816 EXPERIMENT STATION BECORD. 



rado soils (E. S. R., 23, p. 221) the author made a bacteriological study of the 

 nitropen fixing power of these soils in nutrient solutions and in the soils them- 

 selves. A study was also made of the relation of nitrates, other nitrogen com- 

 pounds, and various salts in the nutrient solution to the characteristic brown 

 color of the niter spots. In most of the culture work the mannite solution 

 recommended by Lipnian was used except that tri potassium phosphate (K3PO.1) 

 was substituted for the dipotassium phosphate (K2HPO1). 



The author concludes from the results obtained iu these studies that " the 

 power to fix atmospheric nitrogen is a property common to many cultivated 

 Colorado soils. This power is not confined to nitrogen fixation in solutions, 

 but is manifested in soils as well. 'The rate of fixation of nitrogen obtained 

 is suflicieut to account for the nitrates found in the soil provided that it is 

 nitrified. The rate of nitrification obtained is sufficient to account for the 

 formation of the nitrates found, in most cases if not all of them.' 



" The nitrogen fixing power is not limited to any geographical locality or 

 class of soils, however the adobe shale soils, both in a raw state and newly 

 cultivated, possess little if any nitrogen fixing power. Excessive nitrates either 

 destroy or greatly attenuate the nitrogen fixing flora of a soil. A limited 

 amount of soil nitrate does not seriously affect the niti'ogen fixing power of a 

 soil; Azotohncter nhroococcum appears to be the dominant nitrogen fixing or- 

 ganism in the soils studied. The dark brown color of the niter soils is due, 

 in a large part, to the pigment produced by A. chroococcum. Given a source 

 of energy, the nitrate is the limiting factor in the production of the brown 

 color. In the presence of nitrates, A. cJiroococcum develops a chocolate brown 

 to black pigment ; nitrites, in certain amounts, produce similar results, but to 

 a less degree; nitrogen as NH4CI., (NH4)2S04, asparagin, and peptone has no 

 effect upon this function. The highly colored extracts obtained from certain 

 niter soils suggest that the pigment of A. chroococcum may be soluble in the 

 alkaline soil waters. Excessive soil moisture, by interfering with the growth 

 of A. chroococcum prevents the formation of the brown color on the soil, and 

 makes the fixation of atmospheric nitrogen impossible." 



The fixation of nitrogen by means of Bacillus radicicola without the 

 presence of a leg'ume, E. B. Fred {Virginia Sta. Rpts. 1909-10, pp. 13S-lJi2, 

 figs. 3). — The results of experiments in liquid media, sand, and soil show that 

 the nitrogen assimilation, although very small, " was sufficient to give a reason- 

 able basis for the belief that B. radicicola will live in the soil without the host 

 plant and accomplish a certain amount of nitrogen assimilation." 



The inhibition of nitrification by organic matter, compared in soils and in 

 solutions, F. L. Stevens, W. A. Withers, et al. (North Carolina 8ta. Rpt. 

 1910, pp. 36-51). — Previously noted from another source (E. S. R., 23, p. 721). 



A comparative study of the bacterial content of soils from fields of com 

 and alfalfa, H. H. Waite and D. H. Squires (Nebraska Sta. Rpt. 1910, pp. 

 160-177, figs. J/). — This article reports counts and studies of cultural character- 

 i.stics of the bacteria to a depth of 12 ft. in two fields of loess soil which have 

 been in cultivation for 30 years. The cornfield had never been cropped in 

 alfalfa ; the alfalfa field had been in alfalfa for the past seven years. 



Com soil showed a decidedly greater number of bacteria in the first 3 ft. than 

 the alfalfa soil. "Azotobacters were shown to be in all levels of the alfalfa 

 field except the first, seventh, tenth, and eleventh ; and in all levels of the corn- 

 field except the first, third, fourth, and eighth foot, showing a good distribution 

 of Azotobacters as to depth." 



The great majority of the organisms isolated were acid formers. The methods 

 used are described and a bibliography of 32 references is given. 



