A cross-ecosystem assessment of the effects of land cover and land use on soil emission of selected greenhouse gases and related soil properties in Zimbabwe

Land used for agricultural production can contribute significantly to greenhouse gas (GHG) emissions; however, there is very little information on the role of management and land use change in influencing these emissions in Africa. Thus, exploring GHG emissions that occur at the soil-atmosphere interface is an essential part of the effort to integrate land management strategies with climate change mitigation and adaptation in southern Africa. We measured soil emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from rain-fed perennial tropical grassland, wastewater-irrigated perennial tropical pastureland, recently cleared woodland, miombo woodland, a Eucalyptus plantation, regular cropland and recently cleared-and-cropped land, on two contrasting soils at five sites in one cropping season in Zimbabwe. Gas samples were collected using static chambers and analysed by gas chromatography. Considerably high GHG emissions were found on sewage effluent-irrigated pastureland (means, 190 mg CO2-C m−2 hour−1, 102 µg CH4-C m−2 hour−1 and 6 µg N2O-N m−2 hour−1 from sandy soil) and altered woodlands (mean ranges, 38-70 CO2-C m−2 hour−1, 12-43 µg CH4-C m−2 hour−1 and 20-31 µg N2O-N m−2 hour−1 from deforested and cultivated woodland on clay and sandy soils). Relatively low and less variable emissions were found among the rain-fed perennial tropical grasslands, regular croplands and Eucalyptus plantations (mean ranges, 19-39 mg CO2-C m−2 hour−1, −9.4-2.6 µg CH4-C m−2 hour−1 and 1.0-4.7 µg N2O-N m−2 hour−1). Variability in CO2, CH4 and N2O emissions from soils was to the greatest extent influenced by soil temperature, but soil moisture, mineral-N and pH were also important. The increased N2O emissions from cleared woodland on clay soil were attributed to increased mineralization and N availability when no tree could take up that N, while the N mineralized on the sandy soil could have been largely leached due to the soil's poor nutrient holding capacity, resulting in a relatively lower N2O emission response to clearing. We concluded that the alteration of woodlands by deforestation and cultivation increased soil temperature, resulting in increased soil respiration, while the establishment of Eucalyptus plantations may provide an option for reduction in soil emissions of CO2 and N2O and a sink for CH