The region has an abundance of land, but some of the lowest agricultural yields in the world. Africa's dismal agricultural performance results more from social, economic, political, and institutional problems than from inherent production limitations. Even if one-tenth of the potential is realized, the prospects for meeting the future's food demands appear bright. However, there are constraints as well as opportunities for attaining food security throughout the world. There are several ways to measure crop yield.
Biological yield refers to total plant dry matter production.
Economic yield is the economically useful part of the plant, that is, the harvested portion used for food, fiber, or forage. This measures the proportion of the plant that is economically valuable. The harvest index is often expressed as a percentage. The index suggests that 60 percent of the Georgia Sweet Potato plant is used for food or for another purpose, while 31 percent of a particular wheat variety is economically useful. A high harvest index indicates that future yield increases for that species must come from improving the biological yield.