The effect of different N substrates on biological N2O production from forest and agricultural light textured soils

N₂O emissions from two slightly alkaline sandy soils, from arable land and a woodland, were determined in a laboratory experiment in which the soils were incubated with different sources of nitrogen, with or without glucose, and with 0, 1 and 100 mL C₂H₂ L^-1. Large differences in the rate of N₂O production were observed between the two soils and between the different N treatments. The arable soil showed very low N₂O emissions derived from reduced forms of N as compared with the N₂O which was produced when the soil was provided with NO₂^- or NO₃^- and a C source, suggesting a very active denitrifier population. In contrast, the woodland soil showed a very low denitrification activity and a much higher N₂O production derived from the oxidation of NH₄⁺ and reduction of NO₂^- by some processes probably mediated by autotrophic or heterotrophic nitrifiers or dissimilatory NO₂^- reducers. In both soils, the highest N₂O emissions were induced by NO₂^- addition. Those emissions were demonstrated to have a biological origin, as no significant N₂O emissions were measured when the soil was autoclaved.