ammonia are collected from the air by rain and added to the soil; also, 

 that more or less nitric acid is formed b}^ electrical discharges and 

 added to the supply. Some investigators have attributed the fixation 

 of nitrogen entirely to the latter cause. Recently a iiumber of efi^orts 

 have been made to show that nonsymbiotic or independent bacteria 

 are the chief agents in fixing this element. While it seems certain that 

 some nitrogen is added to the soil by each of these methods, it appears 

 to the writer that there is not sufficient evidence to warrant a conclu- 

 sion that any one of them has been the most important factor in this 

 work. They do not furnish a satisfactory explanation of the presence 

 of such large quantities of nitrogen in the soil. 



NITROGEN FIXATION IN SOIL BY WILD LEGUMES. 



Several experimenters have suggested that wild legumes may have 

 played some part in this work, but they have not generally been con- 

 sidered as important factors. The studies reported in this circular 

 indicate that this subject deserves more thorough investigation than 

 it has yet received and that native legumes have been of much more 

 importance in this r6le than has been thought. 



Several years ago the writer raised the question whether the native 

 legumes of the prairies were sufficiently numerous to have fixed the 

 amount of nitrogen present. A search for published data on the sub- 

 ject was made, but none were found. Accordingly, in the spring of 

 1908 a series of investigations was begun, a preliminary report of which 

 is here given. 



DIFFICULTY OF MAKING INVESTIGATION. 



Many difficulties were experienced in collecting the desired data. 

 Not many tracts of virgin prairie remain in eastern Nebraska and 

 northeastern Kansas, except on land that is too wet or too rough or 

 stony to be easily farmed. Furthermore, most of the grass plots that 

 do remain have been pastured so much that few legumes are left. It 



[Cir. 31] 3 



