The Measurement of Denitrification in Soil, Using ¹³NO₃

Abstract

¹³N, a radionuclide with a half-life of 10 min, has been used for a variety of purposes in medical and agricultural research and in a variety of forms, e.g. as ¹³N₂ for study of nitrogen fixation and translocation in plants, ¹³NH₄ and ¹³NO₃ for studying plant nitrogen uptake, ¹³NO₃ for studying denitrification, and ¹³N₂O in medical research (Straatmann, 1977). The advantages of ¹³N are the ease of detection, measurement and identification of volatile products, and the short half-life that permits several consecutive experiments on the same material. The very small quantities of the label used ensure that there is no alternation of equilibrium reactions, but the short half-life does mean that experiments must be of simple design and must be conducted with minimum preparation of substrate and near the production source of the isotope. Nitrogen flux in soil due to dissimilatory denitrification, a form of anaerobic respiration, is a major component of the nitrogen cycle (Nielsen and MacDonald, 1978) and, in the experiments reported, ¹³N was used to examine the movement of the major components of the cycle in a relatively undisturbed soil and the evolution of gases by different bacterial cultures and soil cores.