SOIL PHYSICS, CHEMISTRY AND MICROBIOLOGY I081 



843 - Researches in Agricultural Bacteriology carried out in Denmark during the Pe- 

 riod 1904-1914. — Christensen H. R. (Director of the State Agricultural Laboratory'). 

 — Communication made to the Internationai Institute of Agriculture by its Correspondent 

 for Denmark, Baron de Rosenkrantz. 

 These investigations were carried out during the period 1905-1909, in 

 the laborator}- of agricultural bacteriolog}' of the Ro3^al Higher School of 

 Veterinary Medicine and Agriculture under Prof. Weiss and, from 1909, in 

 the State Agricultural lyaboratory, the direction of which was taken over 

 by the same gentleman. 



I. — Two jluorescent denitrifyng Bacteria. — These two bacteria, isol- 

 ated by the writer, are distinguished from all other fluorescent denitrify- 

 ing bacteria by the fact that they do not liquefy gelatine. One of them, 

 Bac. denitrificans b, is capable only of reducing nitrates, while the other, 

 Bac. denitrificans a, reduced both nitrites and nitrates (i). 



II. — New Principles of Analysis of Soils in connection with certain 

 data as to the presence and distribution of Azotobacter chroococcnm in various 

 types of soils. — Preliminary considerations as to the progress of soil 

 research in connection with rural economics ; the hygroscopic qualities of 

 soils in Denmark ; the importance of the methods of Roderwald and 

 ]\IiTSCHERLiCH for determination of hygroscopicity, growth in area of par- 

 ticles of earth, the state of subdivision of soil ; on the need for studying 

 the reaction and basic quality of the soil, being properties closely bound up 

 with its microbiological condition. After glancing at the principles hitherto 

 adopted in bacteriological analyses, the writer gives notes on the result 

 of his investigations of a nitrogen-fixing bacillus, Azotobacter chroococcnm. 

 In determining the factors causing its presence in the soil, the method was 

 adopted of comparing an ordinary culture of the soil with other cultures 

 into which large quantities of the microbe had been inoculated whose 

 specific behaviour in different types of soil it was required to study in order 

 to ascertain whether the differences in the tendency to decompose given 

 substances are to be attributed to the microbiological or chemical condi- 

 tion of the soil. It was found that the presence of a growth oi Azotobacter 

 in a solution of mannite (i litre of distilled water, 20 grms of mannite and 

 0.2 grms of bipotassic phosphate) is a reliable indication of the presence of 

 basic compounds of calcium and magnesium in the soil in question, and may 

 also form the criterion for determining the basic quality of the soil. This 

 is perhaps the first example of a specific property of the soil investigated 

 b}'- microbiological methods. An analogous process is represented by the 

 investigations of the presence in the soil of readily soluble phosphoric 

 acid (2). 



III. — New Biological Method for Determination of alkaline Carbonates 

 in the Soil. — There are soils which, when brought into contact with a solu- 

 tion of mannite freed from lime and inoculated with Azotobacter, are un- 



(i) Ccntralblatt filr liakteriolo^^ic, Parnsilenkundc und Iniixtidnxkrankhciten 11, \'(>1. XI, 

 pp. 190-194. Jena, 1904. 



(2) Tidx'ikrifl for Landbni!;ets Plantcavl, Vol. XIII, \)\^. i 15-1 >|- Copcuhagcii, i9(«(>. 



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