Concluding remarks
Over the past two days of this symposium I have been impressed by the interest and enthusiasm shown for the subject of the nitrogen cycle. The programme has been diverse, with agriculturalists, environmentalists, those interested in forestry, aquatic environments, plant physiology and medicine all contributing. Dr Lake has rounded off the general discussion admirably: he has emphasized that there are many questions still to be answered and various speakers and contributors have pointedly emphasized that while we know much about the various reactions of the nitrogen cycle, at least in gross terms, good solid quantitative data on various processes are scarce. Even for N 2 fixation about which, as Professor Postgate rightly said, more is probably known than about any other process of the nitrogen cycle, there is still uncertainty about how much N is fixed in the oceans of the world, despite the fact that these cover the bulk of the Earth’s surface. Professor Fogg has mentioned the difficulties of obtaining such data in so vast an area. But it is not only in the sea that there are problems. As yet we have few good quantitative data on losses by denitrification: how much is lost as N 2 and how much as N 2 O. The studies of Dr Dowdell and his colleagues are an important step in the right direction. Detailed quantitative studies are required on the various processes of the nitrogen cycle. That is where progress will have to be made in the future. I believe that too much time has been spent in the past on mass balance studies and not enough time on getting accurate measurements of the various processes by experimentation.