724 EXPEBIMENT STATION EECOKD. [Vol. . -58 



Sodium nitrate stimulated the nitrification of dried blood, cottonseed meal, 

 and to a less extent ammonium sulphate. This stimulative action was not 

 apparent, secondary reactions, such as increased cell division, with a subse- 

 quent assimilation of nitrates, masking the end point. Large quantities of 

 sodium nitrate depressed nitrification, the amount of the depression depending 

 first upon the sources of nitrifiable material and second upon the soil type. In 

 large quantities sodium nitrate became toxic first to the nitrification of am- 

 monium sulphate, then to dried blood, and lastly to cottonseed meal. 



Sodium nitrate in amounts up to 5.000 lbs. per acre affected Nitrobacter the 

 same as Nitrococcus, while in amounts beyond 5,000 lbs. it stopped the activities 

 of Nitrobacter but not those of Nitrococcus. Sodium nitrate in small quantities 

 stimulated nitrogen fixation by Azotobacter and in large quantities depressed it. 



Large quantities of nitrates were assimilated by organisms in the soils, the 

 amount so assimilated being approximately 20 per cent of the nitrogen applied. 

 Apparently calcium nitrate was as readily a.ssimilated as sodium nitrate. 

 Experiments on the nitrifiability of microbial matter gave widely varying 

 results. 



Of the three nitrogen-transforming groups, sodium nitrate afi'ected the 

 nitrogen-fixing group most adversely, the nitrifying group to a lesser degree, 

 and the ammonifying group least. As used in agi'icultural practice, sodium 

 nitrate generally stimulates the activity of the ammonifying and nitrifying 

 groups, but depresses the activity of the nitrogen-fixing group. In no case is 

 it thought to cause toxicity if applied rationally. 



It is concluded that " the entire study of the influence of the sodium nitrate 

 upon nitrogen transformations in soils seems to indicate rather strongly that in 

 the cases where larger quantities of nitrogen are recovered in the crop than 

 can be accounted for by the amount of sodium nitrate applied this is due to a 

 drawing on the soil's own nitrogen supply. This supply is acted upon by a 

 stimulated bacterial flora, brought about by the presence of sodium nitrate. 

 On the other hand, where more or less of the nitrogen applied is recovered the 

 variations in the recovery may in a large measure be explained on the grounds 

 of assimilation of nitrates by soil organisms." 



The literature of the subject is reviewed at some length and a bibliography of 

 226 titles is given. 



Influence of nitrates on nitrogen-assimilating- bacteria, T. L. Hiij:.s (U. S. 

 Dept. Agr., Jour. Agr. Refsearch, 12 (1918), No. //, pp. 183-230).— ThiR is a re- 

 port of investigations contributed from the Wisconsin Experiment Station, on 

 the influence of ammonium, potassium, sodium, and calcium nitrates in amounts 

 varying from 10 to 300 mg. per 100 gm. of dry soil on the growth and physio- 

 logical activities of Azotobacter and Bacillus radicicola in sterilized silt loam 

 sou containing 2.75 per cent of organic matter and 1.5 mg. of nitrate per 100 gm. 

 of dry soil. The following is a summary of the results : 



" Small quantities of potassium, sodium, and calcium nitrates caused a great 

 increase in the number of Azotobacter in sterilized soil. Ammonium nitrate in 

 the same quantities caused a less marked increase. Higher concentrations were 

 not so favorable to the growth of the organisms. 



" Potassium and sodium nitrates in the concentrations studied caused an in- 

 crease in the amount of nitrogen assimilated by Azotobacter on agar films. 

 Calcium nitrate in the same amounts brought about a decrease in the amount 

 of nitrogen fixed to a point even below that representing the amount assimilated 

 in the absence of nitrates. In soil cultures nitrates of sodium and calcium 

 caused an increase in total nitrogen, wliich was more marked in the unsterilized 

 cultures than in those cultures sterilized and inoculated with a pure culture 

 of Azotobacter. However, the increase in total nitrogen Is not commensurate 

 with the increase in the number of Azotobacter noted under the same conditions. 



