WAEC SSCE - Agricultural Science - 2015 (Essay)

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This question tests four separate areas of agricultural science: the economics of produce marketing, extension teaching methods, plant pathology, and crop improvement. Each part is answered under its own heading so the distinct marking points stay clear.

(a) Four reasons why the prices of most agricultural produce are unstable in West Africa

Price instability means the price of a commodity rises and falls sharply over time rather than staying steady. For farm produce this happens because both supply and demand behave in unusual ways:

1. Seasonal production. Most crops are harvested within a short season, so supply is very large just after harvest (a glut, which pushes prices down) and very small in the off-season (scarcity, which pushes prices up). The same crop therefore fetches very different prices at different times of the year.
2. Perishability of produce. Fruits, vegetables, tubers and other fresh produce spoil quickly and cannot be held back for long. Farmers are forced to sell whatever they harvest almost immediately, so a temporary surplus cannot be smoothed out and prices collapse during a glut.
3. Dependence on weather, pests and diseases. Output is controlled largely by rainfall, drought, flood, and pest or disease outbreaks, which the farmer cannot control. A good season floods the market and lowers prices, while a poor season creates shortage and raises prices, so supply and price swing from year to year.
4. Inelastic demand together with poor storage, processing and transport. The demand for staple foods changes little even when supply changes greatly, so a small change in the quantity available causes a large change in price. Weak storage, processing and transport facilities also cause heavy wastage and prevent produce from being moved from surplus areas to scarce areas, worsening the swings.

(b) Two agricultural extension methods explained

Agricultural extension is the education of farmers to help them adopt improved practices. The two named methods differ mainly in scale and in how directly the farmer takes part.

(i) Method demonstration. This is a teaching method in which the extension agent physically shows a small group of farmers, step by step, exactly how to carry out a particular skill or operation, for example how to bud or graft a seedling, mix and apply a spray, dress seed, or vaccinate a bird, and then allows the farmers to practise the skill themselves under guidance. It teaches a specific "how-to-do-it" skill and is convincing because the farmers see and repeat the correct procedure with their own hands.

(ii) Agricultural shows. These are organised exhibitions or fairs at which farmers, research institutes, input companies and government agencies display improved crop varieties, livestock breeds, farm inputs, tools and machinery, often with competitions and prizes for the best entries. They educate a very large audience at once and motivate farmers to adopt better varieties, breeds and equipment by letting them compare results and see what improved practice can achieve.

(c) Cercospora leaf spot disease

Heading	Answer
Crop affected	Groundnut (it also attacks other legumes such as cowpea).
Causative agent	A fungus, Cercospora species (for example Cercospora arachidicola on groundnut).
Mode of transmission	Air-borne spores spread by wind and by rain splash, and carried over between crops on infected plant debris and seed.
Two symptoms	(1) Brown to dark brown, roughly circular spots appear on the leaves, often surrounded by a yellow halo. (2) The spots enlarge and merge, the leaves turn yellow and fall off, causing premature defoliation and reduced yield.
One preventive measure	Spray the crop with a suitable fungicide (other acceptable measures include planting resistant varieties, practising crop rotation, using clean healthy seed, and destroying infected crop residues).

(d) Four advantages of selection as a method of crop improvement

Selection means choosing plants with the most desirable characters from a population and using them as the parents or seed source for the next generation.

1. It is cheap, simple and does not require specialised laboratory equipment, so ordinary farmers can practise it.
2. It preserves and multiplies the best or most desirable characters already present in the crop, such as large seed size or good taste.
3. It steadily improves yield and quality over successive generations as only the best plants are bred forward.
4. It helps develop varieties that are better adapted to local conditions and more resistant to pests, diseases, drought and other adverse factors.

Examination reminder: In part (a) make each point a genuinely different cause (do not list "perishable" and "spoils quickly" as two separate reasons), and in part (c) keep your answers strictly under the given headings, giving the causative organism as a named fungus rather than a vague "germ".

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(a) Cultivation of cowpea

(i) Soil requirement: Cowpea does best on well-drained sandy-loam soil of moderate fertility and slightly acid to neutral pH (about 5.5 to 6.5); it tolerates fairly poor soils but not waterlogged ones.

(ii) Method of propagation: It is propagated by seeds, sown directly at stake.

(iii) Spacing: About 30 cm within rows by 60 cm to 75 cm between rows (roughly 25 cm x 75 cm), 2 to 3 seeds per hole.

(b) One disease and two field pests of cowpea

Disease: cowpea mosaic (viral) disease (also bacterial blight, Cercospora leaf spot).

Field pests: pod borer (Maruca) and pod-sucking bugs (also aphids, thrips).

(c) Four cultural methods of controlling crop pests

1. Crop rotation.
2. Early/timely planting and use of clean/resistant seeds.
3. Regular weeding and destruction of crop residues/alternate hosts.
4. Correct spacing and proper field sanitation (also flooding, hand-picking).

(d) Four human activities that promote deforestation

1. Bush burning and clearing of forest for farming (shifting cultivation).
2. Indiscriminate logging/timber felling.
3. Building of houses, roads and towns (urbanisation).
4. Fuel-wood/charcoal gathering, mining and overgrazing.

(e) Agro-forestry practices

(i) Alley cropping: Growing arable/food crops in the alleys (spaces) between rows of planted trees or shrubs (usually leguminous), where the trees are periodically pruned and the prunings used as mulch/green manure to enrich the soil.

(ii) Ley farming: A system in which land is put under arable crops for some years and then under grass/pasture (ley) for grazing for some years in rotation, to restore soil fertility.

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(a) Leasehold versus freehold land ownership

In leasehold, an individual holds land for a fixed period on payment of rent to the owner, and the land reverts to the owner when the term expires. In freehold, the individual owns the land outright and permanently, with full title and the right to sell, lease or bequeath it.

(b) Five ways NGOs contribute to agricultural development in West Africa

1. They provide credit/grants and inputs (seeds, fertilizer, tools) to farmers.
2. They train farmers and offer extension/advisory services.
3. They fund and sponsor agricultural research and projects.
4. They help build rural infrastructure, storage and processing facilities.
5. They assist in marketing produce and forming cooperatives, and give relief during disasters.

(c) Four ways rural-urban migration has hindered agricultural development

1. It causes shortage of farm labour in the rural areas.
2. It leaves mainly the aged and children on the farms, reducing productivity.
3. It leads to abandonment of farmland and fall in food production.
4. It reduces the adoption of improved practices as able-bodied, educated youths leave farming.

(d) Three socio-economic uses of land

1. For building of houses, schools and hospitals.
2. For recreation (parks, playgrounds) and worship.
3. For siting of markets, industries and roads.

(e) Two ways each environmental factor affects agricultural production

Soil organisms:

1. They decompose organic matter and release/recycle nutrients, improving fertility.
2. Some (earthworms) improve aeration and drainage, while harmful ones cause plant diseases.

Soil texture:

1. It determines water-holding capacity and drainage of the soil (sandy drains fast, clay holds water).
2. It influences aeration, ease of tillage and root penetration, hence crop growth.

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(a) Biogas as a source of farm power

Two advantages:

1. It is a cheap, renewable source of energy made from farm/animal waste.
2. It is clean and reduces pollution, and the spent slurry is a good manure.

Two disadvantages:

1. It requires a fairly costly digester and technical know-how to set up.
2. Gas production is slow and reduced in cold weather, and the gas is flammable/explosive if mishandled.

(b) Eight simple farm tools

Cutlass (matchet), hoe, rake, spade, shovel, axe, watering can and hand trowel (also file, sickle, garden fork, head-pan).

(c) Storage and processing structures on a farmstead

Two storage structures: barn and crib (also silo).

Two processing structures: the rice/oil mill and the grinding/processing shed (also cassava processing unit, drying floor).

(d) Denitrification

Denitrification is the process by which denitrifying bacteria break down nitrates in the soil and release free nitrogen gas back into the atmosphere, thereby reducing the nitrogen (fertility) available to plants.

(e) Components of the soil

(i) Mineral matter: The inorganic part of the soil formed from weathered rock particles (sand, silt and clay). It gives the soil its texture and supplies mineral nutrients to plants.

(ii) Organic matter: The part of the soil made up of decayed and decaying plant and animal remains (humus). It improves soil structure, water and nutrient retention, and supports soil organisms.

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Given: 1,500 eggs incubated; 25 unfertilized; at hatching 475 chicks were male, the rest female.

(a)(i) Percentage of unfertilized eggs

\[ \frac{25}{1500} \times 100 = 1.67\% \]

(a)(ii) Percentage of fertilized eggs

Fertilized eggs = 1500 - 25 = 1475.

\[ \frac{1475}{1500} \times 100 = 98.33\% \]

(a)(iii) Percentage of male chicks

Total chicks hatched = 1475. Male = 475.

\[ \frac{475}{1475} \times 100 = 32.2\% \]

(a)(iv) Percentage of female chicks

Female = 1475 - 475 = 1000.

\[ \frac{1000}{1475} \times 100 = 67.8\% \]

(Percentages of chicks are taken on the 1,475 eggs that hatched; if taken on all 1,500 eggs, male = 31.7% and female = 66.7%.)

(b) Four signs of approaching parturition in a cow

1. Swelling/enlargement of the udder and dropping of milk (waxing of teats).
2. Swelling and reddening of the vulva with mucous discharge.
3. Restlessness and the cow isolating itself from the herd.
4. Slackening/sinking of the pelvic (tail-head) ligaments and loss of appetite.

(c) Four vegetative materials for propagating ornamental plants

1. Stem cuttings.
2. Suckers.
3. Bulbs/corms.
4. Layers (also rhizomes, offsets).

(d) Four advantages of grafting

1. The offspring is true to type and retains the good qualities of the parent.
2. It brings early maturity/fruiting.
3. It allows a disease-resistant or hardy rootstock to be combined with a high-yielding scion.
4. It is used to propagate plants that do not produce viable seeds, and to repair damaged plants.