1252 SOIL I'lIYSICS, CHIC.MISTRY AND MICROIiK)r.( XiY 



forms which are decomposed under the action of a highh' numerous bacte- 

 rial flora and give rise to the transformation of phosphorus from the non- 

 assimilable state into the assimilable state. On the other hand, the insoluble 

 mineral phosphates pass into the soluble state, as was proved by Stoklasa, 

 under the action of the carbonic, formic, butyric and acetic acids produced 

 by the organic substances formed by the multiplication of the bacteria. 

 With regard to the nitrogen, the increase in this element must be attribut- 

 ed to the fixation of atmospheric nitrogen by the bacteria, and to the organic 

 substances of the soil. 



Passing on to sterilisation, it* is useful to note that the bacteria flora 

 of sterilised tchernoziom exhibits one peculiar feature, namel}-, it develops 

 much less readih- on gelatine than on agar ; according to the analysis made 

 by the writer, it is constituted by the microbes of the air. and therefore it 

 cannot ipiay an important part in the increase of the fertihtj^ of the soil. 

 In order to study the cause of this increase the writer examined 

 the quantity of phosphoric acid soluble in 2 % acetic acid contained 

 in the sterilised and the non-sterilised soils, and he found that the 

 sterilisation results in a substantial increase of soluble phosphoric 

 acid ; in the arable strata the increase varies between 87.87 and 120.67% and 

 and in the strata tying beneath the arable layer, from 47.05 to 76.54%. 

 Among the sources contributing to the increase of phosphoric acid, the writ- 

 er allots the first place to the nucleins, which contain 5.7 % of phosphorus 

 and which, at the temperature of 150" C, decompose with liberation of 

 phosphoric acid. The question of the nitrogen is not so clear as that of the 

 phosphorus, because an equal quantity of it was observed both in the steri- 

 lised and in the unsteriUsed soils. It not being possible, however, to attri- 

 bute an increase of fertility in the sterilised soils exclusively to the 

 increase in soluble phosphoric acid, and taking into account at the 

 same time the fact that by the sterilisation all the microbes were killed, 

 and therefore it is not possible to assume the existence in the soil of 

 the microbiological processes which result in the accumulation of as.simi- 

 lable nitrogen, the Author as.sumes here the influence of the decomposition 

 of organic substances through the action of sterilisation. 



The increase in the quantity of assimilable nitrogen in the sterilised 

 soils was borne out by the fact that the plants, during the entire period of 

 growth, were of a beautiful green colour even more intense than that of 

 the sample which received complete mineral manuring. 



The concrete outcome of the experiments is the following : 



i) Researches into growth carried out on chloroformed samples of 

 tchernoziom and supplemented by bacteriological and chemical investiga- 

 tions prove that the accumulation of the fertilising substances in the tcher- 

 noziom, which depends on the degree of vital intensity of the soil bacteria, 

 does not, even under the best conditions of soil cultivation, supervene with 

 the same intensity' with which it might take place imder other more fa- 

 vourable conditions. 



2) Researches into growth, carried out in sterilised samples of the 

 tchernoziom supplejnented by bacteriological and chemical imestigations, 



