Ammonia exchange from corn foliage during reproductive growth

Developing solutions to atmospheric environmental problems requires a better understanding of chemical processes occurring in each component of the ecosystem. Volatile NH₃ loss from plant foliage complicates the assessment of NH₃ emissions from agricultural activities. The objective of this study was to use ¹³N methodology to identify time of occurrence, magnitude, and direction of NH₃ exchange between corn (Zea mays L.) fertilized with enriched ¹⁵N and the atmosphere during reproductive growth. Ammonia was collected by drawing air over leaves, ear shoots, and whole plants and trapping the NH₃ on oxalic acid-impregnated filter disks. Filter disks were analyzed by ANCA-MS procedures for total N and atom % ¹⁵N. An exchange of NH₃ between corn plants and the atmosphere was found to occur during all sampling periods. This suggests that the release and capture of free NH₃ is an active component of the metabolic processes taking place in corn plants during reproductive growth. For corn under nonlimiting N fertility, the direction, rate, and magnitude of NH₃ exchange from leaves does not appear to he a function of ambient atmospheric NH₃ concentrations. Determining the true loss or gain in N between corn plants and the atmosphere during reproductive growth is very difficult as a result of this continuous exchange of NH₃. The amount of net N lost from a corn crop will be less than the amount indicated by measurements of isotopic loss, because both interchange between plants and deposition on soil and plants may take place within the field.