TECHNICAL PAPER # 17
UNDERSTANDING THE PRODUCTION
OF THE MAJOR
TROPICAL/SUB-TROPICAL ROOT CROPS
SWEET POTATOES, YAMS AND COCOYAMS
Dr. Nail H. Ozerol
Dr. Herbert F. Massey
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 * Fax:
Understanding the Production of the Major
Tropical/Sub-tropical Root Crops
1984, Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in
Assistance to provide an introduction to specific
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their
They are not intended to provide construction or
details. People are
urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and
almost entirely by VITA Volunteer technical experts on a
Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time.
VITA staff included Leslie Gottschalk
and Maria Giannuzzi as editors, Julie Berman handling
and layout, and Margaret Crouch as project manager.
VITA Volunteer Dr. Nail Ozerol, the author of this paper, is
director of N. H. Ozerol & Associates, a consulting firm
in nutrition and preventive medicine.
He was formerly on
the faculty of the Department of International Health,
Medicine, Howard University, and that of the Center of
Meharry Medical College.
He has consulted on nutrition in several
Dr. Herbert F. Massey, reviewer of this
paper, has been a VITA Volunteer for 14 years.
He is the director
of International Programs for Agriculture at the College of
Agriculture, University of Kentucky.
He has consulted on agricultural
teaching and/or research projects in several tropical
countries throughout the world.
VITA is a private, nonprofit organization that supports
working on technical problems in developing countries.
information and assistance aimed at helping individuals and
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and publishes a variety of technical manuals and papers.
UNDERSTANDING THE PRODUCTION OF THE MAJOR
TROPICAL/SUBTROPICAL ROOT CROPS:
POTATOES, SWEET POTATOES, YAMS, AND COCOYAMS
By VITA Volunteer Nail H. Ozerol
Root crops is a general term commonly used for a wide
food plants that have an underground storage organ known as
root, tuber (rhizome), corm, or bulb.
Root crops are rich in
starch, and low in protein and oil.
They are excellent sources of
calories. Some are
consumed as major staples, such as cassava,
potatoes, sweet potatoes, yams, and the aroids (cocoyams).
Others, such as carrots, onions, garlics, parsnips, and
are used as fresh vegetables.
Historically, governments and academic centers have paid
little attention to root crops as compared to grain crops.
These crops have been regarded as inferior food, and
consumed only by the subsistence farmers in the developing
of the world. In
recent years, however, the tropical root crops
have been "rediscovered" by the research
communities and others
who are concerned with the food and nutrition problems of
The tropical root crops, in general, have a great potential
meeting basic food and energy needs of the developing world,
therefore deserve to be fully explored in rural development
projects and strategies.
Reliable estimates suggest that annual
tropical root crop production is in the range of 170 million
metric tons, roughly equivalent, in calorie content, to 50
metric tons of grain.
There is now a sharp increase in
scientific research and investigation in every aspect of
crop in certain well-established research centers, such as:
International Institute of Tropical Agriculture (IITA),
Nigeria; International Center for Tropical Agriculture
Cali, Colombia; and International Potato Center (CIP), Lima,
Peru. The following
factors have been responsible for the growing
international interest in the food potentials of these
A growing interest in and appreciation of a
of rural poor
who depend on these crops for their basic
Increased population growth, and the
relative rise in the
fossil-based energy have contributed a great
interest in root crops as source of food and energy.
World food shortages, and the
ever-increasing need to
frontiers in order to alleviate world hunger.
ADVANTAGES AND DISADVANTAGES OF ROOT CROPS
Root crops have the following advantages:
They are rich in starch and calories.
They grow well in a wide range of soil types
so long as
They require relatively little care in terms
of labor and
used in their production.
Unlike cereals, they can be stored without
drying in a
highly humid environment.
Relatively few serious pests and diseases
with those associated with cereals and
Some root crops, such as cassava, can be
left in the
food resources until required.
The disadvantages of root crops are as follows:
They are low in protein and oil.
Their awkward shapes and large size make
them prone to
transit and secondary infection by micro-organisms.
They are bulky to handle in trade,
marketing, and storage
due to their
high moisture content.
MAJOR USES OF ROOT CROPS
The following three major uses of root crops, both tropical
subtropical, are now universally recognized.
Root Crops as Food
Root crops are a major source of food and calories in many
countries. The Food
and Agriculture Organization estimates
for 1974 suggest that root crops provide 20 percent of the
caloric intake for 11 countries, and nearly 40 percent or
all calories in Zaire, Ghana, and Togo.
Again, they are basic
calorie sources in Brazil and Indonesia and also provide
Root crops are usually prepared to be eaten in another dish,
as in various stews.
The high starch content in the crops helps
to thicken the liquid base, so that it adheres to the meat
vegetables in the stew.
Root Crops as Feed
The use of root crops as feedstuffs in developing countries
studies in Venezuela have demonstrated that
high yields of good-quality protein are obtainable from
leaves at reasonable cost for use in livestock feeding.
cassava leaves have been used for commercial exports as
livestock feeds in Thailand.
Almost all of Thailand's cassava
root crop is exported as dried chips, sometimes pelleted,
for use as animal feed.
In general, cassava products can be
successfully substituted for alternative sources of feed for
different species of livestock in both tropical and
Root Crops as Substrate
Among the most interesting technological developments in the
of root crops are the fermentation processes for the
of sugar, ethyl alcohol, and single-cell protein.
among a few others, has been used extensively as a substrate
(raw material) for the production of ethyl alcohol.
II. MAJOR ROOT CROPS
The five major root crops of the tropics and subtropics are
cassava, potatoes, sweet potatoes, yams, and cocoyams.
other important root crops are listed in Table 1.
Table 1. Important Root Crops
Cassava (Manihot esculenta, Euphorbiaceae) is a perennial
native to South America that is now grown throughout the
Other common names for cassava are tapioca, mandioca,
manioc, sagu, and yuca.
Cassava was brought into cultivation by
the American Indians probably 4,000 years ago, was later
to West Africa in the sixteenth century, and then spread to
other tropical regions of the world.
For a variety of reasons, recent growing research interest
root crops has focused mainly on cassava.
It is a major source
of calories for some 300 million people in the developing
of the world. It is
one of the world's most efficient
plant converters of solar energy to carbohydrates.
more calories of food per unit input of labor efforts than
other crop. It is
relatively resistant to insects and plant
diseases, and requires few inputs of a traditional
system. It is
adaptable to a wide range of agro-climatic conditions,
and performs surprisingly well on acidic soils of poor
fertility. It can be
left in the ground until it is needed.
Fresh cassava roots compare favorably with the other root
in terms of calorie content, but rank at the bottom in terms
roots are generally rich in calcium and ascorbic
acid, and contain significant amounts of thiamine,
and niacin. The
cassava leaves are rich in high-quality protein,
and are consumed in most of the tropical countries.
Cassava is by far the most economically important of the
root crops, with annual production exceeding 100 metric tons
grown on some 12 million hectares.
It is produced in more than 80
countries, but fewer then 20 countries account for 90
A major factor behind the extensive production of cassava is
adaptability to a wide range of soil and moisture
can be successfully grown in areas with rainfall ranging
to 5,000 millimeters.
Except at planting, cassava can withstand
periods of prolonged drought and is, therefore, a valuable
in regions of low or uncertain rainfall.
Light, sandy loams of medium fertility give the best
the crop can be grown successfully on soils with a pH
from 4.5 to 9.0.(*)
Saline and swampy soils are not suitable for
The ideal temperature for cultivating cassava ranges from 18
[degrees] C to
35 [degrees] C; growth stops at 10 [degrees] C.
Cassava is perennial in the tropics,
and annual in the temperate zone.
It can be grown at altitudes up
to 2,000 meters.
Cassava is grown both as a single crop, and in combination
sorghum, maize, groundnuts, cowpeas, yams, sweet potatoes,
rice, and certain other vegetables.
(*) pH indicates the acidity or alkalinity of the soil, and
on a scale of 0 (acid) to 14 (alkaline) with the midpoint of
indicating a neutral soil condition.
Under the typical slash-and-burn agriculture of the tropics,
cassava stem sections are hand-planted just before the rainy
season. If all goes
well, within as little as seven months a number
of starchy roots can be harvested from each plant; however,
the best yields are not obtained until about 16 months
allowed to grow for too long in the soil, the roots become
woody and less edible.
Cassava is planted on ridges and on flat ground, but ridge
is more common.
Cuttings about 20 to 30 centimeters long are
inserted in the soil at a depth of about half their height,
at an angle of 30 to 40 degrees.
Cuttings sprout 7-14 days after
planting, and root bulking begins during the second month
planting. The crop
is planted in May-June, and harvested the
Cassava has a high potassium requirement.
If potassium is not present in the soil in sufficient
amounts, yields are reduced, and the tubers have a low
content and higher hydrogen cyanide (HCN) content.
Harvesting is done by hand by digging up the tubers after
the tops off the plants.
With large-scale production, the tubers
can be mechanically ploughed up, but the yields are often
because a higher percentage of tubers is left in the ground.
Once harvested, the tubers deteriorate rapidly and begin to
after 48 hours. Cold
storage, where possible, at 0 [degrees] C to 2 [degrees] C
and 85 to 95 percent relative humidity has been reported to
extend the storage-life for periods up to 6-1/2 months.
Yields vary greatly depending on the variety of cassava,
climate, age at harvest, etc.
The average is about nine metric
tons of fresh roots per hectare.
Production of cassava in 1975
exceeded 100 million metric tons (fresh roots), of which
than 40 percent was produced in Africa, about 30 percent in
America, and the remaining in Asia.
Approximate estimates suggest
that cassava production since the early 1960s expanded by
Cassava is used in a number of ways.
In addition to its consumption
by humans and as feedstuffs by livestock, it is now commonly
used as a raw material (substrate) in the manufacture of
Starch is the most important such product,
but in Brazil the roots are used to make alcohol.
As a foodstuff, cassava is consumed as a boiled or roasted
or as paste, meal, or flour.
The whole root may be boiled
and has a sticky, heavy consistency, and of itself is rather
Brazil, the roots are usually shredded, then
heated and dried to make a meal known as "farinha de
In Indonesia, the roots are sectioned, dried in the sun, and
later ground into meal.
In the making of tapioca, an important
export from Indonesia, the peeled roots are grated, soaked
water, kneaded, strained, dried, and heated to hydrolyze the
starch to sugar, and gel particles into "pearls"
stirred on a grill.
In Jamaica, the roots are ground into a mush
called "bami" or formed into cakes known as
"casabe." The better
known preparations include "gari" and
"fufu" in West Africa.
A major problem with the use of cassava is the toxicity from
cyanide compounds found in the fresh roots.
The cyanide is
concentrated in or near the skin of the root, and is freed
its active form when the skin is broken.
In this manner, the
cyanide compound contributes to the plant's resistance to
The cyanide content, however, varies from species to
changes under environmental conditions, such as humidity,
and age of plants.
However, in areas where cassava is
the staple food, chronic cyanide poisoning can result if the
is not processed properly.
Chronic cyanide poisoning is
notable in some areas of Africa, particularly in Zaire.
studies in the Lake Kivu region of Zaire suggest that a cassava-based
diet inhibits iodine uptake by the thyroid gland and may
lead to goiter, birth defects, mental retardation, and other
Proper processing of cassava for consumption
is the most effective solution to the problem of cyanide
and its consequences.
Diseases and Pests
Cassava is susceptible to various pests and diseases.
mosaic, a virus disease transmitted by white flies, is the
serious disease of cassava.
It can be spread by infected cuttings.
Bacterial blight, a new and potentially disastrous disease,
first detected in West Africa in 1972.
White thread, a root
disease, has been reported to cause crop losses of 20
more in Ghana. Other
minor diseases are brown leaf spot, white
leaf spot, and anthracnose.
The most serious insect pests are white flies, scale
the variegated grasshopper.
Nematodes are also very serious
cassava parasites, particularly in West Africa.
of termites have also been known to cause damage to cassava
crops, while rodents and wild animals often attack the
The common potato (Solanum tuberosum, Solanaceae) is a
another large and important plant family, Solanaceae, which
among many others, eggplant and tomato.
The genus Solanum
includes more than 2,000 species.
The potato was first seen by Europeans in 1537 when the
landed in what is now called Colombia, and was brought back
Europe by 1570. It
was cultivated throughout the continent before
1600, and in Ireland by 1663.
The cultivated potato is said to
have been first introduced into North America in 1621.
Potatoes are the leading starchy root crop of the
countries, and one of the eight leading staple food crops of
production of potatoes is approximately twice that
of all other edible root crops combined.
However, because of its
limited climatic adaptability, less than 10 percent of
occurs in developing countries.
The International Potato Center
(CIP) in Peru is developing new varieties of this nutritious
crop, which perform well under a variety of soil and
Among the root crops, the potato is known for its high
content. It is
almost equal to rice on a dry weight basis, and
with a protein quality approaching that of beef.
With its high
yields and short maturation periods, the potato outranks all
world food crops in protein production per unit of
food value of the potato varies depending on the variety,
environmental conditions, storage, and handling.
consists of 70 to 80 percent water, 8 to 28 percent starch,
1 to 4 percent protein.
It also contains vitamins such as riboflavin,
ascorbic acid, and trace elements.
It is an important
source of high-quality nutrients for people in the tropical
potato has been a continuous object of research
and investigation all over the world, with special focus of
interest in the International Potato Center (CIP) in
Center is attempting to increase the tolerance of the crop
high temperatures, and once it is accomplished, then it is
that larger areas of West Africa will be open to
Potatoes are grown as a single crop or in combination with
sorghum, millet, maize, cowpeas, groundnuts, sweet potatoes,
Propagation is done by tuber, either whole or
cut. Whole tubers
are less liable to rot in the soil.
material should be free from diseases, pests, and
potato "seeds," free from virus, should be used
Potatoes may be planted by hand or mechanically, and the
crop is usually planted on ridges at a depth of 5 to 15
Most potato varieties have very specific temperature
thereby limiting the adaptability of this crop in tropical
formation is retarded when the soil temperature
rises above 20 [degrees] C; above 29 [degrees] C, little if
any, tuberization takes
young potato plants are very susceptible to hard
frosts, most varieties will tolerate light frosts.
Potatoes require a continuous supply of moisture.
rainfall is considered essential, and drought, even for
short periods, can have serious effects on yields and
Well-drained peat soils are particularly suited;
however, potatoes could grow on most soils if drainage is
A deep, well-drained loam, or sandy loam, with a pH of 5
to 5.6 is considered to be the best.
Potatoes respond well to
manures and chemical fertilizers, and good yields can be
only with adequate fertility.
Fertilizer requirements vary
greatly depending on the variety and growing conditions.
Potatoes do not compete well with weeds, and timely,
weeding, by pulling or tillage, is essential.
zones, the crop is often repeatedly hoed, up to five times
the growing season.
Normally, the crop is ready for harvest in
three to four months.
Harvesting should be done on a dry day,
when the tubers are mature.
The crop can be harvested by hand or
mechanically. If it
is harvested mechanically, a wide range of
equipment can be used, including diggers, spinners, and
Harvested tubers should be stored temporarily in a shaded,
and well-ventilated place for 7 to 10 days to allow the
harden before the potatoes are prepared for market or
Potato yields vary with variety, length of growing season,
and the type of soil.
With efficient farming methods in
temperate climates, yields well in excess of 25 metric tons
hectare are quite common.
Yields are lower in the tropics, averaging
about 14 to 15 metric tons per hectare.
Potatoes can be eaten boiled, roasted, baked, fried, or
They can be made into fried chips or crisps, dehydrated and
flaked, or made into flour.
Potatoes can be pulped and fermented to produce
tubers make an excellent livestock feed and can be fed fresh
dried and used in the form of a meal.
Diseases and Pests
Potato crops are subject to a number of diseases, some of
are of great economic importance in both developed and
rot, or bacterial wilt, is the most serious
potato disease in West Africa.
The disease is carried by seed
bacterial diseases include soft rot, ring rot, and
late blight. Several
other diseases are also of considerable
these are virus diseases that can cause crop
planting stock is essential since there are no
effective treatments for these diseases.
Finally, a number of
pests, particulary aphids and nematodes, have been found to
cause economic losses.
These pests not only harm the crop, but
also spread virus diseases such as leaf roll and mosaic.
Sweet potatoes (Ipomoea batatas, Convolvulaceae) are widely
in tropical, subtropical, and warm temperate areas of the
They originated in tropical America and likely spread to the
Pacific before the time of European exploration.
Japan is probably
the leading sweet potato producer; it is a national staple
and largely consumed there.
In many other parts of the world,
sweet potato is utilized as feedstuff for livestock.
The sweet potato, although a perennial, is normally
an annual crop. The
crop under normal circumstances is harvested
from three to eight months after planting, depending upon
variety and environmental conditions.
Sweet potato varieties
vary considerably in their adaptability to soil and other
They require at least 500 millimeters of rain during the
growing season. For
good yields, an annual rainfall of 750 to
1,250 millimeters is necessary, with drier, weather as the
The sweet potato can tolerate lengthy dry periods
once roots are established.
However, yields are greatly reduced
if soil moisture is inadequate during the period when root
storage begins. The
sweet potato is easily adapted to a considerable
range of soils, but is sensitive to alkaline or saline
It does not tolerate waterlogging.
Warm days and nights
are essential, and a mean temperature above 24 [degrees] C
is required for
optimum crop growth.
At least 25 millimeters of moisture per
week for four to five months is essential.
appears to result in increased protein content of the roots.
Sandy-loam soil, with a pH range from 4.5 to 7.5, appears to
ideal for satisfactory growth.
Tubers reach their ideal conditions
at four to seven days of short-term storage with 85 to 90
After harvest, the tubers should be stored at
12 to 16 [degrees] C with 85 to 90 percent humidity, or
Tubers are rich in carbohydrates, vitamin A, and vitamin C,
also contain significant amounts of calcium and iron.
reports of the International Institute of Tropical
indicate that the yield of sweet potatoes under favorable
is between 20 and 30 metric tons per hectare, and experimental
yields greater than 40 tons/hectare have been obtained.
In most parts of the world, the sweet potato generally is a
garden crop that never goes to market.
It is mainly grown in combination
with other crops such as sorghum, millet, maize, rice,
cowpeas, groundnuts, yams, cassava, potatoes, and
may be propagated by tubers, slips, or vine cuttings.
are the most commonly used planting material.
In slip propagation,
tubers are planted in a nursery bed.
The new plants, which
sprout from the various buds of the tubers, are known as
They are separated and planted and are relatively free from
diseases, and the tubers produced are of a more uniform
shape and size. Vine
cuttings 20 to 45 millimeters long with
seven or more nodes are planted one-half to two-thirds of
length in the soil.
Roots sprout from the subterranean nodes within 5 to 15 days
depending on the quality of the planting material and the
conditions. Once the
crop is established, it requires
minor weeding if the land has been properly prepared, and is
over-infested with weeds.
The growing period generally varies
from four to six months depending upon the variety.
the stems turn from green to brown.
Harvesting usually takes place during the dry season in
Mechanical harvesting of the crop is possible but
losses can be considerable.
Sweet potato tubers are very perishable,
and the methods used to harvest the crop could have a very
significant effect upon the market quality and storage life
Sweet potatoes are harvested primarily for human
the tropics, the major proportion of the crop is eaten
from the ground as a vegetable, after boiling, baking, or
In Malawi, they are sometimes boiled or roasted and pounded
groundnuts to produce "futali."
In some areas, notably India and
parts of East Africa, the peeled tubers are sometimes sliced
dried in the sun to produce chips, which are often ground
potatoes are also a source of starch and are used as
Diseases and Pests
Diseases that attack the sweet potato tubers during storage
more serious than those affecting the crop during cultivation.
Black rot, for example, can be serious especially when the
are damaged during harvesting.
The sweet potato weevil is the
major insect pest.
Its larvae feed on the roots and tubers.
Proper crop rotation helps in its control.
Chemical control also
appears to be promising.
Recently, several weevil-resistant varieties
have been isolated.
The true yam (Dioscorea) is not to be confused with the
potato, which is sometimes incorrectly termed a
"yam." The genus
Dioscorea includes several hundred species, but only a few
importance as food crops.
Of these, the Asiatic species Dioscorea
alata (commonly called the greater yam), and two closely
Western African species, Dioscorea cayanensis, (yellow yam)
and Dioscorea rodundata (white yam), are the most common and
Yams originated in the Far East, spread westward, and have
evolved independently in the Eastern and Western
Yams are now widely grown throughout the tropics, under both
rain forest and savanna conditions, where there is a
of adequate moisture and good drainage.
Yams require adequate
moisture throughout the growing period.
In several countries of
West Africa--the major production zone, with 66 percent of
world's crop--yams are becoming increasingly expensive
their high labor requirements and low yield.
As a result, yams
are being partially replaced by cassava, rice, and wheat,
the fact that they are richer in protein than cassava.
The average growth period is 8 to 11 months.
Yields range from 5
to 15 metric tons per hectare.
Only a very small portion of yams
enters the international market; the bulk of the yams are
as fresh produce or eaten upon harvesting.
requirement appears to be around 25 to 30 [degrees] C.
down below 20 [degrees] C, while temperatures over 30
[degrees] C have an adverse
effect, especially if accompanied by dry conditions.
adequate moisture throughout the growing period, and there
is a positive correlation between moisture supply, vine
and tuber formation.
In West Africa, yams reach their highest productivity in
where there is a dry season of two to four months and a
of 1,200 millimeters or more during the growing season.
drainage is essential for high yields and quality.
best in well-drained sandy-loam soils.
In heavy soils, they are
susceptible to rot, while in very sandy soils favorable
conditions are difficult to maintain.
Yams are influenced by
photoperiodicity--that is, their growth is affected by the
amount of light they get in a day.
However, the effects of
day length on the vines and tuber production have not been
Yams are propagated either by seed yams or sets.
Most yams produce
one or two tubers larger than the rest, and these are the
ones suitable for use as food.
They are cut off near the top,
leaving the crown with the green stem attached.
This is replanted,
and gradually grows again, producing two or more small seed
The production of seed yams usually is not sufficient.
large yams are cut into pieces known as "sets,"
which are then
used for plantings.
On average, seed yams and sets weigh between
170 and 400 grams.
Spacing plays an important role in the growth
generally, the closer the spacing, the higher the
yield. Little or no
chemical fertilizer is used on yams, though
yams respond well to phosphate and potassium fertilizers if
are applied correctly.
Both seed yams and sets are planted in the middle of hills
holes 15 centimeters deep.
Shallow planting may dry out the sets
After planting, the hills are capped with a
layer of dry grasses or weeds about 30 centimeters in
the top of the hill, and kept in position by a thin layer of
soil. In general,
protected yams sprout more quickly than unprotected
yams as they do not dry out.
When young shoots appear,
long yam poles from hardwood trees are installed to support
vines and promote healthy tuber growth.
During the growing season, cultivation includes weeding,
and setting the poles.
While chemical fertilizers are not
commonly used on yams, organic manure is.
Most edible yams
normally reach maturity 8 to 11 months after planting.
is done by hand.
Yams are a starchy staple crop, normally eaten as a
either boiled, baked, or fried.
In West Africa, the major proportion
of the yam crop is eaten as "fufu," a stiff
dough. Yams are
sometimes dried and made into flour.
In villages, peelings and
waste from the yams are often used for feeding poultry or
Diseases and Pests
Among the various diseases affecting yams, shoe string and
back are of major importance.
Varieties resistant to these diseases
are now being developed.
Witches broom has been known to
cause damage to yam crops in West Africa, and a virus
the mosaic type has been reported.
Storage losses from various
fungal rot diseases are generally severe, especially when
tubers are damaged.
Among the insects, yam tuber beetles are by far the most
pests in West Africa.
The cocoyam, commonly called taro or dasheen, is an
staple in Southeast Asia and Polynesia.
It has many varieties.
Colocasia esculenta (Araceae family) is of Asian origin, but
been grown in West Africa for centuries.
It is known as the "old
cocoyam," distinguishing it from Xanthosoma
"new cocoyam" of tropical America, which was
introduced to West
Africa during the nineteenth century.
Like many plants of the Araceae family, called aroids, the
grows from a fleshy corm (tuber) that can be boiled, baked,
or mashed into a meal.
The well-known "poi" of Hawaii is a product
of taro which has been crushed and fermented.
rich in carbohydrates and very low in protein.
The aroids are the least significant of all
tuber crops in terms of production. However, they perform
under hot, humid conditions, and show best results on deep
soils with a high water table.
The maturation period, which
varies according to the variety, ranges from 6 to 18 months.
Yields vary from 10 to 30 metric tons per hectare.
accurate figures are not available, the cocoyam is a major
crop in the forest region of West Africa, accounting for up
to 80 percent of the total world output.
The cocoyam is grown as a rainfed crop.
Small corms or pieces of
corms, or the tip of the main root stock with part of the
corm attached are used for propagation.
Spacing varies widely.
The cocoyam is grown as a single crop, or in combination
maize, rice, and vegetables.
Planting is usually done during the
rainy season. The
cocoyam can be grown on a wide variety of
soils, but deep, well-drained loams with a pH of 5.5 to 6.6
considered to be the best.
Yields are very low in sandy or hard
clay soil. The more
fertile the soil, the higher will be the
yield. Cocoyams are
very sensitive to waterlogging and saline
maximum growth, a mean temperature of 20 to 30 [degrees] C
is a must.
Sprouting usually takes place one to two weeks after
The crop is harvested when the leaves turn yellow.
commercial production of aroids under irrigation and rainfed
conditions is possible in the tropics.
The cocoyam's potential as a calorie source and its adaptability
to unfavorable growing conditions make it a valuable crop
many rural development programs.
Cocoyams are now included in
many agricultural projects, and their cultivation is readily
progressing in most developing countries because of their
to fungal infection, and tolerance of drought.
The corms (the underground part of the cocoyam) and the
(lateral tubers) are rich in starch.
Like potatoes, they can be
eaten after being boiled, baked, roasted, or fried in
young leaves of some cocoyam species are boiled and eaten as
green vegetable. The
peeled tubers, after pre-cooking and
drying, can be used to produce a flour.
Diseases and Pests
Several diseases, viral and fungal in nature, have been
attack the aroid varieties.
Root-knot nematodes can also cause
damage if the soil is heavily infested.
Austin, M.E., and Graves, B.
"Mechanical Harvesting of Sweet
Potatoes." Proceedings of
the Second International Symposium
on Tropical Root
and Tuber Crops (1970).
Improve Your Cassava Crop.
Oklahoma City, Oklahoma:
"The Edible Aroids."
World Crops 20 (1968): 25-30.
Coursey, D.G., and Haynes, P.H.
"Root Crops and their Potential
as Food in the
Tropics. World Crops (July/August
Francois, C.F., and Law, J.M.
Sweet Potato Storage. DAE
429. Baton Rouge, Louisiana:
"Tropical Root Crops and Rural Development."
Working Paper No. 324. Washington,
Hill, D.S., and Waller, J.M.
Pests and Diseases of Tropical
Principles and Methods of Control.
and Co., Ltd., 1982.
International Institute of Tropical Agriculture.
Nigeria: IITA, 1977.
"Plant Science." An
Introduction to World Crops.
W.H. Freeman and Company, 1969.
"The Surprising Sweet Potato," Organic Gardening and
Farming, V. 25,
No. 5, May 1978.
Kassam, A.H. Crops
of the West African Semi-Arid Tropics.
International Crops Research Institute for
Kranz, J.H.S., and Koch, W., eds.
Diseases, Pests and Weeds in
Crops. Berlin, West Germany:
Verlag Paul Parey,
Lambert, Michael, ed., Taro Cultivation in the South Pacific.
22. Noumea, New Caledonia:
South Pacific Commission,
United States Department of Agriculture.
Tropical Yams and Their
Part 3, Dioscorea alata, Agricultural
"Growth and Productivity of Tapioca (Manihot
Agriculture 10 (1974): 9-16.
SOURCES OF INFORMATION
Asian Vegetable Research and Development Center
P.O. Box 42
Shanhua, Tainan, Taiwan
Cameroon National Root Crops Research Institute
Institute of Agricultural Research
Centro Internacional de Agriculture Tropical (CIAT), or
International Center for Tropical Agriculture
Apartado Aeroe 67-13
Food Technology Development Center
P.O. Box 61
International Development Research Centre
Ottawa, Canada K1G 3H9
International Institute of Tropical Agriculture (IITA)
International Potato Center (CIP)
P.O. Box 5969
Mayaguez Institute of Tropical Agriculture
P.O. Box 70
Mayaguez, Puerto Rico
National Root Crops Research Institute
Philippine Root Crop Research & Training Center
Visayas State College of Agriculture
Baybay, Leyte 7127, Philippines
Root and Tuber Crops
Central Research Institute for Agriculture
J1. Merdeka 99