WAEC SSCE - Agricultural Science - 2007 (Essay)

Detalhes da Resposta

(a) Economic importance of rocks:

(i) To man:

• They are quarried for building and construction materials (stones, gravel, sand, cement).
• They are sources of valuable minerals and metals (gold, iron, tin, coal).
• They are used to make roads, dams and other engineering works.
• Some rocks yield mineral fuels and salts used in industry.

(ii) In agriculture:

• They weather to form the soil in which crops grow.
• They release and supply plant nutrients (such as phosphorus, potassium and calcium) to the soil.
• Rock materials such as limestone provide liming materials to reduce soil acidity.
• Rock phosphate and other rocks serve as raw materials for making fertilizers.

(b) Two characteristics of each rock type:

• (i) Igneous rock: It is formed from cooled and solidified molten magma; it is usually hard, crystalline and contains no fossils. Examples are granite and basalt.
• (ii) Metamorphic rock: It is formed when existing rocks are changed by great heat and pressure; it is hard, often has a banded or layered (foliated) appearance and is more compact than the parent rock. Examples are marble and slate.

(c) Mode of formation of sedimentary rocks: Sedimentary rocks are formed from the products of weathering and erosion of existing rocks. Rock fragments, sand, mud and the remains of plants and animals are carried by wind, water and ice and deposited in layers in low areas such as river beds, lakes and the sea. Over a long period these deposits (sediments) accumulate, the upper layers press down on the lower ones (compaction), and dissolved minerals cement the particles together (cementation). The compacted and cemented layers gradually harden into sedimentary rock. They are typically layered (stratified) and often contain fossils. Examples are sandstone, limestone and shale.

Detalhes da Resposta

(a) Pasture: A pasture is an area of land covered with grasses and legumes (herbage) which is used for grazing or feeding livestock.

(b) Three features of natural pastures:

• They grow on their own without being deliberately planted or managed by man.
• They contain a mixture of many different, often unimproved, species of grasses and legumes.
• They are usually of low quality and low carrying capacity, and their growth depends on rainfall.

(c) Calculations:

(i) Population of the legume at one seed per stand:

Area of the circular land, \( A = \pi r^{2} \), with \( r = 200\,\text{m} \) and \( \pi = 3.142 \):

\[ A = 3.142 \times (200)^{2} = 3.142 \times 40000 = 125680\ \text{m}^{2} \]

Spacing \( = 1\,\text{m} \times 50\,\text{cm} = 1\,\text{m} \times 0.5\,\text{m} = 0.5\ \text{m}^{2} \) per stand.

\[ \text{Population} = \dfrac{\text{Area}}{\text{Spacing}} = \dfrac{125680}{0.5} = 251360\ \text{stands} \]

At one seed per stand, the population of the legume \( = 251{,}360 \) plants.

(ii) Expected plant population at 75% germination:

\[ \text{Expected population} = \dfrac{75}{100} \times 251360 = 188520\ \text{plants} \]

(iii) Two ways Stylosanthes gracilis is important in agricultural production:

• Being a legume, it fixes atmospheric nitrogen and improves soil fertility (it is also used as green manure and cover crop to check erosion).
• It provides nutritious, protein-rich forage (fodder) for feeding livestock.

Detalhes da Resposta

(a) Three main extension teaching methods:

1. Individual (personal) method
2. Group method
3. Mass (mass-media) method

(b) Three types under each method:

Individual method:

• Farm and home visits
• Office (personal) calls by the farmer
• Personal letters and telephone calls

Group method:

• Method demonstration
• Result demonstration
• Group meetings, discussions and field days (farm tours)

Mass method:

• Radio and television broadcasts
• Printed matter such as newspapers, bulletins, leaflets and posters
• Exhibitions, agricultural shows and campaigns

(c) Four qualities of a good extension agent:

1. He should be knowledgeable and well trained in agriculture and able to teach and demonstrate practically.
2. He should be patient, friendly and able to relate well with farmers, respecting their customs.
3. He should be hard-working, honest and dedicated, with a genuine interest in helping farmers.
4. He should be a good communicator who can speak the local language and pass on information clearly and simply.

Detalhes da Resposta

(a) Explanation of four management practices:

• (i) Steaming up: This is the extra (increased) feeding of a pregnant animal with concentrates and good rations during the last few weeks before parturition. It builds up the animal's body reserves, ensures the birth of a healthy young one and prepares the mother for heavy milk production.
• (ii) Culling: This is the removal from the herd or flock of animals that are old, unproductive, sickly, deformed or of poor quality, so that only healthy and productive animals are kept. It improves the overall quality and productivity of the stock.
• (iii) Candling: This is the passing of a bright light through an egg in a dark room to examine its internal quality. It is used to detect cracks, blood spots and rotten eggs, and during incubation to check whether the egg is fertile and developing.
• (v) Creep feeding: This is the provision of supplementary feed to young animals (such as piglets or calves) in a special enclosure (creep) that only the young can enter, keeping out the adults. It helps the young to grow fast and prepares them for weaning.

(Tattooing is the marking of an animal for identification by pricking a number or symbol into the skin or ear with ink.)

(b) Five signs of heat in animals:

1. Restlessness and frequent bellowing or bleating.
2. Swelling and reddening of the vulva.
3. Discharge of clear mucus from the vulva.
4. Mounting other animals and standing to be mounted.
5. Loss of appetite and reduced milk yield; frequent urination.

(c) Three reasons for castrating farm animals:

1. To make the animals docile and easy to handle and manage.
2. To improve the quality and tenderness of the meat and remove its offensive smell.
3. To prevent indiscriminate (uncontrolled) mating and allow only selected males to breed.

Detalhes da Resposta

(a) Explanation of terms:

• (i) Primary tillage implement: This is a heavy implement used for the first, deep opening and breaking of the soil to loosen and turn it before planting, for example the disc plough or mouldboard plough.
• (ii) Secondary tillage implement: This is a lighter implement used after primary tillage to break the large clods into a fine, level seedbed and to control weeds, for example the harrow, ridger and cultivator.

(b)(i) Three reasons why disc ploughs are better suited to West African soils than mouldboard ploughs:

1. The disc plough rolls over stumps, roots and stones without being damaged, whereas the mouldboard plough would be broken by them.
2. It works well in hard, dry and sticky soils common in the tropics because the rolling disc scours and does not clog easily.
3. It is not easily worn out by the abrasive tropical soils, so it lasts longer and needs less repair.

(b)(ii) Six major parts of a disc plough:

• Disc (concave steel plate)
• Disc bearing / hub
• Standard (frame arm carrying the disc)
• Scraper
• Beam or main frame
• Furrow wheel and hitch (linkage to the tractor)

(c) Three reasons why secondary tillage is necessary before sowing:

1. To break the large clods left by ploughing into a fine tilth suitable for good seed germination.
2. To level the field and make ridges or beds for easy planting and drainage.
3. To destroy weeds and incorporate manure and crop residues into the soil.

(d) Three precautions when spraying chemicals:

1. Wear protective clothing such as overalls, hand gloves, nose mask and goggles.
2. Spray along the direction of the wind (down-wind), not against it, to avoid drift onto the operator.
3. Do not eat, drink or smoke while spraying, and wash the body and equipment thoroughly after use.

Detalhes da Resposta

Temperature is an important climatic (environmental) factor that strongly affects livestock performance. Its effects on the following are discussed.

(a) Brooding of chicks: Young chicks cannot regulate their own body temperature, so warmth must be supplied artificially during brooding. The correct temperature (about 35 degrees Celsius in the first week, reduced gradually) keeps the chicks comfortable, active and evenly spread under the brooder, and promotes good growth. If it is too cold the chicks huddle together and may be smothered or die of chilling; if it is too hot they pant, move away from the heat source, eat less and grow poorly.

(b) Reproduction in livestock: Moderate temperatures favour normal reproduction, but very high temperature (heat stress) reduces fertility. In males it lowers the quantity and quality of sperm produced, and in females it interferes with the oestrus cycle, weakens the signs of heat and can cause early embryo death and abortion. Very low temperatures also depress reproductive activity.

(c) Milk production: Dairy animals give the most milk within a comfortable (thermo-neutral) temperature range. Under high temperature the animals feel heat stress, eat less feed and use energy to keep cool, so milk yield and the butterfat content fall. Very cold weather also lowers yield because more feed energy is diverted to keeping the body warm.

(d) Egg production: Laying birds produce best at moderate temperatures. When temperature is very high the birds pant, drink more water, eat less and lay fewer eggs with thinner shells and smaller size. Very low temperature increases the feed needed for body warmth and can also reduce the rate of lay.

Detalhes da Resposta

(a) Eight characteristics of agricultural systems in West Africa:

1. Farming is dominated by small-scale, subsistence holdings producing mainly for the family.
2. Simple, crude hand tools such as the hoe and cutlass are widely used, with little mechanisation.
3. Land is largely held under communal or family (traditional) land tenure, causing fragmentation of holdings.
4. Shifting cultivation and bush fallowing are commonly practised to restore soil fertility.
5. Production depends heavily on rainfall (rain-fed agriculture), so it is seasonal.
6. Mixed cropping and mixed farming are common on the same piece of land.
7. There is low use of improved inputs such as fertilizers, improved seeds and agro-chemicals, giving low yields.
8. Farm labour is supplied mainly by the family and unskilled hired hands, and productivity per worker is low.

(Other features: use of local/unimproved crop varieties and livestock breeds, and poor storage, processing and marketing facilities.)

(b) Four ways land tenure systems affect agricultural production:

1. Insecurity of tenure discourages investment: Where a farmer does not own the land permanently, he is unwilling to invest in permanent improvements such as tree crops, irrigation or buildings for fear of losing them.
2. Fragmentation of holdings: Communal and inheritance systems split land into small scattered plots that are uneconomic to work and cannot be mechanised.
3. Difficulty in obtaining credit: A farmer without a registered land title has no acceptable collateral, so he cannot easily secure loans to expand production.
4. Restriction on land use and expansion: Communal ownership and customary rules may prevent an individual from acquiring enough land or from choosing freely how to use it, limiting large-scale production.

Detalhes da Resposta

(a) Three ways by which nitrogen is added to the soil:

1. Biological nitrogen fixation by leguminous plants (Rhizobium bacteria in root nodules) and free-living soil bacteria.
2. Application of nitrogenous fertilizers and organic manures, and decay of dead plant and animal remains.
3. Fixation of atmospheric nitrogen by lightning, which brings it down in rain as nitrates.

(b) Five ways by which nitrogen is lost from the soil:

1. Leaching of soluble nitrates down beyond the root zone.
2. Denitrification, in which bacteria convert nitrates back to free nitrogen gas.
3. Removal (uptake) of nitrogen by crops that are harvested and taken off the land.
4. Volatilisation of ammonia into the air, especially from surface manures and fertilizers.
5. Loss through soil erosion and by burning of vegetation and crop residues.

(c) Importance of the nitrogen cycle: It ensures a continuous natural supply and recycling of nitrogen, keeping the soil fertile so that plants can obtain the nitrates needed to make proteins for growth. It maintains a balance between the nitrogen used up by plants and micro-organisms and the nitrogen returned to the soil and atmosphere.

(d) Three processes leading to formation of nitrate from organic matter:

1. Ammonification: Decomposing bacteria and fungi break down proteins in dead plant and animal matter and release ammonia (ammonium compounds).
2. Nitritation: Nitrifying bacteria (Nitrosomonas) oxidise the ammonium compounds to nitrites.
3. Nitratation: Nitrifying bacteria (Nitrobacter) further oxidise the nitrites to nitrates, the form absorbed by plants. (Nitritation and nitratation together make up nitrification.)

Detalhes da Resposta

(a)(i) Law of diminishing returns: The law states that as successive (equal) units of a variable input are added to a fixed quantity of other inputs, the extra (marginal) output obtained from each additional unit of the variable input first rises, but after a certain point begins to fall, provided technology is held constant.

(a)(ii) How it affects agricultural production: It guides the farmer on how much of an input (such as fertilizer, labour or seed) to apply. Adding more of an input raises total yield only up to the point of diminishing returns; beyond that point each extra unit adds less to output, and eventually total output may fall, so the farmer wastes money. The most profitable level of production is therefore where the value of the extra output just equals the cost of the extra input, and the farmer should not go on adding inputs beyond this optimum.

(b) How each factor affects the supply of agricultural produce:

• (i) Price: When the price of a produce rises, farmers are encouraged to produce and offer more for sale, so supply increases; when the price falls, supply is reduced (direct relationship).
• (ii) Technology: Improved technology such as better seeds, machines and agro-chemicals raises yield per hectare and lowers the cost of production, so more is produced and supply increases.
• (iii) Weather: Favourable weather (adequate rainfall and sunshine) gives good harvests and increases supply, while drought, flood or storms reduce yields and lower supply.
• (iv) Subsidy: A subsidy reduces the cost of inputs such as fertilizer and seed to the farmer, encouraging him to produce more, so supply increases.
• (v) Government policy: Favourable policies such as guaranteed prices, provision of credit, good roads and storage encourage production and raise supply, whereas heavy taxes, bans or unfavourable policies discourage production and reduce supply.

Detalhes da Resposta

(a) Explanation of terms:

• (i) Floriculture: This is the branch of horticulture concerned with the cultivation, management and marketing of flowers and flowering (ornamental) plants for beauty and decoration.
• (ii) Taungya farming: This is a system of agro-forestry in which arable food crops are grown in between young forest tree seedlings on the same land, the farmer tending both until the trees form a canopy.
• (iii) Ley farming: This is a system in which land is put under grasses and legumes (pasture, called a ley) for a few years to graze livestock and restore fertility, then ploughed and used for arable crops in rotation.

(b) Eight uses of ornamental plants to man:

1. For beautification and decoration of homes, offices and surroundings.
2. For landscaping of gardens, parks and recreation grounds.
3. As live fences, hedges and screens for privacy.
4. To provide shade around buildings and along roads.
5. As a source of income when sold as cut flowers and potted plants.
6. To check soil erosion and serve as ground cover.
7. For religious, ceremonial and social occasions (bouquets, wreaths, gifts).
8. To purify and improve the environment and provide a pleasant micro-climate.

(c) Four fibre crops grown in the country:

• Cotton
• Jute
• Kenaf
• Sisal (hemp is also acceptable)