WAEC SSCE - Agricultural Science - 2000 (Essay)
Swali 1 Ripoti
(a) Discuss seven economic importance of insect pests in crop production.
(b) Name two hosts of cotton stainer.
(c) List two soil-dwelling insect pests of crops and state five general control measures of insect pests of crops.
(a) Seven economic importance of insect pests in crop production
Although mostly harmful, insects have both negative and positive economic effects:
- They reduce crop yield by feeding on leaves, stems, roots, flowers and fruits.
- They lower the quality and market value of produce.
- They transmit plant diseases (act as vectors of viruses and other pathogens).
- They cause storage losses by damaging stored grains and produce.
- They increase the cost of production through spending on pesticides and control.
- On the positive side, some (for example bees) pollinate crops, increasing fruit and seed set.
- Also positively, some produce useful products (honey, wax, silk) and predatory/parasitic insects control other pests biologically.
(b) Two hosts of the cotton stainer
- Cotton plant.
- Okra (also hibiscus/kola).
(c) Soil-dwelling insect pests and general control measures
Two soil-dwelling insect pests:
- Termites.
- Cutworms (also white grubs/beetle larvae).
Five general control measures of insect pests:
- Use of insecticides (chemical control).
- Practise crop rotation and clean cultivation (cultural control).
- Use resistant/tolerant crop varieties.
- Biological control using natural enemies (predators and parasites).
- Early planting, proper spacing and destruction of crop residues and alternate hosts.
Maelezo ya Majibu
(a) Seven economic importance of insect pests in crop production
Although mostly harmful, insects have both negative and positive economic effects:
- They reduce crop yield by feeding on leaves, stems, roots, flowers and fruits.
- They lower the quality and market value of produce.
- They transmit plant diseases (act as vectors of viruses and other pathogens).
- They cause storage losses by damaging stored grains and produce.
- They increase the cost of production through spending on pesticides and control.
- On the positive side, some (for example bees) pollinate crops, increasing fruit and seed set.
- Also positively, some produce useful products (honey, wax, silk) and predatory/parasitic insects control other pests biologically.
(b) Two hosts of the cotton stainer
- Cotton plant.
- Okra (also hibiscus/kola).
(c) Soil-dwelling insect pests and general control measures
Two soil-dwelling insect pests:
- Termites.
- Cutworms (also white grubs/beetle larvae).
Five general control measures of insect pests:
- Use of insecticides (chemical control).
- Practise crop rotation and clean cultivation (cultural control).
- Use resistant/tolerant crop varieties.
- Biological control using natural enemies (predators and parasites).
- Early planting, proper spacing and destruction of crop residues and alternate hosts.
Swali 2 Ripoti
(a) Name six Government and four Non-Governmental Organisations (NGOs) that are involved in the improvement of agricultural production in West Africa.
(b) Mention five ways in which Non-Governmental Organisations contribute to agricultural productivity in West Africa.
(c) Explain briefly six ways by which the application of science and technology last helped to boost crop production in your country.
(a) Government and Non-Governmental Organisations improving agriculture in West Africa
Six Government organisations:
- Ministry of Agriculture (Federal/State).
- Agricultural Development Programmes (ADPs).
- National agricultural research institutes (for example NIFOR, IAR, NRCRI).
- Bank of Agriculture / agricultural credit agencies.
- National Agricultural Extension and Research Liaison Services (NAERLS).
- Nigeria Agricultural Quarantine Service / commodity boards.
Four Non-Governmental Organisations:
- Food and Agriculture Organisation (FAO).
- International Institute of Tropical Agriculture (IITA).
- Sasakawa Global 2000.
- USAID / Oxfam (development partners).
(b) Five ways NGOs contribute to agricultural productivity
- They provide credit, grants and farm inputs to farmers.
- They train farmers and provide extension education on improved practices.
- They supply improved seeds, breeds and technology.
- They fund agricultural research and rural infrastructure.
- They help farmers form cooperatives and find markets for produce.
(c) Six ways science and technology have boosted crop production
- Development of improved, high-yielding and disease-resistant crop varieties.
- Use of chemical fertilizers to improve soil fertility and yield.
- Use of agro-chemicals (herbicides, pesticides) to control weeds and pests.
- Mechanisation with tractors and implements, speeding up operations.
- Irrigation technology allowing all-year cropping.
- Improved storage, processing and preservation techniques that reduce losses (and tissue culture/biotechnology for rapid multiplication).
Maelezo ya Majibu
(a) Government and Non-Governmental Organisations improving agriculture in West Africa
Six Government organisations:
- Ministry of Agriculture (Federal/State).
- Agricultural Development Programmes (ADPs).
- National agricultural research institutes (for example NIFOR, IAR, NRCRI).
- Bank of Agriculture / agricultural credit agencies.
- National Agricultural Extension and Research Liaison Services (NAERLS).
- Nigeria Agricultural Quarantine Service / commodity boards.
Four Non-Governmental Organisations:
- Food and Agriculture Organisation (FAO).
- International Institute of Tropical Agriculture (IITA).
- Sasakawa Global 2000.
- USAID / Oxfam (development partners).
(b) Five ways NGOs contribute to agricultural productivity
- They provide credit, grants and farm inputs to farmers.
- They train farmers and provide extension education on improved practices.
- They supply improved seeds, breeds and technology.
- They fund agricultural research and rural infrastructure.
- They help farmers form cooperatives and find markets for produce.
(c) Six ways science and technology have boosted crop production
- Development of improved, high-yielding and disease-resistant crop varieties.
- Use of chemical fertilizers to improve soil fertility and yield.
- Use of agro-chemicals (herbicides, pesticides) to control weeds and pests.
- Mechanisation with tractors and implements, speeding up operations.
- Irrigation technology allowing all-year cropping.
- Improved storage, processing and preservation techniques that reduce losses (and tissue culture/biotechnology for rapid multiplication).
Swali 3 Ripoti
An agricultural research organisation categorised farmers in village X according to the rate of adoption of new ideas and came up with the following: Innovators 10, Early adopters 15, Late adopters 70, Never adopters 25
(a) Calculate the percentage of early adopters and state the implication of this percentage on the extension system.
(b) Suggest four ways of encouraging the innovators.
(c) State four possible reasons for the high number of late adopters.
(d) State two merits of the print media as a channel for agricultural extension.
(a) Percentage of early adopters and its implication
Total number of farmers = 10 + 15 + 70 + 25 = 120.
\[ \text{Percentage of early adopters} = \frac{15}{120} \times 100 = 12.5\% \]
Implication: Only a small proportion (12.5%) of the farmers readily accept new ideas early. This means the extension system is not very effective at getting farmers to adopt innovations, so the extension agents need to intensify their teaching, demonstrations and follow-up to speed up the rate of adoption in the village.
(b) Four ways of encouraging the innovators
- Give them recognition, awards and encouragement for trying new ideas.
- Supply them with improved inputs, credit and technical support.
- Use their farms as demonstration/result plots so others can learn from them.
- Provide regular training, information and visits by extension agents.
(c) Four possible reasons for the high number of late adopters
- Illiteracy and lack of access to information.
- Poverty/lack of funds to buy the new inputs.
- Strong attachment to tradition and fear of the risk of new methods.
- Inadequate extension contact and poor infrastructure (roads, markets).
(d) Two merits of print media as a channel for extension
- The information is permanent and can be kept and re-read for reference.
- It can reach many literate farmers over a wide area at relatively low cost.
Maelezo ya Majibu
(a) Percentage of early adopters and its implication
Total number of farmers = 10 + 15 + 70 + 25 = 120.
\[ \text{Percentage of early adopters} = \frac{15}{120} \times 100 = 12.5\% \]
Implication: Only a small proportion (12.5%) of the farmers readily accept new ideas early. This means the extension system is not very effective at getting farmers to adopt innovations, so the extension agents need to intensify their teaching, demonstrations and follow-up to speed up the rate of adoption in the village.
(b) Four ways of encouraging the innovators
- Give them recognition, awards and encouragement for trying new ideas.
- Supply them with improved inputs, credit and technical support.
- Use their farms as demonstration/result plots so others can learn from them.
- Provide regular training, information and visits by extension agents.
(c) Four possible reasons for the high number of late adopters
- Illiteracy and lack of access to information.
- Poverty/lack of funds to buy the new inputs.
- Strong attachment to tradition and fear of the risk of new methods.
- Inadequate extension contact and poor infrastructure (roads, markets).
(d) Two merits of print media as a channel for extension
- The information is permanent and can be kept and re-read for reference.
- It can reach many literate farmers over a wide area at relatively low cost.
Swali 4 Ripoti
(a) Describe briefly the Gunters' chain.
(b) A farmer surveyed his triangular farmland with a base length of 2 km and a perpendicular length of 1200m. Calculate the area of the farm.
(c) State four necessary precautions that should be taken in order to eliminate errors when chaining a farmland.
(d) List four factors required in choosing a site for a new school garden.
(a) The Gunter's chain
The Gunter's chain is a land-measuring (surveying) chain that is 66 feet (about 20.1 m) long and made up of 100 links, each link being 7.92 inches. It is used to measure horizontal distances on farmland during chain surveying. Ten square chains make one acre, which makes it convenient for computing land area.
(b) Area of the triangular farm
The measurements must be in the same unit. Perpendicular length = 1200 m = 1.2 km, base = 2 km.
\[ \text{Area} = \tfrac{1}{2} \times \text{base} \times \text{perpendicular height} \]
\[ \text{Area} = \tfrac{1}{2} \times 2\,\text{km} \times 1.2\,\text{km} = 1.2\,\text{km}^2 \]
(Equivalently \(\tfrac{1}{2} \times 2000\,\text{m} \times 1200\,\text{m} = 1{,}200{,}000\,\text{m}^2 = 120\ \text{hectares}\).)
(c) Four precautions to eliminate errors when chaining
- Keep the chain straight, taut and horizontal during measurement.
- Use ranging poles to keep the line straight between the two points.
- Count the arrows/pins carefully and record readings correctly to avoid miscounting a chain length.
- Check the chain for stretched, bent or missing links before use and correct for sag and slope.
(d) Four factors in choosing a site for a new school garden
- Fertile, well drained soil.
- Nearness to a reliable source of water.
- Nearness to the school and accessibility.
- A fairly level, gentle land free from erosion, with adequate sunlight.
Maelezo ya Majibu
(a) The Gunter's chain
The Gunter's chain is a land-measuring (surveying) chain that is 66 feet (about 20.1 m) long and made up of 100 links, each link being 7.92 inches. It is used to measure horizontal distances on farmland during chain surveying. Ten square chains make one acre, which makes it convenient for computing land area.
(b) Area of the triangular farm
The measurements must be in the same unit. Perpendicular length = 1200 m = 1.2 km, base = 2 km.
\[ \text{Area} = \tfrac{1}{2} \times \text{base} \times \text{perpendicular height} \]
\[ \text{Area} = \tfrac{1}{2} \times 2\,\text{km} \times 1.2\,\text{km} = 1.2\,\text{km}^2 \]
(Equivalently \(\tfrac{1}{2} \times 2000\,\text{m} \times 1200\,\text{m} = 1{,}200{,}000\,\text{m}^2 = 120\ \text{hectares}\).)
(c) Four precautions to eliminate errors when chaining
- Keep the chain straight, taut and horizontal during measurement.
- Use ranging poles to keep the line straight between the two points.
- Count the arrows/pins carefully and record readings correctly to avoid miscounting a chain length.
- Check the chain for stretched, bent or missing links before use and correct for sag and slope.
(d) Four factors in choosing a site for a new school garden
- Fertile, well drained soil.
- Nearness to a reliable source of water.
- Nearness to the school and accessibility.
- A fairly level, gentle land free from erosion, with adequate sunlight.
Swali 5 Ripoti
(a) State four ways in which ornamental plants are important. [4 marks]
(b) Give two examples each of (i) ornamental trees, (ii) ornamental shrubs. (c) Explain the following: (i) pasture, (ii) forage. (d) State four roles of legumes in agriculture.
(a) Four ways ornamental plants are important
- They beautify the environment (homes, offices, gardens and streets).
- They are used for landscaping and to provide shade.
- They serve as windbreaks, hedges and boundary/screen plants.
- They are a source of income when sold and help purify the air, reducing pollution.
(b) Examples
(i) Ornamental trees: Royal palm, flamboyant (flame of the forest), frangipani.
(ii) Ornamental shrubs: Hibiscus, croton, ixora, bougainvillea.
(c) Explanations
(i) Pasture: Land covered with grasses and/or herbaceous legumes that is grazed directly by livestock, or the herbage itself grown for grazing.
(ii) Forage: The vegetative parts of plants (grasses and legumes) that are eaten by livestock, either grazed fresh in the field or cut and served as hay or silage.
(d) Four roles of legumes in agriculture
- They fix atmospheric nitrogen through root nodule bacteria (Rhizobium), enriching the soil.
- They serve as cover crops that protect the soil from erosion and conserve moisture.
- They provide high-protein food for humans and fodder for livestock.
- They add organic matter (green manure) that improves soil structure and fertility.
Maelezo ya Majibu
(a) Four ways ornamental plants are important
- They beautify the environment (homes, offices, gardens and streets).
- They are used for landscaping and to provide shade.
- They serve as windbreaks, hedges and boundary/screen plants.
- They are a source of income when sold and help purify the air, reducing pollution.
(b) Examples
(i) Ornamental trees: Royal palm, flamboyant (flame of the forest), frangipani.
(ii) Ornamental shrubs: Hibiscus, croton, ixora, bougainvillea.
(c) Explanations
(i) Pasture: Land covered with grasses and/or herbaceous legumes that is grazed directly by livestock, or the herbage itself grown for grazing.
(ii) Forage: The vegetative parts of plants (grasses and legumes) that are eaten by livestock, either grazed fresh in the field or cut and served as hay or silage.
(d) Four roles of legumes in agriculture
- They fix atmospheric nitrogen through root nodule bacteria (Rhizobium), enriching the soil.
- They serve as cover crops that protect the soil from erosion and conserve moisture.
- They provide high-protein food for humans and fodder for livestock.
- They add organic matter (green manure) that improves soil structure and fertility.
Swali 6 Ripoti
(a) Write short notes on the following systems of breeding: (i) In-breeding; (ii) Line-breeding; (iii) Cross-breeding
(b) State three methods of collecting semen from a proven male for use in artificial insemination.
(a) Systems of breeding
(i) In-breeding: The mating of closely related animals, for example brother to sister or parent to offspring, within the same breed. It is used to fix and concentrate desirable characteristics and to produce pure lines, but if continued it can lead to inbreeding depression (loss of vigour and fertility).
(ii) Line-breeding: A milder form of in-breeding in which animals are mated to keep them closely related to one outstanding ancestor (for example grand sire to grand daughter), but not as close as parent-offspring mating. It aims to retain the good qualities of a superior ancestor while reducing the harmful effects of close in-breeding.
(iii) Cross-breeding: The mating of animals of two different breeds. It combines the desirable qualities of both breeds and produces offspring with hybrid vigour (heterosis), which are often more vigorous, faster growing and more productive than either parent.
(b) Three methods of collecting semen from a proven male for artificial insemination
- Use of an artificial vagina.
- Electro-ejaculation (electrical stimulation).
- Massage method (manual massage of the ampullae/rectal massage).
Maelezo ya Majibu
(a) Systems of breeding
(i) In-breeding: The mating of closely related animals, for example brother to sister or parent to offspring, within the same breed. It is used to fix and concentrate desirable characteristics and to produce pure lines, but if continued it can lead to inbreeding depression (loss of vigour and fertility).
(ii) Line-breeding: A milder form of in-breeding in which animals are mated to keep them closely related to one outstanding ancestor (for example grand sire to grand daughter), but not as close as parent-offspring mating. It aims to retain the good qualities of a superior ancestor while reducing the harmful effects of close in-breeding.
(iii) Cross-breeding: The mating of animals of two different breeds. It combines the desirable qualities of both breeds and produces offspring with hybrid vigour (heterosis), which are often more vigorous, faster growing and more productive than either parent.
(b) Three methods of collecting semen from a proven male for artificial insemination
- Use of an artificial vagina.
- Electro-ejaculation (electrical stimulation).
- Massage method (manual massage of the ampullae/rectal massage).
Swali 7 Ripoti
Discuss briefly: (a) Temperature; (b) Relative humidity; (c) Light; in relation to poultry production and state two ways of controlling the effect of each.
Environmental factors in poultry production
(a) Temperature
Temperature affects feeding, growth, egg production and comfort of birds. Very high temperature causes heat stress, reduced feed intake, panting and lower egg production, while very low temperature (especially for chicks) causes chilling, huddling and death.
Two ways of controlling its effect:
- Provide brooders/heat sources (lamps) to warm chicks in cold conditions.
- Provide adequate ventilation, shade and cool clean water, and orientate/insulate the house to reduce heat.
(b) Relative humidity
High relative humidity makes litter damp and cakey, encourages ammonia build-up, moulds and disease, and hampers heat loss from birds. Very low humidity causes dusty conditions and dehydration.
Two ways of controlling its effect:
- Provide good ventilation (open sides, fans) to remove excess moisture.
- Keep the litter dry by regular turning/replacement and avoid water spillage.
(c) Light
Light stimulates activity, feeding and, importantly, the reproductive system, thereby influencing sexual maturity and the rate of egg laying. Too little light reduces egg production; excessive/uncontrolled light can cause restlessness and vices such as cannibalism.
Two ways of controlling its effect:
- Provide artificial (electric) lighting to supplement day length and stimulate laying.
- Regulate the light duration and intensity using timers, dimmers or by curtaining/shading the house.
Maelezo ya Majibu
Environmental factors in poultry production
(a) Temperature
Temperature affects feeding, growth, egg production and comfort of birds. Very high temperature causes heat stress, reduced feed intake, panting and lower egg production, while very low temperature (especially for chicks) causes chilling, huddling and death.
Two ways of controlling its effect:
- Provide brooders/heat sources (lamps) to warm chicks in cold conditions.
- Provide adequate ventilation, shade and cool clean water, and orientate/insulate the house to reduce heat.
(b) Relative humidity
High relative humidity makes litter damp and cakey, encourages ammonia build-up, moulds and disease, and hampers heat loss from birds. Very low humidity causes dusty conditions and dehydration.
Two ways of controlling its effect:
- Provide good ventilation (open sides, fans) to remove excess moisture.
- Keep the litter dry by regular turning/replacement and avoid water spillage.
(c) Light
Light stimulates activity, feeding and, importantly, the reproductive system, thereby influencing sexual maturity and the rate of egg laying. Too little light reduces egg production; excessive/uncontrolled light can cause restlessness and vices such as cannibalism.
Two ways of controlling its effect:
- Provide artificial (electric) lighting to supplement day length and stimulate laying.
- Regulate the light duration and intensity using timers, dimmers or by curtaining/shading the house.
Swali 8 Ripoti
(a) In a tabular form, briefly discuss the following plant nutrients: (i) Potassium; (ii) Phosphorus; (iii) Calcium. Under the following headings: (i) form in which it is absorbed; (ii) three functions; (iii) one deficiency symptom.
(b) Give two examples of nitrogenous fertilizers.
(a) Plant nutrients
| Nutrient | Form absorbed | Three functions | One deficiency symptom |
|---|---|---|---|
| (i) Potassium (K) | K+ (potassium ion) | Promotes formation and translocation of carbohydrates/sugars; strengthens stems and improves disease resistance; aids flowering, fruiting and root development | Scorching/yellowing of leaf margins (marginal leaf scorch) |
| (ii) Phosphorus (P) | H2PO4- and HPO42- (phosphate ions) | Promotes root development; aids flowering, fruiting and seed formation; involved in energy transfer and early maturity | Purple/reddish colouration of leaves and stunted growth |
| (iii) Calcium (Ca) | Ca2+ (calcium ion) | Forms and strengthens cell walls; promotes root and shoot tip growth; neutralises soil acidity and aids nutrient uptake | Death of growing points (terminal buds) and deformed, curled young leaves |
(b) Two examples of nitrogenous fertilizers
- Urea.
- Ammonium sulphate (also calcium ammonium nitrate).
Maelezo ya Majibu
(a) Plant nutrients
| Nutrient | Form absorbed | Three functions | One deficiency symptom |
|---|---|---|---|
| (i) Potassium (K) | K+ (potassium ion) | Promotes formation and translocation of carbohydrates/sugars; strengthens stems and improves disease resistance; aids flowering, fruiting and root development | Scorching/yellowing of leaf margins (marginal leaf scorch) |
| (ii) Phosphorus (P) | H2PO4- and HPO42- (phosphate ions) | Promotes root development; aids flowering, fruiting and seed formation; involved in energy transfer and early maturity | Purple/reddish colouration of leaves and stunted growth |
| (iii) Calcium (Ca) | Ca2+ (calcium ion) | Forms and strengthens cell walls; promotes root and shoot tip growth; neutralises soil acidity and aids nutrient uptake | Death of growing points (terminal buds) and deformed, curled young leaves |
(b) Two examples of nitrogenous fertilizers
- Urea.
- Ammonium sulphate (also calcium ammonium nitrate).
Swali 9 Ripoti
(a) State the law of diminishing returns as it applies to agricultural production. [2 marks] Study the table below and use it to answer questions (b) and (c).
| Size of farm (ha) | Qty of fertilizer used (bags) | Yield of maize (bags) | Change of Qty of fertilizer | Change in yield of maize (bags) |
| 2 | 0 | 8 | - | - |
| 2 | 8 | 24 | - | - |
| 2 | 12 | 48 | - | - |
| 2 | 26 | 80 | - | - |
| 2 | 20 | 120 | - | - |
| 2 | 24 | 150 | - | - |
| 2 | 28 | 170 | - | - |
| 2 | 32 | 180 | - | - |
| 2 | 34 | 180 | - | - |
| 2 | 36 | 170 | - | - |
(b) Complete the table above. (c) Draw a graph from the provided data and use it to explain the law of diminishing returns
(a) The law of diminishing returns states that when additional equal units of a variable factor of production, such as fertilizer, are applied to a fixed factor, such as land, total output will initially increase at an increasing rate, then at a decreasing rate, and may eventually decrease.
(b) Completed table:
| Size of farm (ha) | Quantity of fertilizer used (bags) | Yield of maize (bags) | Change in quantity of fertilizer (bags) | Change in yield of maize (bags) |
|---|---|---|---|---|
| 2 | 0 | 8 | - | - |
| 2 | 8 | 24 | 8 | 16 |
| 2 | 12 | 48 | 4 | 24 |
| 2 | 16 | 80 | 4 | 32 |
| 2 | 20 | 120 | 4 | 40 |
| 2 | 24 | 150 | 4 | 30 |
| 2 | 28 | 170 | 4 | 20 |
| 2 | 32 | 180 | 4 | 10 |
| 2 | 34 | 180 | 2 | 0 |
| 2 | 36 | 170 | 2 | -10 |
(c) Graph of yield of maize against quantity of fertilizer used:
The graph shows that from 0 to 20 bags of fertilizer, maize yield rises at an increasing rate: the successive increases in yield are 16, 24, 32 and 40 bags. This is the stage of increasing returns.
Beyond 20 bags, output still rises but at a decreasing rate. The increases in yield fall from 30 bags to 20 bags and then to 10 bags as fertilizer rises from 20 to 32 bags. This is the stage of diminishing returns.
At 34 bags of fertilizer, the yield is at its maximum of 180 bags and the additional yield is zero. When fertilizer is increased to 36 bags, yield falls from 180 bags to 170 bags, giving a negative return of 10 bags. Thus, after 20 bags of fertilizer, each further addition produces a smaller increase in maize yield, and excessive fertilizer eventually reduces output.
Maelezo ya Majibu
(a) The law of diminishing returns states that when additional equal units of a variable factor of production, such as fertilizer, are applied to a fixed factor, such as land, total output will initially increase at an increasing rate, then at a decreasing rate, and may eventually decrease.
(b) Completed table:
| Size of farm (ha) | Quantity of fertilizer used (bags) | Yield of maize (bags) | Change in quantity of fertilizer (bags) | Change in yield of maize (bags) |
|---|---|---|---|---|
| 2 | 0 | 8 | - | - |
| 2 | 8 | 24 | 8 | 16 |
| 2 | 12 | 48 | 4 | 24 |
| 2 | 16 | 80 | 4 | 32 |
| 2 | 20 | 120 | 4 | 40 |
| 2 | 24 | 150 | 4 | 30 |
| 2 | 28 | 170 | 4 | 20 |
| 2 | 32 | 180 | 4 | 10 |
| 2 | 34 | 180 | 2 | 0 |
| 2 | 36 | 170 | 2 | -10 |
(c) Graph of yield of maize against quantity of fertilizer used:
The graph shows that from 0 to 20 bags of fertilizer, maize yield rises at an increasing rate: the successive increases in yield are 16, 24, 32 and 40 bags. This is the stage of increasing returns.
Beyond 20 bags, output still rises but at a decreasing rate. The increases in yield fall from 30 bags to 20 bags and then to 10 bags as fertilizer rises from 20 to 32 bags. This is the stage of diminishing returns.
At 34 bags of fertilizer, the yield is at its maximum of 180 bags and the additional yield is zero. When fertilizer is increased to 36 bags, yield falls from 180 bags to 170 bags, giving a negative return of 10 bags. Thus, after 20 bags of fertilizer, each further addition produces a smaller increase in maize yield, and excessive fertilizer eventually reduces output.
Swali 10 Ripoti
(a) Define: (i) Taungya farming, (ii) Crop rotation.
(b) State four advantages of taungya farming.
(c) State four principles underlying the choice of a crop rotation system
(d) Enumerate four advantages of crop rotation.
(e) Under what situations would you recommend to a farmer to embark on crop rotation?
(a) Definitions
(i) Taungya farming: A system of forestry in which farmers are allowed to grow food/arable crops in-between young forest tree seedlings on the same piece of land during the early years of the plantation, tending the trees until the canopy closes.
(ii) Crop rotation: The practice of growing different types of crops in a definite order (sequence) on the same piece of land over successive seasons or years to maintain soil fertility and control pests and diseases.
(b) Four advantages of taungya farming
- It provides food crops and income to the farmer while the trees are young.
- It reduces the cost of establishing and maintaining the forest plantation (weeding is done free by farmers).
- It makes better use of land and sunlight in the early years.
- It provides employment and helps control weeds around the tree seedlings.
(c) Four principles underlying the choice of a crop rotation system
- Deep-rooted crops should follow shallow-rooted crops.
- Leguminous crops should be included to restore soil nitrogen.
- Crops of the same family (with similar pests/diseases) should not follow one another.
- Heavy feeders should be followed by light feeders or soil-restoring crops, and cover crops included to protect the soil.
(d) Four advantages of crop rotation
- It maintains and improves soil fertility.
- It controls the build-up of pests, diseases and weeds.
- It reduces soil erosion and improves soil structure.
- It gives higher and more varied yields and income.
(e) Situations under which crop rotation is recommended
Crop rotation is recommended where land is limited and must be cropped continuously, where there is a build-up of soil-borne pests and diseases, where soil fertility is declining, and where the farmer wants a steady supply of varied produce without leaving land to fallow.
Maelezo ya Majibu
(a) Definitions
(i) Taungya farming: A system of forestry in which farmers are allowed to grow food/arable crops in-between young forest tree seedlings on the same piece of land during the early years of the plantation, tending the trees until the canopy closes.
(ii) Crop rotation: The practice of growing different types of crops in a definite order (sequence) on the same piece of land over successive seasons or years to maintain soil fertility and control pests and diseases.
(b) Four advantages of taungya farming
- It provides food crops and income to the farmer while the trees are young.
- It reduces the cost of establishing and maintaining the forest plantation (weeding is done free by farmers).
- It makes better use of land and sunlight in the early years.
- It provides employment and helps control weeds around the tree seedlings.
(c) Four principles underlying the choice of a crop rotation system
- Deep-rooted crops should follow shallow-rooted crops.
- Leguminous crops should be included to restore soil nitrogen.
- Crops of the same family (with similar pests/diseases) should not follow one another.
- Heavy feeders should be followed by light feeders or soil-restoring crops, and cover crops included to protect the soil.
(d) Four advantages of crop rotation
- It maintains and improves soil fertility.
- It controls the build-up of pests, diseases and weeds.
- It reduces soil erosion and improves soil structure.
- It gives higher and more varied yields and income.
(e) Situations under which crop rotation is recommended
Crop rotation is recommended where land is limited and must be cropped continuously, where there is a build-up of soil-borne pests and diseases, where soil fertility is declining, and where the farmer wants a steady supply of varied produce without leaving land to fallow.
