NITROUS-OXIDE EMISSION FROM SOILS AT LOW MOISTURE CONTENTS

The production of nitrous oxide by soils was studied over short periods at a range of moisture contents up to field capacity with a highly-sensitive gas Chromatographic method. Nitrous oxide (N2O) was emitted from all soils studied at all soil moisture contents, which ranged from air dry to field capacity. The rate of emission increased with increasing moisture content and with increasing temperature up to 37°C. The evolution of N2O was not due to displacement of soil air during wetting. It was inhibited by HgCl2 and toluene, and was prevented by formaldehyde and autoclaving. Thus it appeared to be due to microbiological processes. The results of experiments with nitrification and denitrification inhibitors suggest that a considerable part of the N2O was produced by the oxidation of ammonia. Production by denitrification of nitrate cannot be ruled out. The relative importance of these two mechanisms probably depends on the moisture and oxygen content of the soil. It is concluded that the microbial production of N2O is continuous in soil at all moisture contents. The process at low moisture contents constitutes an important component in the cycle which maintains the N2O concentration in the atmosphere. © 1979.