System for Preparing and Applying 15N‐Labeled Anhydrous Ammonia in Field Plot Research

Core IdeasA manifold is described for preparing kilogram quantities of 15NH3.The 15NH3is condensed into a collection tank that allows the use of a nitrification inhibitor.The collection tank connects to a tractor‐mounted toolbar for knifed applications to field plots. Although direct application of anhydrous ammonia (NH3) is a common practice for Midwestern corn (Zea maysL.) 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 NH3from 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 NH3prepared 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.