Root and Stem Tuber Growing

In your community, you might have seen farmers harvest roots for food. Such crops, whose roots or stems are eaten, are called stem or root tubers. A tuber is the swollen underground part of a plant used for storage of food nutrients. A stem tuber forms from thickened rhizomes or stolons. Do you grow any stem or root tubers? A stem tuber grows from the aerial stern just below the soil surface (see Figure 2A.1). Around the underground parent stem, younger stem tubers may form.

A root tuber is a modified root that works as a storage unit for the plant (see Figure 2A.1). The root may be lateral, such as, in sweet potatoes or main root, such as, in carrots. Tuber crops grow in a wide range of geographical areas in Uganda. Most tubers are processed into crisps, chaps, flakes or flour for baking. In this chapter, you will learn to process root and stem tubers for the market.

Meaning of Tuber Crops

Tubers characteristically have high moisture content of about 70 to 80% and a large unit size of about 15 g to 15 kg. The enlarged area of the root-tuber, or storage root, can be produced at the end or middle of a root or involve the entire root. The top sides of the tuber produce shoots that grow into typical stems and leaves, while the undersides produce roots. Use Figure 2A.2 and Activity 2A.1 to explore the meaning of root and stem tubers.

Activity 2A.1 Deriving the meaning of tuber crops

What you need:

Variety of root and stem tubers, notebook, pen

What to do:

1. In groups, you will receive root and stem tuber plants.
2. Observe the crops and write their characteristics.
3. Group the crops into root and stem tubers.
4. Identify the similarities between the root and stem tubers. Record how the similarities help you to understand the meaning of tuber crops?
5. On a newsprint, derive the meanings of tubers, root and stem tubers from the activities done.
6. Display the meanings and characteristics of stem and root tubers at the Agriculture learning station in your classroom.

Value of Root and Stem Tubers in Nutrition

Tubers are a good source of nutrients and a great part of the diet. Tubers contain roughages, starch, proteins and vitamins. The orange-flesh sweet potato is a good source of Vitamin A. Which root or stem tubers do you commonly eat in your community? In Activity 2A.2, explore the value of root and stem tubers in nutrition.

Activity 2A.2 Discovering the nutritional importance of root and stem tubers

What you need:

Variety of root and stem tubers, nutritionist/Food and Nutrition teacher/ catering officer, food test reagents, knife, notebook, pen

What to do:

1. In groups, you will receive root and tuber crop products. 2. Observe the crop products and record their names.
2. Observer the crop products and record their names.
3. Record the explanation of the food specialist on the nutritional benefits of root and stem tubers.
4. Ask the nutritionist to quide you on how to prepare a meal from the products, while maintaining the nutrient composition.
5. Follow these steps to carry out a food test to discover the nutrients in root and stem tubers.

a) Crush some food in a mortar using a pestle.

b) Add a spatula-full of crushed tuber to a boiling tube. .

c) Add 5 cm³ of distilled water and stir

d) Boil and simmer for one minute.

e) Cool and add the test reagent. Record your findings in a table.

6. Ask about the importance of such nutrients in the functioning of the human body.
7. Ask the specialist the recommended rates of consumption of root and stem tubers.
8. Research about the scientific name, part(s) eaten and food nutrients each tuber crop contains. Record your findings in a table and share with peers.

Value of Root and Stem Tubers as a Commodity

Root and stem tuber products contribute to the diversity of food products in food markets and stores. The tubers may be in their natural or processed form.

Processed forms of tubers include flour, potato flakes, chips, chaps and crisps. Identify the stem or root tuber products that you have ever seen or eaten. Using Figure 2A.3 and Activity 2A.3, explore the importance of root and stem tubers as a commodity.

Activity 2A.3 Exploring the importance of root and stem tubers as a commodity

What you need:

Notebook, pen, camera

What to do:

1. In groups, to visit the school canteen or a market place or trading centre near your school.
2. Identify the root and stem crop products in the market or shop. Note down the products. Record the forms in which the tubers are sold.
3. Identify the form of stem and root tuber with the highest demand.
4. Ask the trader to tell you the cost of the product per unit quantity.
5. Inquire about the products obtained from the items seen on sale.

6. Take pictures of the root and stem tuber products on sale identified.

7. Ask the trader the nature of demand (high or low) for the tuber crop products identified.
8. Ask the tuber trader how he or she benefits from trading in tubers.
9. Summarise the findings by filling the following table.

10. With the photographs attached, present your findings to the teacher for feedback.

Selection of Root and Stem Tuber Planting Materials

Have you ever seen a root or stem tuber being planted? From what materials are the root and stem tubers propagated? Root and stem tubers are grown widely across the globe in both tropical and temperate climates. Root tuber crops are grown from cuttings while stem tubers are propagated by using seed tubers. In tuber research laboratories, both root and stem tubers can be grown by tissue culture. Use Figure 2A.4 and Activity 2A.4 to select root and stem tubers for growing.

Activity 2A.4 Selecting root and stem tuber planting

What you need:

Root and stem tuber planting materials, note book, pen

What to do:

1. In groups, you will receive root and stem tuber planting materials.
2. Observe them closely and examine their physical characteristics.
3. In separate groups, with one labelled, ‘suitable for planting’ and another, ‘not suitable, select planting materials and correctly place them in each group.
4. Identify the characteristics of planting materials that you placed in each group.
5. Discuss the differences between the planting materials placed in each group.
6. Examine how you can make the unsuitable planting materials fit for planting.
7. Using the following checklist, examine the qualities of the planting materials that you selected for planting.

Growing of Stem and Root Tuber Crops

Root and stem tuber growing is practised in both low and high altitude areas in Uganda. The climatic and soil requirements of tuber crops do not vary widely giving them a chance to be produced on a wide range of geographical areas and soil types. Routine management is essential in realising optimum yields from tuber crops. What common practices do tuber crop farmers in your community practise?

Common practices include deep tillage of the land, timely planting, proper spacing, fertiliser application, pest and disease control, earthing (in Irish potatoes and carrots) and dehaulming (removing the aerial stem) in Irish potatoes. How important are the practices in tuber crop production? Using Figure 2A.5, Table 2A.2 and Activity 2A.5, practise how to grow root and stem tuber crops.

Stem and Root Tuber Varieties Grown in Uganda

Stem and root tubers are traditional crops that originated from wild varieties. With advancement in plant breeding, many varieties have been developed for faster maturity, pest and diseases resistance and improved nutritive value. See Table 2A.1.

Activity ZA.5 Growing root and stem tuber crops

What you need

Notebook, pen, camera

What to do

1. in groups, visit a tuber crop former near your school. You can alternatively watch a video or look at photographs on tuber crop growing.

2. Observe the root and stem tuber crops that farmer grows. Take photographs of the crops in the field.
3. Ask about the growth requirements of the root and stem tuber crops grown
4. Observe the management practices being or that were carried out on the root and stem tuber crop during the growing period,
5. Ask why each of the management practices is conducted in root and stern tuber crop growing.

6. Record a general criterion that you will use to establish a root and stem tuber crop production project at your school.
7. Follow the criterion to establish and manage a tuber crop production project at school following the routine management practices identified.

8. Follow the correct spacing to avoid over or under population that leads to poor yields. Check the recommended spacing rates for stem and root tubers from Table 2A.2.
9. Control pests and diseases through clean field hygiene, such as, weeding or applying pesticides.
10. Control soil fertility through manuring or using inorganic fertilisers. Sweet potatoes, yams and cassava may produce optimally without the use of inorganic fertilisers.

Handling Tubers Crops During Harvesting

Harvesting means collecting ready crops from the garden after they have reached their physiological maturity. Tuber crops mature at different periods and the indicators of harvesting differ. However, it is advised to carry out timely harvesting to avoid rotting of tubers while still in the field.

Irish potatoes should be dehaulmed (the aerial stems cut) two weeks before harvesting. Root and stem tubers will have reached physiological maturity when the leaves turn yellow and later dry. However, early blight disease in Irish potatoes should not be confused with physiological maturity. Tuber crops are ready for harvesting if tubers are well formed, large and with a tough skin. Use Figure 2A.6 and Activity 2A.6 to carry out harvest handling of root and stem tubers.

Activity 2A.6 a) Harvesting and post-harvesting handling of tubers

What you need:

Notebook, pen, camera, video clips or pictures on harvest and post- harvest handling of tuber crops

What to do:

1. In groups, visit a root and stem tuber crop farmer around your school. Alternatively, you can watch a video or photographs on harvest and post-harvest handling of tuber crops.
2. Ask the farmer how to identify a root and stem tuber crop that is ready for harvesting.
3. Identify the techniques being used to harvest the root and stem tuber crop.
4. Ask for the reasons the specific techniques are used.
5. Ask the farmer to show you the tools and equipment used in harvesting root and stem tuber crops.
6. Ask for permission to use the tools and equipment used in harvesting root and stem tuber crops.
7. Write an article for the school magazine indicating the recommended harvesting techniques for tubers.
8. Follow the techniques to harvest your root and stem tuber crops.

Activity 2A.6 b) Practising post harvest handling of stem and root tubers

What you need:

Physiologically mature tuber crops, harvesting tools, notebook, pen

What to do:

1. Decide on the method of harvesting (piece meal or whole).
2. Use the required tools to harvest tuber crops. Use Table 2A.1 to identify tuber crops that have reached physiological maturity.
3. Use the tools correctly and safely to avoid injuries.
4. Dehaulm (remove the stem) in Irish potatoes two weeks before harvesting. This helps the skin to harden and avoid bruises during harvesting.
5. Remove all the tubers from the soil especially if harvesting by uprooting.
6. Record the harvesting activities and report findings to the teacher.

Post-harvest Handling Tubers

Post-harvest handling refers to all activities you do after harvesting a crop to prevent loss in quality through rotting. Curing, the process of healing wounds when a harvested tuber is held at relatively high temperatures and humidity for a few days after harvest, is most commonly used method of preventing post- harvest losses. In Activity 2A.7, practise post-harvest handling tuber crops.

Activity 2A.7 a) Exploring post-harvest handling of root and stem tubers

What you need:

Notebook, pen, video clips or photographs on post-harvest handling of harvested tuber crops.

What to do:

1. In groups, visit a local food market or hotel, or watch a video or photographs on post-harvest handling of tubers.
2. Identify how harvested tubers are preserved.
3. Find out what causes harvested tubers to quickly go bad.
4. During the visit, check on the:

a) preservation techniques for harvested tubers.

b) kind of ground on which the tubers are stored (cemented or uncemented).

c) walls of stores (smooth or rough).

d) ventilation of the store (adequate or not).

e) store lighting (adequately available or not).

f) roofing of the store (leak proof or leaking).

g) treatment to the tubers (whether given or not).

5. Write a report to the teacher about the findings of the visit.
6. In the report, include the post-harvest handling recommendations for root and stem tubers.

Activity 2A.7 b) Practising post harvest handling of stem and root tubers

What you need:

Harvested tubers, storage facilities, notebook, pen

What to do:

1. In groups, practise post-harvest handling of harvested tuber crops following the recommended practices.
2. Conduct activities to ensure that the storage facility is in good condition not to allow moisture and pests into it.
3. Wash, peel, slice and dry tubers to the recommend moisture content (when it feels floury).
4. Ensure the recommended temperature and humidity are maintained in the store. Check Table 2A.3 for recommended levels.
5. Keep records on the store quantity and quality.
6. Inspect the store to check the condition of the tubers after harvesting.
7. Cure the tubers following the recommendations in the following table.

Solar Drying of Root and Stem Tubers

Have you seen or used any solar dryers for root and stem tubers in your community? Solar drying is an improved mechanism of drying stem and root tubers to the desirable moisture content usually for processing into flour or other dehydrated products like crisps.

Solar drying is faster and more efficient than conventional drying on the floor. The use of solar drying in preservation of harvested tubers produces clean products compared to drying on the ground. In Activity 2A.8, you will construct solar dryer for your harvested root and stem tubers.

Activity 2A.8 a) Planning to construct a solar dryer

What you need:

Notebook, pen

What to do:

1. In groups, brainstorm and draft a design brief (short statement of what the need is) for your solar dryer.
2. Draft your design specifications for the solar dryer (a list of criteria Like material, size, shape, height, transparency, etc.). What will determine the size of the solar dryer?
3. Sketch drawings of the structure of the solar dryer taking different view positions.
4. Draft a budget indicating costs for all the materials needed.
5. Determine the amount of labour and time required to have the solar dryer fully constructed.
6. Secure the funds and procure the materials in place. Find out whic materials to buy, hire or borrow.

7. Design the working processes and procedures as indicated in step 2.
8. Consider the time available for you to accomplish the construction.
9. Inform others about your solar dryer through a presentation of the design journal or design portfolio for feedback.
10. Make adjustments in your design specifications to meet the standards.

Activity 2A.8 b) Constructing a solar dryer for root and stem tubers

What you need:

Claw hammer, nails, glass or transparent hard polythene, hand saw, hack saw, timber of different sizes, notebook, pen

What to do:

1. In groups, assemble the tools and materials required for the construction of the solar dryer.
2. Follow the design specifications and timetable to construct the solar dryer.

3. Complete the construction of the solar dryer. Have some stem and root tubers to be solar dried.
4. Exhibit your solar drier to an external audience and demonstrate how the solar dryer will be used.

5. Show what the solar dried root and stem tubers will be like.
6. Record the complements of the audience to guide you on the design of a solar dryer for your home.

Activity 2A.8 c) Solar drying of tuber crops

What you need:

Solar dryer, notebook, pen

What to do:

1. In groups, wash the tuber crops ready for solar drying.
2. Peel and chop the tuber crop pieces for chips, crisps or flakes.
3. Place the chopped pieces into the solar dryer.
4. Observe and record the changes in moisture content for 3 to 7 days
5. Write a report your findings.

Processing of Root and Stem Tuber Crops

Processing of root and stem tuber products involves dehydrating and subsequent milling. However, the processed product desired determines the process required on the tubers. There is inadequate large-scale tuber crop processing in Uganda. Kisoro Irish Potato plant in Kisoro District that was opened in March 2020 is the only Irish potatoes processing factory in Uganda. We pointed out earlier that tubers can be processed into potato flakes, chips, crisps or chaps. Which of the processed products from tubers can you be able to produce? In Activity 2A.9, process harvested root and stem tubers.

Activity 2A.9 Processing root and stem tuber

What you need:

Knife, root or stem tuber, frying pan, cooking oil, frying spoon, heat source, water, bucket, notebook, pen

What to do:

1. In groups, examine the materials and tools for processing root and stem tubers provided.
2. Wash the root or stem tubers in plenty of water.
3. Peel the root or stem tuber and slice into desirable sizes for chips or crisps.
4. Put the frying pan on a source of heat and add cooking oil and heat to boiling point.
5. Transfer the chopped tubers into a dry container. When the oil warms up, use a frying spoon to scoop some quantity of chopped tubers just enough to be covered by the oil.
6. Continue turning the content to avoid over frying on some sides.
7. When the content turns to slightly brown, remove from the pan.
8. Put the fried content in a container to cool.
9. Pack the product for consumption or marketing.
10. Design a project of processing tuber crop products into crisps, French fries flour chips etc. for income generation.