We have created this Blog and the database to provide a place where the scientific community can share and update the fast growing knowledge and data on the study of greenhouse gas CO2, CH4, and N2O fluxes in Africa.

We are grateful for the numerous researchers and technicians who provide invaluable data. It is impossible to cite all the references due to limited space allowed and we apologize for the authors whose work has not been cited.

Gharahi Ghehi et al 2011. Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda

Gharahi Ghehi, N., Werner, C., Cizungu Ntaboba, L., Mbonigaba Muhinda, J.J., Van Ranst, E., Butterbach-Bahl, K., Kiese, R., Boeckx, P., 2011. Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda. Biogeosciences Discuss. 8, 11631-11660. doi:10.5194/bgd-8-11631-2011, 2011

Globally, tropical forest soils represent the second largest source of N2O and NO. However, there is still considerable uncertainty on the spatial variability and soil properties controlling N trace gas emission. To investigate how soil properties affect N2O and NO emission, we carried out an incubation experiment with soils from 31 locations in the Nyungwe tropical mountain forest in southwestern Rwanda. All soils were incubated at three different moisture levels (50, 70 and 90% water filled pore space (WFPS)) at 17 °C. Nitrous oxide emission varied between 4.5 and 400 μg N m−2 h−1, while NO emission varied from 6.6 to 265 μg N m−2 h−1. Mean N2O emission at different moisture levels was 46.5 ± 11.1 (50% WFPS), 71.7 ± 11.5 (70% WFPS) and 98.8 ± 16.4 (90% WFPS) μg N m−2 h−1, while mean NO emission was 69.3 ± 9.3 (50% WFPS), 47.1 ± 5.8 (70% WFPS) and 36.1 ± 4.2 (90% WFPS) μg N m−2 h−1. The latter suggests that climate (i.e. dry vs. wet season) controls N2O and NO emissions. Positive correlations with soil carbon and nitrogen indicate a biological control over N2O and NO production. But interestingly N2O and NO emissions also showed a negative correlation (only N2O) with soil pH and a positive correlation with free iron. The latter suggest that chemo-denitrification might, at least for N2O, be an important production pathway. In conclusion improved understanding and process based modeling of N trace gas emission from tropical forests will not only benefit from better spatial explicit trace gas emission and basic soil property monitoring, but also by differentiating between biological and chemical pathways for N trace gas formation.

Frimpong et al. 2011. Does incorporation of cowpea-maize residue mixes influence nitrous oxide emission and mineral nitrogen release in a tropical luvisol?

Frimpong, K., Yawson, D., Baggs, E., Agyarko, K., 2011. Does incorporation of cowpea-maize residue mixes influence nitrous oxide emission and mineral nitrogen release in a tropical luvisol? Nutrient Cycling in Agroecosystems 91, 281-292

In the face of climate change, quantification of the emission of nitrous oxide from soils in relation to sufficient N availability for crop uptake has assumed much significance. This study used the 15N stable isotope technique, under controlled laboratory conditions, to quantify the interactive effect on and relative contributions of the component species to N2O emission and mineral N dynamics in a tropical luvisol incorporated with different rates of cowpea-maize residue mixtures. The results show that increasing the maize residue proportion in the mixture significantly decreases N2O emission compared to the sole cowpea incorporation but increases mineral N concentration compared to sole maize residue incorporation. It is concluded that mixing low C:N ratio cowpea residue with high C:N ratio maize residue has potential for N management in tropical legume-cereal intercropping systems with the view to minimizing N2O emission while making N available for crop uptake. 
Keywords  Nitrous oxide emission – Mineral N – Cowpea-maize residue –  15N stable isotope

Hickman et al. 2010. Impacts of Increasing Chemical Fertilizer Use On Nitrous Oxide Emissions From a Smallholder Agricultural System in Western Kenya.

Impacts of Increasing Chemical Fertilizer Use On Nitrous Oxide Emissions From a Smallholder Agricultural System in Western Kenya.

Jonathan Hickman, Tropical Agriculture Program, The Earth Institute at Columbia University, Palisades, NY, Cheryl Palm, Tropical Agriculture and Rural Environment Program, Earth Institute, Columbia University, Palisades, NY, Jianwu (Jim) Tang, The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA and Jerry Melillo, Marine Biological Laboratory, The Ecosystems Center, Woods Hole, MA

SSSA 2010 International annual meetings, Oct. 31 - Nov. 4, Long Beach, CA, USA


Impacts of increasing chemical fertilizer use on N2O emissions from a smallholder agricultural system in western Kenya. Over the last several decades, agricultural soils in many parts of sub-Saharan Africa have become depleted of nitrogen (N) and other nutrients, creating challenges to achieving food security in many countries. At only 8 kg N/ha/yr, average fertilizer application rates in the region are an order of magnitude lower than typical rates in the United States, and well below optimal levels. Increased use of nutrient inputs is a centerpiece of most African Green Revolution strategies, making it important to quantify the impacts of this change in practices. Increased N inputs are invariably accompanied by losses of N to the atmosphere as nitrogen oxides, including the greenhouse gas nitrous oxide (N2O). Several investigations of greenhouse gas emissions from sub-Saharan agricultural systems have been conducted over the last 20 years, but they typically include only two levels of fertilizer additions, and so are unable to identify potentially important thresholds in the response of trace gas emissions to fertilization rate. Here we examine the response function of N2O emissions to 5 different levels of inorganic fertilizer additions in a maize field in Maseno, Kenya during the 2010 long rainy season. We used an RCB design incorporating 5 levels of inorganic fertilizer additions (0, 50, 75, 100, and 200 kg/ha). We measured trace gas fluxes daily for one week starting the day before fertilizer application, followed by weekly measurements until trace gas emissions subsided to control levels. In order to identify thresholds in the N2O response, we use a stepwise backwards regression to identify departures from linearity in the mean chamber flux relative to the level of N fertilizer applied. Preliminary data suggest that N2O emissions may be slow to increase with increasing fertilizer additions, though important threshold effects may emerge. The identification of emission response thresholds combined with information to be collected on crop yield responses can provide insight into how to manage fertilizer use to optimize crop production per unit greenhouse gas emitted.

Source: http://a-c-s.confex.com/crops/2010am/webprogram/Paper61989.html

Palm et al. 2010. Identifying potential synergies and trade-offs for meeting food security and climate change objectives in sub-Saharan Africa

Palm, C.A., Smukler, S.M., Sullivan, C.C., Mutuo, P.K., Nyadzi, G.I., Walsh, M.G., 2010. Identifying potential synergies and trade-offs for meeting food security and climate change objectives in sub-Saharan Africa. Proceedings of the National Academy of Sciences 107, 19661–19666.


Potential interactions between food production and climate mitigation are explored for two situations in sub-Saharan Africa, where deforestation and land degradation overlap with hunger and poverty. Three agriculture intensification scenarios for supplying nitrogen to increase crop production (mineral fertilizer, herbaceous legume cover crops—green manures—and agroforestry—legume improved tree fallows) are compared to baseline food production, land requirements to meet basic caloric requirements, and greenhouse gas emissions. At low population densities and high land availability, food security and climate mitigation goals are met with all intensification scenarios, resulting in surplus crop area for reforestation. In contrast, for high population density and small farm sizes, attaining food security and reducing greenhouse gas emissions require mineral fertilizers to make land available for reforestation; green manure or improved tree fallows do not provide sufficient increases in yields to permit reforestation. Tree fallows sequester significant carbon on cropland, but green manures result in net carbon dioxide equivalent emissions because of nitrogen additions. Although these results are encouraging, agricultural intensification in sub-Saharan Africa with mineral fertilizers, green manures, or improved tree fallows will remain low without policies that address access, costs, and lack of incentives. Carbon financing for small-holder agriculture could increase the likelihood of success of Reducing Emissions from Deforestation and Forest Degradation in Developing Countries programs and climate change mitigation but also promote food security in the region.

Hickman et al. 2011. Current and future nitrous oxide emissions from African agriculture

Hickman, J.E., Havlikova, M., Kroeze, C., Palm, C.A., 2011. Current and future nitrous oxide emissions from African agriculture. Current Opinion in Environmental Sustainability 3, 370-378.


Most emission estimates of the greenhouse gas nitrous oxide (N2O) from African agriculture at a continental scale are based on emission factors, such as those developed by the IPCC Guidelines. Here we present estimates from Africa from the EDGAR database, which is derived from the IPCC emission factors. Resulting estimates indicate that N2O emissions from agriculture represented 42% of total emissions from Africa (though that rises to 71% if all savannah and grassland burning is included), or roughly 6% of global anthropogenic N2O emissions (or 11% including burning). Emissions from African agriculture are dominated by grazing livestock; 74% of agricultural N2O excluding biomass burning was from paddocks, ranges, and pasture. Direct soil emissions represent 15% of agricultural emissions; substantial changes in direct emissions from North Africa helped drive a 47% continental increase in direct soil emissions from 1970 to 2005. Future trends based on the Millennium Ecosystem Assessment scenarios indicate that agricultural N2O emissions may double in Africa by 2050 from 2000 levels. Any regional or continental estimates for Africa are, however, necessarily limited by a paucity of direct measurements of emissions in sub-Saharan agro-ecosystems, and the heavy reliance on emission factors and other default assumptions about nitrogen cycling in African agriculture. In particular, a better understanding of livestock-related N inputs and N2O emissions will help improve regional and continental estimates. As fertilizer use increases in sub-Saharan Africa, emission estimates should consider several unusual elements of African agriculture: farmer practices that differ fundamentally from that of large scale farms, the long history of N depletion from agricultural soils, seasonal emission pulses, and emission factors that vary with the amount of N added.

Yohannes et al. 2011. Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species

Yohannes, Y., Shibistova, O., Abate, A., Fetene, M., Guggenberger, G., 2011. Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species. Forest Ecology and Management 261, 1090-1098.

Variability of soil CO2 efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO2 efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO2 flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO2 efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO2 efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration.