Horticulture

Production

The six leading peanut-producing countries of the world are India, China, the United States, Nigeria, Indonesia, and Senegal. World production of peanuts in the shell for 1992 was 23 million metric tons, with Asia and. Africa producing 90 percent of the total (FAO 1993).

In the United States, the state of Georgia leads the nation in peanut production, followed by Texas, Alabama, and North Carolina (United States Department of Agriculture 1992). The most famous peanut producer in the United States is former President Jimmy Carter.

Cultivation

Peanuts need hot climates with alternating wet and dry seasons and sandy soils. Ideally, rainfall or moisture from irrigation should total at least an inch a week during the wet season. Peanuts are planted after the danger of frost is gone, when soil temperatures are above 65° I; The soil is usually treated with herbicides, limed, fertilized, and plowed before planting. Insecticides may then be applied, and herbicides are applied between preemergence and cracking time (postemergence). Postemergence practices involve cultivation, insecticides if needed, and herbicides for weed control. Calcium sulfate is provided to maximize peanut fruit development. This addition of calcium is important in peanut fertilization, because insufficient levels can lead to empty pods with aborted or shriveled fruit (Cole and Dorner 1992). Peanuts are usually rotated with grass crops such as corn, or with small grains, every three years. This rotation reduces disease and soil depletion. Efforts have been made to intercrop peanuts with other plants, such as the pigeon pea or cotton, but these have not been successful.

Harvesting

Only about 15 percent of peanut flowers produce fruit. The harvest includes both mature and immature varieties, as all fruits do not mature at the same time, and about 30 percent is immature at harvesting. Maturity can be estimated in a variety of ways. The “shell-out method” for recognition of maturity has to do with the darkening of the skin (testa) and the inside of the hull. The “hull scrape method” is done by scraping the outer shell layer (exocarp) to reveal the color of the middle shell (mesocarp), which is black in the mature peanut. Peanut harvesting involves removing plants from the soil with the peanuts attached (the upright plant is better suited to mechanical harvesting). A peanut combine is used to remove the pods from the plant.

Storage

After harvesting, the peanuts are cleaned by removing stones, sticks, and other foreign material with a series of screens and blowers. For safe storage the peanuts are dried with forced, heated air to 10 percent moisture.

Cleaned, unshelled peanuts can be stored in silos for up to six months. Shelled peanuts are stored for a lesser time in refrigerated warehouses at 32-36° F and 60 percent relative humidity, which protects against insects. A high fat content makes peanuts susceptible to rancidity, and because fat oxidation is encouraged by light, heat, and metal ions, the fruit is best stored in cool, dry places (McGee 1988). On the whole, however, unshelled peanuts keep better than shelled.