SOILS — FERTILIZERS. 221 



Contribution to the knowledge of humus compounds, E. Donath {Ztschr. 

 Angeic. Chem., 22 {1909), No. 30, pp. l.',91, IJ,92 ; ah.s. in Chem. Zentbl., 1909, 

 II, No. 13, p. lOl.'i). — A critique of an article by Milclauz on this subject (E. 

 S. K., 21. p. 220) showing the agreement between the latter's results and those 

 of earlier work by the author on the same subject. 



Investigations on Azotobacter chroococcum, S. Krzemeniewski {Bui. In- 

 tcrnat. Acad. tici. Cracovic, CI. Sci. Math, et Nat., 1908, No. 9, pp. 929-1051, 

 pi. 1, figs. 2; ahs. in Ztschr. Landtc. Versiichsw. Osterr., 12 {1909), No. 6, pp. 

 5-'>S. 559). — A report of tliese investigations has already been briefly noted 

 from another source (E. S. II., 21, p. 318). This is an elaborate memoir giving 

 a detailed account of the author's investigations and containing a bibliography 

 of 29 references to the litewiture of the subject. The following are among the 

 more important results referred to in the summary of the memoir : 



Azotobacter chroococcum fixes very small amounts of nitrogen in pure cul- 

 tures in ordinary nitrogen-free nutrient media. Fixation is decidedly increased 

 by the addilion of soil humus either as free humic acid or as salts of iiotassium, 

 sodium, or calcium. Fixation varied, however, with humus derived from differ- 

 ent soils. Artificial humus prepared by boiling sugar with acids could not 

 replace soil humus as an aid to fixation of nitrogen. Natural humus boiled 

 with hydrochloric acid was unich less effective as an aid to fixation than that 

 not so treated. The treatment with acid dissolved a considerable part of the 

 nitrogen comjtounds of the humus. The humus served as a source both of 

 carbon and of nitrogen. 



For each gram of glucose used Azotobacter fixed 17 mg. of nitrogen, and 

 for the formation of 1 gm. of dry substance it required G gm. of glucose. The 

 metabolic products of Azotobacter included acids, alcohol, and hydrogen. Azo- 

 tobacter was shown to be distinctly aerobic. The optimum temperature for 

 its activity was about 28° C. and the limits of its activity appeared to lie 

 between 9 and 33°. The nitrogen-fixing power of the organisms was apparently 

 unaltered after it had been bred for almost a year in an artificial nutrient 

 medium. 



Uadiobactor and other bacteria exerted no infiuence on the nitrogen fixation 

 by Azotobacter. Its nitrogen-fixing power, however, appeared to vary accord- 

 ing to its origin, indicating different physiological races of the organism. In 

 the nutrient solution obtained from Azotobacter cultures nitrogen compounds 

 were obtained of which neither the origin nor the composition are definitely 

 known. 



The bearing of carbon determinations upon nitrogen fixation in soils, 

 P. EiiRENBEKG (FHhHiig'.s Landw. Ztg., 58 {1909), No. 18, pp. 663-671).— The 

 relat'on of the carbon supply in the soil to the activity of nitrogen-fixing 

 organisms is discussed. 



Some conditions favoring nitrifi.cation in soils, T. L. Lyon and J. A. Biz- 

 ZELL {Science, n. scr., 30 {1909), No. 778, pp. 773, 77// ) .—Nitrification tests of 

 sanii)les of soil from limed and unlimed iilats and from plats on which 

 leguminous and nonleguminous plants wei'e grown gave results pointing to the 

 conclusion " that the presence of a certain degree of basicity in the soil, and 

 possibly the growth of certain nodule-bearing legumes, are each favorable to 

 nitrification in the soil. These and other conditions may account for very con- 

 siderable differences in nitrification tests in different soils." 



A contribution to our knowledge of the nitrogen problem under dry 

 farming, F. J. Alway {Abs. in Chem. News, 100 {1909), No. 2600, p. 151; 

 Chem. Abs.. J, {1910), No. 1, p. 77, ) .—Determinations of nitrogen in samples of 

 soils from different parts of the arid region are used as a basis for the dis- 

 cussion of the question of the loss and maintenance of nitrogen in such soils. 



