Yams are a group of monocot plants, precisely speaking, a group of perennial herbaceous vines grown for their starch-rich, edible tubers. They belong to the family Dioscoreaceae and genus Dioscorea. Yams are widely grown in both temperate and tropical parts of the world and considered as an important food crop in the tropical areas of America, Asia and Africa. Yams are a rich source of carbohydrates. There are white yams, purple yams and yellow yams, depending on the colour of the tuber flesh.
Dioscorea Species: The genus Dioscorea contains about 250 species of plants of which all species do not produce edible tubers. Some are weeds or invasive plants while others are cultivated for edible tubers. Among the species cultivated are Dioscorea alata, Dioscorea esculenta, and Dioscorea caryenensis.
In many parts of tropical Asian countries, purple yam is the most popular variety of Dioscorea tubers. Scientific name of purple yam is Dioscorea alata. It is also known as greater yam. The tuber flesh of greater yam is purple and therefore the name, ‘purple yam.’ These plants produce large edible tubers, some of which weigh up to 30 kg. Large tubers are used for propagation purposes while small and medium tubers are used for food purposes.
esculenta is the most commonly grown Dioscorea species in the Indian subcontinent. Tubers of these plants are white coloured. Dioscorea caryenensis is known as ‘yellow yam’ because tubers of these plants are yellow in colour.
Other Species of Yams: D. batatas (Chinese yam) and D. bulbifera, (air potato) are also popular among yam-growers. These yams are grown for their edible aerial tubers.
Origin and Distribution: Yams are believed to be a native of Africa, Asia and America. In some parts of these regions, yams grow naturally as invasive plants.
Food Uses of Yams: Yams are used as vegetables and also as a staple food. Yam tubers can be consumed after baking, boiling, steaming, stir frying, microwave cooking, and roasting. Yams contain some acrid/pungent compounds which are eliminated while cooking by boiling or steaming.
Yams are often confused with sweet potatoes. But true yams, which differ in tuber sizes considerably (from the size of a small potato to the size of over 60-65 Kg tuber), are entirely different from sweet potatoes.
Growing Requirements: A detailed account of growing practices for yams is as given below:
Climate: Yams are tropical plants and hence warm, tropical climate is best for its healthy growth. Plenty of sunlight is needed for these plants.
Soil: Deep, rich, friable, well-drained and loose sandy loam soils are the most ideal for growing yams.
Propagation: Propagation is by division of tubers. These tuber cuttings are planted in a well-prepared nursery beds to allow sprouting. Sprouted tuber cuttings are then transplanted in the main field in pits/holes of appropriate size (at least 5 inches deep and 3 inches wide). While planting care is taken to place the sprouted leaves above the ground level.
Watering: Soon after planting, water the plants. Watering should be done regularly until plants get established in the field. Thereafter, need-based watering is done.
Manure Requirements: Just like other tuber crops, yams also need nitrogen for its vegetative growth and plenty of phosphorous for tuber development. Large quantities of farm yard manure or compost may be added to the top soil to replenish the soil fertility at the time of field preparation. Fertilizers for yams should be high in phosphorous.
Spacing: Under right growing conditions, yam plants grow vigorously and need sufficient space for tuber production. Hence it is recommended that at least one meter spacing should be given between two plants in each way.
Staking: Growing young yam plants may need staking sometimes. Plants are usually staked on bamboo supports or on trellis.
Harvesting: Yams are ready for harvest within 4 months. Harvested tubers are very tender and brittle and so sufficient care is to be taken at the time of handling.
Storage: If yams are stored in a cool, dry, hygienic place, it will last for several months. The best storage temperature is 14 to 15 Degree Celsius.
Medicinal Properties of Yams: Not all yams have medicinal properties. Some wild species of Dioscorea are known to have medicinal properties. Their extracts are used for treatment of arthritis.
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