EFFECTS OF SOIL-MOISTURE, TEMPERATURE, AND INORGANIC NITROGEN ON NITRIC-OXIDE EMISSIONS FROM ACIDIC TROPICAL SAVANNA SOILS

NO fluxes from soils with a wide range of soil moistures, soil inorganic-N concentrations, and soil temperatures were measured during the wet and the dry season at a Venezuelan savannah site. Maximum No emissions (approximately 12 ngN m-2 s-1) were observed at soil gravimetric moistures between 10% and 18%. Deviation from this optimum range results in decreased NO fluxes; very low emissions (< 2 ngN m-2 s-1) were recorded at low (< 2%) and high (> 25%) soil moistures. Both NO production in soil and its transport within the soil play important roles in the emission of NO to the atmosphere. Under most conditions no temperature effect was observed. NO emission was strongly stimulated by the addition of NO3- and only very weakly by the addition of NH4+; at low and moderate soil moistures, soil nitrate and the NO flux were positively correlated. At low (natural) soil nitrate content and comparable soil moisture and temperature, No emissions were greater during the dry season than during the rainy season, suggesting that other factors (i.e., soil physical structure) may also govern No flux from savannah soil.