WAEC SSCE - Agricultural Science - 2020 (Essay)

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(a) Cultivation of Citrus spp

(i) Method of propagation: Citrus is propagated both sexually (by seeds) and, more commonly for commercial orchards, vegetatively by budding (T or shield budding) onto a resistant rootstock such as rough lemon or sour orange. Budding is preferred because it keeps the desirable qualities of the parent, ensures early fruiting and gives uniform trees.

(ii) Spacing in the field: Citrus is planted at about 6 m x 6 m to 8 m x 8 m (approximately 150 to 280 trees per hectare), depending on the species and soil fertility. Wide spacing allows light penetration, air circulation and easy movement for spraying and harvesting.

(iii) Nursery practices:

• Prepare fine, well drained nursery beds and sow rootstock seeds.
• Provide partial shade and water regularly.
• Weed, and apply fertilizer to raise vigorous seedlings.
• Bud the seedlings when the stems reach pencil thickness.
• Harden off seedlings before transplanting to the field.

(iv) Pests: Aphids, citrus leaf miner, fruit flies, mealy bugs, scale insects and citrus psyllid.

(v) Diseases: Citrus canker, gummosis (foot rot caused by Phytophthora), citrus greening (HLB), tristeza virus and sooty mould.

(b) Definitions

(i) Surface irrigation: The application of water to farmland by allowing it to flow over the soil surface by gravity, for example through furrows, basins or borders, so that it infiltrates into the root zone.

(ii) Surface drainage: The removal of excess water from the top of the land surface by means of open channels, ditches or graded slopes so that waterlogging is prevented.

(c) Advantages

(i) Surface irrigation:

• It is cheap and simple, requiring little equipment or technical skill.
• It does not require pumping energy where gravity flow is available.
• It can cover large areas and helps leach out harmful salts from the soil.

(ii) Surface drainage:

• It removes excess water and prevents waterlogging, improving soil aeration.
• It reduces soil erosion and the incidence of water-borne diseases.
• It allows earlier cultivation and prevents root rot, improving crop yield.

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(a) Terms in agricultural ecology:

• (i) Soil texture: The relative proportion (by weight) of the different sizes of mineral particles - sand, silt and clay - that make up the soil. It determines whether a soil is sandy, loamy or clayey.
• (ii) Soil profile: A vertical section of the soil from the surface down to the parent rock, showing the different layers or horizons (topsoil, subsoil, weathered rock and parent material).

(b)(i) Three advantages of grafting:

• It combines the good qualities of the rootstock (for example disease resistance) with those of the scion (good fruit).
• The new plant matures and bears fruit earlier than one raised from seed.
• It keeps the desired variety true to type (the offspring resembles the parent exactly).

(b)(ii) Two crops that could be propagated by grafting:

• Mango
• Citrus (orange) (or cocoa/cashew)

(c) Four cultural practices used to replenish nutrients in the soil:

• Application of organic manure (farmyard manure, compost, green manure).
• Application of inorganic fertilisers.
• Crop rotation, including legumes that fix nitrogen.
• Bush fallowing/cover cropping to allow the soil to recover.

(d) Four measures to control pests in grain stores:

• Dry the grains properly to a safe moisture content before storage.
• Fumigate or dust the grains with approved storage chemicals/insecticides.
• Keep the store clean, dry, airtight and rat-proof (good hygiene).
• Mix the grains with inert materials such as wood ash, or store in hermetic (airtight) containers.

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(a) Two solutions to each problem of agricultural development in Africa:

(i) Poor transportation:

• Construct and maintain good rural/feeder roads linking farms to markets.
• Provide adequate means of transport such as vehicles, and develop railways and waterways.

(ii) Environmental degradation:

• Practise soil-conservation measures such as afforestation, cover cropping, terracing and controlled grazing.
• Avoid bush burning and enforce laws against deforestation and pollution.

(iii) Use of crude farm tools:

• Introduce and subsidise modern machines and improved implements for farmers.
• Train farmers in the use and maintenance of modern equipment and provide credit to buy them.

(b) Three precautions when using each type of farm power:

(i) Animal power:

• Do not overload or overwork the animals; give them rest.
• Feed and water them well and keep them healthy.
• Use well-fitting harnesses to avoid injuring the animals.

(ii) Electrical power:

• Avoid touching electrical wires/switches with wet hands.
• Repair faulty wiring and insulate/earth all connections properly.
• Switch off the mains before servicing equipment and avoid overloading circuits.

(c) Six reasons for maintaining farm tools and implements:

• To make them last longer (increase durability).
• To keep them in good working condition and efficient.
• To prevent rust and damage.
• To reduce the cost of frequent repair and replacement.
• To prevent accidents/injury during use.
• To ensure good quality of work and save time and labour.

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(a)(i) Area of the rectangular farmland

Area of a rectangle = length x breadth. The two measurements must first be in the same unit. Converting the length to kilometres, length = 0.2 km and breadth = 2,200 km.

\[ \text{Area} = 0.2\,\text{km} \times 2{,}200\,\text{km} = 440\,\text{km}^2 \]

(If the breadth is taken as 2,200 m, then converting length 0.2 km = 200 m gives Area = \(200\,\text{m} \times 2{,}200\,\text{m} = 440{,}000\,\text{m}^2 = 44\ \text{hectares}\). The key principle is to keep both dimensions in the same unit before multiplying.)

(a)(ii) Two importance of a balance sheet to a farm manager

• It shows the financial position (assets, liabilities and net worth) of the farm business at a particular date.
• It helps the manager to obtain credit or loans, since lenders assess the farm's solvency from it, and it guides sound financial planning and decision making.

(b) Five sources of agricultural loans in West Africa

• Commercial banks.
• Agricultural development banks (for example the Bank of Agriculture in Nigeria).
• Cooperative societies and thrift/credit unions.
• Government agencies and special credit schemes.
• Money lenders, friends and relatives.

(c) Three reasons wood shavings are preferred to sawdust on a deep litter floor

• Wood shavings absorb moisture well yet remain loose and do not cake, keeping the litter dry.
• Sawdust is fine and dusty and can be eaten by the birds or inhaled, causing respiratory problems and impaction; shavings avoid this.
• Wood shavings allow better aeration and are easier to turn and manage, reducing dampness, ammonia and disease.

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(a) Completed disease table:

(b) Five advantages of the battery cage system in poultry production:

1. Efficient use of space through high stocking density.
2. Eggs are clean and easily collected with little breakage.
3. Diseases and parasites are easily controlled since birds do not touch their droppings.
4. Individual birds are easily observed and poor layers are readily culled.
5. Feed wastage, broodiness and cannibalism are greatly reduced.

(c) Five reasons why some extension programmes are not successful in West Africa:

1. Inadequate funding of extension services.
2. Too few and poorly trained extension agents (a low agent-to-farmer ratio).
3. Poor roads, transport and communication infrastructure.
4. Illiteracy of farmers and their resistance to change.
5. Inconsistent government policies and weak research-extension linkage.

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(a) Life cycle of the variegated grasshopper (Zonocerus variegatus)

The variegated grasshopper undergoes incomplete metamorphosis with three stages:

1. Egg stage: The female lays batches of eggs in egg pods buried in moist soil. The eggs remain in the soil and hatch after the dry season, usually with the onset of rains.
2. Nymph stage: The hatched young ones (nymphs) resemble the adults but are smaller and wingless. They feed on vegetation and pass through several moults (instars), gradually developing wing buds.
3. Adult stage: After the final moult the nymph becomes a fully winged adult with the characteristic variegated (multi-coloured) body. Adults mate, and the females lay eggs, so the cycle continues.

(b) Five ways diseases are spread on crop farms

• By insect vectors (for example aphids and whiteflies transmitting viruses).
• Through infected planting materials such as seeds, cuttings and tubers.
• By wind carrying fungal spores.
• By irrigation and rain water carrying pathogens from plant to plant.
• Through contaminated farm tools, implements and the hands of farm workers.

(Also by soil harbouring pathogens, and by man and animals moving through the field.)

(c) Six characteristics of a good layer

• It has a bright red, well developed comb and wattles.
• It has a soft, large and moist vent.
• It has a wide space (three to four fingers) between the pelvic bones.
• It is alert, active and has bright eyes.
• It has a soft, pliable and expanded abdomen.
• It has bleached (pale) shanks and beak, showing that pigment has gone into egg production, and it lays many large eggs.