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This article in SSSAJ

  1. Vol. 44 No. 6, p. 1326-1327
    Received: Apr 4, 1980
    Accepted: July 9, 1980

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The Magnesium Problem in Nitrate Determination by Steam Distillation1

  1. C. Clausen,
  2. B. R. Bock,
  3. G. A. Peterson and
  4. R. A. Olson2



Steam distillation of NH3 is commonly used to quantify the amount of mineral N in soil and plant materials. A problem with NO3- recovery by this method was encountered in an NH3 volatilization study. When NH4NO3 solutions were collected in acid and analyzed for NH4+-N and NO3--N, incomplete recovery of NO3- occurred. As the volume or normality of H2SO4 added to the distilling solution increased, more of the MgO used to raise the pH of the distilling solution was solubilized, which caused NO3- recovery in the first 25ml of distillate to decrease. Only 80% NO3--N recovery was obtained with 20 ppm of Mg2+ in the distilling solution. Soils with 3 meq exchangeable Mg2+/100 g depressed NO3--N recovery by 15% using the standard distillation procedure. An interaction between Mg2+ and Devarda's alloy evidently inhibits NO3- reduction.

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