Cover Image
close this bookPrimary School Agriculture: Volume I: Pedagogy (GTZ, 1985, 144 p.)
close this folderPart III: Examples for practical use
close this folder1. Teaching sub-units
View the document1.1 The maize harvest-integrating work, observation and classroom teaching
View the document1.2 Surveying farm plots - the use of the plane table
View the document1.3 Results of an experiment on pineapple farming
View the document1.4 Observing the growth of yams
View the document1.5 Planning maize farming

1.4 Observing the growth of yams

Class: Six
Topic of Sub-Unit: Observation of a plot farmed with yams 6-8 weeks after planting General Context: Class 6 farms yams on the school farm. After planting and staking, plant development has to be watched.

Pupils' Characteristics
Class 6 pupils are familiar with farming. They have started the yam plot, are familiar with the crop through earlier lessons, and have already done measuring and observation. They are used to tally marks. (Where this is not the case, it needs practice before doing the actual observation. Such practice cannot be done during the period immediately preceding the observation but should be scheduled for the previous day).

Objectives of the Sub-Unit

1. Agricultural aims
- detect deviations from normal growth,
- take appropriate action,
- forecast yields,
- estimate losses.

2. Skill Development
a) Study Skills
- training the power of observation,
- training the power of judgement,
- using observation for further action;
b) Social Skills
- being able to work in a team,
- being able to work efficiently.

A. Introductory Lesson

- Pupils know the purpose of the unit.
- Pupils are able to recall the main facts about the yam plant and yam farming.
- Pupils have a record/observation sheet ready.
- Pupils are grouped in teams.
- Pupils know what they are to observe.

Bring out the reason for the observation exercise:

- Ask when the class had last been to the yams plot.

- Ask for a description of the yam farm at present and take down the answers (blackboard).

- Suggest to have an exact look, e.g. "Just as a baby is cared for by its mother, so any crop planted on the farm is cared for by the farmer. In order to ensure this care, the farmer has to observe how his crops grow. Only then can he give the crop all the care needed".

- Put the observation sheet on the blackboard while discussing what one would want to observe at this stage of yam growth.

- Explain how to get the information required.

- Pupils copy the observation sheet as presented on the blackboard.

Steps in observation
- In each row, inspect each yam plant according to the observation sheet;
- Put tally marks into the appropriate space;
- Write down observations verbally (e.g. under "remarks");
- Convert tally marks into numbers after having completed the row.

Organizing the class for practical work
It is ideal if all pupils could start observation at the same time. Two to three pupils should work together. If necessary one should form more teams than there are rows and have some or all rows observed twice. This provides a check on the accuracy of observation. If the number of teams is smaller than the number of rows, teams are assigned to rows starting at row 1, any team having finished its assignment reports to the teacher and is assigned another row until all have been done. One team member is responsible for writing down the observations.

B. Practical Work

- Pupils develop the skill of observation and recording.
- Pupils develop the skills required for efficient team work.
- Pupils possess information about the actual stage of yam growth.

Outdoor Activities

Apparatus: Numbered paper labels on pegs, one to a row of yams; the observation sheet in pupils' exercise books; pens.

The teams go to their assigned rows and start their observations. One team member counts, the other one enters the information in the record sheet. Team members take turns.

Supervision and Control
Wilful or careless destruction should be avoided. The use of tally marks must be checked. The teacher makes sure that the right words are used when pupils note down observation. Note: Looking at the observation sheets, the teacher may read "spotted leaves", "blight". He asks the team to show him the affected plants and corrects on the spot where necessary. The teacher is available for questions. Teams having completed their assignments will be kept busy while waiting for teams still doing observation. They might be asked to weed between the plants.

C. Follow-up Lessons

1. Assembling the Observations

Basic Material: observation sheets filled by pupils. Teaching Method: teacher-class dialogue, some group work. Objective: gaining an overall picture of the yam farm at time of observation. Classroom Organization: pupils remain together as teams. This changes the sitting order as long as the observations are the basis of the lesson(s). The teacher puts a table form on the blackboard. It will be used to assemble all the observations made by the different teams. It could be roughly like the following table.

What we Saw on the Yam Plot

The teacher calls the team leaders starting with row 1. Each team leader reads out the observations, the teacher enters them in the table. On completing a row, a line is drawn to separate it from the following row. This makes reference easier and reduces errors.If a row has been observed by more than one team, both sets of observations should be read and compared. Differences are discussed. If necessary, the team leaders go out and do the observations again. All teams copy the completed table from the blackboard.

2. Analysing the Data

- Present the observations collected and tabled in a form that makes teaching about related topics possible.

A number of mathematical operations can be performed in order to reach conclusions. They can profitably be shared out among the teams. This teaches the concepts of division of labour and cooperation: only if all teams contribute their share of work can the overall task be successfully and efficiently completed. The following single tasks can be shared out:

- Calculation of the germination rate per row. This is the percentage of setts that have germinated: setts germinated per row: setts planted per row x 100. Five rows are assigned to each team until all the rows have been given out for calculation.

- Calculation of the germination rate for the whole plot (one team).

Add the number of germinated setts over all the rows.

Add the number of planted setts over all the rows or look it up in the records.

The overall germination rate is total number of germinated setts: total number of planted setts X 100.

- Diseases and damages observed on yams (one team). Add the number of destroyed vines over all rows, of vines not trained over all rows, of vines poorly trained over all rows.

- identification of rows that need remulching (one team); All the rows in which mulching is less than satisfactory are noted down separately.

The teacher supervises the team activities, answers questions, and corrects where necessary. As a result of team work, the observations are now ready for further analysis. Conclusions can be drawn and lines of action defined. The teacher makes sure that all relevant information is copied down by the teams.

3. Germination Rate and Drought

- Pupils know the concept of germination rate.
- Pupils know reasons for poor germination and conditions for good germination.
- Pupils are able to calculate the germination rate.
- Pupils know the effect of drought on yams.

Germination rate
The teacher has calculated the germination rate per row as a preparation for this lesson. He asks the teams to report their results and notes them down row by row on the blackboard, ending with the overall germination rate, and checks pupils' results with his own results.

Germination rate on our yam farm
(figures taken from IPAR-Buea demonstration plot)

Row. No.

Germination rate


























63.2 %







Total farm


Points to be discussed with pupils are:

- Which are the rows with the highest and the lowest germination rate?
- What is the difference between highest and lowest germination rate?
- Looking at the highest and lowest germination rate observed - how satisfactory is the overall germination rate on the farm?
- How can one find out whether more setts will germinate?

This leads to a new observational task:
Teams will inspect their rows again to find out
- how many of the non-germinated setts are rotten,
- how many of the non-germinated setts have dried up,
- how many of the non-germinated setts might still germinate.

Damage by drought:
- How does lack of water affect a plant?
- How serious is the effect of drought?
- How many plants are affected?
- How many plants have already died from drought?
- Is it therefore necessary to do something about it?
- If so, teacher and class organize a duty roster for watering.
- This will be done by teams previously formed.

4. Diseases: Leaf Spots and Tuber Rot

- Pupils are able to recognize leaf spot and tuber rot.
- Pupils know about a few other diseases on yams.
- Pupils know how to prevent tubers from rotting.

Using the list of diseases and damages on the blackboard, the teacher gets pupils to read the name(s) of the disease(s) observed, for each of them, he asks for an exact description. Teacher asks how serious the attack is in terms of the number and the proportion of plants affected and in terms of the consequences for the affected plants: will yields go down? Will the affected plant die off before maturity? In our example, only anthracnose has been observed in 18 out of 36 rows. Half of the rows have been affected by a disease which easily spreads from plant to plants, but "The various leaf spots found do not appear to affect the yield". (Irvine, F.R., West African Crops, 3rd edition, London 1976, p. 172). Anthracnose is a leaf spot. One therefore would not have to bother about it.

The teacher asks what other diseases are common with yams, supplies descriptions and blackboard drawings and informs pupils about ways of fighting these diseases. (For information see volume II.)Teacher asks what other damages had been observed.

Rotting tubers:

- What does rot do to tubers? (Killing the tuber and preventing it from germinating, killing already germinated setts)

- How does a tuber start rotting? (When it is poorly stored: too much wafer' too much heat, too closely packed so that it touches another tuber; when it is poorly handled at harvest: cuts and bruises which become infected)

- What can one do about rotten setts and tubers?

- What can one do during next season to prevent setts from rotting? (be careful during harvest, store them well, prepare them carefully at planting time)

5. Training of Vines and Mulching

- Pupils know the functions of vines.
- Pupils know how vines turn for the main varieties of yams in the area.
- Pupils know the reasons for training vines.
- Pupils know the reasons for mulching.
- Pupils are able to mulch yams correctly.

Assign teams to train vines not yet trained and to improve training of poorly trained vines.

Teacher revises reasons for training yam vines.

Mulching: Teacher revises techniques of mulching and reasons for mulching. He assigns teams to do remulching where necessary.

Concluding Remark

Analysing the observations has led to new tasks:

- More observation in order to know more precisely how many setts have been lost. Only after this will it be possible to estimate yields and losses:

- Watering of the yam farm if the effect of drought is serious;

- Training yam vines;

- Mulching where necessary.