Chikowo et al. 2004. Mineral N dynamics, leaching and nitrous oxide losses under maize following two-year improved fallows on a sandy loam soil in Zimbabwe. Plant Soil 259, 315-330.

Chikowo, R., Mapfumo, P., Nyamugafata, P., Giller, K.E., 2004. Mineral N dynamics, leaching and nitrous oxide losses under maize following two-year improved fallows on a sandy loam soil in Zimbabwe. Plant Soil 259, 315-330.

Abstract

The fate of the added N on a sandy loam soil was determined in an improved fallow - maize sequence field experiment in Zimbabwe. Pre-season mineral N was determined in 20 cm sections to 120 cm depth by soil auguring in seven land use systems. Thereafter, sequential soil auguring was done at two-week intervals in plots that previously had 2-year fallows of Acacia angustissima, Sesbania sesban and unfertilized maize to determine mineral N dynamics. Using the static chamber technique, N₂O fluxes were also determined in the same plots. Pre-season NH₄-N concentrations were >12 kg N ha⁻¹ in the 0–20 cm layer for treatments that had a pronounced litter layer. NO₃-N concentrations below 60 cm depth were <3 kg N ha⁻¹ layer⁻¹ for Sesban, Acacia, Cajanus cajan and natural woodland compared with >10 kg N ha⁻¹ layer⁻¹ in the control plots where maize had been cultivated each year. There was a flush of NO₃-N in the Sesbania and Acacia plots with the first rains. Topsoil NO₃-N had increased to >29 kg N ha⁻¹ by the time of establishing the maize crop. This increase in NO₃-N in the topsoil was not sustained as concentrations decreased rapidly within three weeks of maize planting, to amounts of 8.6 kg N ha⁻¹ and 11.2 kg N ha⁻¹ for the Sesbania and Acacia plots, respectively. Total NO₃-N leaching losses from the 0–40 cm layer ranged from 29–40 kg ha⁻¹ for Sesbania and Acacia plots within two weeks when 104 mm rainfall was received to an already fully recharged soil profile. Nitrate then accumulated below the 40 cm depth during early season when the maize had not developed a sufficient root length density to effectively capture nutrients. At one week after planting maize, N₂O fluxes of 12.3 g N₂O-N ha⁻¹ day⁻¹ from Sesbania plots were about twice as high as those from Acacia, and about seven times the 1.6 g N₂O-N ha⁻¹ day⁻¹ from maize monoculture. This was at the time when mineral N was at its peak in the topsoil. The unfertilized maize showed consistently low N₂O emissions, which never exceeded 2 g N₂O-N ha⁻¹ day⁻¹ for all the eight sampling dates. The decrease of mineral N concentration in the topsoil resulted in reduced N₂O fluxes, despite very high soil moisture conditions. Total N₂O-N emissions were greatest for Sesbania plots with 0.3 kg ha⁻¹ lost in 56 days. We conclude that, under high rainfall conditions, there is an inherent problem in managing mineral N originating from mineralization of organic materials as it accumulates at the onset of rains, and is susceptible to leaching before the crop root system develops. We did not quantify nitric oxide and N₂ gas emissions, but it is unlikely that total gaseous N losses would be significant and contribute to poor N recovery that has been widely reported.

Gharahi Ghehi et al. 2013. Detailed regional predictions of N2O and NO emissions from a tropical highland rainforest

Gharahi Ghehi, N., Werner, C., Hufkens, K., Kiese, R., Van Ranst, E., Nsabimana, D., Wallin, G., Klemedtsson, L., Butterbach-Bahl, K., and Boeckx, P.: Detailed regional predictions of N₂O and NO emissions from a tropical highland rainforest, Biogeosciences Discuss., 10, 1483-1516

Abstract. 

Tropical forest soils are a significant source for the greenhouse gas N₂O as well as for NO, a precursor of tropospheric ozone. However, current estimates are uncertain due to the limited number of field measurements. Furthermore, there is considerable spatial and temporal variability of N₂O and NO emissions due to the variation of environmental conditions such as soil properties, vegetation characteristics and meteorology. In this study we used a process-based model (ForestDNDC-tropica) to estimate N₂O and NO emissions from tropical highland forest (Nyungwe) soils in southwestern Rwanda. To extend the model inputs to regional scale, ForestDNDC-tropica was linked to an exceptionally large legacy soil dataset. There was agreement between N₂O and NO measurements and the model predictions though the ForestDNDC-tropica resulted in considerable lower emissions for few sites. Low similarity was specifically found for acidic soil with high clay content and reduced metals, indicating that chemo-denitrification processes on acidic soils might be under-represented in the current ForestDNDC-tropica model. The results showed that soil bulk density and pH are the most influential factors driving spatial variations in soil N₂O and NO emissions for tropical forest soils. The area investigated (1113 km²) was estimated to emit ca. 439 ± 50 t N₂O-N yr⁻¹ (2.8–5.5 kg N₂O-N ha⁻¹ yr⁻¹) and 244 ± 16 t NO-N yr⁻¹ (0.8–5.1 kg N ha⁻¹ yr⁻¹). Consistent with less detailed studies, we confirm that tropical highland rainforest soils are a major source of atmospheric N₂O and NO.
 

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.