System for preparing and applying¹⁵N-labeled anhydrous ammonia in field plot research

Although direct application of anhydrous ammonia (NH₃) is a common practice for Midwestern corn (Zea mays L.) production in the USA, field studies utilizing ¹⁵N to quantify nitrogen (N) uptake efficiency have long been impeded by the difficulties and safety hazards inherent to a liquified gas that must be handled and applied under pressure. A manifold system is described for transferring known quantities of NH₃ from labeled and unlabeled sources to obtain a desired ¹⁵N enrichment, and for collecting the mixture cryogenically in a tank specifically configured for knifed applications using a tractor-mounted tool bar. Enrichments of 1.2 to 1.5 atom% ¹⁵N were obtained for 3 kg of NH₃ prepared within a normal working day by a 15-fold dilution with 10 atom% ¹⁵N as the starting label. A collection capacity of such magnitude represents a 3000% upscaling over systems previously described for this purpose, providing an essential prerequisite for field plot research to realistically assess the fate and fertilizer value of anhydrous NH₃