1919] SOILS FERTILIZERS. 125 



comprehensive review of the literature dealing with nonsymbiotic nitrogen 

 fixation in the soil. Briefly tracing early studies concerning nitrogen fixation 

 by soil organisms, the author then deals with the distribution and food require- 

 ments of the azofiers ; the reaction of the media ; the effect upon azofication of 

 volatile and nonvolatile antiseptics, organic soil constituents, colloids, manure, 

 watei*, temperature, light and other rays, aeration, season, crop, and climate; 

 sources of energy for Azotobacter ; metabolism and pigment production in 

 Azotobacter ; morphology of the nitrogen-fixing organisms ; the relation of 

 Azotobacter to other organisms and to nitrate accumulations ; the action of 

 azofiers on plant food ; soil inoculation ; and soil gains in nitrogen. 



A bibliography of 211 titles is appended. 



Studies on nitrification in natural soils and its importance from an eco- 

 logical point of view, H, Hesselman {Meddel. Stat. Skogsforsoksanst., No. 

 13-14 {1916-17), pt. 1, pp. 297-528, XXXIII-LVIII, figs. 50).— This paper, in 

 addition to a lengthy discussion of the investigation already noted from another 

 source (E. S. R., 40, p. 418), embraces a detailed presentation of the experi- 

 mental results obtained, together with a bibliography of 87 titles. 



The effect of regeneration measures on the formation of nitrates in the 

 soil and its importance in the regeneration of coniferous forests, H. Hessel- 

 man {Meddel. Stat. Skogsforsoksanst., No. 13-U {1916-17), pt. 2, pp. 923-1076, 

 XCI-CXXVI, figs. JfS). — The author describes investigations having to do with 

 nitrification in forest soils and with the effect upon nitrification of measures 

 usually employed in the care of the forest. The more important results se- 

 cured in coniferous forests may be summarized as follows: 



Little or no nitrification was observed to occur in the humus covering of 

 mossy coniferous forests, the organic nitrogen present not being transformed 

 beyond ammonia, even in the best and most pi-oductive forests. Fellings which 

 permitted a strong access of light exerted a marked influence on the transforma- 

 tion of nitrogen. Where the humus covering was rather thin and loose, being 

 composed chiefly of mosses and fallen needles, felling sometimes resulted in an 

 active transformation of humus nitrogen into nitrate, said to be due, among 

 other things, to a radical alteration in the bacterial flora of the humus cover- 

 ing. An active transformation of humus nitrogen appeared to take place in 

 raw humus but without nitrate formation. 



The covering vegetation was thought to be an index to the nature of the 

 nitrogen changes taking place, nitrification being indicated by the presence of 

 the raspberry, Epilobium angustifolium, Arenaria trinervia, Galeopsis bifida, 

 Seneeio silvaticus, Rumex aceto^clla, etc., while Aira flexuosa predominated 

 where nitrification was lacking. Thorough mixing of the humus with the min- 

 eral soil and decaying brushwood and timber and burning over the area re- 

 sulted in the formation of nitrates even in markedly raw humus. It is stated 

 that a close correlation appeared to exist between nitrification and the regen- 

 erative possibilities of the soil. Raw humus soils without nitrification were 

 found to be difficult of regeneration. Experiments and observations in the field 

 are held to indicate that young pine trees develop to better advantage in the 

 presence of nitrification than without it, as is also thought to be the case with 

 spruce. 



In herbaceous spruce forests nitrification was usually observed, and felling 

 resulted in such an increase of nitrates that nitratophilous vegetation became 

 troublesome to the coniferous plants. In such instances the spruce developed 

 in the small areas which did not lend themselves to any very marked devel- 

 opment of the covering vegetation, and it was often found necessary to check 

 the growth of this vegetation, the competition of which would otherwise prove 

 fatal to the tree plants. 



