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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

1.1 The maize harvest-integrating work, observation and classroom teaching

Any school farm project entails a lot of work, Most of the skills needed for farming children learn from their mothers. Only a few skills like measuring, mulching, compost work, the use of certain tools like the West Indian hoe etc. are genuinely learnt in school. One should are developed and that it can be used directly for classroom teaching.

The following notes try to show how the aim of using school farm work for teaching can be achieved taking the harvesting of maize as an example.

Harvesting is a very important moment in any farm project. The crop harvested is the ultimate measure of success or failure. It is therefore a particularly good moment to revise and critically assess the work done on the crop harvested. Teacher and pupils can assess critically whether they made any mistakes in farming. This of course means using the records, especially the Farm Diary. Since the maize harvest comes up towards the end of the third term, it is ideally suited for an end-of-year revision.

Class: Six Topic of Teaching Unit: Maize Harvesting Time: 10 periods of 40 minutes Size of Plot: 2250 m²

Objectives of Sub-Unit

1. Objectives Concerning Farm Work

- harvesting a crop of maize,
- weigh the crop in preparation for storage and drying.

2. Objectives in Agriculture

- revise and deepen the knowledge about maize farming,
- identify possible causes for the yield recorded,
- discuss ways and means to reduce losses,
- discuss the main pests and diseases of maize,
- teach about weights and weighing,
- teach about the concept of yield per standard unit.

3. Skill Development

a) Study Skills

- do observations,
- sort and grade objects,
- keep records,
- analyse observations and draw conclusions,
- summarize results (use of graphs, charts, and summary reports).

b) Social Skills

- team work during practical work and during classroom work,
- work organization.

Children's Previous Knowledge

The pupils undertook the planting of maize. The pupils know the various tasks to be carried out during the growth of the maize. Pupils have been taught the signs of maturity in maize.

A. Introductory Lessons

1. Lesson on Content Preparation


- Pupils recall the main steps in maize farming.
- Pupils know the main pests and diseases of maize in the farm.
- Pupils know the signs of bird attacks, weevil attacks, and fungus diseases in maize.
- Pupils have an observation sheet for sorting and grading maize cobs.
- Pupils are able to use a balance.

Teacher's Preparation

- Specimen of maize cobs showing the various types of damage are taken to the classroom.
- A table for collecting data on maize is prepared and a sample drawn on the blackboard.


Teacher asks pupils about their maize plot: planting time, preparations for planting, signs of maturity, when are cobs ready to be eaten green, treatment of maize after harvesting.

- Teacher and class recall how last year's maize harvest had been handled.
- Teacher discusses damages to be observed on the maize cobs using specimens from the farm.

The main damages are those due to birds, to weevils, and to smuts. In connection with smuts, fungus diseases are discussed or revised.

If weighing has been taught earlier a short revision will be sufficient. If weighing is a new topic, an extra lesson in mathematics is necessary in order to introduce it.Teacher draws the observation sheet on the blackboard and explains using the specimen cobs.

Observation Sheet

2. Work Organization


- Pupils know the various tasks to be performed during harvesting: harvesting, dehusking, assembling the harvest row by row, sorting and grading, counting cobs, recording observations, weighing.
- Pupils are grouped in teams of two or three.

Lesson: Explanation of Work to be Done on the Farm

The teacher explains in detail the tasks to be performed on the farm:

- harvesting and dehusking maize cobs row by row,
- piling up the harvest of each row at the numbered peg of that row,
- sorting and grading the cobs according to size and damage observed,
- counting the number of cobs in each group,
- recording the result in observation sheets,
- carrying the different groups of cobs to the weighing stand,
- taking turns in weighing.

The class is organized into teams of 2 pupils each and given numbers according to the rows in the school farm. The team leaders copy the observation sheet on the blackboard into their exercise books, using the measurements of columns previously determined by the teacher for uniformity.

B. Practical Work - Harvesting


- Pupils harvest the maize.
- Pupils grade and sort the maize row by row.
- Pupils weigh the maize row by row.
- Pupils record the results of grading, sorting, and weighing row by row.

Teacher's Preparation

- The rows on the school farm are pegged and numbered.
- A stand is made for weighing.


A spring balance.

Paper and pencil by each pupil.

Utensils for carrying of maize (children are instructed to bring them from their homes on the day of harvesting, e.g. buckets, small basins or baskets).


The teams take up their position at the end of the rows assigned to each of them. They carry out their various assignments. The teacher supervises the teams and helps where necessary.

The teams carry each group of cobs separately to the weighing stand and heap them according to grade and quality.

All the maize cobs damaged by smuts should be piled at a corner of the farm and burnt. The other heaps of maize cobs should be weighed separately. During the process pupils should take turns in weighing each heap and record the weight in the observation sheet.

C. Follow-up Lessons

1. Assembling the Observations


- Pupils and teacher have the complete picture of all observations (row by row).
- Pupils know the total number of cobs and the total weight harvested, according to the various grades of cobs and for the whole farm.
- The observations are assembled in a way which permits further analysis in class.


Time: Immediately after farm work.

Teacher draws the observation sheet on the blackboard. The teams read out their observations starting with row 1 and going up to the last row.

Teams are asked to copy the complete table of observations into their exercise books. A number of sums are given out to the teams to work.

2. Lesson on Yield


- Pupils know the yield per hectare realized on the farm.
- Discuss why it is useful to know the yield per standard area (hectare or square meter): farm.
- Pupils assess the yield in comparison with maize yields elsewhere.
- Pupils list the main factors responsible for the yield of maize.


- Discuss why it is useful to know the yield per standard area (hectare or square meter): the need for comparison in order to know whether the result was good or bad.
- From the yield recorded work out the yield per hectare.


Total yield of plot = 194 kg.
Area of plot = 2245.5 sq. metre
Yield per hectare:
If 2245.5 sq. metres yield 194 kg,
1 sq. metre yields 194/2245.5 kg, and
1 hectare = 10000 sq. metres yield
194/2245.5 x 10000/1 = 863.95 kg.

- Compare previous yields from the school farm from records if available. Is this year's yield better or worse?

- From the above figures showing maize yield, compare with other parts of the country (for data on maize yields see volume 11, part II on crops).

- Discuss whether the yield was poor or good.

- Get reasons for good or poor yield from the pupils.

- List out the factors affecting the yield: soil fertility, climatic conditions, seed material, timing of work (planting, weeding, earthing up etc.), pests and diseases.

3. Lesson Topic: How did Sod Fertility Affect our Maize Crop?


- Pupils are able to assess soil fertility at the beginning of maize farming in term of initial soil quality, previous farming, and activities to maintain or improve soil fertility.

- Pupils are able to read a graph and draw conclusions.


Discuss with the class

- whether the soil had already been exhausted by previous crops,
- what had been grown before (rotation),
- what the class had done to improve soil fertility (mulching, manuring, chemical fertilizers, leguminous crops, following),
- whether the soil fertility is the same on the whole farm.

The last question can be tackled by looking at the number of cobs harvested row by row. Are there areas with fewer cobs per row than others? A graph is developed in order to answer this question (Graph l). If so this could be attributed to differences in soil fertility within the plot unless other causes can definitely be established.


Conclusion a) How did soil fertility probably affect the yield? Let the class develop a few sentences which they copy into their Rural Science exercise books. Write into summary table of factors (see summary table of factors, p. 107).b) If there are differences in soil fertility - What can we do? Discussion with the pupils.

4. Lesson Topic: How Did the Climate and the Seed Material Affect the Yield?

- Pupils are able to check the water requirements of maize during its growth against the distribution of rains during past seasons (in terms of observations about particularly dry and wet periods).
- Pupils are able to discuss the properties of the seed material used.
- Pupils recall methods of selecting seed material.
- Pupils are able to state an hypothesis on the effect of seed material on the maize crop.

Revise water requirements of maize - quantity and timing.
Was there much rain or was it unusually dry? Did the rain fall at the right time?
Conclusion - How did the rainfall probably affect our yield?
Let the class develop a few sentences which they copy into their Rural Science exercise books. Write into summary table of factors.

Revise the following
- Variety of maize planted and the yields to be expected from this variety.
- Origin of seed material (school farm, homes, research stations).
- Method of selection of seeds - conscious selection of best grains or using whatever was available.

How did the seed material probably affect our yield?
Which aspects (variety, origin, method of selection) should make for good yields, which ones should make for poor yields?
Let the class develop a few sentences which they copy. Write into summary table of factors.

5. Lesson Topic: How Did our Work Schedule Affect Yields?

- Pupils are able to draw conclusions from a comparison between an ideal crop calendar for maize and the actual work schedule as documented in the Labour Records of past season.
- Pupils are able to identify farm operations that were so badly out of time that they might have affected yields.


- Discuss in general the idea of working to schedule.

- Develop a time chart on the blackboard which makes the comparison between planning and actual work possible (see p. 104).

- Revise the correct timing of work for maize farming, according to the beginning of the rains, and enter into the time chart.

- From farm records enter the dates of the different farm operations (planting, first and second weeding' earthing up' harvesting) into the time chart.

- Find out operations that were not carried out at all or badly out of time (mark in time chart).

Time Chart for Maize farming (Specimen) Season: Dry Season 1977, late Maize

How did timing of work probably affect the yield?
Let the class develop a few sentences which they copy. Write into summary table.

6. Lesson Topic: How Did Pests and Diseases Affect Yields?

- Pupils know the damage done by birds, weevils, and fungus diseases on maize.
- Pupils are able to estimate the loss due to birds, weevils, and smuts, in terms of quantity and in cash value.
- Pupils are able to use a graph in order to find out how different types of damage are distributed over a farm.
- Pupils know simple ways of fighting pests and diseases in the farm.

- Find out from observational data the incidence of damage done by birds, insects, and fungus (smuts).
- Are there areas where these damages are heavily concentrated or are they spread out evenly over the farm?
- Work out percentage of damages row by row and graph (see graphs 2 and 3, p. 105).

How did pests and diseases affect the yield?

Teacher leads pupils to estimate the loss due to the pests and diseases found on the maize. Since the reasoning leading to the estimates is somewhat complicated, teachers should take great care introducing it. The following might be a useful approach:

"What have the birds done? They have eaten some or all the grains of a cob. The cob is partly empty. Maize grains have a weight. If birds eat grains from a cob - is that cob heavier of lighter than if birds had not eaten some grains? The loss is restricted to the grains eaten.

"Using the weight of good cobs and the weight of cobs attacked by birds one can estimate the loss due to birds. The procedure is as follows:

- Calculate the average weight of good cobs:

average weight = weight of all good cobs / number of all good cobs

- Calculate the average weight of cobs damaged by birds:

average weight = weight of all cobs damaged by birds / number of all cobs damaged by birds

Graph 2: Percentage of Maize Cobs Damaged by Weevils(per row); Graph 3: Percentage of MaizeCobs Damaged by Birds (per row)

One assumes that cobs damaged by birds would have had the same average weight as good cobs had they not been attacked by birds. If this is sound, one can calculate the loss due to birds as the difference between the average weight of good cobs and the average weight of cobs attacked by birds. This is the estimated average loss per cob due to bird attack.

Average loss due to birds equal average weight of good cobs minus average weight of cobs damaged by birds.

- Calculate the estimated total loss due to birds: Multiplying the average loss per cob by the number of damaged cobs one arrives at an estimate of the total loss of grains due to birds.

"Some of the cobs have been attacked by weevils. What part of the grains have been eaten by weevils? Has the maize cob lost or gained weight? If the cob is weighed after removing the eaten grains it will be noticed that there is a loss of weight compared to the same cob if it were eaten by weevils.

"Here, a comparison of the weight of good and weevilled cobs is not possible since the weevilled grains on the cobs have gone into the weight but cannot be used. We propose the following procedure:

- Take a sample of 100 weevilled cobs, taking small ones and big ones in the same proportion as in the total harvest.
- Remove all the grains damaged by weevils.
- Weigh the cobs after removing damaged grains.
- Calculate the average weight per cob,
- Calculate the difference between the average weight of good cobs and the average weight of the weevilled cobs. The difference is the estimate for the average loss due to weevils.
- Multiply the average loss by the number of weevilled cobs. The result is the estimate of the total loss due to weevils.

Type of Maize Cobs

No. of Cobs


Average Weight

Average Loss

Total Loss

Good Cobs


58.2 kg

73.9 g



Damaged by Birds


46.6 kg

49.9 g

24.0 g

22.39 kg



89.2 kg

62.7 g

11.2 g¹

17.05 kg



not recorded

73.9 g2

2.14 kg


194 kg

59.3 g

41.58 kg

1 Estimate based on sample of 100 weevilled cobs.

2 It is assumed that cobs attacked by smuts would have had the same average weight as good cobs had they not been attacked by fungus.

"What has smuts done to the grains of maize? It has damaged them badly. They don't look like maize grains any longer. Can they be eaten? They are poisonous. Since the whole cob is bad, cobs attacked by smuts were not weighed. We burnt them straight away."

To estimate losses due to smuts, multiply the average weight per good cob by the number of cobs attacked by smuts.

The table below shows in detail the results of the different steps needed in order to estimate the loss. Using these estimates, the teacher can discuss the following problems:

What would the total yield have been had no damages occured?

What would have been the yield per hectare had no damages occured?

What is the proportion of the yield lost?

Taking maize prices at harvesting time, how much money was lost to birds, weevils, and smuts?

The class now is in a position to discuss whether it is worth while doing something to prevent damages from pests and diseases. Discuss different methods of fighting against pests and diseases and their respective costs.

7. Summary

- Pupils are able to make a summary table of factors affecting maize yields.
- Pupils are able to draw conclusions from a summary table.

- Teacher puts the summary table completed during the last lessons on the blackboard.
- Discussion about the importance of each factor and whether, on the whole, the yield could have been better.
- The class makes recommendations for next season's farming.

Summary Table of Factors Affecting the Yield of Maize Season: Dry

Season 1977, Late Maize


How it was on our Farm

Yield Expected

Soil Fertility

- previous crop

none, plot was fallowed


- measures to preserve/



improve soil fertility

- distribution of soil fertility


less than would have been possible


- amount of rain fall



- timing of rain

stopped too early after flowering and cob formation



- variety

Ekona White


- origin

Agricultural Department


- selection

hand picking


Timing of Work

- planting



- first weeding



- earthing up

not done


- second weeding



- harvesting



Pests and Diseases

- bird attack



- weevil attack



- fungus


no effect