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This article in SSSAJ

  1. Vol. 74 No. 3, p. 1018-1027
     
    Received: Oct 14, 2009
    Published: May, 2010


    * Corresponding author(s): wolfgang.wanek@univie.ac.at
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doi:10.2136/sssaj2009.0389

Alternative Methods for Measuring Inorganic, Organic, and Total Dissolved Nitrogen in Soil

  1. Rebecca Hood-Nowotnya,
  2. Nina Hinko-Najera Umanab,
  3. Erich Inselbacherc,
  4. Petra Oswald- Lachouaniabc and
  5. Wolfgang Wanek *a
  1. a Dep. of Chemical Ecology and Ecosystem Research, Univ. of Vienna, Althanstrasse 14, 1090 Vienna, Austria
    b Dep. of Forest and Ecosystem Science, Univ. of Melbourne, Water St., Creswick, VIC 3363, Australia
    c Dep. of Forest Ecology and Management, Swedish Univ. of Agricultural Sciences, SE-901, 83 Umeå, Sweden

Abstract

There are numerous methods for measuring inorganic, dissolved organic, and microbial N in soils, although many of these are complex or require expensive equipment. We have modified methods for the measurement of NH4 +, NO3 , total dissolved N (TDN), and soil microbial biomass N (SMBN) in soils. The methods are based on a microtiter plate format and are rapid and simple to perform. Ammonium is quantified by a colorimetric method based on the Berthelot reaction. Total dissolved N and SMBN (by CH3Cl fumigation-extraction) are quantified as NO3 after alkaline persulfate oxidation. Nitrate is estimated directly or after persulfate oxidation by reduction of NO3 to NO2 by VCl3 and subsequent colorimetric determination of NO2 by acidic Griess reaction. The new suite of methods was compared with conventional methods such as high-performance anion-exchange chromatography for NO3 and high-temperature catalytic oxidation for TDN. Our methods produced comparable detection limits, linearities, and precisions compared with the conventional methods. Limits of quantification were 7 μg NH4 +–N L−1, 55 μg NO3 –N L−1, and 0.275 mg TDN L−1 The accuracy of the proposed methods was excellent, with recoveries of added NH4 +, NO3 , and glycine ranging between 96 and 99%. Linearities of the respective calibrations were high (R 2 > 0.99), and precisions for NH4 + (CV = 2.1%), NO3 (CV = 3.5%), and TDN (CV = 3.9%) were comparable to the reference methods. The simplicity, rapidity, and low cost of the proposed methods therefore allow an expansion of the scope and range of N cycle studies where sophisticated instrumentation is not available.

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