EVALUATION OF METHODS FOR N-15 ANALYSIS OF INORGANIC NITROGEN IN SOILEXTRACTS .1. STEAM-DISTILLATION METHODS

A study was conducted to evaluate conventional steam-distillation tech niques for N-isotope analysis of inorganic forms of N in soil extracts . Extracts obtained with 2 M KCl from 10 diverse soils were treated wi th: (i) ((NH4)-N-15)(2)SO4 and KNO3 (ii) (NH4)(2)SO4 and (KNO3)-N-15, or (iii) KNO3 and (NaNO2)-N-15. Steam distillations were performed seq uentially to determine NH4+-N and NO3--N, and were also carried out to determine (NO3- + NO2-)-N or (NH4+ + NO3- + NO2-)-N; a pretreatment w ith sulfamic acid was used to determine NO3--N in the presence of NO2- -N. Recovery of added N ranged from 95 to 102%. Significant isotopic c ontamination was observed in sequential distillation of unlabeled NO3- -N following labeled NH4+-N; otherwise, analyses for N-15 were usually within 1% of the values calculated by isotope-dilution equations.