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Nitrogen Tracers in Nitrogen Cycle Studies—Past Use and Future Needs¹

ABSTRACT

Nitrogen research is directed toward two main objectives, food and fiber production and environmental control. To achieve N balance in productive ecosystems, better quantitative estimates of N transformation rates are needed. Nitrogen tracers are indispensable for making many of these estimates. Either ¹⁵N-depleted or ¹⁵N-enriched materials can be used. The use of ¹⁵N-depleted materials is limited to studies where dilution form other N is less than 2,000-fold, but these materials are potentially available in ton amounts.

Use of variation in natural ¹⁵N abundance may be useful in observing qualitative relationships among N cycle processes over large areas or extremely long time periods. Such use is questionable for obtaining quantitative information for short-term N transformation processes.

Obvious information gaps are quantitative data on atmospheric N₂ fixation and denitrification in cropped field soils and N transformation data for many other ecosystems. A program for computer data retrieval and correlation is outlined.

Key Words: N balance • ¹⁵N-enriched tracers • ¹⁵N-depleted tracers • N isotope abundance

¹ Contribution from the National Fertilizer Development Center, Div. of Agricultural Development, Tennessee Valley Authority, Muscle Shoals, Ala. 35660.

² Research Chemist (Soils).

Received for publication July 7, 1972.