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Soil Science Society of America Journal Abstract -

An Application of Autoradiography to Study the Spacial Distribution of 33P-Labelled Orthophosphate Added to Soil Crumbs1


This article in SSSAJ

  1. Vol. 35 No. 6, p. 906-909
    Received: Apr 7, 1971
    Accepted: May 25, 1971

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  1. T. D. Evans and
  2. J. K. Syers2



The penetration of orthophosphate (P) into soil crumbs was studied semiquantitatively using 31P, the low energy isotope 33P, autoradiography on a medium grained film, and solution analysis. Sorption of added P by the soil crumbs was rapid and was followed by penetration. Phosphate was not concentrated in discrete areas, suggesting that it was retained by a sorption rather than a precipitation mechanism. Native and added P, isotopically exchangeable in 1 hour, were confined to the crumb surface. Desorption for 7 days in Cl- or SO42- had little or no effect on the spacial distribution of sorbed added P; 0 and 2.4% of the sorbed added 31P was desorbed by Cl- and SO42-, respectively. Desorption in HCO3- or citrate increased the mobility of sorbed added P resulting in a complete redistribution within the crumbs and release into solution of 14 to 18% or 10 to 61% of sorbed added 31P, respectively. Anomalous estimates of the amount of P sorbed or desorbed, obtained by 31P and 33P analyses, could not always be explained by isotopic exchange.

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