808 



CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL- 

 FERTILITY. I. 



Thk Action of Wax-solvents and the Presence of 

 Thermolabile Bacteriotoxins in Soil. 



By R. Greig-Smith, D.Sc, Macleay Bacteriologist to the 



Society. 



Tt has been known, since 1894, that soil after treatment with 

 carbon bisulphide, produces a greater crop than it would other- 

 wise have done. Girard used the disinfectant to kill nematodes, 

 and noted an increase of crop; Oberlin applied it in order to 

 destroy Phylloxera on grape-vines, and saw an enhanced pro- 

 ductiveness. Other investigators confirmed the fertilising action 

 of carbon bisulphide, and showed that chloroform, ether, benzene 

 and toluene gave similar results. It had also been previously 

 known (Frank, 1888; Leibscher, 1893) that heating the soil, as 

 for example, while sterilising it by steam, increased the solubility 

 or availability of the mineral and organic matter. The beneficial 

 eftect of either of these'treatments was manifest over two seasons, 

 but did not extend to the third crop. Furthermore, from the 

 dark gi-een colour of the foliage it was evident that the treatment 

 brought to the plant an accession of nitrogen, that is to say, the 

 crop behaved as if the soil had been treated with a nitrogenous 

 manure. 



Investigation indicated that the increased fertility was con- 

 nected with an increased activity of the soil-bacteria. There 

 is something in untreated soils which keeps the number of 

 bacteria at a constant level, which naturally depends upon the 

 quality of the soil. Treatment with carbon bisulphide or with 

 heat reduces the number, by killing off the less resistant bacteria. 

 After the partial sterilisation, the more resistant bacteria increase, 



