Comparison of 15NH4+ pool dilution techniques to measure gross N fluxes in a coarse textured soil

We compared gross N fluxes by N-15 pool dilution in a coarse-textured agricultural soil when N-15 was applied to the soil NH4+ pool by either: (i) mixing a (NH4NO3)-N-15 solution into disturbed soil or (ii) injection of (NH3)-N-15 gas into intact soil cores. The two techniques produced similar results for gross N mineralization rates indicating that NH4+ production in soil was not altered by soil disturbance, method of application (gas vs. solution), or amount of N applied. This was not the case for immobilization rates, which were twofold higher when N-15 label was applied to the soil NH4+ pool with the mixing technique compared to the injection technique. This was attributed to the fact that more NH4+ was applied with the mixing technique. Estimates of gross nitrification were accompanied by large error terms meaning differences between N-15 labeling methods could not be accurately assessed for this process rate. (C) 2004 Elsevier Ltd. All rights reserved.