Drivers of soil fertility in smallholder banana systems in the African Great Lakes Region

Banana is a crop of major importance in the African Great Lakes Region, because of the food and cash it provides to about 85% of the population. Despite the management efforts of smallholder farmers, on-farm banana yields are low. Low yields are mainly attributed to poor soil fertility and limited input use, drought or irregular rainfall, pests and diseases and inappropriate management practices. Relying on observations on banana plants, crop management, pests and soils in various agro-ecoregions in Rwanda and South-West Uganda, this PhD-thesis contributes to the understanding of the traditional banana-based systems by (1) ranking constraints and quantifying associated yield losses, (2) evaluating the temporal and spatial variations of soil nutrient pools, (3) relating soil fertility to the mineralogical and organic components of the soil. Hence, a Boundary Line Analysis on the available data shows that the gap between actual production and attainable yield may attain 70-96% and that poor soil fertility is an overall problem in the Great Lakes Region. Further analysis of plant foliar data highlights associated nutritional disorders. Banana production does not only vary at regional scale in function of soils and parent materials, but also changes at inter-regional or intra-farm level. Within-farm differences may relate to differential management of organic matter. In order to assess the human imprint on soil fertility, organic matter and soil minerals are evaluated as nutrient providers and as contributors to the cation exchange capacity of the soil. These analyses quantify soil mineral abundances and emphasize the key role of organic matter in maintaining soil fertility.(AGRO 3) -- UCL, 201