|Better Farming Series 16 - Roots and Tubers (FAO - INADES, 1977, 58 p.)|
Cassava is a shrub that is grown chiefly for its roots.
It has its origin in South America and is now widely grown in tropical Africa.
At its base the plant consists of one or more stems 2 to 3 centimetres in diameter; usually each stem divides into three branches, and each branch in turn divides into three, and so on.
When a stem is cut, the sap that flows is white and looks much like milk. Inside the stem is pith. The stem of cassava is not very hard; it is easily broken by a strong wind.
Cassava leaves have a long stalk and a much divided leaf- blade.
The leaf veins are green or red.
A yam leaf
The flowers are pink, red, yellow or green. There are both male and female flowers in the same cluster.
The fruit is divided into three parts. Each part contains a seed. When the cassava fruit is ripe, it opens.
The farmer grows cassava chiefly for its roots. Some of them become large and fat by storing up food reserves. Other thinner roots continue to feed the plant.
Cassava roots contain a poison, prussic acid.
Some contain a great deal of poison; these are mainly the bitter tubers. Others, the sweet tubers, contain little poison.
The poison can be removed by thoroughly washing the root; by drying it or by cooking it thoroughly.
Before giving cassava to people or to animals, it must always be well cooked.
To grow well, cassava needs a warm, humid climate.
If the rainy season is long, cassava roots grow rapidly.
Cassava is also a plant that will resist drought.
With less rain, the yield is small.
Cassava stems are not tough and dislike high winds.
Cassava is a very strong grower. It will grow even in very poor soil.
But cassava grows best in soil that is permeable, not too compact, in which air and water circulate well. Then the roots fatten up and do not rot.
Cassava makes the soil poor. Besides the fat roots that store up food, many little roots take water and mineral salts from the soil.
After a crop of cassava, the field is very poor and must be left fallow.
Usually, cassava follows several other crops.
For example, first maize, okra, groundnuts are sown, then plantains are planted, and finally cassava.
In some places, cassava is planted at the same time as yams, or soon after.
The cassava cuttings are placed in the sides of the mounds for
In other places, maize is grown between the cassava plants, or beans, fonio or groundnuts.
It is better not to grow several crops together.
To develop well, cassava roots need soil that has been loosened by the hoe or plough. So till deeply, to 20 or 25 centimetres, so that the roots can get well down.
After tilling, at the beginning of the rainy season, make mounds or ridges. This breaks up the soil and it stores up water; the roots have plenty of loose earth in which to develop.
If fertilizers or manure are used, work them into the soil when it is tilled.
Yields are high when the plant finds plenty of nourishment in the soil. Farmyard manure, compost and green manure are the best fertilizers for cassava.
For green manure, sow leguminous cover plants such as:
Phaseolus or beans.
Sow them a little before the rains, and dig them in after 5 to 18 months of leafy growth.
You can also use farmyard manure or compost. These organic manures enrich the soil with organic matter and mineral salts.
To complete the manuring, you can apply mineral fertilizers containing nitrogen, phosphorus and potassium.1
1 The use of mineral fertilizers may be profitable if the farmer sells the cassava to gari or tapioca factories. Many experiments made in Ghana and Nigeria have shown that yields per hectare are increased chiefly by nitrogen fertilizers such as ammonium sulphate (21% nitrogen), urea (46% nitrogen) and phosphorus fertilizers such as single superphosphate (16 to 20% phosphoric acid}, triple superphosphate (46% phosphoric acid) and ground natural phosphate (20 to 40% phosphoric acid). Potassium fertilizers such as potassium chloride (60% potassium) and potassium sulphate 150% potassium! have a less marked effect. However, the yield of cassava falls greatly when the soil lacks potassium fertilizers. If the farmer applies fertilizers and looks after his plantation well, the yield of cassava reaches 25 to 65 tons per hectare.
Cassava is propagated by cuttings, by planting pieces of stem.
The roots of cassava are not used for making a new plantation, and thus all the harvest can be eaten or sold.
To make cuttings, choose stems 2 to 4 centimetres thick, from the strongest plants which are not diseased and which have already produced tubers.
After the harvest, tie the selected stems in bundles. Wait at least 10 days before planting them.
Keep the bundles in a cool, dry place until planting time.
But remember that the cuttings must not be made from the stems until you are ready to plant.
Cut each stem into pieces 20 to 30 centimetres long. There should be 4 to 6 growth buds on each piece. Each stem can be made into 4 or 5 cuttings.
To plant cassava, push into the soil the end of the piece of stem that was nearer to the ground.
Plant the cuttings in mounds or ridges. Plant when the soil is quite wet, after the beginning of the rainy season. Plant the cuttings either straight or slanting. Push them well into the earth, leaving only 2 or 3 buds above ground.
Cassava cuttings may be planted straight or slating
Press the earth well down round the cuttings. Then the roots that develop will be well nourished by the soil.
Usually the rows are 1 to 1.5 metres apart, and the plants 1 metre apart.
With this spacing, there are between 7 000 and 10 000 cassava plants to the hectare.
But the number of cuttings to the hectare varies with the region, soil and variety.
If cassava is planted at the right density, the yield is heavy; the roots occupy all the soil and fewer weeds grow, so that fewer cultivations are needed.
CONTROL OF WEEDS
Weed when the cassava plants are 20 to 25 centimetres high, that is, 3 or 4 weeks after planting.
Weed a second time 1 or 2 months after the first. Earth up the plants at the same time; this greatly helps the formation or tubers, and prevents the wind from blowing the plants down.
After this, the cassava plants are big enough to prevent weeds from growing.
When rain spoils the mounds, they must be remade.
When the soil of the mounds gets too hard, break it up with a hoe, so that water and air can get in to nourish the roots.
CONTROL OF DISEASES
Cassava is often attacked by what is called mosaic disease.
Leaves of plants attacked by mosaic look as though crumpled, and show light spots. If the attack is serious, yields are sharply reduced.
Means of controlling mosaic disease are not yet known. To avoid it, do not take cuttings from plants attacked by the disease.
Choose varieties of cassava that have been bred for resistance to the disease.
To prevent mosaic spreading in a region, burn all the plants attacked by the disease.
Rot damages the roots, especially after 10 months of leafy growth.
Rot often occurs when the cassava field has been flooded for several days. The tubers turn soft and give off an unpleasant smell; they are no longer any good for human or animal food. This means a big loss to the farmer.
To avoid rot, do not plant cassava in a place that is often flooded.
If a cassava field is flooded after heavy rain when the tubers are already ripe, you must get the cassava out of the ground very quickly, before it starts to rot.
CONTROL OF PESTS
Agoutis, rats and rabbits are the chief rodents that may cause great damage in a field of cassava. These animals eat the stems, the young shoots, and especially the roots.
- Wild boars, pigs and other animals
Other animals such as the wild boar and the pig are equally damaging to cassava.
They are very fond of it, and with their powerful snouts they push over the plants and dig up large quantities of roots.
Control all these animals by putting poison in the fields, by laying traps, or by digging deep ditches round the cassava plantations.
- In very dry regions, when cassava is planted a long time before the rains, termites eat the cuttings.
To avoid this damage, wait for the rainy season before planting,
Or you can dip the cuttings in insecticide just before planting them.
- Thrips and certain other insects feed on sap by piercing the stems and leaves of cassava. Other insects eat the leaves and the young shoots. When they come in large numbers they may cause great damage. They are controlled with insecticides such as BHC.
- Red spiders are tiny red creatures no longer than 0.5 millimetre.
Large numbers of them live on the lower surface of cassava leaves. The same red spiders attack castor oil, cotton and rubber plants. They feed on the sap of the plant by piercing the leaves. The leaves attacked get brown spots on the underside. The plants attacked do not grow well, and do not yield much cassava.
To control red spiders, the plants may be sprayed with soapy water and nicotine, with rotenone, white oil, etc.
When diseases, animals and insects cause serious damage, you should quickly inform me agricultural extension officer. He will tell you what to do to control diseases effectively or to get rid of pests.
Depending on the variety, harvesting of cassava for food may begin from the seventh month after planting the cuttings for early varieties, or after the tenth month for late varieties.
Before this, the tubers are too small. In addition, they still contain too much prussic acid.
At harvesting time, that is, between the sixth and the twelfth month, each fully grown tuber of cassava may weigh 1 or 2 kilogrammes, depending on the variety.
In small family plantations you can harvest me tubers as you need them. Without cutting the stems, begin by taking the biggest tubers from each plant, leaving the smaller ones time to fatten up.
If you are selling to a factory, you must harvest all the cassava at the same time. The production of roots and starch is highest 18 to 20 months after planting.
Once lifted, cassava cannot be kept for long. The roots begin to spoil as soon as they are out of the ground.
That is why on a family plantation, you should not harvest more roots than you can eat while they are fresh, or sell immediately.
Cassava keeps longer when it is left in the ground, but the soil must not be too wet.
A cassava root
When you lift the cassava, take good care not to break it. Tubers damaged in lifting go bad even more quickly.
Many peoples of tropical Africa make cassava their staple food.
Cassava tubers can be eaten whole.
But as a rule they are turned into flour or paste.
The reasons for this are:
- to get rid of the poison;
- to keep the cassava for a long time;
- to get foods with a more pleasant taste.
For eating fresh, the sweet varieties are chosen for preference. The poison in cassava is mainly in the peel. Wash the cassava carefully, cut the roots into pieces and steam them.
To make a paste, pound pieces of tuber in a mortar. The pastes are known as foutou, foufou, foufouin or tchokoro.
The fresh roots are peeled, sliced into rounds, and dried in the sun.
Sometimes, instead of being sliced, cassava is grated and then pressed into little balls which are dried.
The balls and the slices can be kept for a long time.
To make flour, the slices or balls are pounded in a mortar, or ground in a mill.
This flour contains all the food elements of cassava. Do not confuse flour with starch.
Gari and atcheke are much liked in Africa.
To make gari, peel and grate fresh cassava. Then press it in baskets or sacks for three or four days, until it begins to ferment. After rubbing it through a sieve, heat it, dry, in a pot, stirring all the time to prevent sticking. Afterwards, remove impurities with a sieve.
To make atcheke, cassava is prepared as for gari. But the flour is steamed instead of being cooked dry in a pot.
After peeling, washing and grating the cassava, the pulp is mixed with water. Then the resulting liquid is strained through a cloth. This is done several times.
The water that passes through the cloth contains the starch. The liquid is allowed to stand for several hours. The water at the top is removed and the starch is left at the bottom of the vessel.
The damp starch is used to make tapioca. As in making gari, the starch is heated in pots and stirred all the time.
After cooking, it is allowed to get cold, and then the tapioca is sieved to separate the lumps of different sizes.
In some places cassava leaves are much liked.
In southern Cameroon cassava leaves are often eaten as a vegetable. They are in fact rich in vitamin C and mineral salts, and contain some protein.