In 1979--1981, experiments were carried out at four field stations near Mainz, Germany, to determine the loss of fertilizer nitrogen into the atmosphere as N2O. Evolution rates from the soil into the atmosphere were measured by using the closed chamber technique. An automatic sampling and analyzing device was developed which allowed frequent determinations of N2O evolution rates (one every 1.5 hours). The N2O production rates were correlated to the surface soil temperature according to the Arrhenius equation and showed a diurnal rhythm with amplitudes reaching, sometimes, 1 order of magnitude. It seems that most of the N2O emitted into the atmosphere is produced in the uppermost soil layer. N2O evolution was stimulated by rain and increased with increasing soil moisture content. Appplication of fertilizer caused a dramatic increase of N2O evolution rates with values up to 1000 μg N2O-N m-2 h-1. The magnitude of the fertilizer-induced N2O evolution rates was dependent on the type, the application form, and the amount of fertilizer used. The total loss of fertilizer nitrogen as N2O was in the range of 0.001 to 0.94%. Based on these figures, as well as on data from the literature, the total source strength of mineral fertilizers for atmospheric N2O is calculated to 0.02 to 8 Tg N2O-N yr-1.