Inorganic N analysis of soil extracts by automated and distillation procedures

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A comparison was made of automated procedures and steam distillation for analysis of NH4 + and NO3 ‐ in KCl extracts of soils. Automated analysis of NH4 + utilized the phenate‐hypochlorite reaction. Nitrate was analyzed by E. coli reduction of NO3 ‐ to NO2‐which was then determined colorimetrically by reaction with sulfanilamide and napthylethylenediamine diHCl. Soil extracts were made with 1 M and 2 M KCl. Extracting with 1 M KCl was as effective as 2 M KCl. Extracts in 1 M KCl did not interfere with E. coli reduction of NO3‐, but 2 M KCl did. The automated procedures when compared to distillation gave similar if not better precision and reduced variation particularly at low N concentrations. The automated procedure tended to give higher values at higher NO3‐concentrations. Reduced time required for the analyses provided an additional advantage for the automated procedures.