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Studies of the Changes occurring in Heated Soils

Published online by Cambridge University Press:  27 March 2009

Spencer Umfreville Pickering
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Extract

The water extracts obtainable from soils are of constant composition as regards organic matter when the time allowed for the extraction varies from 20 to 320 minutes, the temperature from 7° to 23°, and the proportions from 5 to 10 of soil to 100 of water. The inorganic matter is not affected by the time, but is by the temperature and proportions.

The increase in soluble matter produced by heating a soil, and the accompanying toxic qualities towards the germination of seeds in it, is gradually reduced by exposing these soils in a moist condition to the air, even under aseptic conditions, but is not reduced, when the 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 keeping 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, precisely 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 oxidised.

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.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 3 , Issue 3 , September 1910 , pp. 258 - 276
Copyright
Copyright © Cambridge University Press 1910

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References

Page 258 note 1 Journ. Agric. Sci. II. 411, III. 33.Google Scholar

Page 258 note 2 loc cit. p. 422.

Page 267 note 1 Journ. of Agric. Soc. III. 43Google Scholar. In these the point of intersection was at about 80°. Other determinations were made with a series of soils in which grass was grown for 72 days: the curves in that case were closely similar to those here shown, though not quite so regular, and the point of intersection was 75°.

Page 270 note 1 loc. cit. III. 35.Google Scholar

Page 272 note 1 This, and various other facts, disprove the suggestions recently made by Fletcher, F. (The Cairo Scientific Journal, No. 43, Vol. IV. 04 1910)Google Scholar that delayed germination is due to a decreased rate of inhibition, consequent on the increased amount, and not on the nature, of the soluble matter in the heated soil.

Page 273 note 1 The germination curves have been smoothed more than the others: the results for soil heated to 100° lie a good deal off the curves 0 and 106, and, as may be seen from Table V, the values for this soil remained practically constant throughout.