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Farmers in large parts of the tropics have no tradition of aiming at maximum production per hectare; their main concern was to reduce the risk of crop failure. The principal reason is that - except in the main population centres - there were no convenient markets for food surpluses. The traditional farming systems were integrated, based on self-sufficiency and hence on internal supplies and services between different farm components: mixed cropping with a legume supplying nitrogen to a cereal, field crops supplying fodder for livestock in exchange for manure, etc.

Version 4, 2007