The effect of urea and pig slurry fertilization on denitrification, direct nitrous oxide emission, volatile fatty acids, water-soluble carbon and anthrone-reactive carbon in maize-cropped soil from the Po plain (Modena, Italy)

 The use of zootechnical slurries in agriculture can increase N losses as N₂O by direct emission and by denitrification. The aim of this research was to determine the influence of pig slurry, as well as its combination with mineral N, on N₂O emissions in the field and their relationships with some fractions of soil organic matter, with soil moisture and with rainfall. In spite of varying amounts of organic substance applied, the diverse agronomic treatments did not produce substantial differences in N losses due to denitrification. Wide variations between the slurry fertilized and the urea-fertilized plots were not found, whereas the combination of pig slurry with urea usually produced an increase both in N₂O emissions due to denitrification and in direct N₂O emissions (N losses corresponding to about 50% of those due to denitrification). The greatest losses of N₂O-N occurred in the first month following fertilizer administration. N₂O emissions due to denitrification were highest in the days immediately following the administration of fertilizers and lowest in a later period. N₂O emissions due to nitrification occurred later. Therefore, N₂O emission via nitrification differed from N₂O losses via denitrification which, under optimal conditions, presented peaks of activity during the whole growth cycle. The N₂O-N losses were highly influenced by physical parameters, particularly rain. An increase in micropore water creates conditions of scarce oxygenation or of anaerobiosis which influence oxidation-reduction processes and, at the same time, can limit the diffusion of bacteria-produced gas towards the soil surface. Received: 14 January 1998