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

Core Ideas A manifold is described for preparing kilogram quantities of 15 NH 3 . The 15 NH 3 is 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 (NH 3 ) is a common practice for Midwestern corn ( Zea mays L.) production in the USA, field studies utilizing 15 N 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 NH 3 from labeled and unlabeled sources to obtain a desired 15 N 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% 15 N were obtained for 3 kg of NH 3 prepared within a normal working day by a 15‐fold dilution with 10 atom% 15 N 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 NH 3 .