While a lot of work has been done on the methodologies of measuring and estimating terrestrial trace gas emissions, there are still some open fundamental questions. This thesis explores some of these questions. Its scope is necessarily limited to the techniques that have been applied within the course of this work. The studies involving N20 were supported in part by a MAFF (Ministry of Agriculture, Fisheries and Food) funded project on quantifying emissions from fertilised agricultural soils (Grant No. CC0214). All studies involving CH4 and rice plants were part of the EC funded RICEOTOPES project (Grant No. CT97-0408), looking into fluxes and isotopic signatures of CH4 from rice paddies.After the literature review (Chapter I), issues related to the so-called closed chamber technique are investigated in Chapters II and III This is a method, which involves the covering o f a small area (usually < 1 m2) with some type of inverted container and the monitoring of the changing gas concentrations within the headspace so created. While N 20 was used as a target gas in the work described in these chapters, the results are also applicable to other gases. Chapter IV explores the possibility of predicting N 20 emissions through related soil parameters. A simple model has been developed on the basis of closed chamber measurements and the simultaneous measurement of related
soil water and mineral N contents, and temperature. This was then verified against data sets obtained by the same methods. Chapter V describes an automated system of closed chambers for the measurement of CH4 from rice paddies and results obtained with this system over two growing seasons. It includes some technical aspects and an illustration of seasonal variability and variations in the pathways of CH4 emission. Chapters VI and VII investigate two possibilities of measuring CH4 from rice on a larger scale than it is possible with closed chambers.In a general discussion, the different approaches to estimating trace gas emissions from land surfaces previously discussed are compared and an outlook on possible future developments is given
