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

We compared gross N fluxes by 15N pool dilution in a coarse-textured agricultural soil when 15N was applied to the soil NH4(+) pool by either: (i) mixing a 15NH4NO3 solution into disturbed soil or (ii) injection of 15NH3 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 15N 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 15N labeling methods could not be accurately assessed for this process rate.