Microbiological regulation of the biogeochemical nitrogen cycle

Most nitrogen transformations in soil are carried out by micro-organisms. An understanding of the microbiological processes is thus necessary in order for us to devise management practices in agricultural ecosystems, which will optimize plant root uptake of nitrogen and minimize nitrogen losses from the systems. Some aspects of the individual microbiological processes in the nitrogen cycle are discussed and their importance for an efficient management of agroecosystems. In soil various groups of organisms compete for available inorganic nitrogen and quantitative data are needed on the uptake kinetics for these various groups in order to be able to assess their competitive ability under different conditions. The influence of abiotic factors such as oxygen concentration, inorganic nitrogen concentration and pH is discussed in relation to the different processes. The importance of acetylene as a tool in nitrogen cycling studies is discussed briefly.