N-15 TRACER STUDIES ON THE MECHANISM OF T HE N2O FORMATION IN SOILS

Nitrous oxide is a potential environmental hazard responsible for the green house effect and the destruction of the ozone layer in the lower stratosphere. Biological denitrification under anaerobic conditions i n soils results in the formation of both N2O and N-2, whereby highly n itrogen-fertilized agricultural soils contribute to a considerable ext ent of the N2O emission. Latest results in the literature indicate tha t nitrous oxide can also be formed as a byproduct of the microbial nit rification. This is of importance for soils in central Germany because of the non-existence of typical denitrification conditions in a semia ride climate. This study was conducted to measure the path of N2O form ation in Haplic Phaeozem using [N-15] ammonium and [N-15] nitrat and a GC-MS aided incubation system. The kinetic isotope method was used to evaluate the experimental data. The results are: - Under anaerobic co nditions (greater than or equal to 90% of the water holding capacity = WHC) N2O originates mainly from the nitrate pool by denitrification. - As expected, the N2O formation is low under aerobic conditions (less than or equal to 80% WHC) but the gas originates directly from the am monium and not from the nitrate pool, probably as a byproduct of the n itrification process.