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Rheinische Friedrich-Wilhelms-Universität Bonn (2014)

Life cycle assessment of carbon and energy balances in Jatropha production systems of Burkina Faso

Baumert, Sophia

Titre : Life cycle assessment of carbon and energy balances in Jatropha production systems of Burkina Faso

Auteur : Baumert, Sophia

Université de soutenance : Rheinische Friedrich-Wilhelms-Universität Bonn

Grade : Doktor der Agrarwissenschaften (Dr. agr.) 2014

Modern bioenergy offers several advantages to Burkina Faso, a country that is heavily dependent on imported fossil fuel and greatly relying on traditional biomass use. In this context, Jatropha curcas has been recently introduced as a low-maintenance energy crop with the potential to increase energy security while contributing to land rehabilitation and climate change mitigation. This study identified J. curcas cultivation systems practiced in Burkina Faso and analyzed their biomass dynamics and carbon (C) accrual over time as well as soil-C stocks. These data, together with the information on J. curcas seed transformation processes, were integrated in a life cycle assessment (LCA) of the greenhouse gas (GHG) emission and energy-saving potential of the complete biofuel production pathways. The studied J. curcas systems include interplanting with annual crops, intensely managed plantations, afforestation of marginal land, plantings along contour stone walls, and traditional living fences. Destructive above- and below-ground biomass determination enabled the identification of growth stages and development of allometric equations relating total shoot and root biomass with the stem diameter that showed very good fits (R²>0.9). Empirical growth models related woody biomass and tree age by a three-parametric non-linear logistic function. According to the model results, the biomass production of J. curcas plants peaked between the 10th and 15th year after planting, with intercropping and intensely managed systems showing the highest stock (21 t ha-1). Afforestation systems on marginal land had the lowest biomass stocks (<0.1 t ha-1), and could not be modeled due to drastic mortality at an early age in the absence of maintenance. Soil analysis did not reveal a clear trend of soil organic carbon (SOC) dynamics over time when comparing the soil carbon status in 4-year-old J. curcas sites with that in the reference cropland. Only J. curcas living fences exhibited significantly higher SOC stocks in the top 20 cm soil based on a chronosequence study covering 20 years of J. curcas cultivation. All J. curcas production pathways showed GHG emission reductions and energy savings of up to 82% and 85%, respectively, as opposed to fossil fuel. Decentralized production of straight vegetable oil and its consumption in stationary diesel engines showed the best performance. However, J. curcas plantation systems had very low land-use efficiency (6.5-9.5 GJ ha-1) and thus a high land-use replacement potential. Carbon-stock gains were attained when introducing J. curcas on croplands. However, the displacement of agricultural activities to other areas can indirectly result in C losses. Human energy accounted for 24% of the total energy balance, indicating high manual labor requirements in small-scale J. curcas systems. Monetary valuation of C offsets via carbon trading schemes showed returns below US$ 350 over 20 years. Overall, J. curcas biofuel production can contribute to climate change mitigation and national energy independency. However, due to low land-use efficiency, high labor requirements and the unsuccessful cultivation on marginal land, J. curcas becomes a direct competitor with food crops and is a not viable option for smallholder farmers. Whereas J. curcas cultivation is yet to be intensified through improved plant material and optimized agronomic management, the traditional hedge systems are a preferable option for seed production as they offer additional benefits of erosion control and field protection to farmers’ fields.

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Page publiée le 1er septembre 2014, mise à jour le 10 novembre 2021