soil, PHYSICS, CHEMISTRY AND MICROBIOI^OGY I085 



the first there was added to each sample of earth in addition to water sokible 

 acid potassium phosphate (i.33i2g. of P2O5), 3.605 g. of potassium nitrate 

 in order to observe how this addition affects the total fixaction (i. e. that 

 due to physical, chemical and biological factors) of soluble phosphoric acid. 

 These experiments were made with the April fallow soil and the soil 

 long out of cultivation. In the second set of experiments part of the soil 

 was treated with chloroform, to suspend bacterial life and consequently^ 

 the fixation of phosphorus bv these bacteria ; the other part of the soil 

 not being so treated. The object was to differentiate the fixation of sol- 

 uble phosphoric acid produced by physical and chemical factors from the 

 biological fixation due in this case to the activity of the micro-organisms. 

 The quantity of chloroform added was 50 cc. and that of phosphoric acid 

 the same as in the previous case. 



To all the samples of air-dried earth 35 per cent by weight of water 

 was added, to stimulate activit}^ of the micro-organisms ; in order to pre- 

 vent evaporation of water the samples were put into big bottles with ground 

 glass stoppers. During the entire continuance of the experiments (3 

 months) the temperature ranged between 150 and 25° C. The external appear- 

 ance of the samples remained normal until the end of the experiments. 

 On completion of the latter, the soluble phosphoric acid, which had re- 

 mained as such in the soil, was extracted by distilled water, of which 

 4 litres per sample were added. The duration of treatment with water 

 was 8 hours. Care was taken to shake up the solution every 15 or 20 

 minutes. 



The results of the experiments are summed up in the appended Table. 



From the results obtained the writer deduced the following conclusions : 

 i) The process of fixation of water-soluble phosphoric acid depends 

 both on the chemical and physical factors and on the biological factors of 

 the soil. 



2) The intensity of total fixation of the said acid is in direct relation 

 to the cultural conditions of the soil. 



3) The intensity of total fixation of the said acid increases with the 

 addition of potassium nitrate to the soil. 



4) The process of fixation of water soluble phosphoric acid in the 

 non-chloroformed, i. e. the natural, samples of earth takes place with 

 greater intensity than in the chloroformed samples. 



5) The total intensity of fixation and the physical and chemical 

 fixation of water-soluble phosphoric acid is less in the arable layer (from o to 

 17.7 cm. depth) than in that lying immediately beneath (from 17.7 to 



35-5 cm)- 



6) The intensity of the process of assimilation of phosphorus is 



greater in the arable layer than in that immediately beneath. 



r'or better study of the phenomenon of assimilation of phosphorus the 

 writer also carried out experiments on the bacterial flora of each of the samples 

 of soil capable of multi])lying in peptonised meat bouillon, with agar or 

 gelatine, dilute to o.ooi and o.oooi. By calculating the number of bac- 

 teria per gram of absolutely dry soil, data were obtained from which it may 



