Nitrogen‐15‐Depleted versus Nitrogen‐15‐Enriched Ammonium Sulfate as Tracers in Nitrogen Uptake Studies

Abstract Fertilizer particles were prepared from ammonium sulfate with a lower (0.031) than natural (0.366) atom percentage of 15 N. The 15 N‐depleted material was compared with ammonium sulfate of a comparable level of 15 N enrichment (0.734 atom %) in a greenhouse pot experiment which measured plant recovery of applied N. There was no statistical difference in N recovery values for five harvests taken over an 18‐week period at three rates of applied tracer N, with on exception. Accurate and precise measurement of tracer N in plant tissue was obtained for both 15 N‐depleted and 15 N‐enriched materials, using two mass spectrometers with different measurement and rcording systems. A nontracer technique gave lower first harvest and higher combined harvest values of percentage recovery of applied N than either tracer technique.