High-temperature catalytic oxidation method for measuring total dissolved nitrogen in K 2SO 4 soil extracts

Abstract

A high-temperature catalytic oxidation (HTCO) method was evaluated and compared with the Kjeldahl method for determining total dissolved N (TDN) in 0.025 M K 2SO 4 soil extracts used to assess soil microbial biomass nitrogen. First the HTCO method was evaluated for routine analysis for TDN in K 2SO 4 solutions. Nitrogen recoveries measured by HTCO exceeded 98% for compounds containing organic and inorganic N and for concentrations up to 10 mg N l −1. The proposed indirect injection of sample into the furnace safeguards the catalyst and quartz combustion tube. In these conditions, the drift of signal sensitivity during sequence analysis was negligible implying that HTCO can be used for the routine analysis of samples in a 0.025 M K 2SO 4 matrix. The HTCO and Kjeldahl methods were then compared for determining soil microbial biomass nitrogen in different types of soil using the fumigation-extraction method. The TDN concentrations in K 2SO 4 soil extracts measured with both methods were well correlated. Some discrepancies however, were, observed for TDN concentrations >10 mg N l −1 due to a probable underestimation of N in the soil extracts with the Kjeldahl method. The calculated extractable microbial biomass values resulting from the difference in TDN between control and fumigated soils were in good agreement for both methods. HTCO thus provides a very rapid and reliable method for measuring TDN in K 2SO 4 soil extracts used to determine soil microbial biomass nitrogen.