120 Partial Sterilisation of Soil 



nitrogen fixers (§ 29), whilst the nitrifying organisms are absolutely 

 exterminated. 



It might be thought that the removal of nitrifying organisms would 

 seriously interfere with the growth of plants, but, as a matter of fact, 

 it seems to have but little effect ; plants readily take up the decom- 

 position products — ammonia, etc. Nitrification is shown to be economi- 

 cal, but not essential. (§ 44.) The excess of nitrogenous plant food 

 in the partially sterilised soil soon becomes so great that it causes 

 a correspondingly vigorous plant growth. 



§ 11. Partial sterilisation has been found to increase fertility on 

 many types of soil and always by increasing the supply of nitrogenous 

 plant food. There is reason to suppose therefore that the large destruc- 

 tive and competing organisms will be found of common occurrence on 

 ordinary soils, checking the beneficent bacteria and limiting fertility. 

 An important practical problem arises : is it possible to suppress them 

 in ordinary field soils by any economical and practical process ? This 

 problem is under investigation. It is unnecessary at this stage to 

 enlarge on the importance both from the practical and scientific point 

 of view of these large organisms as factors in soil fertility. A fuller 

 study of them will no doubt throw much light on many soil problems, 

 at present obscure. We are now engaged in further investigations 

 of these organisms. 



§ 12. Our results may be summarised as follows : 



(1) The increased productiveness of partially sterilised soils is 

 due to an increase in the amount of ammonia present. 



(2) The excess of ammonia is the result of increased decomposition 

 of soil substances by bacteria. 



(8) Hiltner and Stormer's discovery that the bacteria increase 

 rapidly after partial sterilisation, and finally become much more 

 numerous than in the original, untreated soil, is confirmed. The increase 

 in number ^xoceQ,<\?, pari passu with the increase in ammonia. 



(4) The new bacterial flora arising after partial sterilisation is 

 a more potent decomposing agent than the original flora, but the in- 

 dividual species have not become more, but apparently less potent. 

 The increased decomposing power of the new flora is associated with its 

 numerical superiority over the old flora. 



(5) The rates of decomposition and of bacterial increase in the 

 toluened soil were found to be adversely affected by the addition of the 

 original untreated soil. The original soil therefore contains some factor 

 which limits bacterial action. 



(6) Chemical hypothesis having been found unsatisfactory the 



