Comparison of 15 NH 4 C pool dilution techniques to measure gross N fluxes in a coarse textured soil

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