62 



upon which fixation depends. Depreciate as one may the importance of 

 Azotobacter as a significant source of nitrogen, the striking quantity of that 

 element in virgin soils, its accumulation in fallow lands, its partial main- 

 tenance in cultivated fields can be accounted for by no more plausible 

 theory than by attributing it to the activities of the above mentioned organ- 

 ism to this or to anaerobic bacteria possessing similar faculties for fixation. 



The present paper deals principally with comparative fixation in virgin 

 and cultivated soils of the same type, and with the process as affected by 

 soils of widely different texture. It notes also the quantities of nitrogen in 

 virgin and cultivated soils that have been collected from various sections of 

 the State and the relationship, if any exists, between the original nitrogen 

 content and the increase by fixation. 1 



Virginia is a State of wide variety in its soil types. It presents many 

 gradations from the heavy red clay of the Piedmont section to the fine sandy 

 loam of Tidewater Virginia. The Bureau of Soils of the U. S. Department 

 of Agriculture has surveyed twelve widely different sections of the State 

 and classified the soil types therein. It was on the basis of this classification 

 that the soils used in the present work were collected. A few were obtained 

 outside of the surveyed area yet these were characteristic in their texture. 

 Many soils of the same name and type but from widely separated, areas 

 were collected that various sections as well as soil types might be repre- 

 sented. In practically every case two samples of each type were collected, 

 one uncultivated and the other under cultivation at the present time. The 

 term "virgin" might be properly applied to the uncultivated series, for 

 in the majority of cases they have never received cultivation and all have 

 lain idle for a number of years. 



An agent from the station in many cases did the collecting, and, when 

 this was not the case, instructions were sent to the various county demon- 

 strators, who kindly cooperated in the work. ' About two gallons of 

 soil were obtained for each sample and shipped to the station by express. 

 As soon as they arrived, the soils were screened and placed in covered tin 

 pails especially constructed for the purpose, and from these composite sam- 

 ples were obtained for the various tests. Soils number 1-55 were collected 

 between May 13 and November 25, 1913, and those from 56-93 were collected 

 between April 10 and July 26, 1914. In every case the tests were made im- 

 mediately after the soils were brought to the laboratory. 



FIXATION TESTS. 



The fixation tests Avere carried on in solution. Whether or not this 

 method is representative of field conditions, it is the only satisfactory one we 



!This work was planned and started by Dr. E. B. Fred, formerly bacteriologist in this 

 Experiment Station, before his removal to the University of Wisconsin. The authors wish also 

 to acknowledge their indebtedness to Professor R. J. Holden for suggestions regarding the geology 

 of soil types in this State. 



