DETERMINATION OF NITROGEN BY MICRODIFFUSION IN MASON JARS .1. INORGANIC NITROGEN IN SOIL EXTRACTS

Simple microdiffusion methods are described for determination of NH4+, NO3-, and NO2- in soil extracts. These methods involve diffusion of NH3 in a 473-mL (1-pint) wide-mouth Mason jar, the diffused NH3-N being collected in 3 mL of boric acid-indicator solution in a 60 mm (dia.) Petri dish suspended from the Mason jar lid, for quantitative determination by titrimetry (0.0025 M H2SO4). Magnesium oxide is used to liberate NH4+; Devarda's alloy is used to reduce NO3- and NO2- to NH4+; and sulfamic acid is used to eliminate NO2-. Depending upon the volume of soil extract (10-50 mL), diffusion at room temperature (greater-than-or-equal-to 20-degrees-C) was complete in 18-72 h with orbital shaking, and in 24-86 h without shaking. The methods gave quantitative recovery of NH4+, NO3-, and NO2- added to soil extracts. A potential source of interference in the methods involving use of Devarda's alloy is the liberation of NH4+-N from alkali-labile organic-N compounds.