Seiler et al. 1984. Field studies of methane emission from termite nests into the atmosphere and measurements of methane uptake by tropical soils

Seiler, W., Conrad, R., Scharffe, D., 1984. Field studies of methane emission from termite nests into the atmosphere and measurements of methane uptake by tropical soils. Journal of Atmospheric Chemistry 1, 171-186. doi:10.1007/bf00053839.

Abstract

The flux of CH₄ and CO₂ from termite nests into the atmosphere has been measured in a broad-leafed-type savannah in South Africa. Measurements were carried out on nests of species of six genera, i.e., Hodotermes, Macrotermes, Odontotermes, Trinervitermes, Cubitermes, and Amitermes. The flux rates of CH₄ relative to the flux rate of CO₂ in terms of carbon obtained for the individual species showed ratios of 2.9×10^-3, 7.0×10^-4, 6.7×10^-5, 8.7×10^-3, 2.0×10^-3 and 4.2×10^-3, respectively. Using data published on the assimulation efficiencies of termites, the flux of carbon as CH₄ accounts for 6.0×10^-5 to 2.6×10^-3 of the carbon ingested which results in a global CH₄ emission by termites of 2 to 5×10¹² g/yr. Methane is decomposed in the soil with average decomposition rates of 52 g/m²/h. The annual CH₄ consumption in the tropics and subtropics is estimated to be 21×10¹² g which exceeds the CH₄ emission rate by termites.

Delmas et al. 1991. Sources and sinks of methane in African Savanna. CH4 emissions from biomass burning

Delmas, R.A., Marenco, A., Tathy, J.P., Cros, B., Baudet, J.G.R., 1991. Sources and sinks of methane in African Savanna. CH4 emissions from biomass burning. J. Geophys. Res. 96, 7287-7299. doi:10.1029/90jd02496.


Abstract

Sources and sinks of atmospheric methane are studied in savanna regions of west and central Africa. Flux measured over dry savanna soils, using static chambers, is always negative the average uptake rate being 2 × 10¹⁰ molecules/cm²/s. In these regions, sources are linked to biomass burning. Methane and CO₂ emission from combustion of savanna plants and wood is studied by both field experiments and laboratory experiments using a combustion chamber. For savanna plants most of the carbon (85%) contained in the biomaterial is volatilized as CO₂ and 0.1 to 0.25% as methane. For graminaceous plants like loudetia simplex the ratio C-CH₄/C-CO₂ is 0.11%; it is 0.28% for hyparrhenia the other main type of savanna plants and it attains 1.4% for the combustion of wood. In natural fire plumes this ratio is around 0.26% for savanna fires and 0.56 to 2.22% for forest fires. These results show that methane release is highly dependent on the type of combustion. Methane to CO₂ ratios are also studied in vertical profiles in the troposphere taken during the TROPOZ I campaign, an aerial research expedition carried out over west Africa during the bushfire period. Within polluted layers, the average ratio of CH₄ to CO₂ excess over ambient air concentration is 0.34%. These results show that biomass burning in tropical Africa constitutes an important source of atmospheric methane estimated to about 9.2 × 10⁶ T(CH₄)/yr.

Dick et al. 2006. Effect of N-fixing and non N-fixing trees and crops on NO and N2O emissions from Senegalese soils

Dick, J., Skiba, U., Munro, R., Deans, D., 2006. Effect of N-fixing and non N-fixing trees and crops on NO and N2O emissions from Senegalese soils. Journal of Biogeography 33, 416-423. doi:10.1111/j.1365-2699.2005.01421.x.

Aim Agroforestry systems incorporating N-fixing trees have been shown to be socially beneficial and are thought to be environmentally friendly, both enriching and stabilizing soil. However, the effect of such systems on the emissions of the important greenhouse gas nitrous oxide (N₂O) and the tropospheric ozone precursor nitric oxide (NO) is largely unknown.

Location Soil was collected from the research plots of Institut Sénégalais de Recherches Agricoles at Bandia and Bambey, Senegal, West Africa, and from neighbouring farmers’ fields. Trace gas flux measurements and chemical analysis of the soil were carried out at the Centre for Ecology and Hydrology (CEH), Edinburgh, UK.

Methods Nitric oxide (NO) and nitrous oxide (N₂O) emissions were measured following simulated rainfall events (10 and 20 mm equivalents) from repacked soil cores collected under two tree species (Acacia raddiana) and Eucalyptus camaldulensis) in each of two provenance trails. In addition, soil samples were collected in local fields growing peanut (Arachis hypogaea) and Sorghum (Sorghum vulgare), close to the species trials in Bambey. NO was measured using a flow through system and was analysed by chemiluminescence. Nitrous oxide was measured from the repacked soil core headspace and was analysed by electron capture gas chromatography. Soil mineral N was extracted with KCl and analysed by colorimetric methods on separate soil columns.

Results Light rainfall, which increased the gravimetric soil moisture content to 20%, stimulated an increase in NO emission but there was no detectable N₂O emission. A heavy rainfall event, which increased the gravimetric soil moisture to 30%, stimulated N₂O emission with a subsequent peak in NO emissions when the soils became drier. Soil collected under the N-fixing tree species emitted significantly more N₂O than soil collected under the N-fixing crop species (P < 0.01). NO and N₂O emissions significantly correlated with soil available N (NH₄ and NO₃) (P < 0.05).

Main conclusions Rainfall intensity, supply of mineral N from organic matter and N fixation were the prime drivers of NO and N₂O emissions from seasonally dry tropical soils. The improved soil fertility underneath the trees provided a larger pool of mineral N and yielded larger rates of NO and N₂O emissions.

Dick et al. 2008. The contribution of agricultural practices to nitrous oxide emissions in semi-arid Mali

Dick, J., Kaya, B., Soutoura, M., Skiba, U., Smith, R., Niang, A., Tabo, R., 2008. The contribution of agricultural practices to nitrous oxide emissions in semi-arid Mali. Soil Use and Management 24, 292-301. doi:10.1111/j.1475-2743.2008.00163.x.

Abstract

The yield and flux of nitrous oxide (N₂O) emitted from continuous cereals (with and without urea), legumes/cereal in rotation and cereal/legume in rotation all with or without organic manure was monitored from January 2004 to February 2005. All treatments except continuous cereals had phosphate added. The cereal grown July–October in 2003 and 2004 was pearl millet (Pennisetum glaucum) and the legume was a bean (Phaseolus vulgaris). The 10 m × 10 m plots were established in a semi-arid climate in Mali. The addition of organic manure and both inorganic fertilizers increased yield and N₂O emissions. Continuous cereals treated with both organic manure and urea emitted significantly less N₂O (882 g N/ha per year) than plots receiving no organic manure(1535 g N/ha per year). Growing N-fixing crops in rotation did not significantly increase N₂O emissions. This study supports the new practice of growing cereal and legumes in rotation as an environmentally sustainable system in semi-arid Mali.

Rees et al. 2006. Nitrous oxide fluxes from savanna (miombo) woodlands in Zimbabwe

Rees, R.M., Wuta, M., Furley, P.A., Li, C., 2006. Nitrous oxide fluxes from savanna (miombo) woodlands in Zimbabwe. Journal of Biogeography 33, 424-437. doi:10.1111/j.1365-2699.2005.01423.x.

Aim We test the hypothesis that land use and climate are important controls of nitrous oxide (N₂O) emissions from savanna ecosystems, and that these emissions can be represented by a mechanistic model of carbon (C) and nitrogen (N) transformations.

Location Miombo woodlands in Zimbabwe are part of widespread woody savanna formations in southern and central Africa that cover more than 2.7 million km². The rainfall in this region is around 800 mm and is concentrated in the period between November and March.

Methods Losses of N₂O were measured along transects in two field areas using static chambers over a period of 1 year. The vegetation in both areas was dominated by Julbernardia globiflora and Brachystegia spiciformis, but had differing management systems (burned and unburned), soil properties and site characteristics (slope and drainage). The effects of simulated rainfall and fertilizer additions were studied in laboratory incubations.

Results Patterns of N₂O emissions were strongly linked to rainfall. The highest fluxes at both sites were measured within 18 days of the onset of the first rains in November, with fluxes of up to 42 μg N m⁻² h⁻¹. During the dry season, fluxes were lower, but a large proportion (R² values between 0.8 and 0.95, P < 0.001) of the N₂O flux could be predicted by variations in soil moisture. Soil columns were set up in the laboratory to which simulated rainwater was added, and the amounts and timing of rainwater addition were varied. Losses of N₂O were highest within the first week of the laboratory study. Altering the amount of rainwater addition did not significantly affect N₂O loss; however, a continuous addition of water resulted in higher losses of N₂O (up to 79 μg N m⁻² h⁻¹) than periodic addition of the same amount. A model (denitrification–decomposition) was used to simulate N₂O release over a 12 month period, using meteorological data recorded in the vicinity of the field site. The simulations and field data suggest that nitrification was the main process responsible for N₂O release during the dry season but that denitrification was more important during the wet season.

Main conclusions The release of N₂O from dryland savannas was shown to constitute an important nutrient flux, and emissions were strongly linked to patterns of rainfall; however, there was evidence to suggest that the magnitude of fluxes is also influenced locally by differences in soil organic matter concentration and drainage.

Scholes et al. 1997. NO and N2O emissions from savanna soils following the first simulated rains of the season

Scholes, M.C., Martin, R., Scholes, R.J., Parsons, D., Winstead, E., 1997. NO and N2O emissions from savanna soils following the first simulated rains of the season. Nutrient Cycling in Agroecosystems 48, 115-122. doi:10.1023/a:1009781420199.

Abstract

Data on the emissions of oxides of nitrogen from the soil during the early part of the wet season are reported for nutrient-rich and nutrient-poor sandy soils at Nylsvley, South Africa. The emissions of NO_x and N₂O following the first wetting event of the season are elevated relative to subsequent events. The observed high emission rates (76 ng N-NO m^-2 s^-1) are partially attributed to the sandiness of the soil, which permits NO to diffuse out of the soil rapidly. The pulse of high emissions following wetting is maintained for approximately 72 hours, thereafter continuing at around 20 ng NO m^-2 s^-1 while the soil remains moist. The initial pulse is suggested to be due to the accumulation of a substrate pool during the dry period, coupled with an inability of plants and microbes to use it effectively during the first few days after wetting. There were no significant differences in the peak or subsequent emission rates for either NO or N₂O between two sites of differing nitrogen mineralisation potentials. N₂O emissions averaged 8% of NO_x emissions. The enhanced emissions of NO_x which follow the first wetting after a prolonged dry period do not make a very large contribution to the annual gaseous N emission budget, but could be a significant contributor to the high tropospheric ozone levels observed over southern Africa in springtime.

Serca et al. 1994. Emissions of nitrogen oxides from equatorial rain forest in central Africa

Serca, D., Delmas, R., Jambert, C., Labroue, L., 1994. Emissions of nitrogen oxides from equatorial rain forest in central Africa. Tellus B 46, 243-254. doi:10.1034/j.1600-0889.1994.t01-3-00001.x.


Abstract

Emissions of nitric oxide from soils of equatorial rain forest were measured in the Dimonika Natural Park (4°30′S, 12°30′E) in the Mayombe Forest in Congo. Three research campaigns were carried out in June and July 1991 and in February 1992. Fluxes were measured by dynamic chamber techniques using a chemiluminescence instrument Scintrex LMA3. NO fluxes measured on natural soils are in between 5 and 17 × 10⁹ molecules cm⁻² s⁻¹; they are of the same order of magnitude as those observed in similar tropical forest media. Soil treatment experiments show that the auto-decomposition of HNO₂ in these acid soils (pH# 4) (chemodenitrification) is a potentially important cause of nitric oxide production in this type of ecosystem. Nitrous acid comes from autotrophic nitrification all the year round, and also from biological denitrification, shown by N₂0 emissions, during the rainy season. The regulation of NO release from soils is linked to ammonia production from litter mineralisation and to direct NH₄ input by throughfall.

Zepp et al. 1996. Effects of moisture and burning on soil-atmosphere exchange of trace carbon gases in a southern African savanna

Zepp, R.G., Miller, W.L., Burke, R.A., Parsons, D.A.B., Scholes, M.C., 1996. Effects of moisture and burning on soil-atmosphere exchange of trace carbon gases in a southern African savanna. J. Geophys. Res. 101, 23699-23706. doi:10.1029/95jd01371.

Abstract

Soil fluxes of carbon dioxide (CO₂), methane (CH₄), and carbon monoxide (CO) were measured during a period of extreme drought at semi-arid savanna sites located in the Kruger National Park (KNP), South Africa, as part of the SAFARI-92 experiments (Sept., 1992). Soil respiration in this savanna was little affected by burning, but was strongly stimulated by addition of moisture. Mean soil respiration from the dry soil was 0.4 g C m⁻² d⁻¹ in open savanna plots that had been burned biennially and 0.5 g C m⁻² d⁻¹ in woody savanna plots. A light natural rain (about 0.6 mm) increased the CO₂ flux in the open savanna sites by 5-fold but the effect was short-lived. A simulated heavy rain (25 mm of added distilled water) increased CO₂ fluxes by over an order of magnitude in both burned and control sites and the emissions remained over 5 times pre-wetting values during a week of drying. Over 65% of our measurements indicated no significant soil-atmosphere methane exchange; most of the few non-zero measurements indicated a small (<1 mg CH₄-C m⁻² d⁻¹) flux of methane to the atmosphere. Soil-atmosphere CH₄ exchange was not significantly affected by either burning the grass layer or by the addition of distilled water to the soil. The net soil CO fluxes, which generally increased with increasing soil temperature, were positive up to 356 × 10⁹ molecules cm⁻² s⁻¹ with an average of 8.8 × 10¹⁰ molecules cm⁻² s⁻¹ for the untreated open savanna plots. After burning, the fluxes rose by over an order of magnitude but dropped back to preburn levels within a few days. Observed CO fluxes were higher than those previously reported for southern Africa savannas during non-drought conditions. Added moisture had little effect on CO fluxes during the 3-week period of SAFARI-92.

Predotova et al. 2010. Emissions of ammonia, nitrous oxide and carbon dioxide from urban gardens in Niamey, Niger

Predotova, M., Gebauer, J., Diogo, R.V.C., Schlecht, E., Buerkert, A., 2010. Emissions of ammonia, nitrous oxide and carbon dioxide from urban gardens in Niamey, Niger. Field Crops Research 115, 1-8. doi:10.1016/j.fcr.2009.09.010.

Abstract
Urban and peri-urban agriculture (UPA) contributes significantly to meet increasing food demands of the rapidly growing urban population in West Africa. The intensive vegetable cultivation in UPA gardens with its high nutrient inputs is often reported to operate at large surpluses of nutrients and presumably high turnover rates of organic matter (OM) and nitrogen (N) losses via emanation and leaching. Many of these claims are lacking solid data which would allow suggesting mitigation strategies. Therefore, this study aimed at quantifying gaseous emissions of ammonia (NH₃), nitrous oxide (N₂O), and carbon dioxide (CO₂) in three representative urban gardens of Niamey, Niger using a closed chamber gas monitoring system. Mean annual N emissions (NH₃-N and N₂O-N) in two gardens using river water for irrigation reached 53 and 48 kg N ha⁻¹ yr⁻¹, respectively, while 25 and 20 Mg C ha⁻¹ yr⁻¹ was lost as CO₂-C. In the garden irrigated with sewage water from the city's main wadi, N₂O was the main contributor to N losses (68%) which together with NH₃ reached 92 kg N ha⁻¹ yr⁻¹, while CO₂-C emissions amounted to 26 Mg ha⁻¹ yr⁻¹. Our data indicate that 28% of the total gaseous C emissions and 30–40% of the N emissions occur during the hot dry season from March to May and another 20–25% and 10–20% during the early rainy season from June to July. Especially during these periods more effective nutrient management strategies in UPA vegetable gardens should be applied to increase the nutrient use efficiency in UPA vegetable gardens.

Werner et al. 2007. Soil-atmosphere exchange of N2O, CH4, and CO2 and controlling environmental factors for tropical rain forest sites in western Kenya

Werner, C., R. Kiese, and K. Butterbach-Bahl (2007), Soil-atmosphere exchange of N₂O, CH₄, and CO₂ and controlling environmental factors for tropical rain forest sites in western Kenya, J. Geophys. Res., 112, D03308, doi:10.1029/2006JD007388.


Abstract

N₂O, CH₄ and CO₂ soil-atmosphere exchange and controlling environmental factors were studied for a 3-month period (dry-wet season transition) at the Kakamega Rain forest, Kenya, Africa, using an automated measurement system. The mean N₂O emission was 42.9 ± 0.7 μg N m⁻² h⁻¹ (range: 1.1–324.8 μg N m⁻² h⁻¹). Considering the duration of dry and wet season the annual N₂O emission was estimated at 2.6 ± 1.2 kg N ha⁻¹ yr⁻¹. Large pulse emissions of N₂O were observed after the first rainfall events of the wet season, and the magnitude of N₂O emissions steadily declined thereafter. A comparable trend in soil CO₂ emissions (mean: 71.8 ± 0.3 mg C m⁻² h⁻¹) indicates that the rapid mineralization of litter accumulated during the dry period produced the high N₂O emissions at the start of the wet season. Manual N₂O emission measurements at four additional rain forest sites were comparable to those measured at the main site, whereas N₂O emissions measured at a regrowth site were significantly lower. Spatial differences in N₂O emissions could be explained by differences in soil texture and topsoil C:N-ratio (CO₂: subsoil C and N concentrations), whereas the temporal variability of N₂O and CO₂ emissions was primarily driven by soil moisture. Soils predominantly acted as sinks for CH₄ (−56.4 ± 0.8 μg C m⁻² h⁻¹). For some chamber positions, episodes of net CH₄ release were observed, which could be due to high WFPS and/or termite activity. CH₄ fluxes were weakly correlated with soil moisture levels but showed no relation to temperature, texture, pH, carbon or nitrogen contents.

Nouvellon et al. 2008. Soil CO2 effluxes, soil carbon balance, and early tree growth following savannah afforestation in Congo: Comparison of two site preparation treatments

Nouvellon, Y., Epron, D., Kinana, A., Hamel, O., Mabiala, A., D'Annunzio, R., Deleporte, P., Saint-André, L., Marsden, C., Roupsard, O., Bouillet, J.-P., Laclau, J.-P., 2008. Soil CO2 effluxes, soil carbon balance, and early tree growth following savannah afforestation in Congo: Comparison of two site preparation treatments. Forest Ecology and Management 255, 1926-1936. doi:10.1016/j.foreco.2007.12.026.

Abstract

Eucalyptus plantations have been introduced since 1978 on savannah soils of the coastal plains of Congo, but there is still little information on the effect of silvicultural practices on soil organic carbon dynamics after afforestation on these savannahs. The objectives of this study were to assess the effects of two experimental site preparation treatments on soil CO₂ efflux, tree growth and soil carbon balance during the first year following plantation establishment. One treatment involved mechanical soil disturbance with disk harrowing (D), whereas in the second treatment (H), savannah grasses were killed by herbicide application before planting, without mechanical soil disturbance. Soil respiration and soil water content were monitored for 1 year following treatment application, at 2-week intervals. We hypothesized that mechanical soil disturbance would increase soil CO₂ efflux, but the results did not support this hypothesis. The cumulated soil CO₂ efflux over 1 year was not significantly different in the two treatments and averaged 658 g C m⁻². In contrast, tree growth was significantly increased by disk harrowing, maybe as a result of decreased soil penetration resistance. Carbon inputs to the soil from savannah residues (428 g C m⁻²) were outweighed by the annual carbon outputs through heterotrophic respiration (505 and 456 g C m⁻² in the H and D treatments, respectively) leading to a slightly negative soil carbon budget in both treatments 1 year after afforestation.

Brümmer et al. 2009. Fluxes of CH4 and CO2 from soil and termite mounds in south Sudanian savanna of Burkina Faso (West Africa)

Brümmer, C., H. Papen, R. Wassmann, and N. Brüggemann (2009), Fluxes of CH₄ and CO₂ from soil and termite mounds in south Sudanian savanna of Burkina Faso (West Africa), Global Biogeochem. Cycles, 23, GB1001, doi:10.1029/2008GB003237.

Abstract

The contribution of West African savanna ecosystems to global greenhouse gas budgets is highly uncertain. In this study we quantified soil-atmosphere CH₄ and CO₂ fluxes in the southwest of Burkina Faso from June to September 2005 and from April to September 2006 at four different agricultural fields planted with sorghum (n = 2), cotton, and peanut and at a natural savanna site with termite (Cubitermes fungifaber) mounds. During the rainy season both CH₄ uptake and CH₄ emission were observed in the savanna, which was on average a CH₄ source of 2.79 and 2.28 kg CH₄-C ha⁻¹ a⁻¹ in 2005 and 2006, respectively. The crop sites were an average CH₄ sink of −0.67 and −0.70 kg CH₄-C ha⁻¹ a⁻¹ in the 2 years, without significant seasonal variation. Mean annual soil respiration ranged between 3.86 and 5.82 t CO₂-C ha⁻¹ a⁻¹ in the savanna and between 2.50 and 4.51 t CO₂-C ha⁻¹ a⁻¹ at the crop sites. CH₄ emission from termite mounds was 2 orders of magnitude higher than soil CH₄ emissions, whereas termite CO₂ emissions were of the same order of magnitude as soil CO₂ emissions. Termite CH₄ and CO₂ release in the savanna contributed 8.8% and 0.4% to the total soil CH₄ and CO₂ emissions, respectively. At the crop sites, where termite mounds had been almost completely removed because of land use change, termite fluxes were insignificant. Mound density-based upscaling of termite CH₄ fluxes resulted in a global termite CH₄ source of 0.9 Tg a⁻¹, which corresponds to 0.15% of the total global CH₄ budget of 582 Tg a⁻¹, hence significantly lower than those obtained previously by biomass-based calculations. This study emphasizes that land use change, which is of high relevance in this region, has particularly affected soil CH₄ fluxes in the past and might still do so in the future.

Koerber et al., 2009. Geographical variation in carbon dioxide fluxes from soils in agro-ecosystems and its implications for life-cycle assessment

Koerber, G.R., Edwards-Jones, G., Hill, P.W., Canals, L.M.i., Nyeko, P., York, E.H., Jones, D.L., 2009. Geographical variation in carbon dioxide fluxes from soils in agro-ecosystems and its implications for life-cycle assessment. Journal of Applied Ecology 46, 306-314

Abstract
Exchange of carbon dioxide (CO2) from soils can contribute significantly to the global warming potential (GWP) of agro-ecosystems. Due to variations in soil type, climatic conditions and land management practices, exchange of CO2 can differ markedly in different geographical locations. The food industry is developing carbon footprints for their products necessitating integration of CO2 exchange from soils with other CO2 emissions along the food chain. It may be advantageous to grow certain crops in different geographical locations to minimize CO2 emissions from the soil, and this may provide potential to offset other emissions in the food chain, such as transport. * 2Values are derived for the C balance of soils growing horticultural crops in the UK, Spain and Uganda. Net ecosystem production (NEP) is firstly calculated from the difference in net primary production (NPP) and heterotrophic soil respiration (Rh). Both NPP and Rh were estimated from intensive direct field measurements. Secondly, net biome production (NBP) is calculated by subtracting the crop biomass from NEP to give an indication of C balance. The importance of soil exchange is discussed in the light of recent discussions on carbon footprints and within the context of food life-cycle assessment (LCA). * 3The amount of crop relative to the biomass and the Rh prevailing in the different countries were the dominant factors influencing the magnitude of NEP and NBP. The majority of the biomass for lettuce Lactuca sativa and vining peas Pisum sativum, was removed from the field as crop; therefore, NEP and NBP were mainly negative. This was amplified for lettuces grown in Uganda (−16·5 and −17 t C ha−1 year−1 compared to UK and Spain −4·8 to 7·4 and −5·1 to 6·3 t C ha−1 year−1 for NEP and NBP, respectively) where the climate elevated Rh. * 4Synthesis and applications. This study demonstrates the importance of soil emissions in the overall life cycle of vegetables. Variability in such emissions suggests that assigning a single value to food carbon footprints may not be adequate, even within a country. Locations with high heterotrophic soil respiration, such as Spain and Uganda (21·9 and 21·6 t C ha−1 year−1, respectively), could mitigate the negative effects of climate on the C costs of crop production by growth of crops with greater returns of residue to the soil. This would minimize net CO2 emissions from these agricultural ecosystems.

Nsabimana et al., 2009. Soil CO2 flux in six monospecific forest plantations in Southern Rwanda

Nsabimana, D., Klemedtson, L., Kaplin, B.A., Wallin, G., 2009. Soil CO2 flux in six monospecific forest plantations in Southern Rwanda. Soil Biology and Biochemistry 41, 396-402

Abstract

Forest soils contain the largest carbon stock of all terrestrial biomes and are probably the most important source of carbon dioxide (CO2) to atmosphere. Soil CO2 fluxes from 54 to 72-year-old monospecific stands in Rwanda were quantified from March 2006 to December 2007. The influences of soil temperature, soil water content, soil carbon (C) and nitrogen (N) stocks, soil pH, and stand characteristics on soil CO2 flux were investigated. The mean annual soil CO2 flux was highest under Eucalyptus saligna (3.92　[mu]mol m-2 s-1) and lowest under Entandrophragma excelsum (3.13　[mu]mol m-2 s-1). The seasonal variation in soil CO2 flux from all stands followed the same trend and was highest in rainy seasons and lowest in dry seasons. Soil CO2 flux was mainly correlated to soil water content (R2　=　0.36-0.77), stand age (R2　=　0.45), soil C stock (R2　=　0.33), basal area (R2　=　0.21), and soil temperature (R2　=　0.06-0.17). The results contribute to the understanding of factors that influence soil CO2 flux in monocultural plantations grown under the same microclimatic and soil conditions. The results can be used to construct models that predict soil CO2 emissions in the tropics.

Ali, A., 2008. Factors Affecting on Response of Broad Bean and Corn to Air Quality and Soil CO2 Flux Rates in Egypt

Ali, A., 2008. Factors Affecting on Response of Broad Bean and Corn to Air Quality and Soil CO2 Flux Rates in Egypt. Water, Air, & Soil Pollution 195, 311-323

Abstract
In response to worldwide increases in the burning of fossil fuels to meet energy demands for electric power generation and transportation, atmospheric CO2 concentrations are currently rising at approximately 0.5% per year and ground-level O3 values are increasing at a rate of 0.32% per year. Some plants showed positive increases in response to elevated atmospheric CO2 concentrations, but are depressed when exposed to enhanced O3 air pollution. The objective of this research was to examine relationships between alterations in leaf plant characteristics in response to air quality treatments and soil CO2 flux activities during the growing season. Field studies were conducted in 2-m diameter × 2-m height open-top chambers (OTC’s) at Sharkia Province during 2004 and 2005 involving the growth of broad bean (Vicia faba L. cv. Giza 40) and corn (Zea mays L. cv. 30 K8) in rotations using no-till management while being subjected full-season to five air quality treatments: charcoal-filtered (CF) air; CF + 150　µL CO2 L−1; non-filtered (NF) air; NF + 150　µL CO2 L−1 and ambient air (AA). Leaf photosynthesis (Ps), leaf area index (LAI), and vegetative carbohydrate contents were determined during pre- and post-anthesis in the two crops and soil CO2 flux rates were monitored monthly during two growing seasons (2004–2005). Multiple and stepwise regression analyses were performed to establish linkages between plant canopy characteristics and soil CO2 flux rates with results combined over growth stages and year for each crop. Increasing the atmospheric CO2 concentration typically stimulated leaf Ps, soluble and total leaf carbohydrate contents, LAI values, and soil CO2 flux rates throughout the growing season in both crop; however, the elevated O3 treatments in NF air tended to lower these values compared to CF air. Soil CO2 flux rates were significantly correlated with LAI, soluble and total sugar contents at P ≤ 0.01 and with Ps rates at P ≤ 0.05 in broad bean leaves, but with soluble and total sugar contents of leaves in corns at P ≤ 0.01 only. Results of this study provided solid evidences linking the impact of changing air quality on plants factors processes and possible indirect effects on soil CO2 flux activities throughout the growing season.

Epron et al., 2004. Spatial and temporal variations of soil respiration in a Eucalyptus plantation in Congo

Epron, D., Nouvellon, Y., Roupsard, O., Mouvondy, W., Mabiala, A., Saint-André, L., Joffre, R., Jourdan, C., Bonnefond, J.-M., Berbigier, P., Hamel, O., 2004. Spatial and temporal variations of soil respiration in a Eucalyptus plantation in Congo. Forest Ecology and Management 202, 149-160

Abstract
Our objectives were to quantify soil respiration in a 3-year-old Eucalyptus plantation in coastal Congo and to investigate both temporal and spatial variations of this major component of ecosystem respiration. Soil respiration exhibited pronounced seasonal variations that clearly reflected those of soil water content, with minimum values below 1.6　[mu]mol　m-2　s-1 at the end of the dry season in September and a maximum value of 5.6　[mu]mol　m-2　s-1 after re-wetting in December. An empirical model describing the relationship between soil respiration and soil water content predicts the seasonal variations in soil respiration reasonably well (R2 = 0.88), even if the effects of soil temperature and soil water content may be confounded since both factors co-vary across seasons. Spatial heterogeneity of soil respiration was clearly affected by management practices with higher respiration rate in slash inter-rows which received higher amounts of detritus at the logging stage, and lower respiration rate in haulage inter-rows used for heavy vehicle traffic. Higher values of soil respiration were also recorded in the vicinity of trunks than in the middle of the inter-rows. While soil water content is the main determinant of seasonal variation of soil respiration, it poorly accounts for its spatial variability over the experimental stand, except for days with low soil water content. Soil respiration was related neither to root biomass nor to soil carbon content, but was positively correlated with both leaf and total aboveground litter (i.e. leaf, bark and woody debris). Plots exhibiting the highest soil respiration also contained the highest amounts of aboveground litter. Microbial respiration associated with litter decomposition is likely a major component of soil respiration, and the spatial heterogeneity in litter fall probably accounts for most of its spatial variability in this Eucalyptus plantation.

Castaldi et al., 2010. CO2, CH4 and N2O fluxes from soil of a burned grassland in Central Africa

Castaldi, S., de Grandcourt, A., Rasile, A., Skiba, U., Valentini, R., 2010. CO2, CH4 and N2O fluxes from soil of a burned grassland in Central Africa. Biogeosciences 7, 3459-3471. doi:10.5194/bg-7-3459-2010

Abstract
The impact of fire on soil fluxes of CO2, CH4 and N2O was investigated in a tropical grassland in Congo Brazzaville during two field campaigns in 2007–2008. The first campaign was conducted in the middle of the dry season and the second at the end of the growing season, respectively one and eight months after burning. Gas fluxes and several soil parameters were measured in each campaign from burned plots and from a close-by control area preserved from fire. Rain events were simulated at each campaign to evaluate the magnitude and duration of the generated gas flux pulses. In laboratory experiments, soil samples from field plots were analysed for microbial biomass, net N mineralization, net nitrification, N2O, NO and CO2 emissions under different water and temperature soil regimes. One month after burning, field CO2 emissions were significantly lower in burned plots than in the control plots, the average daily CH4 flux shifted from net emission in the unburned area to net consumption in burned plots, no significant effect of fire was observed on soil N2O fluxes. Eight months after burning, the average daily fluxes of CO2, CH4 and N2O measured in control and burned plots were not significantly different. In laboratory, N2O fluxes from soil of burned plots were significantly higher than fluxes from soil of unburned plots only above 70% of maximum soil water holding capacity; this was never attained in the field even after rain simulation. Higher NO emissions were measured in the lab in soil from burned plots at both 10% and 50% of maximum soil water holding capacity. Increasing the incubation temperature from 25 °C to 37 °C negatively affected microbial growth, mineralization and nitrification activities but enhanced N2O and CO2 production. Results indicate that fire did not increase post-burning soil GHG emissions in this tropical grasslands characterized by acidic, well drained and nutrient-poor soil.

Makumba et al., 2007. Long-term impact of a gliricidia-maize intercropping system on carbon sequestration in southern Malawi

Makumba, W., Akinnifesi, F.K., Janssen, B., Oenema, O., 2007. Long-term impact of a gliricidia-maize intercropping system on carbon sequestration in southern Malawi. Agriculture Ecosystems & Environment 118, 237-243.

Abstract
Tree/crop systems under agroforestry practice are capable of sequestering carbon (C) in the standing biomass and soil. Although studies have been conducted to understand soil organic C increases in some agroforestry technologies, little is known about C sequestered in simultaneous tree/crop intercropping systems. The main objective of this study was to determine the effect of agroforestry practice on C sequestration and CO2-C efflux in a gliricidia-maize intercropping system. The experiment was conducted at an experimental site located at the Makoka Agricultural Research Station, in Malawi. The studies involved two field plots, 7-year (MZ21) and 10-year (MZ12), two production systems (sole-maize and gliricidia-maize simultaneous intercropping systems). A 7-year-old grass fallow (Grass-F) was also included. Gliricidia prunings were incorporated at each time of tree pruning in the gliricidia-maize. The amount of organic C recycled varied from 0.8 to 4.8 Mg C ha(-1) in gliricidia-maize and from 0.4 to 1.0 Mg C ha(-1) in sole-maize. In sole-maize, net decreases of soil carbon of 6 Mg C ha(-1) at MZ12 and 7 Mg C ha(-1) at MZ21 in the topsoil (0-20 cm) relative to the initial soil C were observed. After 10 years of continuous application of tree prunings C was sequestered in the topsoil (0-20 cm) in gliricidia-maize was 1.6 times more than in sole-maize. A total of 123-149 Mg C ha(-1) were sequestered in the soil (0-200 cm depth), through root turnover and pruning application in the gliricidia-maize system. Carbon dioxide evolution varied from 10 to 28 kg ha(-1) day(-1) in sole-maize and 23 to 83 kg ha(-1) day(-1) in gliricidia-maize. We concluded that gliricidia-maize intercropping system could sequester more C in the soil than sole-maize.