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This article in SSSAJ

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

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

  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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