Legumes: Importance and Constraints to Greater Use

Legumes, broadly defined by their unusual flower structure, podded fruit, and the ability of 88% of the species examined to date to form nodules with rhizobia (de Faria et al., 1989), are second only to the Graminiae in their importance to humans. The 670 to 750 genera and 18,000 to 19,000 species of legumes (Polhill et al., 1981) include important grain, pasture, and agroforestry species. Cohen (1977; cited by Bryan [2000]) reported domestication of lentils (Lens esculenta) at a site in Iran dating to 9,500 to 8,000 BP; Roosevelt et al. (1996) noted the use of Hymenaea as a food source in Amazonian prehistory. Bean (Phaseolus vulgaris) and soybean (Glycine max), staple crops in the Americas and Asia, respectively, were each domesticated more than 3,000 years ago (Hymowitz and Singh, 1987; Kaplan and Lynch, 1999). Use of legumes in pastures and for soil improvement dates back to the Romans, with Varro (37 BC; cited by Fred et al. [1932]) noting "Legumes should be planted in light soils, not so much for their own crops as for the good they do to subsequent crops." This paper briefly overviews the legumes and their importance in different agricultural and natural environments.