Abstract
Natural vegetation represents an important sink for greenhouse
gases (GHGs); however, there is relatively little information available
on emissions from southern African savannas. The effects of clearing
savanna woodlands for crop production on soil fluxes of N2O, CO2 and CH4
were studied on clay (Chromic luvisol) and loamy sand (Ferric acrisol)
soils in Zimbabwe. Maize (Zea mays L.) was the test crop. Gas samples
were measured from undisturbed, cleared and cultivated woodlands using
the static chamber methodology involving gas chromatography for ample
air analysis. Site and climatic variables were particularly important
determinants of GHG emissions. Over an average of 154 days emissions of
0.8 – 2.5 kg N2O-N ha-1, 1146 – 2847 kg CO2-C ha-1 and 7.4 – 38.5 kg
CH4-C ha-1 were estimated during a season that followed a relatively
drier one. Fertiliser-N significantly increased GHG emissions on cropped
plots (clay soil). The undisturbed woodland with a relatively higher
tree density (loamy sand) was an important GHG source. The high CH4
fluxes from woodlands provide ground based validation of satellite
observations of CH4 hotspots in sub-Saharan Africa, and have
considerable implications on regional GHG balance.
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