SOILS — FERTILIZERS. 323 



Edaphon, R. II. France (Das Edaphon. MuuicJi, 1913, pp. 00, figs. 3o). — 

 Edaphon, in contrast to plankton, is hero understocvd to be the plant and animal 

 organisms of the soil. The author deals in some detail with the conditions of 

 soil favorable to the life and activity of these organisms, giving a systematic 

 classification and discussion of 120 different organisms and the results and 

 conclusions of a general ecological investigation of the types. 



Light was found to influence more or less the distribution of the organisms 

 near the surface and in the soil depths. The edaphon was found to reach the 

 minimum number and distribution in the winter, due to frosts, and the maxi- 

 mum in the spring and fall. Increasing soil moisture was ordinarly found to 

 increase the number and distribution. In most of middle Europe no difference 

 was observed in the edaphic development of soils under like ecological condi- 

 tions, but ordinarily the number of organisms varied with increasing eleva- 

 tion according to their kind within well defined limits, and independently of the 

 variations caused by other local conditions. The number and distribution was 

 also found to be closely related to the geology of a locality and to the petro- 

 graphic conditions of the substrata. The edaphon in humus-poor soils showed 

 silica-loving characteristics and many of the organisms were found to exist in 

 entirely humus-free soils. On the other hand, the presence of considerable 

 humus was extremely favorable to their growth. It is concluded that the 

 edaphic organisms are active in the formation of humus, in the development of 

 organic matter in new soils, and also in the weathering of rocks. 



In examinations of neutral and acid forest soils many more edaphic organ- 

 isms were found in the former than in the latter, the most of which were 

 Difluggia and relatively large forms. Further Investigations led to the conclu- 

 sion that the Cladosporium which were present in large numbers have no fixed 

 Influence on the number and distribution of the remaining edaphic organisms. 



The siliceous alg?e were found to predominate the year round in cultivated 

 soil and the rhizopods, nematodes, and Cladosporium In the forest soils. The 

 large numbers of rhizopods in forest soils are concluded to be due not only to 

 the greater water content but also to the greater humus content and to the 

 chemical influence of amphibious vegetation. Amphibious vegetation influenced 

 the numbers of soil organisms through its influence on humus, but the edaphic 

 development of the soil was found to increase with the factors which make the 

 soil hygrophytic. Fertilization was most favorable to the growth and increase 

 of the edaphon. A discussion of symbiotic relations leads to the conclusion that 

 the edaphon have symbiotic relations similar to those of plankton. In general it 

 is concluded that the edaphic organisms are indispensable as decomposers of 

 organic matter and as soil ventilators for the metabolism of productive soils, 

 and that their method of multiplying is such as to aid the soil ferments and 

 increase its productiveness. 



Studies on nitrog-en assimilation by free living organisms, H. B. Hutch- 

 inson (Rpt. Brit. Assoc. Adv. ScL, 1912, pp. IJfO, 741). — Spring applications of 

 carbohydrates to field soil were followed by decreased crop yields, while autumn 

 applications resulted in a decided increase of yield, due, it is thought, to stimula- 

 tion of nitrogen assimilation by such organisms as Azotohactcr chroococcum. 



" Pot and laboratory experiments show that when plant residues are added to 

 soil or sand a vigorous decomposition of the cellulose by aerobic organisms 

 ensues, and appreciable quantities of nitrogen are assimilated from the 

 atmosphere." 



Some effects of humates on plant growth, W. B. Bottomley (Rpt. Brit. 

 Assoc. Adv. ScL, 1912, p. 680). — ^The author found that peat moss litter is 



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