CasProj

School Science Lessons
Cassava Project
Updated: 2008-03-29
Please send comments to: J.Elfick@uq.edu.au
See also: Interesting websites

Preface
Before teaching this project, discuss the content of the lessons with a field officer of the Ministry of Agriculture and get advice on planting material, planting distances, site for planting, approved mulch, composting, and control of pests and diseases. Use only the procedures, agricultural chemicals and insecticides recommended by the local field officer of the Ministry of Agriculture. If you cannot control insects by hand-picking, ask the Ministry of Agriculture to recommend a chemical spray. All insect sprays are dangerous. Show the students how to use them safely. Do not get the spray onto your hands. Do not breathe in the spray. Wash your hands well after using spray. Keep the spray container in a safe place where students cannot get it. Spray on a day of no wind but if you must spray when there is a wind, spray down wind. Make sure the spray does not blow on other people.

Table of contents
1.0 Cassava project
2.0 Preparing the cassava garden
3.0 Planting Cassava
4.0 Keeping records
5.0 Learning about Cassava
6.0 Stems
7.0 Leaves
8.0 Flowers
9.0 Roots
10.0 Cassava varieties
11.0 Feeding Cassava
12.0 Plant enemies
13.0 Plant care
14.0 Cassava as food
15.0 Harvesting

1.0 Cassava Project - Cassava or tapioca, Manihot esculenta
To teach this project, the children must help you to plant a garden as early as possible in the year. The first lessons tell you how to do this. The most important rules to remember are these:
1. The children should do all the work of growing the plants.
2. They should watch the plants carefully and keep a record of the growth of the plant.
3. You should never teach about any part of the plant unless you can bring that part of the plant into the classroom or take children outside to see real plants.
This in this project should be spread over a year. Don't teach the lessons together. There may be 3 weeks between one lesson and another.
The aim in this project is not to grow a large area of cassava, but to grow a small area so students can easily watch it growing and keep it free of weeds. A good size for a cassava garden is 10 m long and 2 m wide. The ground should be dug well twice. Double digging is needed to make the soil soft and to kill the weeds.

2.0 Preparing the cassava garden
See also 6.9.14 Composting
1. Mark out a flat place for a cassava garden.
2. Dig the soil well and bury the weeds and grass.
3. Dig the soil again two weeks after the first time.
4. Make the soil fairly flat and level.

3.0 Planting Cassava
Cassava is planted in different ways in different islands. You should plant it the way that is common in your island, but first it is very important to teach the students the general rules about planting. These are the rules:
1. Cassava is planted from pieces of stem about 30 cm long.
2. The pieces must always be planted the right way up - not upside down.
3. There are three ways of planting:
4. In some islands the pieces of stem are planted on a slope, like you see in the picture. For instance in Fiji, three pieces are planted close together in this way. When planted this way the roots will grow mostly on the side opposite to the slope of the stem.
5. In some islands the pieces of stem are planted straight up. When this is done the roots form on all sides of the stem, but the plant may be easily blown over by the wind.
6. In some islands the pieces of stem are buried fiat under the soil. When this is done too many stems grow up and the sizes of the roots may be small.
7. When roots grow at the base of the stem, most of them come from the lowest part and not from the buried eyes.

1. Use the blackboard to show students the 3 ways of planting cassava. Explain what happens in each case.
2. Draw a picture of a buried stem and show where most of the roots form.
The students should collect some long stems of cassava and cut them into lengths of about 25 cm. They should then plant the pieces 60 cm apart in two rows 120 cm apart. The pieces should be planted on a slight slope.
3. Cut stems into planting pieces. They lay the pieces all the same way so upper ends are at one end of bundle.
4. Plant the pieces of stem.

4.0 Keeping Records
See also 6.9.20.0: Understanding the records
It is very important that the students keep good records of the growth of the plants. They should look at the plants on the same day each week. They should
1. Write down the date each time.
2. Make a small drawing of each growth stage.
3. When the plants grow too tall, their growth stage can be written down in words. The pictures in the diagram show some early stages that can be seen.

1. Watch the plants each week and see what happens.
2. Draw the cuttings.
3. Record the date when cuttings planted.
4. Record the growth reached in the first week.
5. Study the plants each week until harvest.

5.0 Learning about Cassava
Cassava in some islands is called tapioca or tavioka. In other islands it is called manioc. This plant is being grown more by the people of the Pacific islands, for these reasons:
1. It is easy to grow.
2. It makes much food.
3. It does not get many diseases.
4. It is good to eat.
5. Do not grow cassava year after year in the same soil because it takes much plant food from the soil.

6.0 Stems
While the plants are growing, it is now time to teach the students a lot about Cassava plants. Look at a piece of stem at least 60 cm long. Where a leaf has dropped off the stem, it leaves a leaf scar. These may be quite flat, but usually the leaf scar forms a small lump that sticks out from the stem. The central part of the scar is round, but the sides extend into a ridge. just above each leaf scar there is a small bud. Sometimes this bud is too small to see, but the place where it is can be seen. This bud can grow into a leafy stem if a cutting is made and the stem planted. Now mark one scar low down on the stem. Then go upwards counting leaf scars as you go. The scars are so placed that you make two turns around the stem before you come to the next scar that is directly above the one you started from. You will pass five scars on the way up to the next scar above.
1. Give each group of students a length of stem 30 cm long.
2. Ask them to look at the leaf scar and make a drawing of it.
3. Ask them to see if they can find the bud just above the scar.
4. Show them that every fifth scar is directly above one below it.
5. that the reason for this is so that leaves will not keep the sun off each other.

7.0 Leaves
Most cassava leaves are palmate that is, there are many leaflets that grow out like a fan from the top of the leaf stalk or petiole. The number of leaflets depends on the stage of growth and the variety. Most cassava leaves have five or seven leaflets, but there may be more or less than this. However there is usually an odd number of leaflets because one is light in the centre. When the plant has grown for a long time, it may make flowers. When it does this, the leaves change shape. They become single leaflets on short stalks as you see in the picture. The leaf stalk of the leaf is called the petiole and it is usually long. It may be light or dark green, or blue green, or red in colour.
1. Bring some cassava leaves into the classroom. Give some to the students.
2. Count the leaflets on different leaves.
3. Study the petioles.
4. Make simple drawings of leaves.

8.0 Flowers
The first sign that the cassava plant is starting to make its flowers is that it makes some leaves that have fewer leaflets. Also the stem may become thinner and may branch. The flowers are made in small clusters. Each has five petals joined. Inside the flower there are two groups of male stamens - five on the outside and five on the inside. In the centre of the flower is a small green ovary that turns into a seed box. When the flower is fertilized, it turns into a small brown seed case that has three parts. The small seeds are formed inside the seed case.
1. If you can find some cassava flowers bring them into the classroom.
2. Leaves are a different shape when flowers are made.
3. Study the inside of a flower.
4. Study a dry seed case.

9.0 Roots
Some roots of cassava swell up to make the part that is eaten. This is the place where the food is stored. The food is made by the leaves, goes down the stem and is stored in the roots. The roots are usually long in shape and they usually have pointed ends. However, there are two kinds of roots:
1. In some varieties the outside skin of the root is rough and is usually brown or dark brown in colour.
2. In other varieties the outside skin of the root is smooth and the colour is a very light brown or pink colour. The colour of the inside of the root is usually white, but may be pale yellow occasionally.

1. Bring two kinds of roots into the classroom.
2. Study two main kinds of skin - rough and smooth.
3. Study two main colours of roots - light or dark.

10.0 Cassava varieties
There are many varieties of cassava, although there may only be five or six varieties near your school. These are the main ways in which one variety may differ from another:
1. Whether roots are rough skinned and dark in colour or smooth skinned and light in colour.
2. Whether the stem is single or branched.
3. Whether leaflets are long and narrow or more rounded in shape.
4. The number of leaflets in each leaf.
5. The average length of the middle leaflet.
6. The average width of the middle leaflet.
7. The colour of the young leaves may be green, blue green or red blue.
8. The colour of the petioles may be green or red.
9. The colour of the stems may be brown, yellow or silver.
10. The colour just under the outside of the root may be white, cream or yellow.
11. The leaf scars on the stem may be smooth or large and raised or very large.

11.0 Feeding Cassava
Cassava will grow better if there is enough plant food in the soil. Two things can be done:
1. Give the plants some fertilizer especially nitrogen fertilizer. This can be sprinkled on the soil alongside the plants as they are growing. There is no need to dig it in.
2. Make some compost and spread this over the soil under the plants. It will be better if some animal manure has been used to make the compost.

1. Need for cassava to have enough plant food in the soil.
2. Spread fertilizer lightly over the soil under the plants.
3. Put compost on the soil.

12.0 Plant enemies
Weeds are the worst enemies of cassava. They should be cut out with a hoe or some tool that does not dig deeply. Weeds have these bad effects: 1.0 They steal water from the cassava. 2.0 They steal plant foods from the cassava. 3.0 They may keep sunlight off the plants.

13.0 Plant care
Cassava plants need water in the soil so they can grow well. If it comes to a dry time, the plants may stop growing. Putting a mulch of dead grass on the soil around the plants will help to keep the water in the soil. It will keep the soil moist.
1. Mulch on the ground keeps water in the soil.
2. Put a grass mulch around the plants.

14.0 Cassava as food
Cassava consists of starch. It has almost no protein food, so it is only an energy food and should not be eaten alone. Some protein food like fish is needed also.
1. The four types of food - energy, protein, vitamins and minerals.
2. Cassava is only an energy food. It contains almost no protein.
3. So some protein food is needed plus the cassava.

15.0 Harvesting
Cassava does not keep well after it has been dug. So it is most important to do two things:
1. Only dig cassava if it can be eaten or sold straight away.
2. Dig the roots very carefully and try not to damage them. Damaged roots go bad very quickly.

1. Cassava does not keep well like yams. Take care not to damage roots.
2. Dig some cassava roots.
3. Cut the stems into pieces for planting again.
4. Record the date when the crop was harvested.

History
These teaching materials were originally written and illustrated by Mr J. A. Sutherland, Faculty of Education, University of New England, Armidale, Australia and later edited by Dr J. Elfick, School of Education, University of Queensland, Brisbane, Australia.