Changing tropical soil fertility paradigms: from Brazil to Africa and back

The development of tropical soil fertility paradigms in subhumid Brasil and subhumid Africa and the interaction between the regions is described and discussed. The first paradigm: overcome soil constraints through the application of fertilizers and amendments to meet plant requirements, was successfully applied in domesticating the Brazilian savanna (Cerrado) during 1970s and 1980s. The second paradigm: optimize biological efficiency: rely more on biological processes, to optimize nutrient cycling, minimize external inpusts and maximize the efficiency of their use has evolved gradually, first with the concept of adapting plants for tolerance to aluminum toxicity and for phosphorus efficiency, followed by overall nutrient management, and the deliberate incorporation of soil biological processes. A combination of both paradigms was essentially started in the 1990s, which also incorporates ecological and social considerations. The Brazilian experience in managing acid tropical soils is relevant to much of subhumid Africa. The main difference lies in socio-economic conditions, with Africa dominated by smallholder farmers, largely female. Soil fertitily depletion on smallholder farms of Africa is beginning to be recognized as the fundamental biophysical limiting factor responsible for the declining per-capita food production. Current thinking on natural resource management has resulted in an alternative approach for situations where the first paradigm has not worked: replenish soil fertility as a capital investment in natural resources. This is conceptually similar to what Brazil did in the Cerrado during the 1970s and 1980s. African soils-related research also has several concetps to contribute to Brazil as well, as a third, more integrated paradigm gradually emerges