Soil emissions of nitrous oxide in fire-prone African savannas

Only few estimates of soil emissions of nitrous oxide (N2O) are available from African savanna ecosystems, which account for two thirds of the savannas worldwide. Field measurements of soil emissions of N2O were conducted in seasonally dry savannas in Ethiopia and Ghana in order to study temporal and spatial variation in emission rates and to examine the effects of fire on the N2O flux. Soil emissions of N2O were measured by an enclosure technique. Soil emission rates were lowest in the dry season averaging 0.5 μg N2O‐N m−2 h−1, and the mean flux increased from 1.7 in the beginning to 3.5 in the middle and 5.5 μg N2O‐N m−2 h−1 by the end of the rainy season. Minor spatial variation in emissions according to differences in drainage capacity, vegetation type, and fire severity was associated with high spatial variation at field scale. The variation in water‐filled pore space in soil explained only 44% of the variation in the N2O flux. In an experiment separating the effect of fire and ash, the N2O flux was not different across treatments 1 week after the low‐intensity burning. In another experiment, the flux at early and late burn sites did not differ and was not different from an unburned site. The study clearly demonstrates that more measurements are needed to fully understand the seasonal and spatial variability of soil emissions of N2O in savanna ecosystems.