The effect of urea and pig slurry fertilization on denitrification, directnitrous 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 N2 O by direct emission and by denitrification, The aim of this research was t o determine the influence of pig slurry, as well as its combination with mi neral N, on N2O emissions in the field and their relationships with some fr actions of soil organic matter, with soil moisture and with rainfall, In sp ite of varying amounts of organic substance applied, the diverse agronomic treatments did not produce substantial differences in N losses due to denit rification. Wide variations between the slurry fertilized and the urea-fert ilized plots were not found, whereas the combination of pig slurry with ure a 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 denitrific ation were highest in the days immediately following the administration of fertilizers and lowest in a later period. N2O emissions due to nitrificatio n occurred later. Therefore, N2O emission via nitrification differed from N 2O losses via denitrification which, under optimal conditions, presented pe aks of activity during the whole growth cycle. The N2O-N losses were highly influenced by physical parameters, particularly rain. An increase in micro pore water creates conditions of scarce oxygenation or of anaerobiosis whic h influence oxidation-reduction processes and, at the same time, can limit the diffusion of bacteria-produced gas towards the soil surface.