Abstract
The soil order of Alfisols is one of the most intensively used for agriculture in the tropics, exhibiting not only signs of erosion but also declining levels of productivity as measured by crop yields. Data sources from Nigeria and the United States, with supplementary information from Indonesia and Australia, are used to establish the form of the relationship between cumulative erosion and yield levels of crops. For the most critical types of Alfisol - those with a strong textural and/or chemical contrast between topsoil and subsoil - initial yield decline is dramatic. The implication is that yield decline under tropical conditions may be at least an order of magnitude greater than under equivalent temperate conditions, but that much more information is urgently needed in order to cost accurately the on-site impacts of allowing erosion to continue unchecked.
