112 Partial Sterilisation of Soil 



the earlier paper were obtained with fertile soils, but we have obtained 

 precisely similar results with an exhausted Rothamsted soil. (See 

 Plate VIII, Figs. 1 and 2 and Table 1.) 



Several hypotheses have been put forward to account for the 

 increased productiveness. It was first supposed that a chemical reaction 

 took place between the antiseptic and the soil whereby plant food was 

 rendered more available ; this view was soon discarded, but has recently 

 been revived by Pickering'. Koch suggested a purely physiological 

 hypothesis; the antiseptic was supposed to stimulate the plant roots to 

 greater activity in extracting food from the soil. Such an action might 

 have gone on in Koch's experiments where the antiseptic was left in 

 the soil, but can hardly have taken place in ours, since all the antiseptic 

 had been removed before the seeds were sown. Hiltner and Stormer 

 attribute the action to the changed bacterial flora. They showed that 

 the first effect of the antiseptic is to reduce the number of organisms, 

 but when the conditions again became favourable the survivors multiply 

 with extraordinary rapidity, and bring about a more intense production 

 of nitrogenous plant food in the soil. They supposed that a larger 

 amount of atmospheric nitrogen is " fixed," and the complex substances 

 thus formed in the bacterial cells are slowly broken down to yield plant 

 food. The decomposition processes normally taking place in the soil 

 are probably hastened also, whilst the loss of nitrogen by denitrification 

 is diminished. Other investigators have also supposed that increased 

 nitrogen fixation is the main cause of the increased productiveness ; on 

 the other hand Koch- maintains that nitrogen fixation is decreased by 

 partial sterilisation. Stormer^ considers that the larger organisms are 

 killed and decomposed by the surviving bacteria with production of 

 ammonia. The dark green colour of the plants grown on partially 

 sterilised soils has generally been regarded as an indication that the 

 nitrogenous food stuff in the soil has in some way been increased by 

 the treatment. 



Part 1. 



§ 1. We propose to give in this part a short statement of our 

 experiments and the conclusions to which they lead, reference being made 

 at each step to the paragraph in Part 2, where the full details and figures 



1 S. U. Pickering, Journal of Agricultural Science, 1909, Vol. iii. p. 411. 



2 Koch, Journal filr Landicirtschaft, 1907, Bd. 55, S. 355. 



•^ Stormer, Jahresber. d. Vereinigung fiir Angeioandte Botanik, 1907, S. 113. 



