Acacia senegal, soil organic carbon and nitrogen contents : a study in north Kordofan, Sudan

Abstract: In 2001, the Intergovernmental Panel on Climate Change approved human impact (mainly through the emission of carbon dioxide (CO2)) on global warming. The Kyoto Protocol is a global contract that proposes the reduction of CO2 and five other greenhouse gases by 2012 to at least 5% below the level of 1990. One reduction strategy included in the Protocol is the Clean Development Mechanism (CDM). It suggests that industrialized countries invest in projects in developing countries that sequester carbon and promote sustainable development in the host country. A controversial issue within the Protocol is the acceptance of carbon sequestration in sinks (soils and vegetation) as a means to reduce atmospheric CO2. This master thesis was conducted in collaboration with the Centre for Environmental Studies at Lund University (MICLU) in the context of carbon sequestration in soils of semi-arid regions. MICLU’s research is concentrated on North Kordofan, Sudan, a region suffering from severe environmental degradation. The basic idea of the study was to investigate if soils beneath Acacia senegal have the potential to sequester soil organic carbon (SOC) on a higher level than other land use types. Acacia senegal is a leguminous tree species traditionally cultivated during fallow periods. Fieldwork was carried out during February 2002 and included interviews with farmers, soil sampling and biomass measurements. The thesis focused on the following questions: (1) Does Acacia senegal influence SOC and nitrogen content of the topsoil? (2) Does nitrogen influence the SOC content beneath Acacia Senegal stands? (3) Are SOC contents simulated by the Introductory Carbon Balance Model (ICBM) similar to my field observations? The study shows that: (1) There is a significant difference between SOC and nitrogen content in the topsoil of fallow fields with Acacia senegal and that of crop fields. (2) There is a significant positive correlation between SOC and nitrogen content under both fallow fields with Acacia senegal and under undisturbed sites without Acacia senegal. (3) The SOC content simulated by the ICBM does not coincide with the SOC content measured in 2002. The number of soil samples taken was small and further research has to be done to confirm the results of this study. The ICBM has to be calibrated to semi-arid conditions with a time series of a well-investigated area before it can be used as a meaningful tool for soil carbon simulations.