The Bremner Contribution to Controlling Nitrogen Transformations in Soils.

Control of nitrogen (N) transformations in soils through addition of inhibitory compounds or through naturally-occurring processes can have major impacts on N losses to the environment and on the effectiveness of N fertilizers in crop production.  Research in Professor Bremner’s program addressed the control of important N transformations in soils and the consequences of managing these processes.  Increasing concerns with nitrate losses from cropland and the emergence of urea as the major agricultural N fertilizer material focused the research efforts on inhibition of nitrification and urease activity with associated studies of the effects of inhibitors on other N transformations such as denitrification, ammonia volatilization, and soil N mineralization. Specifically, his work included evaluation of numerous compounds that were patented or proposed as inhibitors of urea hydrolysis and nitrification, identification of the most effective inhibitors, and studies of the mechanisms of inhibition and the consequences of inhibitor use on N losses and associated N transformations.  Many widely-used pesticides were studied for their effects on N transformations and the factors affecting the performance of numerous inhibitory compounds were determined.  Urease inhibitors were evaluated for their ability to minimize adverse effects of urea on seed germination and early plant growth, and their use for controlling ammonia volatilization in turf was studied.  Numerous naturally occurring compounds such as phenolic acids, terpenoids, and sulfur-containing amino acids were studied for their effects on N transformations. Major findings from this work included: identification of the most effective inhibitors; elucidation of the mechanisms of inhibition; description of the effects of inhibitor use on associated N transformations and potential losses of N; and use of inhibitors in research to better understand soil N dynamics.  Collectively, these studies provided the science base for use of inhibitors to enhance agronomic N efficiency and minimize N losses to the environment.