Agriculture and Environment: Commodities
Overview: Cashews (Anacardium occidentale)
The cashew is native to northeast Brazil. At the time of Portuguese colonisation, cashew was a major food crop for Indians throughout the region.
Large native stands of cashew trees were found throughout the northeast, especially on coastal lands but also well inland.
Toxic leaf compound, caustic seed cover The leaf of the cashew tree contains compounds that are toxic to other plants and animals. Leaf fall discourages the growth of other vegetation under the cashew tree.
Also, the seed is surrounded by a concentrated caustic solution that burns the skin. This prevents wild animals from eating the seeds. These two characteristics encourage the growth of large stands of cashew trees that dominate the landscape.
Quite old, quite huge
Cashews can grow to be quite old. Unlike many trees, however, as they get older they tend to sprawl and branches touch the ground, take root, and become the base of other trunks that continue to sprawl, take root, and expand the tree farther and farther from the original base.
The oldest and largest cashew tree now alive in Brazil is so old that it has spread over an entire hectare of land (Morton 1987). While little more than a foot in diameter at the main trunk, the tree is estimated to be more than a thousand years old.
Mature trees commonly have a canopy diameter of 12 metres. However, studies of roots show that while they often grow quite deep to tap into water sources, they also spread laterally at distances that are commonly twice that of the canopy.
Dry conditions favour flowering
The cashew is unusual because it flowers, sets fruit, and maintains a full leaf covered during the driest part of the year. Good yields occur when it is dry during the peak flowering period. About 14% of flowers are hermaphroditic; the remainder are male. About 70% of the hermaphroditic flowers fail to produce nuts. The crop is mainly cross-pollinated. Insects play an important pollinating role, as does the wind. The period from flowering to fruit fall is from 55 - 70 days.
Good source of controlling soil erosion
In the sixteenth century, the Portuguese took cashew seeds to Africa, India, the Middle East, and other parts of the world. The value of the plant at that time was as cheap food (fruits and kernels), but more importantly it was a way to stop soil erosion in coastal areas. Cashews grow well in sandy soils and are extremely tolerant of saline soils. Cashews are grown throughout coastal areas in the tropics.
Traded for its nuts
The trees produce nuts, fruits, gum, and charcoal. The only cashew product traded in any quantity internationally, however, is the nuts. The cashew fruit is as unusual as the rest of the tree. The shell of the nut is leathery and sponge like, not brittle, and contains a thick oil.
Credits
