Wheat Volatilized Ammonia and Resulting Nitrogen Isotopic Fractionation
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.
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