PARTIAL STERILISATION OF SOIL 



133 



Several considerations show that the production of ammonia sub- 

 sequent to the small initial gain on heating, or treating with toluene, is 



TABLE LV. NUMBERS OF BACTERIA AND AMOUNTS OF AMMONIA PRODUCTION IN 

 PARTIALLY STERILISED SOILS. 



mainly the work of micro-organisms. The curves belong to the type 

 associated with bacterial, rather than purely chemical, change. Soil 

 which has been heated to 125 C. (at which temperature all organisms 

 are killed) shows no increase in ammonia-content after the first small 

 gain. There is no rapid period of gain if enough toluene is left in to 

 inhibit bacterial action, nor if the water supply is insufficient. Further, 

 the numbers of bacteria increase/<2n' passu with the amount of ammonia ; 

 and as addition of ammonium salts to untreated soil led to no such 

 increase as is observed here, it was concluded that the increased pro- 

 duction of ammonia was due to the increased numbers of bacteria. 



The new flora arising after partial sterilisation was found to be more 

 active than the original flora in effecting the decomposition of nitro- 

 genous organic matter, such as peptone, and in hydrolysing urea. But 

 there is no evidence that the individual species surviving the treatment 

 have become more active on the contrary organisms isolated from the 

 partially sterilised soils proved less active than others of the same kind 

 from the untreated soil. Nor can the difference in the rate of ammonia 

 production be attributed to a change in the type of bacterial flora. 

 Examination of the gelatin plates showed that the flora establishing 

 itself in the heated soil is altogether different from that originally pre- 

 sent ; while the flora of the soil treated with toluene did not appear to 

 have altered very much. The curves showing thei amount of ammonia 

 produced in the soil treated with toluene and in the heated soil are very 

 much alike, but the bacterial flora of the soils is very different ; the curves 

 for the untreated soil and the soil treated with toluene are fundamen- 

 tally different, whilst the bacterial flora is not. Lastly, reintroduction 



1 After four days ; the nine days' count was lost by plates liquefying. 



