Greenhouse gas emissions from natural ecosystems and agricultural lands in sub-Saharan Africa: synthesis of available data and suggestions for further research

Abstract

This paper summarizes currently available data on greenhouse gas (GHG) emissions from African natural ecosystems and agricultural lands. The available data are used to synthesize current understanding of the drivers of change in GHG emissions, outline the knowledge gaps, and suggest future directions and strategies for GHG emission research. GHG emission data were collected from 75 studies conducted in 22 countries (n = 244) in sub-Saharan Africa (SSA). Carbon dioxide (CO 2 ) emissions were by far the largest contributor to GHG emissions and global warming potential (GWP) in SSA natural terrestrial systems. CO 2 emissions ranged from 3.3 to 57.0 Mg CO 2 ha −1 yr −1 , methane (CH 4 ) emissions ranged from −4.8 to 3.5 kg ha −1 yr −1 (−0.16 to 0.12 Mg CO 2 equivalent (eq.) ha −1 yr −1 ), and nitrous oxide (N 2 O) emissions ranged from −0.1 to 13.7 kg ha −1 yr −1 (−0.03 to 4.1 Mg CO 2 eq. ha −1 yr −1 ). Soil physical and chemical properties, rewetting, vegetation type, forest management, and land-use changes were all found to be important factors affecting soil GHG emissions from natural terrestrial systems. In aquatic systems, CO 2 was the largest contributor to total GHG emissions, ranging from 5.7 to 232.0 Mg CO 2 ha −1 yr −1 , followed by −26.3 to 2741.9 kg CH 4 ha −1 yr −1 (−0.89 to 93.2 Mg CO 2 eq. ha −1 yr −1 ) and 0.2 to 3.5 kg N 2 O ha −1 yr −1 (0.06 to 1.0 Mg CO 2 eq. ha −1 yr −1 ). Rates of all GHG emissions from aquatic systems were affected by type, location, hydrological characteristics, and water quality. In croplands, soil GHG emissions were also dominated by CO 2 , ranging from 1.7 to 141.2 Mg CO 2 ha −1 yr −1 , with −1.3 to 66.7 kg CH 4 ha −1 yr −1 (−0.04 to 2.3 Mg CO 2 eq. ha −1 yr −1 ) and 0.05 to 112.0 kg N 2 O ha −1 yr −1 (0.015 to 33.4 Mg CO 2 eq. ha −1 yr −1 ). N 2 O emission factors (EFs) ranged from 0.01 to 4.1 %. Incorporation of crop residues or manure with inorganic fertilizers invariably resulted in significant changes in GHG emissions, but results were inconsistent as the magnitude and direction of changes were differed by gas. Soil GHG emissions from vegetable gardens ranged from 73.3 to 132.0 Mg CO 2 ha −1 yr −1 and 53.4 to 177.6 kg N 2 O ha −1 yr −1 (15.9 to 52.9 Mg CO 2 eq. ha −1 yr −1 ) and N 2 O EFs ranged from 3 to 4 %. Soil CO 2 and N 2 O emissions from agroforestry were 38.6 Mg CO 2 ha −1 yr −1 and 0.2 to 26.7 kg N 2 O ha −1 yr −1 (0.06 to 8.0 Mg CO 2 eq. ha −1 yr −1 ), respectively. Improving fallow with nitrogen (N)-fixing trees led to increased CO 2 and N 2 O emissions compared to conventional croplands. The type and quality of plant residue in the fallow is an important control on how CO 2 and N 2 O emissions are affected. Throughout agricultural lands, N 2 O emissions slowly increased with N inputs below 150 kg N ha −1 yr −1 and increased exponentially with N application rates up to 300 kg N ha −1 yr −1 . The lowest yield-scaled N 2 O emissions were reported with N application rates ranging between 100 and 150 kg N ha −1 . Overall, total CO 2 eq. emissions Published by Cop...

Impacts of climate and land use on N2O and CH4 fluxes from tropical ecosystems in the Mt. Kilimanjaro region, Tanzania

“…Kim, Thomas, et al. () show that the in situ, mean annual N 2 O emissions from an extensively managed homegarden (0.35 kg N ha −1 year −1 ) were much lower than those for tropical agroforestry systems (7.7 ± 3.3 kg N ha −1 year −1 ). However, most of the data used in this review are from more intensive monoculture systems with higher N fertilizer loads and less tree cover.…”

“…An increase in nitrogen fertilizer use is expected to double agricultural N 2 O emissions in Africa by 2050. There are currently no estimates of future CH 4 emission for Africa for this same time period (Kim, Thomas, et al., ).…”

The influence of trees, shrubs, and grasses on microclimate, soil carbon, nitrogen, and CO2 efflux: Potential implications of shrub encroachment for Kalahari rangelands

“…There are complex temporal variations in soil moisture profiles, associated with rainfall, infiltration, and evaporative pressure (Figure ), all of which will be affected by vegetation. Across the continent, land use changes, particularly conversion of natural land to agriculture and agricultural intensification, have been identified as accelerating CO 2 efflux from African soils (Kim et al, ). Our results demonstrate that shrub encroachment is another driver that will lead to significantly greater CO 2 efflux from dryland sand soils.…”

Land Use, Land Use History, and Soil Type Affect Soil Greenhouse Gas Fluxes From Agricultural Landscapes of the East African Highlands

“…In East Africa, quantification of GHG fluxes from smallholder agriculture is limited and the little information that is available covers few agricultural land uses and activities (Kim et al, ). Quantification of GHG fluxes is constrained by the fact that smallholder systems in East Africa are diverse across climates and soils.…”