WEST LAFAYETTE, Ind. — After decades of bad news, at least three major trends are turning Africa's way: agricultural policies, rural demography and farm productivity all promise improved opportunities for farm families across the continent.

Novelties get the most attention, such as the possibility that outside investors might control large areas of farmland. Spatial diversity is also important, because it ensures that each place differs from the aggregate average. For Africa as a whole, at least three slow trends have had recent turning points that offer game-changing new incentives for entrepreneurs and governments.

The first turning point is political. New data from a World Bank study shows for the first time just how far today's African governments have gone to reduce the cost to farmers of export taxes, marketing boards and other interventions imposed by previous regimes.