Fava Bean

What is a fava bean?

The fava bean is the Mediterranean's own nitrogen fixer. It has been grown around this sea for so long that no one knows its wild form: charred beans from Neolithic sites in Lower Galilee show that people were farming it about 10,200 years ago, yet the wild plant from which it descends has never been found. Since then it has fed people, livestock and soil.

Its rhythm fits the Mediterranean climate exactly. It is sown with the first autumn rains, grows through the cool, wet winter and ripens in spring, before the summer drought begins. During this time it fixes nitrogen in its root nodules. Among the nitrogen-fixing plants it is the classic of the winter half-year: food, fodder and green manure in one plant.

Origin and growth

The fava bean comes from the Near East, the region where wheat, barley, lentil and pea were also domesticated. It is an upright annual with a square, hollow stem, blue-green leaves divided into a few broad leaflets, and white flowers with a black spot, much visited by bees. The pods stand upright at first, later hang, and contain a few large seeds. Over millennia of cultivation many forms have arisen, from the large-seeded vegetable bean to the small-seeded field bean used as fodder and green manure.

Requirements

The fava bean is a cool-season crop. It grows best in mild, moist weather and suffers in heat. In the Mediterranean it therefore belongs to winter: sown in October or November, it lives on winter rain and needs no summer water. It tolerates light frost, but how well depends less on the minimum temperature than on hardening. In a trial with 24 varieties at two Italian sites, more plants died at mild Foggia (minus 3.4 °C, eight frost days) than at Lodi in the north (minus 7.3 °C, 54 frost days), because the plants in the south had not hardened before late frosts. It prefers deep, loamy soils that are not too acidic, and full sun.

Role in the soil: nitrogen, biomass and mulch

Its partner is Rhizobium leguminosarum symbiovar viciae, which also nodulates peas, vetches and lentils. The fava bean is one of the strongest fixers among the cool-season grain legumes: according to a review in Field Crops Research it draws about 70 to 95 percent of its nitrogen from the air. Matching bacteria are common in farmland; a study in northern Britain found effective strains even in fields without recent legume cropping. More on the partnership is in the article on rhizobia.

What happens to that nitrogen depends on the harvest. Dry beans take much of it away. Cut at flowering, the whole plant becomes green manure or mulch and returns most of its nitrogen to the soil. Even after a bean harvest, roots and stems leave nitrogen and organic matter behind. That is why the small-seeded field bean is a traditional green manure in olive groves and vineyards in Italy: sown in autumn, cut in spring, left on the ground.

In the food forest

In a food forest the fava bean belongs to the herb layer, and to the winter. Between young trees it fills the ground in the season when the trees are dormant and light falls through. In syntropic agriculture such crops make up the first, shortest-lived stage: they are sown together with trees and shrubs, harvested or cut after one season, and their remains feed the plants that stay. Because it grows in winter and is gone by summer, it does not compete with summer crops for water. As a cover crop it protects bare soil from the heavy winter rains.

In the Mediterranean climate

Here the fava bean is at home. It has been grown in Sardinia, Sicily, Spain, Greece and the Levant since antiquity and belongs to the traditional winter cultivation of the whole region. Mediterranean breeding aims at varieties adapted to autumn sowing, and in southern Italy early winter sowing gave better yields than late sowing in field trials. The main risks are a late cold snap after a mild winter, spring drought during flowering and pod fill, and the black bean aphid on the shoot tips in spring.

The fava bean is a field crop and not on any list of invasive species.

Propagation and care

Fava beans are sown directly in autumn, about five centimetres deep. They need no fertiliser nitrogen. Tall varieties are staked in windy places. Pinching out the shoot tips after flowering reduces aphid damage. For green manure the plants are cut at full flowering and left on the bed; for beans they are harvested green in spring or left to dry.

A word of caution belongs here, especially in Sardinia. People with an inherited G6PD deficiency can suffer a severe breakdown of red blood cells after eating fava beans, known as favism. The deficiency is relatively common in Sardinia; in the district of Sassari, according to a study from the early 1990s, about 7.5 percent of males have it.

How Terra Humana understands it

At Sa Medada the fava bean stands for the oldest form of soil care in this landscape: a winter crop that feeds people and leaves nitrogen behind. It connects the new planting with a peasant practice that is far older than any of the trees. That it belongs to the place is clear; what it can contribute between young trees is what remains to be seen.