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xxxvni. 



CHANGES IN SOILS BROUGHT ABOUT BY HEATING. 

 By miss a. WILSON, B.A. 



[communicated by prof. H. H. DIXON, F.R.S.] 

 [Read Mabch 23. Publisiied May 10, 1915.] 



In his work on the partial sterilization of soil, Russell (5) has shown that 

 increased production of ammonia in heated soil, or in soil treated with 

 toluene, is due to increased numbers of bacteria, rather than to any other 

 cause. He ascribes this increase in the number of bacteria to the absence 

 from the treated soil of larger organisms, such as infusoria, amoebae, and 

 other protozoa. 



In 1888 Erank (1) had shown that the effect of heat on soil was to 

 increase the soluble mineral and organic matter, and also the productiveness 

 of the soil. Pfeffer and Eranke (4) and Kriiger and Schneidewind (2) 

 showed that plants actually take more food from a heated than from an 

 unheated soil. 



Seaver and Clark (6) showed that in soil heated during a period of two 

 hours at various temperatures up to 120°, the growth of plants was greater 

 in soils exposed to the liigher temperatures. In samples heated above this 

 temperature the number and growth of fungi increased, while higher plants 

 remained stunted. By chemical analysis of extracts from heated soils Seaver 

 and Clark (6) showed that this result was due to increase in the amount of 

 soluble materials, and to the acid reaction of the extract. They ascribed both 

 these factors to decomposition of some of the soil constituents. G. W. 

 Wilson (7) has also shown that the growth of all plants is accelerated in soil 

 heated up to 95°. Retardation of growth occurred in soil heated between 

 135'^ and 175°, and there was greater susceptibility to parasitic fungi, as well 

 as a larger number of soil fungi. 



In considering the effects of lieated soil on plant growth, both the amount 

 of soluble material in the soil and the absence of larger organisms seem 

 therefore to be important. I am indebted to Dr. Atkins, at whose suggestion 

 the researcli was undertaken, for the methods of studying the changes in 

 solubilities and for advice during the course of the work. 



SCIENT. PEOC. R.D.S., VOL. XIV., NO. XXXVIII. 4 N 



