Tropical agriculture presents special challenges for the achievement of the potential yield of major food crops. Many tropical agroecosystems are characterised by strongly weathered, Oxidic and Kaolinitic soils of inherently poor fertility, acid and often young soils that are formed on resistant minerals present in coarse textures (Sanchez, 1977). Rainfall patterns vary from dry and semi-arid areas with unreliable distributions, to areas of excess rainfall interrupted only by a brief dry season. The latter, together with the absence of a cold season (frost) allows weeds, pests and diseases (and also natural control agents) to complete their cycle many times during the year. In the majority of cases, cropping systems in the tropics co-exists with greater biological diversity than in temperate regions. Agricultural production takes place to a large extent in smallholder family farming systems. Farmer priorities and objectives are not always to maximise yields but sometimes just to minimize risks. Tropical agriculture is often embedded in contexts of wide diversity of social traditions and institutions that govern the use of natural resources. Yield gap analyses are particularly challenging in tropical agriculture due to uncertainties with yield potential measures and the lack of experimental references. Under farmers' conditions strictly bio-physical yield-determining factors are often confounded with the impact of local practices, traditions and a multiplicity of production objectives. For instance, what would be the yield potential of cereals intercropped with legumes or other food crops, including perennial crops such as cassava or fruit trees, as practised in several regions of the tropics? The mere determination of average yields under smallholder conditions is poses challenges, du to high spatial variability across and within farms and wide inter-annual variability due to climate, especially in zones of savannah. In many tropical regions of the world, however, m