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This article in SSSAJ

  1. Vol. 61 No. 3, p. 936-942
    Received: June 5, 1996

    * Corresponding author(s): mulvaney@uiuc.edu
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Accelerated Diffusion Methods for Inorganic-Nitrogen Analysis of Soil Extracts and Water

  1. S. A. Khan,
  2. R. L. Mulvaney  and
  3. C. S. Mulvaney
  1. Dep. of Natural Resources and Environmental Sciences, 1102 S. Goodwin Ave., Univ. of Illinois, Urbana, IL 61801
    426 N. Fisler Road, Monticello, IL 61856



The major limitation of diffusion methods for N analysis is the time required to obtain the results — typically from one to several days. Methods were developed that involve a much shorter period for diffusion. In these methods, 10- to 100-mL samples of 2 or 4 M KCl soil extract or water were treated with MgO, or MgO plus Devarda's alloy, in a 473-mL (1-pint) wide-mouth Mason jar to liberate NH4-N, NO3-N, and/or NO2-N as NH3. The jar was placed on an electric griddle maintained at 45 to 50°C. Gaseous NH3 was collected in 5 mL of H3BO3 indicator solution in a petri dish attached to the Mason jar lid, for quantitative determination by acidimetric titration. Complete recovery of 4 mg of N was achieved from 10 or 20 mL in 1.5 to 5 h. Recovery from 50 or 100 mL was complete in 5 to 8.5 h with 1 to 2 mg of N. The methods permit 15N analysis of the diffused NH3-N. Isotopic analyses of labeled soil extracts were accurate to within 3%, as determined by isotope-dilution calculations. Diffusions from 10 to 50 mL were subject to very little, if any, interference from decomposition of alkali-labile organic-N compounds.

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