Bateganya et al. 2015. Carbon and nitrogen gaseous fluxes from subsurface flow wetland buffer strips at mesocosm scale in East Africa.

Bateganya, N.L., Mentler, A., Langergraber, G., Busulwa, H. and Hein, T., 2015. Carbon and nitrogen gaseous fluxes from subsurface flow wetland buffer strips at mesocosm scale in East Africa. Ecological Engineering, 85: 173-184.

Abstract

This study investigated carbon (CH₄, CO₂) and nitrogen (N₂O) gaseous fluxes as finger prints for microbial wastewater treatment processes in vertical (VF) and horizontal (HF) subsurface flow mesocosms, planted with Cyperus papyrus and operated under batch hydraulic loading. The closed chamber method was used to measure gaseous emissions for 12 weeks (April–June 2014) in Kampala, Uganda. Organic matter (OM) (BOD₅ and COD) and inorganic nitrogen (NH₄⁺ and NO₃⁻) nutrient concentrations were monitored to estimate OM degradation rates and potential nitrification and denitrification. The highest mean CH₄ flux (mg CH₄C m⁻² h⁻¹) was 38.3 ± 3.3 in unplanted HF compared to the lowest (3.3 ± 0.4) established in planted VF mesocosms. CO₂ fluxes (mg CO₂C m⁻² h⁻¹) were significantly higher (P < 0.05) in planted mesocosms, with no significant difference (P > 0.05) between the planted HF (2213.5 ± 122.4) and VF (2272.8 ± 191.0) mesocosms. The high CO₂ flux was attributed to efficient degradation of the inflow organic carbon facilitated by sufficient oxygen supply especially in the planted mesocosms. Although N₂O flux was relatively higher in HF mesocosms, it did not vary significantly (P > 0.05) in all treatments. Generally the results indicated significant nitrification, especially in the planted mesocosms. However, high fluxes of N₂O comparable to other denitrifying CWs suggested potential for coupled nitrification and denitrification in these systems. Overall, compared to CH₄ and N₂O, CO₂ was found to be the most significant gaseous flux under induced aerobic conditions enhanced by use of C. papyrus plants and an intermittent loading regime.

Pelster et al. 2015. Smallholder African farms in western Kenya have limited greenhouse gas fluxes

Pelster, D.E., Rufino, M.C., Rosenstock, T., Mango, J., Saiz, G., Diaz-Pines, E., Baldi, G., Butterbach-Bahl, K., 2015. Smallholder African farms in western Kenya have limited greenhouse gas fluxes. Biogeosciences Discuss. 12, 15301-15336.

Abstract
Few field studies examine greenhouse gas (GHG) emissions from African agricultural systems resulting in high uncertainty for national inventories. We provide here the most comprehensive study in Africa to date, examining annual CO₂, CH₄ and N₂O emissions from 59 plots, across different vegetation types, field types and land classes in western Kenya. The study area consists of a lowland area (approximately 1200 m a.s.l.) rising approximately 600 m to a highland plateau. Cumulative annual fluxes ranged from 2.8 to 15.0 Mg CO₂-C ha⁻¹, −6.0 to 2.4 kg CH₄-C ha⁻¹ and −0.1 to 1.8 kg N₂O-N ha⁻¹. Management intensity of the plots did not result in differences in annual fluxes for the GHGs measured (P = 0.46, 0.67 and 0.14 for CO₂, N₂O and CH₄ respectively). The similar emissions were likely related to low fertilizer input rates (≤ 20 kg ha⁻¹). Grazing plots had the highest CO₂ fluxes (P = 0.005); treed plots were a larger CH₄ sink than grazing plots (P = 0.05); while N₂O emissions were similar across vegetation types (P = 0.59). This case study is likely representative for low fertilizer input, smallholder systems across sub-Saharan Africa, providing critical data for estimating regional or continental GHG inventories. Low crop yields, likely due to low inputs, resulted in high (up to 67 g N₂O-N kg⁻¹ aboveground N uptake) yield-scaled emissions. Improving crop production through intensification of agricultural production (i.e. water and nutrient management) may be an important tool to mitigate the impact of African agriculture on climate change.

Borges et al. 2015. Globally significant greenhouse-gas emissions from African inland waters

Borges A V, Darchambeau F, Teodoru C R, Marwick T R, Tamooh F, Geeraert N, Omengo F O, Guerin F, Lambert T, Morana C, Okuku E and Bouillon S 2015 Globally significant greenhouse-gas emissions from African inland waters. Nature Geosci doi:10.1038/ngeo2486.

Abstract

Carbon dioxide emissions to the atmosphere from inland waters—streams, rivers, lakes and reservoirs—are nearly equivalent to ocean and land sinks globally. Inland waters can be an important source of methane and nitrous oxide emissions as well, but emissions are poorly quantified, especially in Africa. Here we report dissolved carbon dioxide, methane and nitrous oxide concentrations from 12 rivers in sub-Saharan Africa, including seasonally resolved sampling at 39 sites, acquired between 2006 and 2014. Fluxes were calculated from published gas transfer velocities, and upscaled to the area of all sub-Saharan African rivers using available spatial data sets. Carbon dioxide-equivalent emissions from river channels alone were about 0.4 Pg carbon per year, equivalent to two-thirds of the overall net carbon land sink previously reported for Africa. Including emissions from wetlands of the Congo river increases the total carbon dioxide-equivalent greenhouse-gas emissions to about 0.9 Pg carbon per year, equivalent to about one quarter of the global ocean and terrestrial combined carbon sink. Riverine carbon dioxide and methane emissions increase with wetland extent and upland biomass. We therefore suggest that future changes in wetland and upland cover could strongly affect greenhouse-gas emissions from African inland waters.

Kimaro et al. 2015. Is conservation agriculture ‘climate-smart’for maize farmers in the highlands of Tanzania?

Kimaro, A. A., Mpanda, M., Rioux, J., Aynekulu, E., Shaba, S., Thiong’o, M., ... & Rosenstock, T. S. (2015). Is conservation agriculture ‘climate-smart’for maize farmers in the highlands of Tanzania?. Nutrient Cycling in Agroecosystems, 1-12.

 

Abstract

Conservation agriculture (CA) is promoted extensively to increase the productivity and environmental sustainability of maize production systems across sub-Saharan Africa and is often listed as a climate-smart agriculture (CSA) practice. However, the impacts of CA on food security, resilience/adaptive capacity and climate change mitigation are location-dependent and it is unknown whether CA can simultaneously address CSA’s multiple objectives. Here we evaluate four variations of CA: reduced tillage plus mulch (mulch), reduced tillage plus mulch and leguminous cover crop (Lablab), reduced tillage plus mulch and leguminous trees (CAWT), and reduced tillage plus mulch and nitrogen fertilizer (CA + F)—for their effect on CSA-relevant outcomes in highland Tanzania maize production. By comparison to conventional practice in the region, intensification of maize production by Lablab, CAWT, and CA + F significantly increases yields by 40, 89 and 77 %, respectively. Likewise, rainfall use efficiency was highest in these three treatments and significantly greater than conventional practices in 7 of 12 comparisons. Seasonal and annual greenhouse gas fluxes were similar across all treatments; however, yield-scaled global warming potential (Mg CO₂ eq Mg grain⁻¹) was lower in CAWT (2.1–3.1) and CA + F (1.9–2.3) than conventional practice (1.9–8.3), averaging 62 and 68 % of the emission intensity of conventional practice, respectively. The findings demonstrate that CA can deliver benefits consistent with the objectives of CSA for farmers in this region, particularly when soil nitrogen limitation is alleviated, providing other constraints to adoption are removed.

http://link.springer.com/article/10.1007/s10705-015-9711-8

 

Goenster et al. 2015. Gaseous emissions and soil fertility of homegardens in the Nuba Mountains, Sudan

Goenster, S., Wiehle, M., Predotova, M., Gebauer, J., Ali, A. M., and Buerkert, A.: Gaseous emissions and soil fertility of homegardens in the nuba mountains, sudan, J. Plant Nutr. Soil Sci., 178, 413-424, 10.1002/jpln.201400292, 2015.

 Abstract

Intensification of homegardens in the Nuba Mountains may lead to increases in C and nutrient losses from these small-scale land-use systems and potentially threaten their sustainability. This study, therefore, aimed at determining gaseous C and N fluxes from homegarden soils of different soil moisture, temperature, and C and N status. Emissions of CO₂, NH₃, and N₂O from soils of two traditional and two intensified homegardens and an uncultivated control were recorded bi-weekly during the rainy season in 2010. Flux rates were determined with a portable dynamic closed chamber system consisting of a photo-acoustic multi-gas field monitor connected to a PTFE coated chamber. Topsoil moisture and temperature were recorded simultaneously to the gas measurements. Across all homegardens emissions averaged 4,527 kg CO₂-C ha⁻¹, 22 kg NH₃-N ha⁻¹, and 11 kg N₂O-N ha⁻¹ for the observation period from June to December. Flux rates were largely positively correlated with soil moisture and predominantly negatively with soil temperature. Significant positive, but weak (r_s < 0.34) correlations between increasing management intensity and emissions were noted for CO₂-C. Similarly, morning emissions of NH₃ and increasing management intensity were weakly correlated (r_s  = 0.17). The relatively high gaseous C and N losses in the studied homegardens call for effective management practices to secure the soil organic C status of these traditional land-use systems.

Hickman et al. 2015. A potential tipping point in tropical agriculture: Avoiding rapid increases in nitrous oxide fluxes from agricultural intensification in kenya

Hickman, J. E., Tully, K. L., Groffman, P. M., Diru, W., and Palm, C. A. C. J. G.: A potential tipping point in tropical agriculture: Avoiding rapid increases in nitrous oxide fluxes from agricultural intensification in Kenya, Journal of Geophysical Research: Biogeosciences, doi: 10.1002/2015jg002913, 10.1002/2015jg002913, 2015.

Abstract

There are national and regional efforts aimed at increasing fertilizer use in sub-Saharan Africa, where nitrogen (N) inputs must be increased by an order of magnitude or more to reach recommended rates. Fertilizer inputs increase N availability and cycling rates and subsequently emissions of nitrous oxide (N₂O), a powerful greenhouse gas and the primary catalyst of stratospheric ozone depletion. We established experimental maize (Zea mays L.) plots in western Kenya to quantify the relationship between N inputs and N₂O emissions. Mean N₂O emissions were marginally, but not significantly, better described by an exponential model relating emissions to N input rate in 2011; in 2012, an exponential relationship provided the best fit compared to linear and other nonlinear models. Most N₂O fluxes occurred during the 30 days following the second fertilizer application. Estimates of fertilizer N lost as N₂O annually were well below the 1% Intergovernmental Panel on Climate Change default emission factor, ranging from 0.07% to 0.11% in 2011 and from 0.01% to 0.09% in 2012. In both years, the largest impact on annual N₂O emissions occurred when inputs increased from 100 to 150 kg N ha⁻¹: fluxes increased from 203 to 294 g N₂O-N ha⁻¹ yr⁻¹ in 2011 and from 168 to 254 kg N ha⁻¹ in 2012. Our results suggest that exponential emission responses are present in tropical systems and that agricultural intensification in western Kenya may be managed for increasing crop yields without immediate large increases in N₂O emissions if application rates remain at or below 100 kg N ha⁻¹.

Sommer et al. 2015. Nitrogen dynamics and nitrous oxide emissions in a long-term trial on integrated soil fertility management in western Kenya

Sommer, R., Mukalama, J., Kihara, J., Koala, S., Winowiecki, L., and Bossio, D.: Nitrogen dynamics and nitrous oxide emissions in a long-term trial on integrated soil fertility management in western kenya, Nutrient Cycling in Agroecosystems, 10.1007/s10705-015-9693-6, 2015.

Abstract

Integrated soil fertility management (ISFM) is a concept that includes the management of organic matter in smallholder farming systems for sustainable intensification. To determine whether ISFM is also eco-efficient, we measured and simulated nitrogen (N)-dynamics and nitrous oxide (N₂O) emissions in an ISFM long-term maize trial in Western Kenya. The total annual N-balance averaged over 10.5 years was negative for all continuous maize treatments that received only inorganic N-fertilizer. The N-balance was zero or positive when maize was grown in rotation with the green manure cover crop, Tephrosia candid, and/or to which 4 Mg ha⁻¹ season⁻¹ farm yard manure (FYM) added. These results thus substantiate the importance of organic matter management in tropical ecosystems. They also underpin that mineral N-fertilizer application alone does not guarantee agro-ecosystem sustainability, which should be considered in fertilizer (subsidy) policies. Treatments that included Tephrosia and FYM application emitted the largest amounts of N₂O. Highest emissions (12.0 kg N₂O–N ha⁻¹) were simulated for the maize–Tephrosia rotation to which FYM and 30 kg ha⁻¹ of mineral fertilizer N was added and 2 Mg ha⁻¹ maize stovers retained. Such treatments had the highest N-emission intensity. The slope of the linear regression equation describing the N₂O emission–N-input relationship of all considered treatments (0.023) was twice as high as the IPCC-Tier-1 emission factor. Maize–Tephrosia treatments had the highest seasonal maize yields. These were, however, not high enough to compensate for the inclusion of Tephrosia into the system as compared to growing maize continuously, compromising adoption by smallholder farmers.