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Soil Science Society of America Journal Abstract -

The Effect of Calcium and Magnesium on Soil Nitrate Determination by Automated Segmented-flow Methods1


This article in SSSAJ

  1. Vol. 51 No. 3, p. 664-667
    Received: July 10, 1986

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  1. S. Ananth and
  2. J. T. Moraghan2



An automated procedure, involving the reduction of NO-3 to NO-2 by an alkaline solution of hydrazine sulfate containing traces of Cu2+, is commonly used for determination of small quantities of NO-3-N in electro-ultrafiltration (EUF) extracts of soils. When this reduction method was employed to determine NO-3-N in aqueous extracts from certain Calciaquolls, low and erratic results were obtained with 24 of 46 soil samples. The problem extracts contained high levels of Ca2+ and Mg2+ that interfered with the method. Soil extracts with <40 mg Ca2+ L−1 and 15 mg Mg2+ L−1 presented no analytical problems. Placement of a cation exchange resin column between the sampler and pump of a Technicon AutoAnalyzer II overcame the interference, due presumably to removal of Ca2+ and Mg2+ from the flow line. Solution studies revealed that Ca2+ and especially Mg2+ prevented quantitative reduction of NO-3 to NO-2. No analytical problems were encountered with any of the soil extracts when a Cd-Cu column was used to reduce NO-3 to NO-2. Any hydrazine sulfate reduction method should be carefully evaluated when newly introduced as an analytical procedure for soil NO-3-N determination.

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