Browsing by Author "Tumwebaze, Susan"
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Item Allometric relationships and carbon content for biomass-carbon estimation of East African Highland Bananas (Musa spp. AAA-EAHB) cv. Kibuzi, Nakitembe, Enyeru and Nakinyika(African Journal of Agricultural Research, 2018) Kamusingize, Daphine; Mwanjalolo Majaliwa, Jackson; Komutunga, Everline; Tumwebaze, Susan; Nowakunda, Kephas; Namanya, Priver; Kubiriba, JeromeGlobally, interests to increase carbon stocks have gained momentum in both woody and non-woody ecosystems. Despite efforts made to generate appropriate methods to estimate these stocks, most equations developed do not cater for intraspecific variabilities across e.g. species, regions or growth stages; especially in the case of bananas. Therefore, there is need to develop more robust equations to improve on the precision of biomass-carbon prediction especially at local scales to facilitate estimation of specific carbon stocks often lost in global assessments. This study aimed at developing cultivarspecific biomass estimation relationships and determining carbon content of EAHB cultivars at two growth stages. Plant data were collected purposively using destructive sampling techniques on farmers’ plots for 4 cultivars (Kibuzi, Nakitembe, Enyeru and Nakinyika) in two agro-ecological zones: the L. Victoria crescent and the South-western farmlands in the districts of Lwengo and Mbarara respectively. Results show that biomass differed across cultivars (P<0.001); hence four equations (Enyeru, Nakinyika, Kibuzi_Nakitembe and Generic) were developed following an exponential function, y=Aexp(ax), using diameter at breast height (DBH) as the predictor variable with an R2 range of 82-94%. EAHB mean carbon content varied significantly with growth stage (P<0.05) (47.6% for maiden plants before flowering and 48.8% for mature plants with a developed bunch). This study concludes that it is important to develop cultivar-specific equations for biomass-carbon estimation of EAHB cultivars to help assess their contribution to the carbon cycle especially in future studies.Item Carbon sequestration potential of East African Highland Banana cultivars (Musa spp. AAA-EAHB) cv. Kibuzi, Nakitembe, Enyeru and Nakinyika in Uganda(Journal of Soil Science and Environmental Management, 2017) Kamusingize, Daphine; Mwanjalolo Majaliwa, Jackson; Komutunga, Everline; Tumwebaze, Susan; Nowakunda, Kephas; Namanya, Priver; Kubiriba, JeromeDespite the global interest to increase the world's carbon stocks, most carbon sequestration strategies have largely depended on woody ecosystems whose production is threatened by the continuous shortage of land, hence the need to explore viable alternatives. The potential of bananas to sequester carbon has been reported but there is limited knowledge on the performance of various cultivars as specific carbon stocks are often lost in global assessments. Therefore, this study aimed at exploring the potential of and variability in carbon stocks of selected East African Highland Banana (EAHB) cultivars. Plant and soil data were collected using destructive and non-destructive techniques in 30×30m2 sampling plots for 4 cultivars Kibuzi, Nakitembe, Enyeru and Nakinyika growing in two agroecological zones of Uganda being the L.Victoria Crescent and the South-western region. Total carbon and Soil Organic Carbon (SOC) stocks did not differ considerably across cultivars (P>0.05). However, there was significant variation (P<0.05) in plant carbon stock being lowest in two cultivars: Nakinyika at 0.37±0.19 Mgha-1 and Nakitembe at 0.40±0.19Mgha-1; and highest in Enyeru at 1.64±0.18 Mgha-1. The SOC stock variation difference across depth was 2.9-8.5 Mgha-1 being higher in top soil than sub-soil. Despite the small plant carbon stock amounts, the system enables much more carbon to be stored in the soil considering the proportion of what is contained in the plant to that in the soil across all cultivars (0.4-2%). The study therefore recommends revision of existing carbon frameworks to incorporate the contribution of non-woody perennials like bananas in the carbon cycle so that the poor small scale farmers who cannot afford large acreages to establish tree plantations can also benefit from such initiatives.Item The Economics Of The Carbon Sequestration Potential Of Plantation Forestry In South-Western Uganda(a Journal of Forest Science, 2016) Kiyingi, Isaac; Edriss, Abdi-Khalil; Phiri, Alexander MR; Mukadasi, Buyinza; Tumwebaze, Susan; Agaba, HillaryThis study assessed the amount of carbon stored and the economic viability of the small-scale Clean Development Mechanism (CDM) carbon offsets in Pinus caribaea and Eucalyptus grandis plantations under varying rotations. Volume equations were used to estimate carbon stocks and merchantable wood volume in the plantations, while net present value (NPV) and annual equivalent value (AEV) were used as measures of profitability at the optimum economic rotation age as well as at the CDM-defined crediting period of 20 years. The findings show that over a 20-year rotation, E. grandis and P. caribaea plantations sequestered 638 and 418 t CO2-e ha−1, respectively. The NPVs of E. grandis and P. caribaea with carbon credits over the CDM carbon-crediting period of 20 years were US$2 540 ha−1 and US$1 814 ha−1, respectively. This is higher than the NPVs without carbon credits of US$1 543 ha−1 and US$1 390 ha−1 for E. grandis and P. caribaea, respectively. The AEV of E. grandis harvested at its optimal economic rotation of 10 years was US$316 ha−1. This is slightly higher than the AEV of US$298 ha−1, utilising the CDM carbon-crediting period of 20 years. In contrast, the AEV of P. caribaea under the 20-year CDM carbon-crediting period was higher than harvesting at the optimal economic rotation of 16 years without carbon credits. When the average CDM contract establishment costs exceed US$500 ha−1 and US$1 000 ha−1 for P. caribaea and E. grandis woodlots, respectively, it is not economically viable for one to participate in the CDM forest carbon offsets programme. In conclusion, the study results indicate that whereas E. grandis has a higher biological potential to sequester carbon than P. caribaea, it is currently not economically viable for participation in the CDM forest carbon offset scheme. In contrast, it is economically viable for P. caribaea plantations to participate in the CDM, if the CDM contract establishment costs are low.Item Effect of Two Years of Conservation Agricultural Practices on Weed Seed Banks Evaluated Using Three Techniques(East African Nature and Science Organization, 2024-07-06) Otim, Godfrey Anyoni; Ocan, David; Kumakech, Alfred; Tumwebaze, Susan; Obia, AlfredUnderstanding the soil seed bank is very important when developing integrated weed management technologies and detecting the influence of crop management practices on weeds. In conventional weed control, farmers tend to focus on the above-ground, yet the above-ground vegetation is related to the below-ground soil seed bank. Several soil seed bank estimation methods have been used to estimate the soil seed bank, but varying results have been obtained under different field management practices and soil depths. In this study, we compared three methods for estimating the soil seed bank: seedling emergence method and two direct seed extraction methods (floatation and cloth bag) for determining weed seed density and diversity from different soil depths under conservation farming practices. The three methods had significant differences in estimating weed densities from the soil seed bank (p<0.001). The greenhouse seedling emergence method had a mean number of 5.06, cloth bag had 4.07 while floatation method had the lowest number of 3.38 per 300g of soil. The mean highest weed density was obtained from soil depth of 0-15 cm (5 weeds/300g vs 1.6 weeds/300g of soil from 15-30 cm depth). For soil seed bank diversity, cloth bag method had the highest mean value followed by greenhouse emergence and lastly floatation method with Simpsons diversity index of 2.72, 1.79 and 1.31, respectively. Shannon Weiner diversity index followed the same pattern for the three methods. The methods had different sensitivity to density and diversity and therefore greenhouse emergence method should always be combined with cloth bag method. The greenhouse emergency method detected a total of 26 weed species, cloth bag detected 22 weed species and Floatation method detected 18 weed species. Despite, the greenhouse emergence method detecting more species than the cloth bag at 26 and 22 weed species, respectively, it had a lower Simpson’s diversity index than the cloth bag method due to lower species evenness. Sampling of the entire soil plough layer of 0-30 cm depth for disturbed agricultural soils may produce the best results. Seasons significantly influenced soil seed bank diversity and not soil seed bank density where second season (B) significantly increased soil seed bank diversity. Soil cover practice through intercropping maize with soybean significantly reduced soil seed bank density and not diversity in both minimum and conventional tilled plots. This positive influence on weed density and diversity is a good indicator for integration into a weed management programItem Minimum Tillage and Soil Surface Cover Reduced Weed Density but Not Diversity Over Four Growing Cycles(East African Nature and Science Organization, 2024-10-01) Otim, Godfrey Anyoni; Ekwangu, Joseph; Tumwebaze, Susan; Obia, AlfredThis study investigated use of cultural practices to address weed challenges that present one of the highest costs to farmers. The parameters explored included the effects of tillage and soil cover practices on weed density and diversity, evaluated in a split plot experimental design. Increasing rainfall amounts significantly increased weed density and weed diversity. Minimum tillage significantly suppressed weeds with a density of 80/m2 compared to conventional tillage density of 124/m2. Soil cover practices similarly suppressed weed density (p<0.05) compared to sole crops without soil cover intervention. Maize with mulch had the lowest density (64/m2) followed by maize intercropped with one line of soybean between maize being more effective in weed suppression (92/m2 vs 113/m2). Sole maize and sole soybeans treatment both had a density of ~121/m2. Weed diversity, as measured by Shannon-Weiner index and Simpsons index were not statistically different across treatment (p>0.05). However, weed species count was higher in minimum tillage by 05% compared to conventional tillage, hence it calls for investment in minimum tillage and intercropping practices to allow a more diverse weed community that will be less competitive, less prone to dominance by highly adapted weeds, hence promoting ecological sustainabilityItem Pathogenicity of Teratosphaeria species on Eucalyptus grandis and selected hybrids in Uganda(Journal of Forest Research, 2021) Syofuna, Agatha; Nakabonge, Grace; Namayengo, Sarah; Tumwebaze, Susan; Banana, AbwoliTeratosphaeria stem canker is one of the most important diseases to have emerged on non-native plantation-grown Eucalyptus trees cultivated globally. The study assessed the pathogenicity of two Teratosphaeria species associated with Teratosphaeria stem canker and the susceptibility of Eucalyptus grandis and six commonly grown Eucalyptus hybrids to these fungal species in Uganda. The inoculation trials indicated that Eucalyptus species and hybrids were susceptible to fungal pathogens used. A comparison of Eucalyptus species and hybrids for each fungal species showed that GC 540 and GC 796/2 are the most susceptible hybrids to T. zuluensis and T. gauchensis respectively while hybrid clone GU 8 had a higher tolerance to both fungal species. GC 540 was also tolerant to T. gauchensis while F2 and GC 550 were tolerant to T. zuluensis. Eucalyptus grandis sourced from Australia (F2) showed a higher tolerance than Eucalyptus grandis from South Africa (F1). The results further revealed that both Teratosphaeria zuluensis and Teratosphaeria gauchensis are pathogenic to Eucalyptus species and hybrids. The generated information indicates that there is an opportunity to sustainably manage Teratosphaeria stem canker disease if tolerant species are grown in areas with high disease impact.