Use of diffusion for automated nttrogen‐15 analysis of soil extracts

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Abstract
Studies to evaluate the use of diffusion for automated 15N analysis of inorganic N in soil extracts showed that serious error can arise from use of the Devarda's alloy recommended for steam distillations and that the error can be avoided by using a commercial product of higher purity. These studies showed that serious error can also arise when NO3 ‐‐N is diffused following NH4 +‐N and that separate diffusions should be performed for NH4 +‐N and (NH4 + + NO3‐)‐N. Other work demonstrated that the plastic specimen containers employed for diffusion can be reused if acid‐washed, that diffusions can be performed using either light or heavy MgO without ignition to decompose carbonate, and that labeled NO2‐is completely removed from soil extracts by treatment with sulfamic acid before diffusion. A comparison of 15N analyses by steam distillation and diffusion using extracts from two soils revealed better agreement for the soil having a lower content of organic matter. Substantial differences in analyses by the two techniques for the soil having a higher organic‐matter content were attributed to enzymatic conversions of inorganic N during the 6‐d diffusion period.