Little Effect of Land Use on N<sub>2</sub>O and NO Emission Pulses Following Rewetting of Dry Soils Across Seasonally Dry sub‐Saharan Africa
Jonathan E. Hickman, Bocary Kaya, Abhraham Kebede, Serigne Kandji, Laura Fitch, Christopher Neill, Gerson Nyadzi, Willy Diru, Cheryl Palm
Abstract
Abstract In seasonally dry ecosystems, which are common in sub‐Saharan Africa, precipitation after dry periods can cause large pulses of nitrous oxide (N 2 O), a greenhouse gas, and of nitric oxide (NO), a precursor to tropospheric ozone pollution. Agricultural practices can change soil characteristics, affecting trace N gas emissions. To evaluate the effects of land use on trace gas pulses at the start of the rainy season, we conducted laboratory measurements of N 2 O and NO fluxes from soils collected from four pairs of agricultural and natural savannah sites across the Sudano‐Sahelian zone. We also conducted in situ wetting experiments, measuring NO fluxes from fallow sandy soils in Tanzania and NO and N 2 O fluxes from clayey soils in Kenya with different histories of fertilizer use. In incubation studies, NO increased by a factor of 7 to 25 following wetting, and N 2 O fluxes shifted from negative to positive; cumulative NO fluxes were an order of magnitude larger than cumulative N 2 O fluxes. In Kenya and Tanzania, NO increased by 1 to 2 orders of magnitude after wetting, and N 2 O increased by a factor of roughly 5 to 10. Cumulative NO fluxes ranged from 87 to 115 g NO‐N ha −1 across both countries—a substantial proportion of annual emissions—compared to roughly 1 g N 2 O‐N in Kenya. There were no effects of land use or fertilization history on the magnitude of NO or N 2 O pulses, though land use may have been confounded with differences in soil texture potentially limiting the ability to detect land use effects.