Nitrogen isotope ratios in surface and sub-surface soil horizons

Nitrogen isotope analysis of surface soils and soil-derived nitrate for selected chernozemic and luvisolic soils showed mean delta 15N values of 11.7 and 11.3, respectively. Isotope enrichment of the total N reached a maximum in the lower B horizon. Sub-soil parent material samples from the one deep profile included in the study indicated a delta 15N value (NO3-N) of 1/3 that of the Ap horizon, at a depth of 180 cm. The delta 15N of sub-surface soil horizons containing residual fertilizer N were low (-2.2) compared to the surface horizon (9.9). The data reported from this preliminary survey suggest that the natural variations in 15N abundance between different soils and horizons of the same soil reflect the cumulative effects of soil genesis and soil management. More detailed knowledge and understanding of biological and other processes which control N isotope concentrations in these soils must be obtained before the data reported can be interpreted. (author)