Wheat Volatilized Ammonia and Resulting Nitrogen Isotopic Fractionation
1989
O'Deen, W. A.
Many agricultural crops show significant losses of N from flowering to maturity (during senescence). This research employs ¹⁵N fertilization to measure volatilization of NH₃ directly from plants. A Plexiglas chamber was designed to isolate the aerial part of winter wheat (Triticum aestivum L. cv. Vona) from its growth medium following anthesis. The system was a continuous free-flow, open design. Volatilized ammonia was trapped in surfaces of 0.1 M HO continuously for three separate 90 d runs conducted in 1983, 1984, and 1985. The potted wheat yielded sensitive double-peaked senescent N bands representing 3 to 4% of the N within the in-chamber crop. The NH¹⁵-N emission was from the internal N pool of the plant. Wheat tissue total N was determined by gravimetric Kjeldahl procedures employing tube diffusion. Fractionation of ¹⁴N and ¹⁵N isotopes, previously observed with tube diffusion and steam distillation, provided a basic model for similar fractionation caused by wheat volatilization of NH3. The varying atom percent ¹⁵N trends fit a model of continuously increasing wheat ¹⁵N content due to volatilization of NH₃ with lower ¹⁵N content. Contribution from the USDA-ARS in cooperation with the Colorado State Univ. Dep. of Agronomy. Part of a dissertation submitted by the author in partial fulfillment of the requirements for the Ph.D. program.
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