N2O and NO emissions from soils of the northern part of the Guayana Shield, Venezuela

Soil fluxes of N 2 O and NO were measured in a scrub grass savanna and a nearby semideciduous forest in the savanna climatic region of Venezuela, during October 1988. The forest soil produces significantly larger emissions of N 2 O (ranging from 5.7 to 25.0×10 9 molecules cm −2 s −1 ) than the savanna soil (−3.6 to 14.0×10 9 molecules cm −2 s −1 ). This suggests that “long‐term” deforestation could produce a reduction of the N 2 O emissions to the atmosphere. In comparison with previous results from another site in the Venezuelan savanna region, very low emissions of NO, of the order of 1 to 2×10 9 molecules cm −2 s −1 , were recorded. Considering that the NO/N 2 O emission ratio was much lower than 1, that practically no changes in the emission were observed after the fertilization with NH 4 Cl, and that very low concentration of NO 3 − is found in the natural soil, it is likely that under undisturbed conditions N 2 O and NO are mainly produced by denitrification and that there is a lack of nitrifying bacteria in these soils. Both N 2 O and NO emissions increased after application of NaNO 3 . Since the emission of NO remained larger than the N 2 O emission (with a ratio of ∼4/1), a significant change in the production pattern must have occured after fertilization with nitrate.