Nitrogen: Recent developments in related microbial processes

Nitrogen is a key nutrient for the production of crops on earth. More than any other, it is the growth-limiting nutrient for plant and therefore, it h as been added to arable land as fertiliser in enormous quantities, all over the world. Due to its (bio)chemical "flexibility" and its mobility, nitrog en is easily lost to the environment, where it has become a major polluting element in the atmosphere, water and soil. Thus, sound management of the n itrogen resources is a prerequisite for sustainable agriculture and for a c lean environment. This calls for understanding of the fate of nitrogen in p lant/soil systems. Here, three examples of recent developments in research on nitrogen will briefly be discussed, with emphasis on microbiological pro cesses. These cases are the modelling of nitrogen flow through the soil foo d web, the use of molecular biological techniques for the identification of ammonium-oxidising bacteria and the mechanisms of host recognition by symb iotic nitrogen-fixing bacteria. They also exemplify progress that has been made in the science on terrestrial ecosystems during the period of the pres ent OECD programme on Biological Resource Management, progress that is need ed to develop future strategies for proper management of the biological nit rogen resources.