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This article in SSSAJ

  1. Vol. 22 No. 4, p. 323-326
    Received: Jan 10, 1958
    Accepted: Mar 25, 1958

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Ion Exchange in Soil-Plant Root Environments: III. The Use of Mg28 for the Measurement of Magnesium Absorption by Plants1

  1. D. A. Brown and
  2. Joe P. Wells2



The availability of the Mg28 isotope having a half-life of 21.3 hours has presented the possibility of its use in the measurement of the available magnesium in soils. Data are presented to show the relative proportions of fertilizer and soil magnesium adsorbed by cation-exchange resin sheets over time periods up to 96 hours. The percentage of magnesium adsorbed from the tagged magnesium fertilizer remained relatively constant for exchange periods from 48 to 96 hours; being of the order of 76.6, 57.8, and 53.9% for soils with 50, 150, and 250 pounds per acre of exchangeable magnesium, respectively.

Four-week-old corn plants adsorbed adequate Mg28 during a 96-hour period for radioactive analysis of the nonadsorbed, adsorbed magnesium on corn roots, and permitted the analysis of the absorbed magnesium in the roots and tops. Increasing the rate of magnesium fertilizer increased the percentage of magnesium derived from the fertilizer in each of the different stages of nutrient uptake. Conversely, at any one fertilization rate, increasing the level of soil magnesium reduced the percentage of magnesium derived from the applied fertilizer.

These data indicate that the Mg28 isotope is usable up to periods of at least 7 half-lives for nutrient uptake and cation-exchange studies.

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