Turnover of15N ammonium sulfate with dicyandiamide under aerobic and anaerobic soil conditions

The influence of the nitrification inhibitor dicyandiamide (DCD) on the turnover of¹⁵N-labelled ammonium sulfate (AS) was investigated in two soils under aerobic and waterlogged conditions. Nitrification of ammonium sulfate was markedly inhibited by addition of DCD in both soils. Up to 45% of the supplied N was transformed into a non-extractable N form, which only slowly released nitrogen over 147 or 264 days. This immobilization was higher in the presence of DCD than without DCD. In all aerobic experiments, the recovery was 100% ± max. 2.4%, indicating that no gaseous losses of N occurred.If aerobic preincubation of 28 or 42 days was followed by water-logging with H₂O or a solution of glucose, considerable N losses occurred only in presence of the carbohydrate. DCD retarded nitrification and thus reduced losses by denitrification from 61 to 15%.DCD application resulted in an increased immobilization of labelled N into the non-exchangeable soil N fraction. This amounted to more than 50% of the applied N, compared to 39% without DCD.The late Dr. Klaus Vilsmeier, a very dedicated and talented young scientist, died before he was able to finish completely the revised version of this article. We will always keep him in our minds and kindly remember his kind personality as well as his sense of humour and justice. Prof. Dr. Heiner Goldbach on behalf of all members of the department.