Advances in Methodology for Research on Nitrogen Transformations in Soils.

Advances in analytical instrumentation and techniques have played a key role in the proliferation of research during the past 25 yr concerning the nature and transformations of soil N, particularly as regards agricultural productivity and environmental quality. This is apparent, for example, from the discovery that nitric oxide (NO) emission is a common occurrence in the field, which has been demonstrated through numerous studies using highly sensitive chemiluminescent analyzers. A growing trend in soil N research has been toward the use of automated analytical systems for N isotope analysis or quantitative determination of total, inorganic, or gaseous N. There also has been a trend toward the improvement of manual methods for soil N analysis, notably involving the development of simple diffusion techniques for quantitative and/or isotopic analysis of different forms of soil N. Such progress has generated an array of new experimental options, with fewer constraints from excessive size or complexity. Yet some caution is warranted regarding the growing need for a thorough understanding of methodological limitations and assumptions, so as to ensure data integrity and avoid unsound interpretations that impede scientific progress. This is best accomplished by using methodology that has been evaluated rigorously, under conditions appropriate for the specific application.