414 Biochemical Studies of Heated Soils [Mar, 



the unheated soil removed nearly all the soluble matter in the deeply 

 colored extracts allowed to percolate through it. This interesting 

 phenomenon has been noticed by us repeatedly, but whether it is due 

 to chemical, physical or physico-chemical action we can not say. 

 Since we first became interested in the effects produced by heating 

 soil several other investigators have published the results of their 

 studies on this subject. We have confined ourselves to the use of 

 dry heat, while nearly all the others used steam heat. 



DISCUSSION OF THE WORK OF OTHER INVESTIGATORS 



At the Rothamsted Experiment Station in England, Russell and 

 Hutchinson^ studied the effects on soils produced by heating to a 

 low temperature (98° C.) and by treatment with volatile antiseptics. 

 Under these conditions they found that the fertility of the soil was 

 enhanced and that this was due to an increase in the nitrogenous 

 food thus made available. This effect seemed to be the result of the 

 quickened activities of certain nitrifying bacteria not present to 

 so great an extent in unheated soils. These authors' experiments 

 show that the inhibition of the beneficial organisms in untreated soil 

 is not due to a toxic substance, but that it is caused by the presence 

 in untreated soils of large protozoan organisms which destroy the 

 useful bacteria. Heat and antiseptics kill the protozoa and most 

 of the bacteria, but the latter soon take a new lease of life from 

 the unharmed spores, and finding themselves unattacked by their 

 enemies, they reproduce in great numbers, meanwhile causing large 

 increases in the soluble nitrogenous matter of treated soils. Ex- 

 periments with crops demonstrated that the higher plants made 

 growths on treated soils which were much better than on soils not 

 treated. In summing up Russell and Hutchinson's work we may 

 say that their idea is to credit the increased productiveness of 

 heated and toluened soils to the consequent destruction of protozoa 

 which in ordinary soils prey upon the beneficial ammonifying bac- 

 teria and nearly exterminate them. 



Lyon and Bizzell^ at the Cornell Experiment Station published 



' Russell and Hutchinson : The eflfect of partial sterilization of soils on the 

 production of plant food. Jour. Agric. Sei., 3: 1 11-144. 190g. 



* Lyon and Bizzell : Effect of steam sterilization on the water-soluble matter 

 in soils. Bull. 275. Cornell Experiment Station, Ithaca, N. Y. 1910, 



