WAEC SSCE - Agricultural Science - 2008 (Essay)

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(a) Definition of soil erosion

Soil erosion is the gradual wearing away and removal of the fertile top layer of the soil from the land surface by natural agents such as running water, wind, or by the activities of humans and animals.

(b) Four factors that influence nutrient availability in the soil

1. Soil pH (degree of acidity or alkalinity)
2. Soil moisture content
3. Soil texture and structure
4. Organic matter (humus) content

(c) Two roles of each factor in soil formation

(i) Climate

• Rainfall causes chemical weathering (leaching, hydration and solution) that breaks parent rock into soil particles.
• Alternate heating and cooling (temperature change) causes expansion and contraction of rocks, leading to physical breakdown.

(ii) Living organisms

• Burrowing animals such as earthworms and termites mix and aerate the soil and bring lower materials to the surface.
• Decomposition of dead plants and animals by micro-organisms adds humus and enriches the forming soil.

(iii) Topography

• Steep slopes encourage rapid run-off and erosion, producing shallow, stony soils.
• Gentle or flat land allows water to sink in and materials to be deposited, producing deep, well-developed soils.

(d) Four problems associated with overhead irrigation

1. High cost of installation and maintenance of the equipment.
2. It wets the foliage and so encourages the spread of fungal and other leaf diseases.
3. Wind causes uneven distribution of water over the field.
4. Much water is lost through evaporation before reaching the soil.

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(a) Definitions

(i) Demand: Demand is the quantity of a commodity that consumers are willing and able to buy at a given price over a given period of time.

(ii) Price elasticity of demand: It is the degree of responsiveness of the quantity demanded of a commodity to a change in its price. It is expressed as:

\[ E_d = \frac{\%\ \text{change in quantity demanded}}{\%\ \text{change in price}} \]

(b) Why the demand curve slopes downwards

The demand curve slopes downwards from left to right because of the law of demand: the quantity demanded rises as price falls and falls as price rises, showing an inverse relationship between price and quantity demanded. This is due to the income effect (a fall in price raises the consumer's real income) and the substitution effect (a cheaper good replaces more costly substitutes).

(c) Four agents of agricultural marketing

1. Wholesalers
2. Retailers
3. Middlemen or brokers
4. Cooperative marketing societies

(d) Two advantages and one disadvantage of each teaching method

(i) Newspapers

Advantages:

1. They can reach a large number of literate farmers at once.
2. The information can be kept and referred to again later.

Disadvantage: They are of little value to illiterate farmers who cannot read.

(ii) Television

Advantages:

1. It combines sound and moving pictures, so practices can be demonstrated clearly.
2. It reaches a very large audience at the same time.

Disadvantage: It is expensive and needs electricity, so many rural farmers cannot afford or use it.

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(a)(i) Definition of crop rotation

Crop rotation is the practice of growing different types of crops in a planned and definite sequence on the same piece of land over successive cropping seasons or years, in order to maintain soil fertility and reduce the build-up of pests and diseases.

(a)(ii) A four-year crop rotation using yam, cassava, maize and groundnut

The land is divided into four plots so that every crop is grown each year, and each plot carries a different crop in turn. The legume (groundnut) is placed to restore nitrogen, and the heavy-feeding root crops are separated.

Year	Plot A	Plot B	Plot C	Plot D
1	Yam	Maize	Cassava	Groundnut
2	Maize	Cassava	Groundnut	Yam
3	Cassava	Groundnut	Yam	Maize
4	Groundnut	Yam	Maize	Cassava

Note: Groundnut, a legume, is always followed by the heavy-feeding yam so that the nitrogen it fixes is used by the next crop.

(b) Four reasons why weeds are difficult to control

1. They produce very large numbers of seeds within a short time.
2. Their seeds can remain dormant but viable in the soil for many years.
3. They have efficient means of seed dispersal (wind, water, animals).
4. Many reproduce vegetatively from rhizomes, stolons and tubers even after the tops are removed.

(c) Two effects of diseases on crop production

1. They reduce the yield and quality of the crop produce.
2. They may kill the plants or increase the cost of production through control measures.

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(a)(i) Definition of agriculture

Agriculture is the art and science of cultivating crops and rearing of animals for man use, and for the production of food, fibre and other useful products, as well as the processing and marketing of these products.

(a)(ii) Six branches of agriculture

1. Crop production (agronomy).
2. Animal production (livestock/husbandry).
3. Horticulture.
4. Fishery.
5. Forestry.
6. Agricultural economics and extension.
7. (Also: soil science and agricultural engineering.)

(b) Five differences between commercial and subsistence agriculture

Commercial agriculture	Subsistence agriculture
Produces mainly for sale/profit.	Produces mainly for the family.
Large area of land is cultivated.	Small area of land is cultivated.
Requires large capital.	Requires little capital.
Uses machines and modern techniques.	Uses simple/crude tools and hired family labour.
Output/yield is high.	Output/yield is low.
Skilled labour is employed.	Mostly family labour is used.

(c) Three merits of using animal power on the farm

• It is cheaper than buying and running machines.
• The animals provide manure (dung) for the farm.
• The animals can later be sold or used for meat, and they can work where tractors cannot reach.

Three demerits of using animal power

• Animals work slowly, so large areas take a long time.
• Animals need feeding, housing and veterinary care even when not working.
• They may be affected by diseases and are unsuitable for very heavy or deep cultivation.

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(a)(i) Farm surveying

Farm surveying is the process of measuring and mapping out a piece of farmland to determine its size, shape, boundaries, position and the relative levels of points on it, so that a plan of the farm can be drawn.

(a)(ii) Four reasons why farm surveying is important

• It shows the exact size, shape and boundaries of the farmland.
• It helps in proper planning and layout of the farm, structures and roads.
• It helps to settle boundary disputes and provides proof of ownership.
• It helps in determining the slope of the land for drainage, irrigation and erosion control.

(b) Six problems facing agricultural development in West Africa

• Inadequate capital and poor access to credit.
• Use of crude/simple tools and low level of mechanisation.
• Poor storage, processing and transportation (marketing) facilities.
• Land tenure problems that limit access to large farmland.
• Pests, diseases and unfavourable/unreliable weather.
• Inadequate improved inputs (seeds, fertilizer) and poor extension services.
• (Also: illiteracy of farmers and rural-urban migration of youths.)

(c) Four factors that affect the efficiency of draught animals

• The health and physical condition of the animal.
• The age and breed/size of the animal.
• The feeding and nutrition of the animal.
• The nature/type of the soil and the load or implement being pulled.
• (Also: the weather/temperature and how well the animal is trained.)

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(a) Definition of soil

Soil is the thin, loose, uppermost layer of the earth crust made up of weathered mineral particles, organic matter, water, air and living organisms, in which plants grow and obtain support and nutrients.

(b)(i) Four components of soil

1. Mineral matter (weathered rock particles).
2. Organic matter (humus).
3. Soil water (soil solution).
4. Soil air.

(b)(ii) Percentage of each component by volume

Component	Approximate % by volume
Mineral matter	45%
Organic matter	5%
Soil water	25%
Soil air	25%

(c) Making compost by the pit method

(i) Materials

• Plant remains (grasses, crop residues, leaves, weeds), animal dung/droppings, wood ash, top soil, and water; a pit is dug for the process.

(ii) Preparation

• Dig a pit of a suitable size in a well-drained site.
• Spread the first layer of chopped plant materials (about 30 cm) at the bottom.
• Add a layer of animal dung, then a sprinkling of wood ash and a thin layer of top soil.
• Water each set of layers to keep it moist and repeat the layering until the pit is filled above ground level.
• Insert a stick or provide vents to aid aeration, and cover the heap.
• Turn the heap at intervals (about every two to three weeks) to aid decomposition; it is ready in about three to four months when it becomes dark, crumbly and odourless.

(iii) Storage

• The finished compost is removed, kept in a cool, shaded and dry place (or bagged) and protected from rain and sun until it is applied to the farm.

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(a) Four methods of identification in cattle production

1. Ear tagging
2. Branding (hot or freeze branding)
3. Ear notching
4. Tattooing

(b) Three reasons for each practice

(i) Culling of poultry

1. To remove unproductive or poor-laying birds and cut feeding costs.
2. To remove sick or diseased birds and check the spread of disease.
3. To improve the general quality and productivity of the flock.

(ii) Dehorning of cattle

1. To prevent injury to other animals and to the handlers.
2. To make the animals docile and easy to manage.
3. To reduce the space required per animal at the feeding trough.

(c) Botanical names of four pasture legumes grown in West Africa

1. Centrosema pubescens
2. Stylosanthes gracilis
3. Pueraria phaseoloides
4. Calopogonium mucunoides

(d) Four ways of preserving harvested fish

1. Smoking
2. Salting
3. Sun-drying
4. Freezing or refrigeration

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(a) Four breeds of rabbits

1. New Zealand White
2. Californian
3. Chinchilla
4. Flemish Giant

(b) Two reasons why oestrus detection is important

1. It shows the right time to mate or artificially inseminate the female for successful conception.
2. It helps the farmer to identify infertile or non-cycling animals for culling or treatment.

(c) Four functions of each hormone

(i) Androgen (e.g. testosterone)

1. Brings about the development of male secondary sexual characteristics.
2. Stimulates the production and maturation of sperm (spermatogenesis).
3. Promotes libido or sexual drive in the male.
4. Promotes growth of the male reproductive organs and general body/muscle growth.

(ii) Oestrogen

1. Brings about the development of female secondary sexual characteristics.
2. Induces heat (oestrus) in the female.
3. Prepares the reproductive tract (uterus) for mating and implantation.
4. Stimulates the development of the mammary glands for milk production.

(d)(i) Two viral diseases of poultry

1. Newcastle disease
2. Fowl pox

(d)(ii) Two ecto-parasites of poultry

1. Lice
2. Mites (e.g. red mite)

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(a) Four factors that cause a change in supply of agricultural produce

1. Change in the cost of production (prices of inputs).
2. Change in technology used in production.
3. Weather and climatic conditions.
4. Government policy (taxes and subsidies).

(b) Fixed cost and variable cost distinguished

Fixed cost	Variable cost
Cost that does not change with the level of output and must be paid whether or not production takes place.	Cost that changes directly with the level of output.

Two examples of fixed cost: rent on land; depreciation of machinery.

Two examples of variable cost: cost of seeds and fertilizers; wages of casual labour.

(c) Explanation of the agricultural extension teaching methods

(i) Posters: A poster is a printed visual aid, usually a sheet or chart carrying a short message with bold pictures and very few words, displayed in public places such as markets and clinics. It quickly attracts the attention of passers-by and passes a single agricultural idea to many farmers at a glance.

(ii) Field trips: A field trip is an organised visit by a group of farmers to a farm, research institute or demonstration site so that they can see improved practices being carried out and learn at first hand. It is a group teaching method that lets farmers observe results directly before adopting them.

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(a) Crop improvement is the application of genetic and agronomic principles (selection, hybridization, mutation and modern biotechnology) to produce new or better crop varieties that possess desirable qualities such as high yield, early maturity, resistance to pests and diseases, and improved nutritional or market quality.

(b) Completed dihybrid Punnett square for the cross TtCc \( \times \) TtCc (gametes TC, Tc, tC, tc):

	TC	Tc	tC	tc
TC	TTCC	TTCc	TtCC	TtCc
Tc	TTCc	TTcc	TtCc	Ttcc
tC	TtCC	TtCc	ttCC	ttCc
tc	TtCc	Ttcc	ttCc	ttcc

Counting the 16 offspring gives the classic dihybrid ratio 9 : 3 : 3 : 1: 9 Tall coloured (T_C_), 3 Tall white (T_cc), 3 Dwarf coloured (ttC_) and 1 Dwarf white (ttcc).

(c) Percentage of each phenotype (each box represents \( \frac{1}{16} \) of the plants):

• (i) Tall coloured = \( \frac{9}{16}\times100 = 56.25\% \)
• (ii) Tall white = \( \frac{3}{16}\times100 = 18.75\% \)
• (iii) Dwarf coloured = \( \frac{3}{16}\times100 = 18.75\% \)
• (iv) Dwarf white = \( \frac{1}{16}\times100 = 6.25\% \)