ABSTRACT
Sound generalisations and predictions of soil processes are difficult to make with confidence because of the chemical, physical and biological variations that occur in soil at all scales in both space and time. Natural abundance studies have been used in a wide range of soil-nitrogen (N) investigations and have provided some insights to the complexity of soil N, but at the same time the complexity of the soil often confounds interpretation in stable isotope studies. This chapter outlines the microbial processes of N transformation, the distribution of N and 15N in soils in general and the variability in space and time of N and 15N. It discusses some of the more recent insights to soil N transformations that have been gained from 8N measurements. The tremendous spatial variability of soils, which can occur on scales measured in µm through to km and, unlike the oceans and atmosphere, the virtual absence of any mixing are constant factors in soil investigations.
