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Stable Isotopes

Stable Isotopes in Agriculture


Dr. Richard Mulvaney
Department of Natural Resources and Environmental Sciences
University of Illinois, Champaign/Urbana

Tracer techniques using isotopic N have been employed since the 1940s to investigate such topics as N transformations and cycling in agricultural and other soils, N sources for crop uptake, the fate and behavior of fertilizer N applied to soils, the nature and extent of soil and fertilizer losses, and fertilizer N uptake efficiency. The value of these techniques is apparent from their effect on analytical sensitivity, which can be a crucial issue in defining the topic under investigation. For example, tracer techniques provide the only means to detect microbial or chemical immobilization or to distinguish between plant uptake of soil versus fertilizer N. Numerous studies have demonstrated that a substantial proportion of fertilizer N, typically between 10 and 30%, remains in the soil after the growing season, and that, even when highly fertilized, the soil itself often supplies the majority of N removed at harvest. There is growing evidence to implicate biological mineralization as the key process affecting soil N availability, and thus, fertilizer N requirements. Moreover, recent work suggests that a soil’s capacity for mineralization can be estimated from alkali-labile N determined by simple diffusion methodology, which provides new hope that fertilizer N recommendations can become more accurate through the use of soil testing. This methodology may be employed for N-isotope analyses by direct combustion of the classical Rittenberg process, creating numerous opportunities for tracer research to advance our understanding of soil N cycling and improve fertilizer N management.

Stable Isotope studies allow researchers to understand nitrogen fixation in the atmosphere, in plants and other organisms, and in industrial processes. Additionally the determination of the authenticity and origin of foods, such as wines, beef, and olive oil, and the adulteration of natural products, like honey, fruit juices, jams, and syrups, can be made using stable isotope tracers.

Isotec® offers a wide range of 15N and 13C labeled compounds for use in these applications.