lo June. 1910.] Sterilizaiiou of Soils. 365 



STERILIZATION OF SOILS. 



W. LaidUnc. B.Sc, Micro-Biologist : and C. A. Price, Microscopist. 



Our experiments in connexion witli tl"ie sterilization of eel-worm affected 

 soils, led to some curious results on plant growth, and was the means of 

 inducing us to undertake some further experiments and research into the 

 cause of the increased productiveness of soils sterilized by steam or par- 

 tially sterilized bv chemical treatment. The effect of heat on the soil 

 was discovered incidentally about 25 years ago, and the action of carbor 

 bisulphide was first noted some years later by a vine grower when using 

 it for the purpose of combating the ravages of phylloxera. 



In both instances it was noted that the soil which had undergone 

 treatment became more productive and yielded larger crops. Many theories 

 have been advanced as to the cause of this increased productiveness, and 

 the subject has been studied by several investigators, notably Koch, 

 Hiltner, Stormer, Rus.sell, and Darbi-shire. In a paper recently published 

 by the two last named it is shown that this increased productiveness after 

 sterilization is a property of all soils and for all plants, excepting those 

 of the Leguminosa (Pea family). They showed that soil heated to 

 95 deg. C. (203 F.) had its productiveness increased two, three, and 

 sometimes four times, whilst treatment with volatile antiseptics led to an 

 increase in crop varying between 20 and 50 per cent, this increase taking 

 place in both fertile and exhausted .soils. 



Theories as to the Cause of Increased Productiveness. 



Where volatile antiseptics were used it was supposed that a chemical 

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

 was rendered more available. This theory was .soon cHscarded but 

 Pickering revived it recently {Journal of Agricidtural Science, Vol. iii.). 



Koch suggested that the action was physiological, the antiseptic being 

 supposed to stimulate the plant roots to greater activity ; this may have 

 happened in Koch's experiments where the antiseptic was left in the soil. 

 Drs. Russell and Darbishire, however, got the increased results after 

 the removal of the antiseptic from the soil. In our experiments also, the 

 chemicals were allowed to volatalize before sowing the .seed. 



Hiltner and Stormer ascriljed the increase in productiveness to the 

 changed bacterial flora, and showed that the first effect of antiseptic treat- 

 ment was to reduce the organisms, but when the conditions again become 

 favourable they multiplied with extraordinary rapidity and brought about a 

 more intense production of nitrogenous plant food in the soil. 



Some observers say that increased nitrogen fixation is the main cause 

 of the increased productiveness. Koch, however, maintains that nitrogen 

 fixation is decreased by partial sterilization. 



Stormer considers the increa.sed production of ammonia is due to the 

 decomposition of the larger organisms by the surviving bacteria. 



The dark green colour of plants grown in partially sterilized soils has 

 generally been regarded as an indication that the nitrogenous food stuff in 

 the soil is in some way increased by the treatment. 



Russell and Hutchinson used heat to 98 deg. C. ; Toluene (4 per cent.) 

 was used and at the end of three days it was allowed to evaporate by 

 spreading out the soil in a thin layer. They found that the difference 

 between toluene evaporated and heated (98 deg. C.) soils was only one of 

 degree. The evidence of the formation of ammonia becomes evident 



