MacCarthy et al., 2018. Assessment of Greenhouse Gas Emissions from Different Land-Use Systems: A Case Study of CO2 in the Southern Zone of Ghana

Dilys Sefakor MacCarthy, Robert B. Zougmoré, Pierre Bienvenu Irénikatché Akponikpè, Eric Koomson, Patrice Savadogo, and Samuel Godfried Kwasi Adiku, “Assessment of Greenhouse Gas Emissions from Different Land-Use Systems: A Case Study of CO2 in the Southern Zone of Ghana,” Applied and Environmental Soil Science, vol. 2018, Article ID 1057242, 12 pages, 2018. doi:10.1155/2018/1057242

Abstract

The emission of greenhouse gases (GHGs) results in global warming and climate change. The extent to which developing countries contribute to GHG emissions is not well known. This study reports findings on the effects of different land-use systems on GHG emissions (CO2 in this case) from two locations in the southern zone of Ghana, West Africa. Site one (located at Kpong) contained a heavy clay soil while site two (located at Legon) contained a light-textured sandy soil. Land-use systems include cattle kraals, natural forests, cultivated maize fields, and rice paddy fields at site one, and natural forest, woodlots, and cultivated soya bean fields at site two. CO2 emissions were measured using the gas entrapment method (PVC chambers). Trapping solutions were changed every 12–48 h and measurement lasted 9 to 15 days depending on the site. We found that, for the same land-use, CO2 emissions were higher on the clay soil (Kpong) than the sandy soil (Legon). In the clay soil environment, the highest average CO2 emission was observed from the cattle kraal (256.7 mg·m−2·h−1), followed by the forest (146.0 mg·m−2·h−1) and rice paddy (140.6 mg·m−2·h−1) field. The lowest average emission was observed for maize cropped land (112.0 mg·m−2·h−1). In the sandy soil environment, the highest average CO2 emission was observed from soya cropped land (52.5 mg·m−2·h−1), followed by the forest (47.4 mg·m−2·h−1) and woodlot (33.7 mg·m−2·h−1). Several factors influenced CO2 emissions from the different land-use systems. These include the inherent properties of the soils such as texture, temperature, and moisture content, which influenced CO2 production through their effect on soil microbial activity and root respiration. Practices that reduce CO2 emissions are likely to promote carbon sequestration, which will consequently maintain or increase crop productivity and thereby improve global or regional food security.

Ngwabie et al., 2018. Quantifying greenhouse gas emissions from municipal solid waste dumpsites in Cameroon

Ngwabie, N.M., Wirlen, Y.L., Yinda, G.S., VanderZaag, A.C., 2018. Quantifying greenhouse gas emissions from municipal solid waste dumpsites in Cameroon. Waste Management. https://doi.org/10.1016/j.wasman.2018.02.048

Abstract

Open dumpsites that receive municipal solid waste are potentially significant sources of greenhouse gas (GHG) emissions into the atmosphere. There is little data available on emissions from these sources, especially in the unique climate and management of central Africa. This research aimed at quantifying CH4, N2O and CO2 emissions from two open dumpsites in Cameroon, located in Mussaka-Buea, regional headquarters of the South West Region and in Mbellewa-Bamenda, regional headquarters of the North West Region. Emissions were measured during the wet season (May 2015 and August 2016) at the Mussaka and Mbellewa dumpsites respectively. Dumpsite surfaces were partitioned into several zones for emission measurements, based on the current activity and the age of the waste. Static flux chambers were used to quantify gas emission rates thrice a day (mornings, afternoons and evenings). Average emissions were 96.80 ± 144 mg CH4 m−2 min−1, 0.20 ± 0.43 mg N2O m−2 min−1and 224.78 ± 312 mg CO2 m−2 min−1 in the Mussaka dumpsite, and 213.44 ± 419 mg CH4 m−2 min−1, 0.15 ± 0.15 mg N2O m−2 min−1 and 1103.82 ± 1194 mg CO2 m−2 min−1 at the Mbellewa dumpsite. Emissions as high as 1784 mg CH4 m−2 min−1, 2.3 mg N2O m−2 min−1 and 5448 mg CO2m−2 min−1 were measured from both dumpsites. Huge variations observed in emissions between the different zones on the waste surface were likely a result of the heterogeneous nature of the waste, different stages in waste decomposition and different environmental conditions within the waste. Management activities that disturb waste, such as spreading and compressing potentially increase gas emissions, while covering waste with a layer of soil potentially mitigate gas emissions. Recommendations were for dumpsites to be upgraded to sanitary landfills, and biogas production from such landfills should be exploited to reduce CH4 emissions.

Gütlein et al., 2018. Impacts of climate and land use on N2O and CH4 fluxes from tropical ecosystems in the Mt. Kilimanjaro region, Tanzania

Gütlein, A., Gerschlauer, F., Kikoti, I., Kiese, R., 2018. Impacts of climate and land use on N2O and CH4 fluxes from tropical ecosystems in the Mt. Kilimanjaro region, Tanzania. Global Change Biology 24, 1239-1255.

Abstract

In this study, we quantify the impacts of climate and land use on soil N2O and CH4 fluxes from tropical forest, agroforest, arable and savanna ecosystems in Africa. To do so, we measured greenhouse gases (GHG) fluxes from 12 different ecosystems along climate and land‐use gradients at Mt. Kilimanjaro, combining long‐term in situ chamber and laboratory soil core incubation techniques. Both methods showed similar patterns of GHG exchange. Although there were distinct differences from ecosystem to ecosystem, soils generally functioned as net sources and sinks for N2O and CH4 respectively. N2O emissions correlated positively with soil moisture and total soil nitrogen content. CH4 uptake rates correlated negatively with soil moisture and clay content and positively with SOC. Due to moderate soil moisture contents and the dominance of nitrification in soil N turnover, N2O emissions of tropical montane forests were generally low (<1.2 kg N ha−1 year−1), and it is likely that ecosystem N losses are driven instead by nitrate leaching (~10 kg N ha−1 year−1). Forest soils with well‐aerated litter layers were a significant sink for atmospheric CH4 (up to 4 kg C ha−1 year−1) regardless of low mean annual temperatures at higher elevations. Land‐use intensification significantly increased the soil N2O source strength and significantly decreased the soil CH4 sink. Compared to decreases in aboveground and belowground carbon stocks enhanced soil non‐CO2 GHG emissions following land‐use conversion from tropical forests to homegardens and coffee plantations were only a small factor in the total GHG budget. However, due to lower ecosystem carbon stock changes, enhanced N2O emissions significantly contributed to total GHG emissions following conversion of savanna into grassland and particularly maize. Overall, we found that the protection and sustainable management of aboveground and belowground carbon and nitrogen stocks of agroforestry and arable systems is most crucial for mitigating GHG emissions from land‐use change.

Majiwa et al., 2018. Increasing agricultural productivity while reducing greenhouse gas emissions in sub-Saharan Africa: myth or reality?

Majiwa, E., Lee, B.L., Wilson, C., 2018. Increasing agricultural productivity while reducing greenhouse gas emissions in sub-Saharan Africa: myth or reality? Agricultural Economics 49, 183-192.

Abstract

The motivation for this study stems from two major concerns that are interlinked. The first is the decades long food insecurity crisis faced by sub‐Saharan African (SSA) countries which is still prevalent. The second is the negative impact greenhouse gas (GHG) emissions from agriculture may have on future food production and which is likely to worsen the food insecurity problem. The conundrum SSA farmers face is how to increase food output through productivity growth while minimizing GHG emissions. To measure changes in productivity growth and GHG emissions, this study evaluates the agricultural performance of 18 SSA countries by utilizing the Malmquist–Luenberger index to incorporate good and bad outputs for the years 1980–2012. The empirical evidence demonstrates that productivity is overestimated when bad outputs are not considered in the production model. The analysis provides a better understanding of the effectiveness of previous mitigation methods and which informs an appropriate course of action needed to achieve the twin objectives of increasing agriculture productivity while reducing GHG emissions.

Hickman et al., 2017. Nonlinear response of nitric oxide fluxes to fertilizer inputs and the impacts of agricultural intensification on tropospheric ozone pollution in Kenya

Hickman, J.E., Huang, Y., Wu, S., Diru, W., Groffman, P.M., Tully, K.L., Palm, C.A., 2017. Nonlinear response of nitric oxide fluxes to fertilizer inputs and the impacts of agricultural intensification on tropospheric ozone pollution in Kenya. Global Change Biology 23, 3193-3204.

Abstract

Crop yields in sub‐Saharan Africa remain stagnant at 1 ton ha−1, and 260 million people lack access to adequate food resources. Order‐of‐magnitude increases in fertilizer use are seen as a critical step in attaining food security. This increase represents an unprecedented input of nitrogen (N) to African ecosystems and will likely be accompanied by increased soil emissions of nitric oxide (NO). NO is a precursor to tropospheric ozone, an air pollutant and greenhouse gas. Emissions of NO from soils occur primarily during denitrification and nitrification, and N input rates are a key determinant of emission rates. We established experimental maize plots in western Kenya to allow us to quantify the response function relating NO flux to N input rate during the main 2011 and 2012 growing seasons. NO emissions followed a sigmoid response to fertilizer inputs and have emission factors under 1% for the roughly two‐month measurement period in each year, although linear and step relationships could not be excluded in 2011. At fertilization rates above 100 kg N ha−1, NO emissions increased without a concomitant increase in yields. We used the geos‐chem chemical transport model to evaluate local impacts of increased NO emissions on tropospheric ozone concentrations. Mean 4‐hour afternoon tropospheric ozone concentrations in Western Kenya increased by up to roughly 2.63 ppbv under fertilization rates of 150 kg N ha−1or higher. Using AOT40, a metric for assessing crop damage from ozone, we find that the increased ozone concentrations result in an increase in AOT40 exposure of approximately 110 ppbh for inputs of 150 kg N ha−1 during the March–April–May crop growing season, compared with unfertilized simulations, with negligible impacts on crop productivity. Our results suggest that it may be possible to manage Kenyan agricultural systems for high yields while avoiding substantial impacts on air quality.

Ortiz-Gonzalo et al., 2018. Multi-scale measurements show limited soil greenhouse gas emissions in Kenyan smallholder coffee-dairy systems.

Ortiz-Gonzalo, D., de Neergaard, A., Vaast, P., Su찼rez-Villanueva, V., Oelofse, M., Rosenstock, T.S., 2018. Multi-scale measurements show limited soil greenhouse gas emissions in Kenyan smallholder coffee-dairy systems. Science of the Total Environment 626, 328-339.

Abstract

Efforts have been made in recent years to improve knowledge about soil greenhouse gas (GHG) fluxes from sub-Saharan Africa. However, data on soil GHG emissions from smallholder coffee-dairy systems have not hitherto been measured experimentally. This study aimed to quantify soil GHG emissions at different spatial and temporal scales in smallholder coffee-dairy farms in Murang'a County, Central Kenya. GHG measurements were carried out for one year, comprising two cropping seasons, using vented static chambers and gas chromatography. Sixty rectangular frames were installed on two farms comprising the three main cropping systems found in the area: 1) coffee (Coffea arabica L.); 2) Napier grass (Pennisetum purpureum); and 3) maize intercropped with beans (Zea mays and Phaseolus vulgaris). Within these fields, chambers were allocated on fertilised and unfertilised locations to capture spatial variability. Cumulative annual fluxes in coffee plots ranged from 1 to 1.9 kg N2O-N ha− 1, 6.5 to 7.6 Mg CO2-C ha− 1 and − 3.4 to − 2.2 kg CH4 -C ha− 1, with 66% to 94% of annual GHG fluxes occurring during rainy seasons. Across the farm plots, coffee received most of the N inputs and had 56% to 89% higher emissions of N2O than Napier grass, maize and beans. Within farm plots, two to six times higher emissions were found in fertilised hotspots – around the perimeter of coffee trees or within planted maize rows – than in unfertilised locations between trees, rows and planting holes. Background and induced soil N2O emissions from fertiliser and manure applications in the three cropping systems were lower than hypothesized from previous studies and empirical models. This study supplements methods and underlying data for the quantification of GHG emissions at multiple spatial and temporal scales in tropical, smallholder farming systems. Advances towards overcoming the dearth of data will facilitate the understanding of synergies and tradeoffs of climate-smart approaches for low emissions development.

Graphical abstract

Pryor et al., 2017. Impact of agricultural practices on energy use and greenhouse gas emissions for South African sugarcane production.

Pryor, S.W., Smithers, J., Lyne, P., van Antwerpen, R., 2017. Impact of agricultural practices on energy use and greenhouse gas emissions for South African sugarcane production. Journal of Cleaner Production 141, 137-145.

Abstract

The environmental footprint of agricultural production can vary significantly both between countries and within a country based on regional conditions and agricultural practices. A life cycle assessment approach was used to model primary fossil fuel energy inputs and greenhouse gas emissions associated with the production of sugarcane in South Africa. Results were calculated for sugarcane produced in two distinct regions, the irrigated North and the non-irrigated North Coast. Regional differences also include terrain, soil, and use of mechanization. Models were adapted to estimate the impacts of burning prior to harvest, leaving a biomass mulch blanket with green cane harvesting, and increasing the level of mechanization for harvest and other field operations. Irrigation contributes to a higher energy input in the irrigated North but differences are mitigated by the lower fertilizer, agro-chemical, and diesel use per ton of sugarcane produced there. Despite higher energy inputs in the irrigated North, greenhouse gas emissions are similar for sugarcane produced in each region. Green cane harvesting reduces energy inputs and greenhouse gas emissions by 4% and 16%, respectively, in both regions. Impacts of mechanization on soil compaction and stool damage result in lower yields and proportionally higher energy inputs and greenhouse gas emissions. Results demonstrate the potential for variability in LCA results based on regional differences in production practices within a country.

Wanyama et al., 2018. Land Use, Land Use History, and Soil Type Affect Soil Greenhouse Gas Fluxes From Agricultural Landscapes of the East African Highlands

Wanyama, I., Rufino, M.C., Pelster, D.E., Wanyama, G., Atzberger, C., Asten, P., Verchot, L.V., Butterbach?륛ahl, K., 2018. Land Use, Land Use History, and Soil Type Affect Soil Greenhouse Gas Fluxes From Agricultural Landscapes of the East African Highlands. Journal of Geophysical Research: Biogeosciences 123, 976-990.

This study aims to explain effects of soil textural class, topography, land use, and land use history on soil greenhouse gas (GHG) fluxes in the Lake Victoria region. We measured GHG fluxes from intact soil cores collected in Rakai, Uganda, an area characterized by low‐input smallholder (<2 ha) farming systems, typical for the East African highlands. The soil cores were air dried and rewetted to water holding capacities (WHCs) of 30, 55, and 80%. Soil CO2, CH4, and N2O fluxes were measured for 48 h following rewetting. Cumulative N2O fluxes were highest from soils under perennial crops and the lowest from soils under annual crops (P < 0.001 for all WHC). At WHC of 55% or 80%, the sandy clay loam soils had lower N2O fluxes than the clay soils (P < 0.001 and P = 0.041, respectively). Cumulative soil CO2 fluxes were highest from eucalyptus plantations and lowest from annual crops across multiple WHC (P = 0.014 at 30% WHC and P < 0.001 at both 55 and 80% WHC). Methane fluxes were below detectable limits, a shortcoming for using soil cores from the top soil. This study reveals that land use and soil type have strong effects on GHG fluxes from agricultural land in the study area. Field monitoring of fluxes is needed to confirm whether these findings are consistent with what happens in situ.

Ortiz-Gonzalo et al., 2017. Farm-scale greenhouse gas balances, hotspots and uncertainties in smallholder crop-livestock systems in Central Kenya

Ortiz-Gonzalo, D., Vaast, P., Oelofse, M., de Neergaard, A., Albrecht, A., Rosenstock, T.S., 2017. Farm-scale greenhouse gas balances, hotspots and uncertainties in smallholder crop-livestock systems in Central Kenya. Agriculture, Ecosystems & Environment 248, 58-70.

Abstract

Climate-smart approaches have gained momentum in tropical, agricultural development. However, to date, few studies have examined whole-farm greenhouse gas (GHG) balances in smallholder crop-livestock systems. This study aimed to quantify GHG balances at farm-scale, identify GHG hotspots and assess mitigation options in coffee-dairy farms undergoing agricultural intensification in Central Kenya. In recent decades, decreasing farm size has forced the shift from extensive practices to zero-grazing systems and higher nitrogen (N) inputs. We hypothesised that different farm strategies and intensification levels determine the farm’s GHG balance. A farm typology was constructed through principal component analysis (PCA) and hierarchical clustering from 125 farms surveyed. Four farm types were identified ranging relatively from small to large farms, low to high livestock intensities, and low to high N input rates. Whole-farm GHG balances were estimated using an adapted version of the Cool Farm Tool (CFT). Farms were found to be net sources of GHG, averaging from 4.5 t CO2 eq ha−1 yr−1 in less intensive farms to 12.5 t CO2 eq ha−1 yr−1 in high intensive farms. Within the farm GHG hotspots identified, methane (CH4) from enteric fermentation processes accounted for 26–39% of total farm GHG emissions; nitrous oxide (N2O) and CH4 from manure management systems (MMS) for 26–38%; soil background and fertilizer induced N2O emissions for 24–29%; off-farm production of feeds and agrochemicals for 10–22%; and crop residue management (CRM) for the remaining 1–3%. Within the mitigation practices assessed, zero-grazing stalls already lowered the livestock maintenance energy requirements, reducing enteric fermentation emissions. Stall-feeding, however, brings the necessity-opportunity to manage the manure and our results showed that MMS can be a determining factor in the GHG balance. Increasing the frequency of manure collection from stalls in favour of solid storage systems can reduce N2O emissions by up to 75%. Furthermore, dry manure storage reduced the CH4emissions of liquid slurry systems by more than 70%. Further benefits in terms of carbon (C) sequestration were identified along farm types from manure and crop residues applications in soils (with averages of −1.3 to −2.3 t CO2 eq ha−1 yr−1) and biomass growth in agroforestry systems (−1.2 to −2 t CO2 eq ha−1 yr−1). Together, soils and woody biomass offset 25–36% of farm emissions. We conclude that reduced farm size and increased livestock density lead to higher emissions per unit area, though this increase is smoothed by larger negative fluxes in soils (by higher C inputs) and woody biomass (by higher tree densities) until a steady state is reached. Average yield-scaled emissions, or product carbon footprints (CFs), resulted in 1.08 kg CO2 eq kg coffee berry−1, 0.64 kg CO2 eq kg maize−1 and 1.05 kg CO2 eq kg milk−1 on average. CFs did not always differ between farm types and intensification levels, meaning that increases in productivity were not higher than increases in GHG fluxes from intensification. This may be due to: 1) increases in productivity are the result of more processes other than N inputs; and/or 2) emissions from N inputs are overestimated by EFs and GHG calculators. Smallholders may benefit in the near future from climate initiatives and further field characterisation, models calibration and monitoring are required to overcome critical levels of uncertainty and provide more accurate estimations of GHG balances at farm-scale.

Graphical abstract

Farm-scale livelihood activities, greenhouse gas emissions (GHG) and carbon (C) sequestration in integrated smallholder crop-livestock system of Kenya. The numbers (1–5) represent farm components: (1) livestock, (2) manure management systems (MMS), (3) soil, (4) crops and (5) trees. The letters (a–e) are associated with fluxes of C and N: (a) fodder, crop residues and concentrates, (b) dung, urine and bedding materials, (c) inorganic fertiliser, manure and crop residues, (d) nitrogen uptake by crops, (e) the biomass harvested that can follow different pathways: livestock feed, compost heap or mulch.

Six, J., 2017. Greenhouse gas emissions from forest and agroecosystems in Sub-Saharan Africa

Six, J., 2017. Greenhouse gas emissions from forest and agroecosystems in Sub-Saharan Africa. EGU General Assembly Conference Abstracts, vol 19, p. 19401.

The Sub-Saharan African (SSA) landscape is vulnerable to ongoing land use change and climatic variability, which significantly influences carbon and greenhouse gas (GHG) dynamics. However, empirical data on GHG emissions from SSA ecosystems is lacking; hence, limiting our understanding of the potential effects of rapid land use and climate change. Here, I will present information on GHG dynamics in agroecosystems, aquatic ecosystems and forest ecosystems across multiple spatial and temporal scales to elucidate key drivers of GHG emissions from plots to regions.

Kurgat, et al., 2018. Livelihood and climate trade-offs in Kenyan peri-urban vegetable production

Kurgat, B.K., Stöber, S., Mwonga, S., Lotze-Campen, H., Rosenstock, T.S., 2018. Livelihood and climate trade-offs in Kenyan peri-urban vegetable production. Agricultural Systems 160, 79-86.

Abstract

Trade-offs between livelihood and environmental outcomes due to agricultural intensification in sub-Saharan Africa are uncertain. The present study measured yield, economic performance and nitrous oxide (N2O) emissions in African indigenous vegetable (AIV) production to investigate the optimal nutrient management strategies. In order to achieve this, an on-farm experiment with four treatments – (1) 40 kg N/ha diammonium phosphate (DAP), (2) 10 t/ha cattle manure, (3) 20 kg N/ha DAP and 5 t/ha cattle manure and (4) a no-N input control – was performed for two seasons. Yields and N2O emissions were directly measured with subsampling and static chambers/gas chromatography, respectively. Economic outcomes were estimated from semi-structured interviews (N = 12). Trade-offs were quantified by calculating N2O emissions intensity (N2OI) and N2O emissions economic intensity (N2OEI). The results indicate that, DAP alone resulted at least 14% greater yields, gross margin and returns to labour in absolute terms but had the highest emissions (p = 0.003). Productivity-climate trade-offs, expressed as N2OI, were statistically similar for DAP and mixed treatments. However, N2OEI was minimized under mixed management (p = 0.0004) while maintaining productivity and gross margins. We therefore conclude that soil fertility management strategies that mix inorganic and organic source present a pathway to sustainable intensification in AIV production. Future studies of GHG emissions in crop production need to consider not only productivity but economic performance when considering trade-offs.

Abdalla et al. 2016. Long-term annual burning of grassland increases CO2 emissions from soils

Abdalla, K., Chivenge, P., Everson, C., Mathieu, O., Thevenot, M., Chaplot, V., 2016. Long-term annual burning of grassland increases CO2 emissions from soils. Geoderma 282, 80-86.

Abstract

Grasslands have potential to mitigate against climate change because of their large capacity to store soil organic carbon (SOC). However, the long-term impact of grassland management such as burning, which is still common in many areas of the world, on SOC is still a matter of debate. The objective of this study was to quantify the long-term effects of annual burning on CO₂ output from soils and SOC stocks. The study was performed on a 62 years old field trial comparing annual burning (AB) to no burning associated with tree encroachment (NB), and to annual mowing (AM) with all treatments laid out in randomized block design with three replicates per treatment. CO₂ emissions from soil were continuously measured over two years and were correlated to soil chemical and physical properties. AB and AM produced 30 and 34% greater CO₂ emissions from soil than NB (1.80 ± 0.13 vs. 2.34 ± 0.18 and 2.41 ± 0.17 g C-CO₂ m^− 2 d^− 1 for NB, AB and AM respectively). AB and AM also produced greater CO₂ emissions from soil and per gram of soil carbon (1.32 ± 0.1 and 1.35 ± 0.1 mg C-CO₂ g C^− 1 d^− 1, respectively) than NB (1.05 ± 0.07 mg C-CO₂ g C^− 1 d^− 1), which corresponded to significant differences of respectively 26% and 29%. Overall, CO₂ emissions from soil (per m²) significantly increased with soil water content (r = 0.72) followed by SOC stocks (r = 0.59), SOC content (r = 0.50), soil bulk density (r = 0.49), soil temperature (r = 0.47), C:N ratio (r = 0.46) and mean weight diameter (r = 0.38). These findings suggest that long-term annual burning increases CO₂ output from soils. Additional greenhouse gases emissions from burning itself and alternative grassland management techniques were finally discussed.

Chaplot et al. 2015. Surface organic carbon enrichment to explain greater CO2 emissions from short-term no-tilled soils.

Chaplot, V., Abdalla, K., Alexis, M., Bourennane, H., Darboux, F., Dlamini, P., Everson, C., McHunu, C., Muller-Nedebock, D., Mutema, M., Quenea, K., Thenga, H., Chivenge, P., 2015. Surface organic carbon enrichment to explain greater CO2 emissions from short-term no-tilled soils. Agriculture, Ecosystems & Environment 203, 110-118.

Abstract

The impact of agricultural practices on CO₂ emissions from soils needs to be understood and quantified to enhance ecosystem functions, especially the ability of soils to sequester atmospheric carbon (C), while enhancing food and biomass production. The objective of this study was to assess CO₂ emissions in the soil surface following tillage abandonment and to investigate some of the underlying soil physical, chemical and biological controls. Maize (Zea mays) was planted under conventional tillage (T) and no-tillage (NT), both without crop residues under smallholder farming conditions in Potshini, South Africa. Intact top-soil (0–0.05 m) core samples (N = 54) from three 5 × 15 m² plots per treatment were collected two years after conversion of T to NT to evaluate the short-term CO₂ emissions. Depending on the treatment, cores were left intact, compacted by 5 and 10%, or had surface crusts removed. They were incubated for 20 days with measurements of CO₂ fluxes twice a day during the first three days and once a day thereafter. Soil organic C (SOC) content, soil bulk density (ρ_b), aggregate stability, soil organic matter quality, and microbial biomass and its activity were evaluated at the onset of the incubation. CO₂ emissions were 22% lower under NT compared with T with CO₂ emissions of 0.9 ± 0.10 vs 1.1 ± 0.10 mg C–CO₂ gC⁻¹ day⁻¹ under NT and T, respectively, suggesting greater SOC protection under NT. However, there were greater total CO₂ emissions per unit of surface by 9% under NT compared to T (1.15 ± 0.03 vs 1.05 ± 0.04 g C–CO₂ m⁻² day⁻¹). SOC protection significantly increased with the increase in soil bulk density (r = 0.89) and aggregate stability (from 1.7 ± 0.25 mm to 2.3 ± 0.31, r = 0.50), and to the decrease in microbial biomass and its activity (r = −0.59 and −0.57, respectively). In contrast, the greater NT CO₂ emissions per m² were explained by top-soil enrichment in SOC by 48% (from 12.4 ± 0.2 to 19.1 ± 0.4 g kg⁻¹, r = 0.59). These results on the soil controls of tillage impact on CO₂ emissions are expected to inform on the required shifts in agricultural practices for enhancing C sequestration in soils. In the context of the study, any mechanism favoring aggregate stability and promoting SOC allocation deep in the soil profile rather than in the top-soil would greatly diminish soil CO₂ outputs and thus stimulate C sequestration.

Roland et al. 2016. Anaerobic methane oxidation in an East African great lake (Lake Kivu)

Roland, F. A. E., Darchambeau, F., Morana, C., Crowe, S. A., Thamdrup, B., and Borges, A. V.: Anaerobic methane oxidation in an East African great lake (Lake Kivu), Biogeosciences Discuss., doi:10.5194/bg-2016-300, in review, 2016. 

 Abstract
 This study investigates methane (CH₄) oxidation in the water column of Lake Kivu, a deep meromictic tropical lake containing large quantities of CH₄ in the anoxic deep waters. Depth profiles of dissolved gases (CH₄ and nitrous oxide (N₂O)) and of the different potential electron acceptors for anaerobic methane oxidation (AOM) (nitrate, sulfate, iron and manganese) were determined during six field campaigns between June 2011 and August 2014. Bacterial abundance all along the vertical profiles was also determined by flow cytometry during three field campaigns, and denitrification measurements based on stable isotopes were performed twice. Incubation experiments were performed to quantify CH₄ oxidation and nitrate consumption rates, with a focus on AOM, without and with an inhibitor of sulfate-reducing bacteria activity (molybdate). Nitrate consumption rates were measured in these incubations. Substantial CH₄ oxidation activity was observed in oxic and anoxic waters, and in the upper anoxic waters of Lake Kivu, CH₄ is a major electron donor to sustain anaerobic metabolic processes coupled to AOM. The maximum aerobic and anaerobic CH₄ oxidation rates were estimated to 27 ± 2 and 16 ± 8 µmol L⁻¹ d⁻¹, respectively. We observed a decrease of AOM rates when molybdate was added for half of the measurements, strongly suggesting the occurrence of AOM linked to sulfate reduction, but an increase of AOM rates was observed for the other half. Nitrate reduction rates and dissolved manganese production rates tended to be higher with the addition of molybdate, but the maximum rates of 0.6 ± 0.02 and 11 ± 2 µmol L⁻¹ d⁻¹, respectively, were never high enough to explain AOM rates observed at the same depths. We also put in evidence a difference in relative importance of aerobic and anaerobic CH₄ oxidation between the seasons, with a higher importance of aerobic oxidation when the oxygenated layer was thicker (in dry season).

Kimaro et al. 2016. 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?셭, M., Mutuo, P., Abwanda, S., Shepherd, K., Neufeldt, H., Rosenstock, T.S., 2016. Is conservation agriculture 'climate-smart' for maize farmers in the highlands of Tanzania? Nutrient cycling in agroecosystems 105, 217-228.

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.

Rosenstock et al. 2016. Greenhouse gas fluxes from agricultural soils of Kenya and Tanzania

Rosenstock, T.S., Mathew, M., Pelster, D.E., Butterbach-Bahl, K., Rufino, M.C., Thiong'o, M., Mutuo, P., Abwanda, S., Rioux, J., Kimaro, A.A., Neufeldt, H.C.J.G., 2016. Greenhouse gas fluxes from agricultural soils of Kenya and Tanzania. Journal of Geophysical Research: Biogeosciences, DOI: 10.1002/2016JG003341.

Abstract

Knowledge of greenhouse gas (GHG) fluxes in soils is a prerequisite to constrain national, continental, and global GHG budgets. However, data characterizing fluxes from agricultural soils of Africa are markedly limited. We measured carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) fluxes at ten farmer-managed sites of six crop types for one year in Kenya and Tanzania using static chambers and gas chromatography. Cumulative emissions ranged between 3.5 – 15.9 Mg CO₂-C ha^-1 yr^-1, 0.4 – 3.9 kg N₂O-N ha^-1 yr^-1, and -1.2 – 10.1 kg CH₄-C ha^-1 yr^-1, depending on crop type, environmental conditions, and management. Manure inputs increased CO₂ (p = 0.03), but not N₂O or CH₄, emissions. Soil cultivation had no discernable effect on emissions of any of the three gases. Fluxes of CO₂ and N₂O were 54 – 208% greater (p  < 0.05) during the wet versus the dry seasons for some, but not all, crop types. The heterogeneity and seasonality of fluxes suggest that the available data describing soil fluxes in Africa, based on measurements of limited duration of only a few crop types and agroecological zones, are inadequate to use as a basis for estimating the impact of agricultural soils on GHG budgets. A targeted effort to understand the magnitude and mechanisms underlying African agricultural soil fluxes is necessary to accurately estimate the influence of this source on the global climate system and for determining mitigation strategies.

Pelster et al. 2016. Methane and Nitrous Oxide Emissions from Cattle Excreta on an East African Grassland

Pelster, D.E., B. Gisore, J. Goopy, D. Korir, J.K. Koske, M.C. Rufino, and K. Butterbach-Bahl. 2016. Methane and Nitrous Oxide Emissions from Cattle Excreta on an East African Grassland. J. Environ. Qual. 0. doi:10.2134/jeq2016.02.0050

Abstract

Greenhouse gas (GHG) emission measurements from livestock excreta in Africa are limited. We measured CH₄ and N₂O emissions from excreta of six Boran (Bos indicus) and six Friesian (Bos taurus) steers near Nairobi, Kenya. The steers were fed one of three diets (T1 [chaffed wheat straw], T2 [T1 + Calliandra calothyrsus Meissner – 0.2% live weight per day], and T3 [T1 + calliandra – 0.4% live weight every 2 d]). The T1 diet is similar in quality to typical diets in the region. Calliandra is a leguminous fodder tree promoted as a feed supplement. Fresh feces and urine were applied to grasslands and emissions measured using static chambers. Cumulative 28-d fecal emissions were 302 ± 52.4 and 95 ± 13.8 mg CH₄–C kg⁻¹ dry matter for Friesen and Boran steers, respectively, and 11.5 ± 4.26 and 24.7 ± 8.32 mg N₂O–N kg⁻¹ dry matter for Friesian and Boran steers, respectively. For urine from Friesian steers, the N₂O emissions were 2.8 ± 0.64 mg N₂O–N 100 mL urine⁻¹. The CH₄ emission factors (EFs) (246 ± 49.5 and 87 ± 12.7 g CH₄–C yr⁻¹ animal⁻¹ for Friesan and Boran, respectively) were lower than the International Panel on Climate Change EFs (750 g CH₄–C animal⁻¹ yr⁻¹), whereas the N₂O EFs (0.1 and 0.2% for the Friesian and Boran feces, respectively, and 1.2% for urine) were also lower than International Panel on Climate Change estimates. The low N content of the excreta likely caused the low emissions and indicates that current models probably overestimate CH₄ and N₂O emissions from African livestock manure.

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.