A METHOD USING PEROXYDISULFATE DIGESTION FOR TOTAL N-ANALYSES IN SOILS AND IN SOIL MICROBIAL BIOMASS EXTRACTS

The persulphate oxidation (TPN) and the Kjeldahl methods (TKN) were co mpared for measurement of total N in soils and soil extracts. The TPN method was adapted for optimum recovery and precision in the determina tion of total N. Measurement of total N with TPN and TKN procedures sh owed the methods to be comparable for both mineral soils and soil extr acts. For soil samples with a high content of C (> 5%) and N (> 0.5%), the total N content was highest with TKN. The Flow Injection Analysis (FIA) was very suitable for anlaysis of nitrate in persulphate digest ions. The TPN method combined with FIA estimation of nitrate is recomm ended for analysis of total N in soils and in soil extracts for microb ial biomass determinations.