Impact de la culture du cacao sur la séquestration du carbone dans le sol et la communauté microbienne au Ghana et en Côte d'Ivoire

Abstract

Results of the present study provide relevant social and ecological insights on cocoa agroforestry system in West Africa. In general, cocoa land use tends to have major implication on soil properties due to unstainable land conversion and management, and climate change, thereby making soils of these production systems function below their productive capacity and stability. Understanding how this cultivation system under climate change impact soil properties, and cocoa plant growth is crucial for sustainable soil management, climate change mitigation and conservation actions under climate and land use changes in Ghana and Côte d'Ivoire. Specifically, the study assessed farmers’ perceptions and views of relevant stakeholders of how sustainable agroforestry should be designed to be able to achieve climate change mitigation and biodiversity conservation through the cocoa supply chain in Ghana and Côte d'Ivoire. Evaluated the impact of cocoa agroforestry management on soil physico-chemical properties and soil organic carbon sequestration. It has also characterized soil microbial population and communities common to the cocoa agroforestry farms in these countries. Finally, it has determined the growth rate and anatomical traits, and the climate-growth relationship of cocoa trees. To achieve these objectives, a face-to-face interview and semi-structured questionnaire were used to assess 201 (CI=100 and GH=101) farmers’ perceptions of sustainable agroforestry, climate change mitigation and biodiversity conservation and how it can be achieved through the cocoa supply chain. Soil properties were analyzed from samples collected from the surface (0-15 cm) and subsurface (15-30 cm) soil depths of treatment plots from three stands of different aged cocoa agroforestry, designated as 5, 15 and 30 years old farms in Ghana and Côte d'Ivoire. Dendrochronological studies were used to investigate the anatomical growth responses of cocoa tree to climate. The results indicate that high proportion of the respondents (89 and 88 % from Côte d'Ivoire and Ghana respectively) were not very much aware of soil carbon and its management, agroforestry and biodiversity and lack knowledge of strategies through which they can be achieved on the cocoa farmers farm. Farmers were very much aware of the drivers of climate change. Further results show that soil organic carbon and microbial communities differed considerably between farms (5, 15 and 30 years old) and between sites. Generally, SOC, SOCD sequestration were higher in the cocoa agroforestry farms in Ghana than Côte d'Ivoire. The results further showed that 15 years old farm in both countries perform higher in terms of most of the soil properties measured. The results obtained indicate positive correlations between soil pH and soil nutrient and their interactions. Analysis of the anatomical characteristics of the wood of the cocoa tree revealed the formation of distinct growth rings. The results show irregular growth trends and anatomical vessel traits varied across farms. Climate has significant influence on the growth and anatomical characteristics of cocoa. The study shows that immediate calls for education and more training are needed on sustainable management practices within the cocoa agroforestry system, the reinforcement of soil system and restoration actions are crucial for achieving future agriculture and forest sustainability in Ghana and Côte d’Ivoire.