IMPROVED DIFFUSION METHODS FOR DETERMINATION OF INORGANIC NITROGEN INSOIL EXTRACTS AND WATER

Diffusion methods previously developed for inorganic-N analysis of soi l extracts were modified to improve reliability, increase the dynamic range, extend the scope of applications. and simplify the processing o f samples for N-isotope analysis. In these methods, the soil extract i s 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 i n a Petri dish suspended from the Mason-jar lid and determined quantit atively by acidimetric titration. With the modifications described, an alyses can be performed on 10- to 100-ml samples of water, 0.5 M K2SO4 , 1 M KCl, 2 M KCl, or 4 M KCl, at temperatures between 20 and 30 degr ees C. Recovery from 10 or 20 ml was quantitative in 18-80 h with up t o 4 mg N; recovery from 50 or 100 ml was quantitative in 3-13 days wit h up to 2 mg N. Removal of H3BO3 for N-isotope analysis by the Rittenb erg process was effected using methanol. Mason-jar diffusion methods a re much simpler and more convenient than conventional steam distillati ons. Comparative studies showed that quantitative determinations are m ore accurate and precise by diffusion than by distillation.