Accelerated Diffusion Methods for Inorganic-Nitrogen Analysis of Soil Extracts and Water
- S. A. Khan,
- R. L. Mulvaney and
- C. S. Mulvaney
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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