The oil crisis of the early 1970s highlighted the ever increasing cost of synthetic nitrogen fertilizers for crop production, and their pollution of the atmosphere and water systems has become a major environmental concern throughout the world.

Since then in the Centre for Crop Nitrogen Fixation at the University of Nottingham we have sought ways to find a biological symbiotic substitute for synthetic nitrogen fertilizers in agriculture. Our aim was to match Haber's ingenuity, in producing NH3 from N2 and H2 at high temperature and pressure, by the use of naturally occurring nitrogen-fixing bacteria interacting symbiotically with crop plants. This would utilise their nitrogenase enzyme to reduce N2 to NH3 at ambient temperature and pressure and thereby grow and sustain agriculture without sacrificing the environment.

Legume crops such as peas and beans which already fix nitrogen from the air symbiotically, thereby eliminating the need for synthetic nitrogen fertilizers, are able to interact with nitrogen fixing rhizobia bacteria which become established intracellularly within nodules on their roots. Our approach for more than two decades was to attempt to imitate this nodulation interaction of legumes by inoculating cereals and other non-legume crops with a wide range of species of rhizobia in national and international collaborations with support from BBSRC, the Rockefeller Foundation, The Royal Society and DFID. We clearly established that in response to inoculation nodulation, which is genetically controlled by the plant, could occur but that there was no intracellular colonization of the cells of the nodules by rhizobia and therefore no resultant symbiotic nitrogen fixation.