282 SOIL CONDITIONS AND PLANT GROWTH 



the soluble mineral and organic matter and also the produc- 

 tiveness. Later work by Pfeiffer and Franke (224^^) and by 

 Kriiger and Schneidewind (156^) showed that plants actually 

 take more food from a heated than from an unheated soil. 

 Heat undoubtedly causes decomposition of some of the soil 

 constituents, quite apart from its effect on the soil flora ; it 

 also produces physical effects ; ^ all these actions probably 

 play a part in determining the increased productiveness of 

 heated soils. 



Other explanations of the effects of partial sterilisation 

 have been put forward. Pickering {226b) finds that the 

 amount of soluble matter in the soil is increased by treatment 

 with volatile antiseptics. Greig Smith supposes that soils 

 contain a harmful waxy material which he calls "agricere" 

 and which he gupposes to be removed during partial sterilisa- 

 tion. Russell and Hutchinson were unable to confirm this 

 at Rothamsted, nor could J. P. du Buisson at Cornell, who 

 found that extraction with volatile antiseptics gave no better 

 results than addition of liquid and subsequent evaporation.^ 

 Bolley supposes that soils normally contain parasitic fungi 

 which are destroyed by partial sterilisation. Russell and 

 Hutchinson (241^) consider that the soil population is complex 

 and that some of its numbers act detrimentally on the bacteria 

 which produce plant nutrients: these detrimental forms are 

 more readily killed than the useful bacteria, with the result 

 that the new population produces more ammonia and nitrate 

 than the old one. The detrimental organisms are provision- 

 ally identified with protozoa (p. 288). 



It is agreed by all who have seriously studied the subject 

 that the effects produced by partial sterilisation are complex : 

 several factors operate simultaneously. In consequence, a 

 particular factor cannot be regarded as established until its 

 operation has been proved by some wholly independent 



1 For chemical effects see 2416 and also Pickering, jfourn. Ag. Set., iii., 

 171-178; Seaver and Clark, Biochem. Bull., 1912, I, 413 ; and Schreiner and 

 Lathrop, U.S. Dept. of Ag. Bureau of Soils, Bull. 89, 1912. For physical 

 effects see Czermak, Landw. Versuchs-Stat., 1912, 76, 75, 



2 Sot/ Set., 3, 353-392. 



