SOILS FERTILIZERS. 421 



conditions, but is not reduced wlien tlie soils are kept moist in the absence of 

 air. The destruction of the toxic substance is probably, therefore, due to 

 oxidation. 



" Unheated soils, or soils heated only to a low temperature, exhibit on keep- 

 ing an increase in soluble matter; this occurs whether air is admitted or not, 

 and this change, therefore, is probably not an oxidation process. The substance 

 formed, moreover, in such cases appears to have little or no toxic action on 

 germination. This increase of soluble matter, due to the formation of a non- 

 toxic substance, is preceded by a preliminary diminution of soluble matter, pre- 

 cisely similar to the diminution of toxic matter occurring continuously in the 

 more highly heated soils. Such toxic matter, therefore, appears to be present 

 in all soils, whether heated or not, though, in the latter case, it is present in 

 such small quantities that it soon becomes completely oxidized. 



"Air-dried soils, heated and unheated, when kept for some months show an 

 appreciable reduction in soluble constituents, and also in toxic properties 

 (where such properties were originally present), closely similar to the reduction 

 exhibited by moist soils kept in air for about ten days." 



• Plant growth in heated soils, S. IT. Pickering {Jour. Agr. 8ci., 3 (1910), 

 No. 3, pp. 211-281}, pis. 3; abs. in Jour. Soc. Chem. Indus., 29 (1910), No. 20, p. 

 1217). — Pot experiments with various plants grown on heated soils are reported. 



The author states that "however contradictory the results may appear at 

 first sight, they are fully in accord with the information obtained from a study 

 of the changes occurring in heated soils and with the experiments on the germi- 

 nation of seeds. On heating a soil, the soluble matter available for nutrition is 

 increased and changes in the bacterial condition are brought about, which — the 

 latter especially — conduce to increased vigor of the plants growing in them ; 

 but the heating also results in the formation of some substance or substances 

 which are actively toxic and which tend to arrest growth. The proportion of 

 toxin formed at low temperatures is small and is generally insufficient to coun- 

 teract those conditions favoring increased growth, but this proportion increases 

 at a very rapid rate as the temperature of heating rises above 100° and its 

 baleful influence in such soils is generally the preponderating factor. Hence 

 the results obtained of increased vigor with soils heated up to about 100°, and 

 of greatly decreased vigor with those heated to higher temperatures. But the 

 toxic substance is unstable and gradually disappears by the action of air and 

 moisture, so that the results obtained in any individual series will vary con- 

 siderably with the circumstances obtaining. When the soils are used at once 

 after heating, and when the cultivation and the access of air are reduced to a 

 minimum, the toxic action will prevail and no increased vigor of growth may 

 obtain in any case; whereas, under conditions favoring oxidation, the toxic 

 action disappears and increased growth becomes the predominant feature. .The 

 gradual recovery of plants grown in strongly heated soils, and the smallness 

 of the toxic action in the case of second crops, are illustrations in point." 



The experiments did not show whether the substance which was toxic toward 

 plant growth was the same as that which was toxic toward germination, 

 although the indications were that it was the same toxin which was active in 

 both cases. The experiments showed wide differences in the susceptibility of 

 different plants to the action of the toxin. Many of the grasses were much less 

 susceptible than other plants. The formation of the toxic body was traced down 

 to such a low temperature of heating " that it is impossible to avoid the con- 

 clusion that some of it must be present in so-called unheated soils." 



The moisture content of packed and unpacked soils, F. T. Shutt ( Canada 

 Expt. Farms Rpts. 1910, pp. 21^, 215). — Comparative tests of the subsoil packer 



