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Improved diffusion methods for determination of inorganic nitrogen in soil extracts and water
Authors:R L Mulvaney  S A Khan  W B Stevens  C S Mulvaney
Institution:(1) Department of Natural Resources and Environmental Sciences, Turner Hall, University of Illinois, 1102 South Goodwin Avenue, Urbana, IL 61801, USA, US;(2) Department of Crop Sciences, University of Illinois, Urbana, IL 61801, USA, US;(3) 426 North Fisler Road, Monticello, IL 61856, USA, US
Abstract:Diffusion methods previously developed for inorganic-N analysis of soil extracts were modified to improve reliability, increase the dynamic range, extend the scope of applications, and simplify the processing of samples for N-isotope analysis. In these methods, the soil extract is treated with MgO, or MgO plus Devarda‘s alloy, in a 473-ml (1-pint) wide-mouth Mason jar to convert NH4 +-N, NO3 -N, and/or NO2 -N to NH3-N. The NH3 thereby liberated is collected in H3BO3-indicator solution in a Petri dish suspended from the Mason-jar lid and determined quantitatively by acidimetric titration. With the modifications described, analyses can be performed on 10- to 100-ml samples of water, 0.5MK2SO4, 1MKCl, 2MKCl, or 4MKCl, at temperatures between 20 and 30°C. Recovery from 10 or 20ml was quantitative in 18–80h with up to 4mgN; recovery from 50 or 100ml was quantitative in 3–13 days with up to 2mgN. Removal of H3BO3 for N-isotope analysis by the Rittenberg process was effected using methanol. Mason-jar diffusion methods are much simpler and more convenient than conventional steam distillations. Comparative studies showed that quantitative determinations are more accurate and precise by diffusion than by distillation. Received: 15 May 1996
Keywords:Ammonium analysis  15N  Nitrate  Nitrite  Inorganic N  Soil extract diffusion method
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