CHAPTER XXV 



HEATED AND TREATED SOILS 

 (Reports, IX, Appendix; XIII, Appendix) 



FROM a study of the changes produced in the nature and 

 behaviour of soils when they are heated, or when they are treated 

 with antiseptics, to the action of grass on fruit trees, would 

 appear to be a far cry ; yet these studies are but different chapters 

 of the work on the effect of one crop on another, which figures 

 so largely in the investigations at Wo burn, and the one has a 

 very intimate bearing on the other. Though the examination 

 of such soils was not .made till after the work on the effect of 

 crops on each other had been in progress for several years, the 

 results may be more conveniently described as a preliminary to 

 the main work. 



The researches of Russell and Hutchinson x were the first to 

 establish satisfactorily that, when soil is heated to a temperature 

 of 80 to 100, though there is a considerable mortality amongst 

 the bacteria present, there is a complete mortality of the pro- 

 tozoa which live upon the bacteria, and that, consequently, 

 after such heating, the surviving bacteria multiply unchecked, 

 and attain to a degree of activity much greater than they do 

 in unheated soil. The beneficial effect of treatment with anti- 

 septics is explained on similar lines. These facts must now be 

 regarded as beyond dispute ; but it is a question still how far 

 they explain the increased growth of plants in heated or treated 

 soils ; it is certain that such heating and treating brings about 

 changes other than bacterial ones, changes which are purely 

 chemical in their nature, and which must effect the behaviour 

 of the soil very materially. 



Plants depend for their sustenance on the soluble matter in 

 the soil, and, when this is heated, the amount of soluble matter 

 in it is rapidly increased ; when the temperature of heating, for 



1 E. J. Russell and H. B. Hutchinson, Journ. Agric. Sci., 1909, III, 

 111-114; 1913, V, 152-221. 



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