Emissions of N 2O and CO 2, denitrification measurements and soil properties in red clover and ryegrass stands

Abstract

The relationships between the fluxes of nitrous oxide (N 2O) and carbon dioxide (CO 2), and their concentrations in the soil air, three different measures of potential denitrification, soil moisture, soil temperature and precipitation were investigated in soils from beneath ryegrass ( Lolium multiflorum Lam.), red clover ( Trifolium pratense L.) and mixture of ryegrass–red clover stands on a gleic cambisol. Investigations were carried out in order to test the hypothesis that the measure(s) of potential denitrification are good predictor(s) of N 2O fluxes and thus may be used in empirical models of N 2O emission. Potential denitrification characteristics used in this study involved (i) short-term denitrifying enzyme activity (DEA), (ii) long-term denitrification potential (DP), both determined in soils amended with nitrate and glucose, and (iii) denitrification rate (DR) measured using intact soil cores. Flux measurements were made using cylindrical chambers (internal diameter 31 cm, volume 0.015 m 3). The fluxes of N 2O and CO 2 and many other characteristics showed large spatial and temporal variability. Emissions of N 2O from the grass plots were closely related to N 2O concentrations in the soil atmosphere at 22.5 cm depth. Most soil properties did not correlate with N 2O fluxes. It was concluded that DP was not a good predictor for N 2O flux. DEA did not show significant relationship with N 2O flux, but it is suggested that if determined in representative, large soil samples, DEA could be a predictor of N 2O fluxes; this assumption needs, however, verification. The only potential denitrification characteristic which was significantly related to N 2O emission both in grass and clover treatments was DR, which was determined in soil cores.