Castaldi et al. 2013. Nitrous oxide emissions from soil of an African rain forest in Ghana

Castaldi, S., Bertolini, T., Valente, A., Chiti, T., and Valentini, R.:2013. Nitrous oxide emissions from soil of an African rain forest in Ghana, Biogeosciences, 10, 4179-4187

Abstract
Recent atmospheric studies have evidenced the imprint of large N₂O sources in tropical/subtropical lands. This source might be attributed to agricultural areas as well as to natural humid ecosystems. The uncertainty related to both sources is very high, due to the scarcity of data and low frequency of sampling in tropical studies, especially for the African continent. The principal objective of this work was to quantify the annual budget of N₂O emissions in an African tropical rain forest. Soil N₂O emissions were measured over 19 months in Ghana, National Park of Ankasa, in uphill and downhill areas, for a total of 119 days of observation. The calculated annual average emission was 2.33 ± 0.20 kg N-N₂O ha⁻¹ yr⁻¹, taking into account the proportion of uphill vs. downhill areas, the latter being characterized by lower N₂O emissions. N₂O fluxes peaked between June and August and were significantly correlated with soil respiration on a daily and monthly basis. No clear correlation was found in the uphill area between N₂O fluxes and soil water content or rain, whereas in the downhill area soil water content concurred with soil respiration in determining N₂O flux variability. The N₂O source strength calculated in this study is very close to those reported for the other two available studies in African rain forests and to the estimated mean derived from worldwide studies in humid tropical forests (2.81 ± 2.02 kg N-N₂O ha⁻¹ yr⁻¹).

Lompo et al. 2012. Gaseous emissions of nitrogen and carbon from urban vegetable gardens in Bobo-Dioulasso, Burkina Faso. Journal of Plant Nutrition and Soil Science 175, 846-853

Lompo, D.J.-P., Sangaré, S.A.K., Compaoré, E., Papoada Sedogo, M., Predotova, M., Schlecht, E., Buerkert, A., 2012. Gaseous emissions of nitrogen and carbon from urban vegetable gardens in Bobo-Dioulasso, Burkina Faso. Journal of Plant Nutrition and Soil Science 175, 846-853 

 

Abstract

Urban and peri-urban agriculture (UPA) is an important livelihood strategy for the urban poor in sub-Saharan Africa and contributes to meeting increasing food demands in the rapidly growing cities. Although in recent years many research activities have been geared towards enhancing the productivity of this land-use system, little is known about turnover processes and nutrient efficiency of UPA. The aim of our study therefore was to determine horizontal fluxes of N, P, K, and C as well as gaseous N and C emissions in urban vegetable gardens of Bobo-Dioulasso, Burkina Faso. Two gardens referred to as “Kodéni” and “Kuinima” were selected as representative for urban and peri-urban systems classified as: (1) “commercial gardening + field crops and livestock system” and (2) “commercial gardening and semicommercial field crop system”, respectively. A nutrient-balance approach was used to monitor matter fluxes from March 2008 to March 2009 in both gardens. Ammonia (NH₃), nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from the respective soils were measured during the coolest and the hottest period of the day using a closed-chamber system. Annual partial balances amounted to 2056 kg N ha^–1, 615 kg P ha^–1, 1864 kg K ha^–1, and 33 893 kg C ha^–1 at Kodéni and to 1752 kg N ha^–1, 446 kg P ha^–1, 1643 kg K ha^–1, and 21 021 kg C ha^–1 at Kuinima. Emission rates were highest during the hot midday hours with peaks after fertilizer applications when fluxes of up to 1140 g NH₃-N ha^–1 h^–1, 154 g N₂O-N ha^–1 h^–1, 12 993 g CO₂-C ha^–1 h^–1 were recorded for Kodéni and Kuinima. Estimated annual gaseous N (NH₃-N + N₂O-N) and C (CO₂-C + CH₄-C) losses reached 419 kg N ha^–1 and 35 862 kg C ha^–1 at Kodéni and 347 kg N ha^–1 and 22 364 kg C ha^–1 at Kuinima. For both gardens, this represented 20% and 106% of the N and C surpluses, respectively. Emissions of NH₃, largely emitted after surface application of manure and mineral fertilizers, accounted for 73% and 77% of total estimated N losses for Kodéni and Kuinima. To mitigate N losses nutrient-management practices in UPA vegetable production of Bobo-Dioulasso would greatly benefit from better synchronizing nutrient-input rates with crop demands.

Nyamadzawo et al. 2012. The Effect of Catena Position on Greenhouse Gas Emissions from Dambo Located Termite (Odontotermes transvaalensis) Mounds from Central Zimbabwe. Atmospheric and Climate Sciences, 2(4), 502-509

Nyamadzawo, G., Gotosa, J., Muvengwi, J., Wuta, M., Nyamangara, J., Nyamugafata, P., & Smith, J. L. (2012). The Effect of Catena Position on Greenhouse Gas Emissions from Dambo Located Termite (Odontotermes transvaalensis) Mounds from Central Zimbabwe. Atmospheric and Climate Sciences, 2(4), 502-509

Abstract
Methane (CH₄), carbon dioxide (CO₂) and nitrous oxide (N₂)O) are greenhouse gases (GHGs) which cause global warming. Natural sources of GHGs include wetlands and termites. Previous studies have quantified GHG emissions from upland termites and no study has reported GHG emissions from seasonal wetlands (dambo) located termite mounds. The objective of this study was to evaluate the effect of dambo catena position on termite mound distribution and GHG emissions. It was hypothesized that mound density and GHG emissions from Odontotermes transvaalensis mounds, vary with catena position. The evaluated catena positions were margin, mid-slope, lower slope and bottom. Mound density was significantly lower in the bottom when compared to the other catena positions. The mean GHG fluxes were 88 µg m² hr^-1, 0.78 mg m² hr^-1 and 1361 mg m² hr^-1 for N₂) O, CH₄ and CO₂ respectively. Fluxes varied with catena position and were 0.48, 0.72, 1.35 and 0.79 mg m^-2 hr^-1 for CH₄ , and 1173.7, 1440.7, 1798.7 and 922.8 mg m^-2 hr^-1 for CO₂ in the margin, mid-slope, lower slope and the bottom catena position respectively. For N₂) O, there were no significant differences between catena positions. It was concluded that dambo located Odontotermes transvaalensis termite mounds are an important source of GHGs, and emissions varied with catena position for CO₂ and CH₄.

Rees et al. 2012. Nitrous oxide emissions from European agriculture; an analysis of variability and drivers of emissions from field experiments, Biogeosciences Discuss., 9, 9259-9288, doi:10.5194/bgd-9-9259-2012, 2012.

Rees, R. M., Augustin, J., Alberti, G., Ball, B. C., Boeckx, P., Cantarel, A., Castaldi, S., Chirinda, N., Chojnicki, B., Giebels, M., Gordon, H., Grosz, B., Horvath, L., Juszczak, R., Klemedtsson, Å. K., Klemedtsson, L., Medinets, S., Machon, A., Mapanda, F., Nyamangara, J., Olesen, J., Reay, D., Sanchez, L., Sanz Cobena, A., Smith, K. A., Sowerby, A., Sommer, M., Soussana, J. F., Stenberg, M., Topp, C. F. E., van Cleemput, O., Vallejo, A., Watson, C. A., and Wuta, M. 2013. Nitrous oxide emissions from European agriculture; an analysis of variability and drivers of emissions from field experiments, Biogeosciences, 10, 2671-2682, doi:10.5194/bg-10-2671-2013

Nitrous oxide emissions from a network of agricultural experiments in Europe and Zimbabwe were used to explore the relative importance of site and management controls of emissions. At each site, a selection of management interventions were compared within replicated experimental designs in plot based experiments. Arable experiments were conducted at Beano in Italy, El Encin in Spain, Foulum in Denmark, Logården in Sweden, Maulde in Belgium, Paulinenaue in Germany, Harare in Zimbabwe and Tulloch in the UK. Grassland experiments were conducted at Crichton, Nafferton and Peaknaze in the UK, Gödöllö in Hungary, Rzecin in Poland, Zarnekow in Germany and Theix in France. Nitrous oxide emissions were measured at each site over a period of at least two years using static chambers. Emissions varied widely between sites and as a result of manipulation treatments. Average site emissions (throughout the study period) varied between 0.04 and 21.21 kg N₂O-N ha⁻¹ yr⁻¹, with the largest fluxes and variability associated with the grassland sites. Total nitrogen addition was found to be the single most important determinant of emissions, accounting for 15% of the variance (using linear regression) in the data from the arable sites (p < 0.0001), and 77% in the grassland sites. The annual emissions from arable sites were significantly greater than those that would be predicted by IPCC default emission factors. Variability in N₂O within sites that occurred as a result of manipulation treatments was greater than that resulting from site to site and year to year variation, highlighting the importance of management interventions in contributing to greenhouse gas mitigation.

Gharahi Ghehi et al. 2012. Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda, Biogeosciences, 9, 1451-1463

Gharahi Ghehi, N., Werner, C., Cizungu Ntaboba, L., Mbonigaba Muhinda, J. J., Van Ranst, E., Butterbach-Bahl, K., Kiese, R., and Boeckx, P.: Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda, Biogeosciences, 9, 1451-1463, doi:10.5194/bg-9-1451-2012, 2012. 


Abstract. 
Globally, tropical forest soils represent the second largest source of N₂O and NO. However, there is still considerable uncertainty on the spatial variability and soil properties controlling N trace gas emission. Therefore, we carried out an incubation experiment with soils from 31 locations in the Nyungwe tropical mountain forest in southwestern Rwanda. All soils were incubated at three different moisture levels (50, 70 and 90 % water filled pore space (WFPS)) at 17 °C. Nitrous oxide emission varied between 4.5 and 400 μg N m⁻² h⁻¹, while NO emission varied from 6.6 to 265 μg N m⁻² h⁻¹. Mean N₂O emission at different moisture levels was 46.5 ± 11.1 (50 %WFPS), 71.7 ± 11.5 (70 %WFPS) and 98.8 ± 16.4 (90 %WFPS) μg N m⁻² h⁻¹, while mean NO emission was 69.3 ± 9.3 (50 %WFPS), 47.1 ± 5.8 (70 %WFPS) and 36.1 ± 4.2 (90 %WFPS) μg N m⁻² h⁻¹. The latter suggests that climate (i.e. dry vs. wet season) controls N₂O and NO emissions. Positive correlations with soil carbon and nitrogen indicate a biological control over N₂O and NO production. But interestingly N₂O and NO emissions also showed a positive correlation with free iron and a negative correlation with soil pH (only N₂O). The latter suggest that chemo-denitrification might, at least for N₂O, be an important production pathway. In conclusion improved understanding and process based modeling of N trace gas emission from tropical forests will benefit from spatially explicit trace gas emission estimates linked to basic soil property data and differentiating between biological and chemical pathways for N trace gas formation.

Caquet et al. 2012. Soil carbon balance in a tropical grassland: Estimation of soil respiration and its partitioning using a semi-empirical model

Caquet, B., De Grandcourt, A., Thongo M’bou, A., Epron, D., Kinana, A., Saint André, L., and Nouvellon, Y.: Soil carbon balance in a tropical grassland: Estimation of soil respiration and its partitioning using a semi-empirical model, Agricultural and Forest Meteorology, 158-159, 71-79, 2012.

Abstract

In savannah and tropical grasslands, which account for 60% of grasslands worldwide, a large share of ecosystem carbon is located below ground due to high root:shoot ratios. Temporal variations in soil CO₂ efflux (R_S) were investigated in a grassland of coastal Congo over two years. The objectives were (1) to identify the main factors controlling seasonal variations in R_S and (2) to develop a semi-empirical model describing R_S and including a heterotrophic component (R_H) and an autotrophic component (R_A). Plant above-ground activity was found to exert strong control over soil respiration since 71% of seasonal R_S variability was explained by the quantity of photosynthetically active radiation absorbed (APAR) by the grass canopy. We tested an additive model including a parameter enabling R_S partitioning into R_A and R_H. Assumptions underlying this model were that R_A mainly depended on the amount of photosynthates allocated below ground and that microbial and root activity was mostly controlled by soil temperature and soil moisture. The model provided a reasonably good prediction of seasonal variations in R_S (R² = 0.85) which varied between 5.4 μmol m⁻² s⁻¹ in the wet season and 0.9 μmol m⁻² s⁻¹ at the end of the dry season. The model was subsequently used to obtain annual estimates of R_S, R_A and R_H. In accordance with results reported for other tropical grasslands, we estimated that R_H accounted for 44% of R_S, which represented a flux similar to the amount of carbon brought annually to the soil from below-ground litter production. Overall, this study opens up prospects for simulating the carbon budget of tropical grasslands on a large scale using remotely sensed data.

Kim, D.-G., 2012. Estimation of net gain of soil carbon in a nitrogen-fixing tree and crop intercropping system in sub-Saharan Africa: results from re-examining a study.

Kim, D.-G., 2012. Estimation of net gain of soil carbon in a nitrogen-fixing tree and crop intercropping system in sub-Saharan Africa: results from re-examining a study. Agroforestry Systems, doi:10.1007/s10457-011-9477-1

 

Abstract

Nitrogen (N)-fixing tree and crop intercropping systems can be a sustainable agricultural practice in sub-Saharan Africa and can also contribute to resolving climate change through enhancing soil carbon (C) sequestration. A study conducted by Makumba et al. (Agric Ecosyst Environ 118:237–243, 2007) on the N-fixing tree gliricidia and maize intercropping system in southern Malawi provides a rare dataset of both sequestered soil C and C loss as soil carbon dioxide (CO₂) emissions. However, no soil C gain and loss estimates were made so the study failed to show the net gain of soil C. Also absent from this study was potential benefit or negative impact related to the other greenhouse gas, nitrous oxide (N₂O) and methane (CH₄) emissions from the intercropping system. Using the data provided in Makumba et al. (Agric Ecosyst Environ 118:237–243, 2007) a C loss as soil CO₂ emissions (51.2 ± 0.4 Mg C ha⁻¹) was estimated, amounting to 67.4% of the sequestered soil C (76 ± 8.6 Mg C ha⁻¹ in 0–2 m soil depth) for the first 7 years in the intercropping system. An annual net gain of soil C of 3.5 Mg C ha⁻¹ year⁻¹ was estimated from soil C sequestered and lost. Inclusion of the potential for N₂O mitigation [0.12–1.97 kg N₂O–N ha⁻¹ year⁻¹, 0.036–0.59 Mg CO₂ equivalents (eq.) ha⁻¹ year⁻¹] within this intercropping system mitigation as CO₂ eq. basis was estimated to be 3.5–4.1 Mg CO₂ eq. ha⁻¹ year⁻¹. These results suggest that reducing N₂O emission can significantly increase the overall mitigation benefit from the intercropping system. However, significant uncertainties are associated with estimating the effect of intercropping on soil N₂O and CH₄ emissions. These results stress the importance of including consideration of quantifying soil CO₂, N₂O and CH₄ emissions when quantifying the C sequestration potential in intercropping system.