Nyamadzawo et al. 2013. Greenhouse Gas Emissions from Intermittently Flooded (Dambo) Rice under Different Tillage Practices in Chiota Smallholder Farming Area of Zimbabwe

G. Nyamadzawo, M. Wuta, N. Chirinda, L. Mujuru and J. Smith, "Greenhouse Gas Emissions from Intermittently Flooded (Dambo) Rice under Different Tillage Practices in Chiota Smallholder Farming Area of Zimbabwe," Atmospheric and Climate Sciences, Vol. 3 No. 4A, 2013, pp. 13-20. doi: 10.4236/acs.2013.34A003.

ABSTRACT

Agriculture is one of the biggest sources of greenhouse gases. Rice production has been identified as one of the major sources of greenhouse gases, especially methane. However, data on the contributions of rice towards greenhouse gas emissions in tropical Africa are limited. In Zimbabwe, as in most of Sub-Saharan Africa, there are very few studies that have explored greenhouse gas emissions from agricultural lands. This study reports the first dataset on greenhouse gas emissions from intermittently flooded rice paddies in Zimbabwe. The objective of this study was to quantify greenhouse gas emissions from dambo rice under different tillage treatments, which were conventional tillage, no tillage, tied ridges, tied fallows, and mulching. Average soil nitrous oxide emissions were 5.9, 0.2, 5.4, 5.2 and 7.8 μg·m^-2·hr^-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. Average methane emission was 0.35 mg·m^-2·hr^-1 and maximum as 1.62 mg·m^-2·hr^-1. Average methane emissions for the different tillage systems were 0.20, 0.18, 0.45, 0.52 and 0.38 mg·m^-2·hr^-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. Carbon dioxide emissions were 98.1, 56.0, 69.9, 94.8 and 95.5 mg·m^-2·hr^-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. The estimated emissions per 150 day cropping season were 1.4, 3.6 and 0.6 kg·ha^-1 for methane, carbon dioxide and nitrous oxide respectively. We concluded that intermittently saturated dambo rice Paddys are a potential source of greenhouse gases which is important to global greenhouse gas budgets, thus, they deserve more careful study.

Krüger et al. 2013. Greenhouse gas emission peaks following natural rewetting of two wetlands in the southern Ukhahlamba-Drakensberg Park, South Africa

Krüger, J.P., Beckedahl, H., Gerold, G., Jungkunst, H.F., Greenhouse gas emission peaks following natural rewetting of two wetlands in the southern Ukhahlamba-Drakensberg Park, South Africa. South African Geographical Journal, DOI:10.1080/03736245.2013.847798

Abstract

The global importance of wetlands in the carbon and nitrogen cycles is well documented, but the specific greenhouse gas characteristics of South African wetlands are less well known. These wetlands most likely differ from more prominent wetlands from continuously humid climate zone (boreal, temperate and tropics). Particular wetlands in the southern Drakensberg are adapted to the seasonal drying during the winter months. Greenhouse gas emissions were measured during natural rewetting at two wetlands. A rapid reaction and significant positive correlation between greenhouse gas fluxes and ground water level were determined. Methane emissions were observed after two days of rewetting at one of the wetlands, and nitrous oxide emissions started within a day of rewetting at the other wetland. The high nitrous oxide emissions may be caused by the recent winter burning of vegetation, which most likely resulted in a greater availability of nitrogen in the soil. High nitrous oxide emissions following natural rewetting (the annual cyclical process in these wetlands) could contribute significantly to the local greenhouse gas budget. Hence, besides the methane emissions, the nitrous oxide emissions of wetlands in southern Africa should be taken into account.

Yohannes Y et al. 2013. Forest Management Influence on the Carbon Flux of Cupressus lusitanica Plantation in the Munessa Forest, Ethiopia

Yohannes Y, Shibistova O, Asaye Z, Guggenberger G (2013) Forest Management Influence on the Carbon Flux of Cupressus lusitanica Plantation in the Munessa Forest, Ethiopia. Forest Res 2:111. doi: 10.4172/2168-9776.1000111

Abstract

The effect of plantation forests on the global carbon balance is controversially discussed in recent times. As soil respiration is a decisive component in the carbon exchange between terrestrial ecosystems and atmosphere, effects of forest management measures (e.g. thinning) in the context of driving parameters of soil CO2 efflux is a key issue in optimizing carbon friendly land management. In the present study, we report the effects of thinning, soil temperature and soil moisture, and biotic parameters on soil CO2 efflux rate. Soil CO2 efflux was measured by using an Infrared Gas Analyzer. We selected thinned and un-thinned stands within six years old Cupressus lusitanica plantation forest. Soil respiration rate ranged from 1.47 to 6.92 μmol m-2s-1 (thinned) and 1.31 to 5.20 μmol m-2s-1 (control stand). Generally higher soil respiration rates were measured during wet than in dry season. Seasonal variability of soil CO2 efflux was significantly (p<0.05) correlated with soil moisture, but poorly correlated with soil temperature. Soil respiration increased with increasing soil moisture and reached maximum at 31% but after this threshold it start to decline. In general, soil CO2 efflux rate in the first and second year after thinning was 24% and 14% higher in the  thinned stand. Increased soil temperature at the thinned stand contributed minor to the larger soil CO2 efflux, the more important reason appeared to be the trees’ direct response. Higher fine root production together with larger microbial concentrations representing different groups infers a higher autotrophic respiration by roots and associated mycorrhizal fungi as well as by heterotrophic respiration. Despite the higher CO2 losses with soil respiration, the organic C and total N concentrations in soil rather tended to increase, indicating higher organic matter input to soil at the thinned stand.

Millar et al. 2004. Nitrous oxide emissions following incorporation of improvedfallow residues in the humid tropics. Global Biogeochem. Cycles, 18, GB1032

Millar, N., J. K. Ndufa, G. Cadisch, and E. M. Baggs (2004), Nitrous oxide emissions following incorporation of improved fallow residues in the humid tropics, Global Biogeochem. Cycles, 18, GB1032, doi:10.1029/2003GB002114.


Abstract

The rotation of crops with fast-growing tree, shrub, and herbaceous N₂-fixing legume species (improved fallows) is a central agroforestry technology for soil fertility management in the humid tropics. Maize yields are increased following improved fallows compared with continuous maize cropping or traditional natural-fallow systems consisting of broadleaved weeds and grasses. However, the effect of these improved-fallow systems on N availability and N₂O emissions following residue application has yet to be determined. Emissions from these systems not only have a detrimental effect on the environment, but are of additional concern in that they represent a potentially significant loss of N and a reduction in N-use efficiency. Emissions of N₂O were measured from improved-fallow agroforestry systems in western Kenya, being characteristic of agroforestry systems in the humid tropics. Emissions were increased after incorporation of fallow residues and were higher after incorporation of improved-fallow legume residues (Sesbania sesban, Crotalaria grahamiana, Macroptilium atropurpureum) than natural-fallow residues (mainly consisting of Digitaria abyssibica, Habiscus cannabinus, Bidens pilosa, Guizotia scabra, Leonotis nepetifolia, Commelina benghalensis). Following incorporation of Sesbania and Macroptilium residues (7.4 t dry matter ha⁻¹; 2.9% N) in a mixed fallow system, 4.1 kg N₂O-N ha⁻¹ was emitted over 84 days. The percentages of N applied emitted as N₂O following residue incorporation in these tropical agroforestry systems were of the same magnitude as in temperate agricultural systems. N₂O (log_e) emissions were positively correlated with residue N content (r = 0.93; P < 0.05), and thus the residue composition, particularly its N content, is an important consideration when proposing management practices to mitigate N₂O emissions from these systems.

Valentini et al. 2013. The full greenhouse gases budget of Africa: synthesis, uncertainties and vulnerabilities

Valentini, R., Arneth, A., Bombelli, A., Castaldi, S., Cazzolla Gatti, R., Chevallier, F., Ciais, P., Grieco, E., Hartmann, J., Henry, M., Houghton, R. A., Jung, M., Kutsch, W. L., Malhi, Y., Mayorga, E., Merbold, L., Murray-Tortarolo, G., Papale, D., Peylin, P., Poulter, B., Raymond, P. A., Santini, M., Sitch, S., Vaglio Laurin, G., van der Werf, G. R., Williams, C. A., and Scholes, R. J.: The full greenhouse gases budget of Africa: synthesis, uncertainties and vulnerabilities, Biogeosciences Discuss., 10, 8343-8413, doi:10.5194/bgd-10-8343-2013, 2013.

Abstract
 
This paper, developed under the framework of the RECCAP initiative, aims at providing improved estimates of the carbon and GHG (CO₂, CH₄ and N₂O) balance of continental Africa. The various components and processes of the African carbon and GHG budget were considered, and new and available data derived by different methodologies (based on inventories, ecosystem fluxes, models, and atmospheric inversions) were integrated. The related uncertainties were quantified and current gaps and weakness in knowledge and in the monitoring systems were also considered in order to provide indications on the future requirements. The vast majority of the results seem to agree that Africa is probably a small sink of carbon on an annual scale, with an average value of −0.61 ± 0.58 Pg C yr⁻¹. Nevertheless the emissions of CH₄ and N₂O may turn Africa into a source in terms of CO₂ equivalents. At sub-regional level there is a significant spatial variability in both sources and sinks, mainly due to the biome's differences and the different anthropic impacts, with southern Africa as the main source and central Africa, with its evergreen tropical forests, as the main sink. Emissions from land use change in Africa are significant (around 0.32 ± 0.05 Pg C yr⁻¹) and even higher than the fossil fuel ones; this is a unique feature among all the continents. In addition there can be significant carbon losses from land even without changes in the land use (forest), as results from the impact of selective logging. Fires also play a significant role, with 1.03 ± 0.22 Pg C yr⁻¹ of carbon emissions, mainly (90%) originated by savanna and woodland burning. But whether fire carbon emissions are compensated by CO₂ uptake during the growing season, or are a non-reversible loss of CO₂, remains unclear. Most of these figures are subjected to a significant interannual variability, on the order of ± 0.5 Pg C yr⁻¹ in standard deviation, accounting for around 25% of the year-to-year variation in the global carbon budget.

These results, even if still highly uncertain, show the important role that Africa plays in the carbon cycle at global level, both in terms of absolute values and variability.

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.